Kepler-1898 b: a small, hot world orbiting an ancient star

Kepler-1898 b is a small terrestrial exoplanet that would be easy to overlook in the ever-growing catalog of worlds beyond the Solar System. It is less than Earth in size, circles its star in only 4.8 days, and lies more than 1,000 light-years away. Yet the planet is scientifically interesting for a reason that goes beyond its modest dimensions: Kepler-1898 b appears to belong to an old, metal-poor planetary system, providing a glimpse into the kinds of terrestrial worlds that formed much earlier in the history of the Milky Way.

The planet orbits the star Kepler-1898, also known as KIC 3328080 and KOI-3075. The system is located in the constellation Cygnus at a distance of about 361 parsecs, or roughly 1,177 light-years, according to the current NASA Exoplanet Archive data. The host star has a radius of about 0.82 times that of the Sun and an effective temperature of approximately 5,575 kelvin, making it broadly comparable to the Sun in temperature, although its other properties differ significantly.

Kepler-1898 b was identified through the transit method. This technique looks for the tiny, periodic decrease in a star's brightness that occurs when a planet passes across the stellar disk as seen from Earth. In the case of Kepler-1898 b, the signal is exceptionally small: the transit depth is about 68 parts per million in the Kepler data. In other words, the planet blocks only around seven hundredths of one percent of its star's light. Detecting such a subtle signal repeatedly is precisely the kind of measurement for which the Kepler space telescope was designed.

The orbital period of Kepler-1898 b is approximately 4.7656 days. That means the planet completes more than 76 orbits around its star during the time Earth takes to make a single trip around the Sun. Its orbital distance is only about 0.05 astronomical units, roughly one-twentieth of the distance between Earth and the Sun. NASA currently lists an orbital radius of 0.05063 AU, while the Kepler catalog solutions give approximately 0.0522 AU. These small differences arise from different sets of stellar and planetary parameters used in the analyses rather than from any meaningful uncertainty about the planet's extremely close orbit.

In size, Kepler-1898 b is remarkably close to Earth. NASA gives it a radius of about 0.934 times Earth's radius. That makes it approximately 6.6 percent smaller in radius than our planet. Its estimated mass is about 0.76 Earth masses, placing it below Earth's mass as well. The NASA catalog consequently classifies it as a terrestrial planet.

The combination of a roughly Earth-sized radius and a sub-Earth mass is particularly interesting because the radius alone does not tell us what an exoplanet is made of. A planet with a radius close to Earth's could, in principle, have a substantially different internal structure depending on its iron content, rocky mantle, volatile inventory, and thermal history. For Kepler-1898 b, however, the available mass and radius estimates are not sufficiently precise to justify a detailed interior model comparable to what astronomers can construct for some of the best-characterized nearby exoplanets. It is therefore safer to describe it as a small terrestrial world than to claim that its composition is definitively Earth-like.

Its environment is very different from Earth's. Because Kepler-1898 b orbits only about 0.05 AU from its star, it receives vastly more stellar radiation than Earth does. Earlier Kepler-based solutions give an equilibrium temperature of roughly 1,170 K, although equilibrium temperature is a model-dependent quantity rather than a direct measurement of the planet's surface temperature. The high irradiation means that Kepler-1898 b is not considered an Earth-like habitable-zone planet. NASA's catalog classifies it simply as terrestrial rather than suggesting that it has conditions suitable for life.

The short orbital period also has important consequences for the planet's long-term evolution. At such a small star-planet separation, tidal interactions are expected to be much stronger than those experienced by Earth. Depending on the planet's internal structure, orbital history, and tidal dissipation, such interactions could have influenced its rotation and geological evolution. Some theoretical studies have consequently included Kepler-1898 b among small planets whose tidal environment may be relevant when considering possible geological activity, although these calculations should not be interpreted as observations of active volcanism or tectonics on the planet.

Perhaps the most intriguing characteristic of the system is not the planet itself but the apparent age and composition of its host star. One stellar solution associated with the California-Kepler Survey gives Kepler-1898 an estimated age of about 13.18 billion years, with an uncertainty of roughly +0.62 and −0.88 billion years. The same source gives a metallicity of about [Fe/H] = −0.45, meaning that the star contains substantially less iron relative to hydrogen than the Sun. The current NASA Exoplanet Archive also reports a metal-poor star, although the exact stellar parameters vary among the different solutions collected in the archive.

If the older age estimate is correct, Kepler-1898 b would be part of a planetary system that formed when the Milky Way itself was considerably younger. An age of around 13 billion years would place the system among the oldest known planetary systems, although the large uncertainty in the stellar age is important and should not be ignored. Stellar ages are notoriously difficult to determine precisely, especially for individual field stars, and different stellar models and input data can produce substantially different results.

The low metallicity is equally significant. In astronomy, "metallicity" refers to the abundance of elements heavier than hydrogen and helium. These heavier elements are essential ingredients for building rocky planets: iron, silicon, magnesium, oxygen and other elements contribute to planetary cores, mantles and crusts. A metal-poor star therefore formed from material containing fewer heavy elements than the material from which the Sun formed.

The existence of a small rocky planet around such a star illustrates an important point about planet formation. Rocky planets do not require a chemical environment identical to the Sun's to form. The discovery of Kepler-1898 b therefore contributes to the broader evidence that terrestrial planets can emerge in chemically diverse environments and at very different stages of Galactic history.

Kepler-1898 b's history as a discovery is also a useful illustration of how modern exoplanet science increasingly relies on statistical validation and machine learning. The object was originally identified in Kepler observations as KOI-3075.01, a candidate transit signal. It was subsequently included among the planets validated by ExoMiner, a deep-learning system developed to examine Kepler transit signals and their associated diagnostic information. The ExoMiner study reported the validation of 301 new exoplanets and was designed to reproduce aspects of the diagnostic reasoning used by human experts when distinguishing genuine planetary transits from astrophysical false positives.

This distinction matters because detecting a periodic dip in stellar brightness is not, by itself, enough to prove that a planet exists. Eclipsing binary stars, background stars, instrumental effects and other phenomena can produce signals that resemble planetary transits. Kepler-1898 b therefore passed through the broader process of candidate vetting before being incorporated into the confirmed-planet catalog. NASA's current Exoplanet Archive lists it as a confirmed planet and identifies Valizadegan et al. (2022) as the reference associated with its confirmation.

There is another reason to be cautious when interpreting its published parameters. The NASA Exoplanet Archive contains multiple historical solutions for both the star and the planet. For example, the stellar mass estimates range from roughly 0.76 to 0.98 solar masses depending on the source, while the stellar radius has also changed as improved measurements became available. The planetary radius has similarly evolved from earlier estimates with large uncertainties to the more precise value now displayed by NASA. This is normal in exoplanet astronomy: the apparent properties of a planet depend partly on how accurately the properties of its host star are known.

The planet's present catalog values should therefore be regarded as the best currently assembled description rather than immutable numbers. NASA lists a radius of 0.9335 Earth radii, a mass of 0.76 Earth masses, a period of approximately 4.8 days, an orbital radius of 0.05063 AU and zero orbital eccentricity in its catalog presentation. The NASA Exoplanet Archive gives the more precise period as 4.765620232 days in the Valizadegan et al. solution.

Despite its proximity to its star, Kepler-1898 b is not a gas giant or a mini-Neptune. Its radius is firmly in the terrestrial-planet regime, and its estimated mass is less than Earth's. The planet is consequently an example of a class of worlds that is particularly valuable for understanding how common small rocky planets may have been throughout Galactic history. Kepler's enormous survey demonstrated that planets of roughly Earth size are abundant, but individual systems such as Kepler-1898 help astronomers investigate whether the formation of small planets depends strongly on the age and chemical composition of their stellar environments.

There is also a striking contrast between its physical scale and its historical importance. Kepler-1898 b is only slightly smaller than Earth, yet its year lasts less than five Earth days. It receives hundreds of times more stellar energy than Earth according to the earlier Kepler-derived irradiation estimates, and it orbits a star whose chemical composition appears substantially poorer in heavy elements than the Sun's. If the oldest age estimate is approximately correct, the planet may have formed when the Milky Way was still in a very different phase of its evolution.

For now, however, Kepler-1898 b remains much better characterized in terms of its orbit and size than its atmosphere or surface. There is no direct observation establishing an atmosphere, oceans, continents, clouds or volcanic activity. Its small size and faint host star, combined with its distance of more than a thousand light-years, make detailed atmospheric characterization considerably more challenging than it is for the closest and brightest exoplanet systems. The planet's scientific value consequently comes primarily from what its existence tells us about planetary demographics, formation and evolution rather than from the possibility of directly studying its surface.

Kepler-1898 b is therefore not another "Earth 2.0," and describing it that way would obscure what makes it genuinely interesting. It is a hot, compact terrestrial world on an extremely short orbit, apparently associated with an unusually old and metal-poor star. Its discovery also demonstrates how the combination of the Kepler mission, improved stellar measurements and sophisticated statistical validation can transform a faint dip in a distant star's brightness into evidence for a new planetary system. In the expanding census of worlds beyond the Solar System, Kepler-1898 b stands as a small but revealing reminder that rocky planets were forming—and surviving—across the Milky Way long before our own Solar System came into existence.

Kepler-1890 b: the small, hot world hidden in Kepler's data

Among the thousands of worlds discovered beyond the Solar System, Kepler-1890 b is easy to overlook. It is not a giant planet with a spectacular atmosphere, nor does it orbit a well-known nearby planetary system. It is a small, terrestrial world more than 1,700 light-years from Earth, circling its star once every five days. Yet Kepler-1890 b illustrates something important about modern exoplanet science: some of the most interesting discoveries are not made by looking at a new star with a new telescope, but by finding previously hidden planets in enormous archives of old observations.

Kepler-1890 b orbits a star designated Kepler-1890, located in the constellation Cygnus at a distance of roughly 530 parsecs, or about 1,727 light-years from Earth. The system was observed by NASA’s Kepler Space Telescope, whose principal mission was to identify planets by watching stars for tiny, repeated decreases in brightness. The planet is now listed by NASA as a confirmed terrestrial exoplanet.

The planet itself is considerably smaller than Earth. NASA gives it a radius of about 0.869 times Earth's radius and a mass of approximately 0.587 Earth masses. In other words, Kepler-1890 b has only about 87 percent of Earth's radius and roughly 59 percent of its mass. It therefore belongs to a very different part of the exoplanet population from the enormous gas giants that often dominate artists’ impressions of distant planetary systems. Its physical parameters instead place it among the small, rocky or terrestrial-sized worlds that are particularly important to understanding how common Earth-like planets may be.

There is, however, an important distinction between saying that a planet is terrestrial-sized and saying that it is Earth-like. Kepler-1890 b is not considered a second Earth. Its orbit is extraordinarily close to its parent star: the planet travels at an average distance of only about 0.056 astronomical units, roughly 8.4 million kilometers. Earth, by comparison, orbits the Sun at an average distance of one astronomical unit. Kepler-1890 b therefore completes an entire orbit in only about 4.8 days.

That proximity has profound consequences. The planet receives vastly more stellar radiation than Earth does, making its environment far more extreme. A cataloged equilibrium-temperature estimate is around 1,328 K, although this is a calculated value rather than a direct measurement of the planet's atmosphere or surface. At such temperatures, conventional ideas of an Earth-like habitable environment become implausible. Kepler-1890 b should therefore be thought of primarily as a compact, intensely irradiated terrestrial planet rather than a potentially habitable Earth analog.

The star itself is another reason the system deserves careful attention. NASA's current catalog describes Kepler-1890 as an F-type star, while other astronomical databases classify the host as approximately G0IV-V, with an effective temperature near 6,000 K and a mass of roughly 1.1 times that of the Sun. These differences reflect the fact that stellar parameters can be revised as improved observations and stellar models become available. For scientific accuracy, it is therefore preferable not to attach excessive significance to a single catalog classification when discussing the system.

Kepler-1890 b was not discovered in the traditional sense of astronomers seeing the planet directly. Like most of the planets found by Kepler, it was detected through the transit method. When a planet passes between its star and the telescope, it blocks a tiny fraction of the star's light. If the decrease in brightness repeats at regular intervals, astronomers can infer the existence of an orbiting object and determine its orbital period. The depth and shape of the transit also provide information about the planet's size and orbit. Kepler-1890 b's repeated transit signal was buried within the enormous quantity of photometric data collected by the Kepler mission.

The story of Kepler-1890 b is particularly interesting because the original signal was not simply announced as a brand-new discovery from a single observation. The object had been cataloged among Kepler's planetary candidates, under the designation KOI-2970.01, before later analysis established it as a validated planet. The NASA Exoplanet Archive records Kepler-1890 b as a confirmed planet and identifies the original Kepler candidate as K00574.02 in its database.

A major step came with ExoMiner, a machine-learning system developed to analyze the enormous number of potential planetary signals generated by Kepler and TESS. The research team led by Hamed Valizadegan used deep learning to examine the enormous number of potential planetary signals generated by Kepler and TESS. Their 2022 paper reported the validation of 301 previously unconfirmed exoplanets from the Kepler archive. ExoMiner was designed to reproduce many of the diagnostic checks that human experts use when deciding whether a transit-like signal is genuinely planetary or instead produced by an eclipsing binary, instrumental artifact, or another source of false positives.

This is an important part of Kepler-1890 b's significance. The discovery of exoplanets is no longer simply a matter of building increasingly powerful telescopes and pointing them at the sky. Modern astronomy is also an exercise in data mining. Kepler produced an immense archive containing thousands of possible transit signals, and researchers can continue extracting discoveries from those observations years after the spacecraft stopped collecting data. ExoMiner demonstrated how machine learning can help astronomers systematically distinguish genuine planets from false signals. The published study found that, at a fixed precision of 99 percent, ExoMiner recovered 93.6 percent of the exoplanets in its test set, compared with 76.3 percent for the best existing classifier used for comparison.

Kepler-1890 b is therefore part of a broader transformation in the way exoplanets are discovered. The first exoplanets were astonishing precisely because they were so difficult to find. Today, the challenge is almost the opposite: astronomers have accumulated so much data that identifying the planets hidden inside it requires sophisticated statistical and computational techniques. A small world such as Kepler-1890 b can remain buried in a database until a new method reveals that an apparently insignificant variation in starlight contains the signature of a planet.

Its size also makes it scientifically valuable. For decades, astronomers expected that planets smaller than Neptune would be common, but determining their actual distribution requires large and carefully vetted samples. Kepler-1890 b contributes to that population. With a radius below Earth's and a short orbital period, it occupies the class of compact planets that help astronomers investigate how planetary systems produce and retain small rocky worlds under intense stellar irradiation. The planet cannot tell us whether life exists elsewhere, but it does provide another data point in the much larger question of how planetary systems are assembled and how diverse terrestrial planets can be.

There is currently no evidence that Kepler-1890 b has an atmosphere, oceans, continents, or life. Its small size and intense irradiation would make atmospheric characterization difficult, and the available catalog data do not provide a measured atmospheric composition. Even its mass, while listed by NASA, should not be interpreted as a direct measurement comparable to the precision available for some nearby planets; exoplanet parameters can depend strongly on the methods and stellar properties used to derive them. The scientifically responsible picture is therefore a modest one: we know that a small planet orbits Kepler-1890, we know its approximate size and orbital period, and we know that it travels extremely close to its host star. Much about the planet itself remains unknown.

The planet's orbit is listed as essentially circular, with an eccentricity of zero in the current NASA catalog. That does not mean astronomers have mapped the planet's orbit with the same precision with which the Earth's orbit is known; rather, the available solution is consistent with a circular orbit. Its inclination is approximately 77.5 degrees, which is sufficient for the planet to pass across the face of its star from our viewpoint and produce the transits that reveal its existence.

Kepler-1890 itself may also have a more complicated stellar environment than the basic planetary catalog suggests. A 2025 entry in the Extrasolar Planets Encyclopaedia notes a faint object about 4.51 arcseconds from the primary star, interpreted as a likely M-dwarf companion at a projected separation of roughly 2,390 astronomical units. If that association is confirmed and the object is gravitationally bound, Kepler-1890 would not be an entirely isolated star. Such a distant companion would nevertheless be far enough away that it would not resemble the tightly packed binary systems in which planets experience strong dynamical interactions.

The system also demonstrates why exoplanet catalogs should be treated as living scientific resources rather than immutable lists of facts. Values such as stellar mass, radius, temperature, distance, planetary radius, and even the classification of the host star can change as astronomers incorporate new stellar catalogs, Gaia measurements, improved models, and revised analyses of the original Kepler data. The NASA Exoplanet Archive and NASA's public catalog are continually updated precisely because the scientific description of a distant world can become more accurate long after its initial detection.

There is something almost paradoxical about Kepler-1890 b. In one sense, it is remarkably similar to Earth: it is a relatively small planet with a radius less than Earth's and a mass well below that of a gas giant. In another sense, it could hardly be more different. Instead of taking one year to orbit its star, it completes a revolution in less than five days. Instead of receiving the comparatively gentle amount of sunlight Earth receives from the Sun, it exists only a few hundredths of an astronomical unit from its star. And instead of being a promising candidate for surface habitability, its estimated thermal environment places it among the intensely heated terrestrial worlds that challenge simple distinctions between "rocky" and "Earth-like."

Most importantly, Kepler-1890 b reminds us that an exoplanet does not have to be a second Earth to be scientifically important. The true value of an individual planet often emerges when it is considered as part of a population. Every small world added to the catalog helps astronomers refine the statistical picture of planetary formation: how frequently rocky planets appear, how their sizes are distributed, how close they can orbit their stars, how stellar properties influence planetary architectures, and where the boundary lies between worlds resembling Earth and worlds that only superficially share its size.

More than 1,700 light-years away, Kepler-1890 b is far beyond any realistic human journey with present-day technology. We cannot see its surface directly, and we do not yet know what its atmosphere, if any, is made of. What we can do is detect its gravitational and photometric signature, measure the tiny dip it produces in its star's light, and use physics to reconstruct a world that no human has ever seen. That is the extraordinary achievement behind the otherwise cryptic name Kepler-1890 b: a planet invisible to the naked eye, hidden in archival data, transformed by mathematics and machine learning into a confirmed world orbiting a distant star.

Kepler-1890 b is not a new Earth waiting to be explored. It is something more scientifically useful: a small, hot, distant planet that expands our understanding of how ordinary—and how strange—terrestrial worlds can be. Its discovery shows that the search for other worlds is no longer limited by what our telescopes can immediately see. Increasingly, it is also limited by how well we can interrogate the vast astronomical archives we have already collected. In that sense, Kepler-1890 b is not merely a planet discovered by Kepler. It is a planet rediscovered by the combination of precision astronomy, statistical analysis, and artificial intelligence.

Kepler-1130 c: the small, hot exoplanet orbiting a star 800 light-years away

Kepler-1130 c is a small terrestrial exoplanet located roughly 800 light-years from Earth in the constellation Lyra. It is one of several planets known to orbit the star Kepler-1130, a relatively quiet, Sun-like G-type star, and it is an especially interesting example of how the Kepler mission continues to reveal compact planetary systems that are far more complex than they initially appeared. Although Kepler-1130 c is less than four-fifths the radius of Earth, its orbit is extraordinarily close to its parent star: the planet completes one revolution in only about 3.3 days.

According to NASA's current exoplanet catalog, Kepler-1130 c has a radius of about 0.792 Earth radii and a mass of approximately 0.422 Earth masses. Its orbital distance is just 0.04236 astronomical units, meaning that it circles its star at only about 6.3 million kilometers. For comparison, Mercury—the innermost planet in our Solar System—travels around the Sun at an average distance of about 58 million kilometers and needs 88 days to complete an orbit. Kepler-1130 c therefore occupies a very different planetary environment from anything in the Solar System.

The planet's small size places it firmly in the terrestrial category. With a radius roughly 20.8% smaller than Earth's and a mass less than half that of Earth, Kepler-1130 c is not a mini-Neptune or a gas giant. Its measured parameters are consistent with a small rocky world, although the available observations do not provide a direct measurement of its surface composition or geological state. Using the cataloged mass and radius, its mean density would be roughly 85% of Earth's, corresponding to about 4.7 grams per cubic centimeter. That calculation should be regarded as a derived estimate rather than a direct measurement of the planet's interior.

Kepler-1130 c was detected by the transit method. The technique is conceptually simple but extraordinarily demanding: astronomers monitor a star for tiny, repeated decreases in brightness caused when a planet passes across the star's disk from our perspective. The depth and timing of those dips reveal the planet's size and orbital period. In the case of Kepler-1130 c, the transit signal is extremely small because the planet is less than one Earth radius across. Kepler's long, continuous observations were therefore essential for accumulating enough repeated transits to establish the signal reliably.

The history of Kepler-1130 c is particularly interesting because the planet was not originally announced as a confirmed world when the Kepler mission first identified its transit signal. It was associated with the Kepler Object of Interest designation K02169.02. The candidate was subsequently validated as a planet, with its discovery announced in 2021. NASA and the NASA Exoplanet Archive now list Kepler-1130 c as a confirmed planet.

Its validation was part of a broader effort to use machine learning to examine the enormous quantity of transit data produced by Kepler. The ExoMiner system, developed to emulate many of the diagnostic checks astronomers use when evaluating transit signals, was used in the validation of hundreds of Kepler planets. The study reported 301 newly validated exoplanets, demonstrating how modern computational techniques can extract new discoveries from archival observations rather than requiring a new telescope observation for every planet.

Kepler-1130 c is not alone. The system contains at least three confirmed transiting planets: Kepler-1130 b, Kepler-1130 c, and Kepler-1130 d. Their orbital periods are approximately 5.45, 3.27, and 4.27 days, respectively. There is also another object, KOI-2169.04, with a reported period of about 2.19 days that remains a planet candidate rather than a confirmed planet in the current NASA Exoplanet Archive. The unusual ordering of the planetary letters reflects the history of their discovery and confirmation rather than their distance from the star: Kepler-1130 c actually orbits inside Kepler-1130 b.

This compact architecture makes Kepler-1130 c more scientifically interesting than its modest size might suggest. The three confirmed planets are all small, with radii in the general range of Earth-sized worlds. Kepler-1130 c occupies an intermediate orbital position between the innermost candidate and the two other confirmed planets. Such compact multiplanet systems provide astronomers with valuable laboratories for studying how small planets form, migrate, and remain dynamically stable over billions of years.

The star itself is also unusual. Kepler-1130 is approximately 250 parsecs away, equivalent to about 815 light-years, based on the distance currently listed in the NASA Exoplanet Archive. Its effective temperature is around 5,400 K, somewhat cooler than the Sun's approximately 5,780 K, which places it toward the cooler end of the G-star class. The host is therefore broadly Sun-like but is not an exact solar twin. Its apparent visual magnitude is about 12.5, making it far too faint to see with the naked eye.

The amount of radiation received by Kepler-1130 c is one of the most important facts about the planet. Because it orbits at only about 0.042 AU from its star, it receives hundreds of times more stellar energy per unit area than Earth receives from the Sun. NASA's catalog gives an equilibrium temperature of roughly 1,086 K under one of the commonly used stellar-parameter solutions, while other historical solutions give values between roughly 1,070 and 1,160 K.

An equilibrium temperature of about 1,100 K does not mean that the planet's actual surface temperature is exactly 1,100 K. Equilibrium temperature is a theoretical quantity that depends on the incident stellar radiation and assumptions about how efficiently the planet redistributes and emits energy. A real surface temperature could be considerably different depending on atmospheric composition, circulation, albedo, and other properties. Nevertheless, the number makes one conclusion unavoidable: Kepler-1130 c is not in the habitable zone of its star. It is a highly irradiated world, and conventional surface environments similar to Earth's are not expected.

The planet's orbital eccentricity is currently listed as zero in NASA's catalog, meaning that its orbit is modeled as essentially circular. At such a short orbital distance, tidal interactions with the star would be expected to play an important role in its long-term evolution. If the orbit has indeed remained close to circular, Kepler-1130 c would experience comparatively little variation in its star-planet distance during each orbit. Whether the planet is tidally locked, however, is not something that should be presented as an established observational fact. A very short orbital period makes tidal synchronization plausible, but demonstrating the planet's rotational state would require observations that are not currently available.

Kepler-1130 c is also interesting because the planetary system has a much more complicated gravitational environment than its small planets initially suggested. Long-term radial-velocity observations obtained with the Keck Observatory revealed evidence for a massive stellar companion, designated Kepler-1130 B. The companion is on a highly eccentric, very long-period orbit. The 2024 Kepler Giant Planet Search analysis found that the available radial-velocity data were consistent with a stellar-mass companion whose orbit has not yet been completely mapped. The companion passed through periastron around 2022, but the observing baseline does not cover enough of its full orbit to determine all of its orbital parameters with high confidence.

This companion is not simply a distant star with negligible relevance to the planetary system. The Keck analysis estimated a minimum companion mass of roughly 222 Jupiter masses and an orbital period of around 16,000 days, or approximately 44 years, although the orbital solution remains uncertain. Its inferred periastron distance is only about 4 astronomical units. That is remarkably close compared with the typical size of a protoplanetary disk around a young Sun-like star. Researchers have therefore suggested that such a massive companion could have truncated the original planet-forming disk, potentially influencing the formation and final architecture of the small planets around Kepler-1130.

There is a second stellar companion as well. Gaia observations identified a much fainter comoving star at an angular separation of roughly 3.5 arcseconds. At the system's distance of about 250 parsecs, that corresponds to a projected physical separation of approximately 875 astronomical units. This distant companion is distinct from the massive object responsible for the large radial-velocity variations observed over decades.

The presence of a massive, eccentric stellar companion makes Kepler-1130 c an intriguing case for planet-formation studies. The planets themselves are tiny compared with the stellar companion, yet they occupy very tight orbits close to the primary star. According to the 2024 Keck study, Kepler-1130 and Kepler-444 stood out because they combined systems of very small planets with unusually massive and eccentric stellar companions. The authors noted that the periastron distances of these stellar companions are substantially inside the characteristic size expected for a primordial protoplanetary disk, raising the possibility that the companions helped truncate the disks from which the planets formed.

That does not mean astronomers have established a complete formation history for Kepler-1130 c. Several possibilities remain. The planets could have formed relatively close to their present locations, or they could have migrated inward through interactions with the original protoplanetary disk. The stellar companion may have altered the disk's structure and evolution, but precisely how that affected the formation of the individual Earth-sized planets remains an open question. More observations and detailed dynamical modeling will be required to reconstruct the system's history.

Another important limitation is that Kepler-1130 c is not currently a promising target for detailed atmospheric characterization. Its radius is only about 0.79 Earth radii, its atmosphere—if it retains a substantial one—is unknown, and the host star is relatively distant and faint. The planet's high equilibrium temperature makes it scientifically interesting, but detecting atmospheric signatures from such a small planet is far more difficult than studying the atmospheres of large gas giants or sub-Neptunes. At present, the most secure knowledge about Kepler-1130 c comes from its transit, orbital period, size, and inferred mass rather than from direct atmospheric spectroscopy.

Its distance also puts the system into perspective. Light from Kepler-1130 takes roughly eight centuries to reach Earth. When the photons recorded by the Kepler telescope left the system, human civilization was living in the early Middle Ages. The planet we describe today is therefore not Kepler-1130 c as it exists at this exact moment, but Kepler-1130 c as it was roughly 800 years ago. Astronomical distance is also a form of time travel: every observation of a distant exoplanet is an observation of its past.

Kepler-1130 c is consequently a good illustration of what makes modern exoplanet science so compelling. On paper, it is a small number in a catalog: approximately 0.79 Earth radii, 0.42 Earth masses, a 3.3-day orbit, and a distance of only 0.042 AU from its star. Yet those numbers describe a world profoundly unlike Earth, embedded in a compact system of multiple small planets and accompanied by an enormous stellar companion moving on an eccentric orbit lasting decades.

The most important lesson from Kepler-1130 c may therefore not be that it is an Earth-like planet—it is not—but that Earth-sized planets can exist in remarkably diverse environments. Its discovery demonstrates how planets smaller than Earth can be detected across hundreds of light-years, how machine learning can recover worlds hidden in archival data, and how long-term radial-velocity observations can reveal an entirely different layer of a planetary system years after the planets themselves have been discovered. Kepler-1130 c is a small, hot world, but its system is a reminder that even an apparently ordinary Kepler target can conceal a complex planetary and stellar history.

As of the latest NASA catalog information, Kepler-1130 c remains a confirmed terrestrial exoplanet with a radius of about 0.79 Earth radii, a mass of about 0.42 Earth masses, a 3.3-day orbital period, an orbital distance of roughly 0.042 AU, and an equilibrium temperature of around 1,086 K. Its atmosphere, surface, geological activity, and detailed interior remain unknown. Those uncertainties are not shortcomings of the discovery; they are precisely what make the planet scientifically valuable. Kepler-1130 c is another example of how the inventory of known exoplanets has progressed from a handful of exotic worlds to a population containing small rocky planets in planetary systems whose architecture can rival the complexity of our own.

Rubin Observatory's COSMOS image reveals more than 500,000 galaxies in an unprecedented deep view of the Universe

The Vera C. Rubin Observatory has once again demonstrated why it is poised to transform modern astronomy by releasing one of the deepest and most detailed images of the Universe ever captured. The newly unveiled view of the famous COSMOS field showcases more than 500,000 galaxies alongside over 50,000 stars from our own Milky Way, offering scientists and the public an extraordinary glimpse into the vastness of the cosmos.

The image represents the first Early Data Preview based on observations made with the Rubin Observatory's revolutionary LSST Camera, the largest digital camera ever built for astronomy. Instead of relying on a single exposure, researchers combined hundreds of individual observations collected between April 2025 and January 2026 to create an exceptionally deep composite image capable of revealing galaxies across billions of years of cosmic history.

What makes this achievement remarkable is not only the staggering number of visible galaxies but also the incredible range of distances they represent. The COSMOS field, located in the constellation Sextans, has long been one of the most intensively studied regions of the sky because it lies away from the dense plane of the Milky Way, allowing astronomers to peer deep into the distant Universe with minimal interference from foreground stars and dust. The Rubin Observatory's new image pushes this field to unprecedented levels of detail, revealing spiral galaxies, elliptical galaxies, galaxy clusters, interacting systems, and countless faint objects that were previously difficult or impossible to study.

The LSST Camera is uniquely designed for this type of scientific work. With an astonishing resolution of 3,200 megapixels, each image covers an area of the sky roughly equivalent to 45 full moons while maintaining extraordinary sharpness. This combination of an enormous field of view and exceptional sensitivity enables Rubin to observe vast regions of the sky without sacrificing fine detail, a capability unmatched by any previous survey telescope.

Although the released image is breathtaking on its own, it represents only a tiny fraction of Rubin Observatory's full scientific mission. During its decade-long Legacy Survey of Space and Time (LSST), the observatory will repeatedly photograph the entire southern sky every few nights. This continuous monitoring will allow astronomers to detect changes across the Universe, from exploding stars and variable galaxies to potentially hazardous asteroids, comets, and other transient phenomena that appear or disappear over time.

Repeated observations also allow scientists to combine multiple exposures into increasingly deeper images. Every new observation adds more light, making extremely faint and distant galaxies easier to detect while improving image quality. The COSMOS release serves as a powerful demonstration of this technique, showing how Rubin's data will become progressively richer throughout its mission.

Beyond creating beautiful astronomical images, Rubin Observatory is expected to address some of the biggest unanswered questions in cosmology. By mapping billions of galaxies and tracking their evolution across cosmic time, researchers hope to better understand the distribution of dark matter, investigate the mysterious force known as dark energy, and reconstruct how large-scale structures formed throughout the Universe. The enormous dataset will also help scientists study galaxy evolution, star formation, black holes, and the history of the cosmos with unprecedented statistical precision.

The observatory's ability to repeatedly scan the night sky will fundamentally change how astronomers study dynamic events. Instead of taking isolated snapshots, Rubin will effectively produce a time-lapse movie of the Universe, capturing changes that occur over days, months, and years. This approach is expected to lead to countless discoveries, many of which cannot yet be predicted.

For the public, the COSMOS image is equally inspiring. Zooming into the full-resolution version reveals an almost endless sea of galaxies, each containing billions of stars and potentially countless planetary systems. Most of the tiny points of light visible in the image are not stars within our own galaxy but entire galaxies located millions or even billions of light-years away, emphasizing both the immense scale of the Universe and humanity's growing ability to explore it.

The Rubin Observatory's latest release is more than just another spectacular space photograph. It is an early demonstration of what promises to become one of the most ambitious astronomical surveys ever undertaken. As the observatory continues collecting data over the coming years, scientists anticipate discoveries that will reshape our understanding of the Universe, while the public gains access to some of the most detailed cosmic views ever produced. The COSMOS image is only the beginning of a scientific journey that is expected to redefine observational astronomy for decades to come.

Kepler-1934 b: everything we know about this scorching Earth-sized exoplanet

Kepler-1934 b is one of thousands of confirmed exoplanets discovered by NASA's Kepler Space Telescope, yet it stands out as an intriguing example of a small, rocky world orbiting perilously close to its parent star. Although it is unlikely to host life as we know it, the planet provides astronomers with valuable insights into the diversity of terrestrial exoplanets and the extreme environments that exist throughout the Milky Way.

The planet was confirmed in 2021 after detailed analysis of data collected during the Kepler mission. Like the overwhelming majority of Kepler's discoveries, Kepler-1934 b was detected using the transit method. This technique identifies planets by measuring the tiny, periodic decrease in a star's brightness as an orbiting planet passes in front of it from our point of view. Even though the resulting dimming is incredibly small, modern space telescopes can measure these subtle changes with extraordinary precision, allowing scientists to determine a planet's size and orbital characteristics.

Kepler-1934 b orbits the Sun-like star Kepler-1934, a G-type star with an effective temperature of approximately 5,930 Kelvin. The star is slightly larger than our Sun and is located roughly 1,400 light-years from Earth in the direction of the constellation Cygnus. Because of this enormous distance, direct imaging of the planet is currently impossible, making transit observations the primary source of information about the system.

The exoplanet itself is remarkably similar to Earth in size. It has a radius of approximately 0.91 Earth radii, making it slightly smaller than our planet. Current estimates place its mass at about 0.70 Earth masses, indicating that it is most likely a terrestrial world composed primarily of rock and metal rather than gas or ice. These measurements distinguish it from the much larger gas giants and mini-Neptunes that dominate many exoplanet catalogs.

Despite its Earth-like dimensions, Kepler-1934 b is anything but Earth-like in terms of its environment. The planet completes an orbit around its host star in just 1.42 days, compared with Earth's 365-day year. This astonishingly short orbital period means it circles extremely close to its star, at an average distance of only about 0.0247 astronomical units. For comparison, Mercury orbits the Sun at approximately 0.39 astronomical units, placing Kepler-1934 b nearly sixteen times closer to its star than Mercury is to ours.

Such proximity exposes the planet to an extraordinary amount of stellar radiation. Estimates suggest that it receives well over 1,800 times the solar energy that Earth receives from the Sun. As a result, its equilibrium temperature is believed to be around 1,700 Kelvin, or roughly 1,430 degrees Celsius. At these temperatures, rocks could partially melt, many metals would become liquid, and no known form of life could survive on the surface.

The orbit of Kepler-1934 b appears to be essentially circular, with an eccentricity very close to zero. Circular orbits are common among planets located extremely close to their stars because tidal forces gradually eliminate orbital eccentricity over millions or billions of years. Those same tidal interactions almost certainly mean that Kepler-1934 b is tidally locked, with one hemisphere permanently facing its star while the opposite side remains in perpetual darkness. This configuration would produce enormous temperature differences between the day and night sides, although any atmosphere—if one still exists—could redistribute some of that heat.

Whether the planet retains a significant atmosphere remains an open question. The intense stellar radiation and powerful stellar winds associated with such close orbits can gradually strip away atmospheric gases. If Kepler-1934 b once possessed a thick atmosphere, much of it may have been lost over geological time. Alternatively, if volcanic activity remains vigorous, the planet could still maintain a thin atmosphere replenished from its interior. Future observations with next-generation telescopes may help answer this question.

Kepler-1934 b also contributes to one of the most important areas of modern exoplanet research: understanding the population of rocky planets in our galaxy. Every newly confirmed terrestrial exoplanet improves statistical models that describe how planets form and evolve. By comparing worlds like Kepler-1934 b with larger super-Earths, mini-Neptunes, and gas giants, astronomers can better understand why planetary systems exhibit such extraordinary diversity.

The Kepler mission revolutionized astronomy by demonstrating that planets are common throughout the Milky Way. Before its launch in 2009, only a few hundred exoplanets were known. Today, thanks largely to Kepler's observations and subsequent follow-up studies, thousands of confirmed exoplanets have been cataloged. Kepler-1934 b is one of many discoveries that continue to refine our understanding of planetary formation and the frequency of Earth-sized worlds in our galaxy.

Although Kepler-1934 b is far too hot to be considered habitable, its discovery remains scientifically significant. It illustrates that rocky planets can exist under conditions vastly different from those found in our Solar System. Studying these extreme worlds helps astronomers test theories about planetary interiors, atmospheric evolution, tidal interactions, and the long-term effects of intense stellar radiation.

As new observatories continue to expand humanity's ability to study distant planetary systems, worlds like Kepler-1934 b will become increasingly important. While this small, scorched planet may never be a candidate for life, it represents another crucial piece of the cosmic puzzle, reminding us that the universe contains an astonishing variety of planets far beyond anything found in our own celestial neighborhood.

Kepler-1693 c: everything we know about this Earth-sized exoplanet

Kepler-1693 c is an Earth-sized exoplanet orbiting a distant star approximately 2,480 light-years from Earth in the constellation Cygnus. Although it is far too hot to support life as we know it, the planet represents an important piece of the growing catalog of small rocky worlds discovered by NASA's Kepler Space Telescope. Its confirmation demonstrates how modern data analysis techniques continue to uncover previously overlooked planets hidden within the enormous Kepler dataset, expanding our understanding of the diversity and architecture of planetary systems throughout the Milky Way.

The planet orbits the star Kepler-1693, a G-type star that is somewhat smaller and slightly cooler than the Sun. The host star has a radius of roughly 0.86 times that of the Sun and an effective temperature of about 5,500 K, making it broadly solar-like despite being somewhat less luminous. Located nearly 760 parsecs from Earth, the system is too distant for direct imaging with current technology, meaning astronomers rely on indirect observational methods to investigate its planets.

Kepler-1693 c was detected using the transit method, the same technique responsible for the majority of Kepler's discoveries. As the planet passes between its star and Earth, it blocks a tiny fraction of the star's light. These periodic dips in brightness reveal the planet's existence and allow astronomers to determine several of its physical properties. Because the amount of dimming depends on the relative size of the planet and the star, researchers can estimate the planetary radius with remarkable precision, even when the planet itself cannot be seen directly.

Although Kepler originally observed the transit signal years earlier, Kepler-1693 c was not immediately confirmed as a planet. Instead, it remained listed as a planetary candidate while astronomers continued refining detection algorithms and statistical validation techniques. In 2021, it was confirmed as a genuine exoplanet through improved analyses of archival Kepler observations, illustrating how scientific discoveries often continue long after a space mission has ended. Rather than requiring new telescope observations, researchers extracted additional value from existing data by applying more sophisticated computational methods.

Kepler-1693 c has a radius of approximately 0.98 Earth radii, making it almost the same size as our own planet. Because only its radius has been measured directly, its mass remains uncertain. However, planets of this size are generally expected to be predominantly rocky unless future observations suggest otherwise. Without an accurate mass measurement, astronomers cannot yet determine its density, surface gravity, or detailed internal composition with confidence.

The planet completes one orbit around its star every 5.36 days, placing it extremely close to its host star compared with Earth's distance from the Sun. Such a short orbital period means the planet receives an enormous amount of stellar radiation. Estimates indicate that Kepler-1693 c receives nearly 300 times the amount of energy that Earth receives from the Sun, resulting in an equilibrium temperature of roughly 1,060 K, or nearly 790°C (about 1,450°F). At such temperatures, any Earth-like oceans would be impossible, and much of the planetary surface would likely be intensely heated.

Its proximity to the host star also makes tidal locking a plausible outcome. If this has occurred, one hemisphere would permanently face the star while the opposite side would remain in perpetual darkness. Many close-in exoplanets are expected to evolve into this configuration because gravitational interactions gradually synchronize their rotational and orbital periods. Whether Kepler-1693 c is tidally locked has not been directly measured, but theoretical models suggest it is a reasonable possibility for planets orbiting so close to their stars.

The Kepler-1693 system itself is known to host multiple planets. Alongside Kepler-1693 c, astronomers have confirmed Kepler-1693 b, another small planet orbiting farther from the star with a period of approximately 12 days. The system also contains additional planetary candidates that have yet to receive full confirmation. Multi-planet systems like this are especially valuable because they allow scientists to investigate how planetary systems form, migrate, and remain dynamically stable over billions of years.

Because Kepler-1693 c transits its star, it may eventually become a target for future atmospheric studies if observational capabilities improve. At present, however, the star is relatively faint, making detailed atmospheric characterization difficult even for powerful observatories such as the James Webb Space Telescope. Nevertheless, each confirmed Earth-sized transiting planet adds to the statistical sample astronomers use to understand the frequency and diversity of terrestrial worlds across the Galaxy.

Kepler-1693 c is not considered potentially habitable. Its extreme stellar irradiation places it well inside the inner boundary of the habitable zone, where temperatures are far too high for liquid water to remain stable on the surface. Even if the planet formed with substantial amounts of water or a thick atmosphere, prolonged exposure to intense radiation would likely have dramatically altered its environment over time.

Despite its inhospitable conditions, Kepler-1693 c holds considerable scientific importance. Every confirmed Earth-sized planet helps refine theoretical models describing how rocky planets form, evolve, and survive in different stellar environments. Small exoplanets are especially significant because they bridge the gap between our Solar System and the enormous diversity of planetary systems discovered throughout the Milky Way. Understanding why some rocky planets become scorching worlds while others may remain temperate is one of the central goals of modern exoplanet science.

The discovery of Kepler-1693 c also highlights the enduring scientific legacy of NASA's Kepler mission. Although the spacecraft ended operations in 2018, its archive continues to yield new discoveries as researchers develop increasingly sophisticated analytical techniques. The mission transformed planetary science by demonstrating that planets are extraordinarily common throughout our galaxy, with thousands of confirmed worlds ranging from giant gas planets to bodies smaller than Earth. Kepler-1693 c is one more example of how valuable archival astronomical data can remain for decades after it is collected, continually revealing new worlds that deepen our understanding of the universe.

HD 23472 e: a dense Earth-size exoplanet in a remarkable five-planet system

HD 23472 e is a small, intriguing exoplanet orbiting the K-type star HD 23472, also known as TOI-174. Located roughly 127 light-years from Earth, the planet is part of an unusually compact system containing five confirmed worlds. Its discovery and subsequent characterization have attracted particular interest because HD 23472 e is approximately Earth-sized yet appears to have a remarkably high density, raising the possibility that it belongs to the rare class of planets sometimes described as "super-Mercuries."

The planet was identified in 2022 as part of a major study of the HD 23472 planetary system. Researchers combined transit observations with extremely precise radial-velocity measurements obtained with ESPRESSO, the high-resolution spectrograph installed on the European Southern Observatory's Very Large Telescope. This combination was crucial: the transit method revealed the planet's size, while the star's subtle motion under the planet's gravitational influence provided an estimate of its mass. The result was one of the more technically demanding detections of a small exoplanet, demonstrating the ability of modern instruments to measure planetary masses well below that of Earth.

According to the NASA Exoplanet Archive, HD 23472 e has a radius of approximately 0.82 times that of Earth and a mass of about 0.72 Earth masses, although the mass uncertainty is substantial. Its orbital period is just 7.91 days, meaning that a year on HD 23472 e lasts less than eight Earth days. The planet orbits its host star at an average distance of approximately 0.068 astronomical units, far closer to its star than Earth is to the Sun. The measured orbital eccentricity is modest, around 0.07, although the uncertainty is large enough that the precise shape of its orbit remains relatively poorly constrained.

Its physical properties make HD 23472 e particularly interesting. Combining its estimated mass and radius gives an average density of roughly 7.5 grams per cubic centimeter, with large uncertainties. For comparison, Earth's mean density is about 5.5 grams per cubic centimeter, while Mercury's is approximately 5.4 grams per cubic centimeter. The central estimate for HD 23472 e is therefore surprisingly high for a planet of its size. The original research suggested that the two innermost planets in the system, HD 23472 d and HD 23472 e, could be "super-Mercuries"—small planets with unusually large iron cores relative to their overall size. This interpretation is not yet definitive, however, because the uncertainties in their masses and densities remain significant.

The term "super-Mercury" is useful as a description of a possible composition rather than a formally established planetary category. In the case of HD 23472 e, the hypothesis is that a substantial fraction of the planet's interior could consist of iron and other dense materials, leaving a relatively small rocky mantle. Such a structure could have important implications for planetary formation. One possibility is that intense irradiation from the host star removed part of an originally more volatile-rich planet. Another is that the planet formed from material unusually enriched in refractory elements, or that giant impacts stripped away a significant portion of its mantle. At present, the available observations do not uniquely distinguish between these possibilities.

The location of HD 23472 e within its planetary system makes the story even more compelling. The planet is not an isolated world but one member of a tightly packed sequence of five planets. Moving outward from the star, the system contains HD 23472 d, e, f, b, and c, with orbital periods of approximately 3.98, 7.91, 12.16, 17.67, and 29.80 days, respectively. Their estimated radii range from less than Earth's size for the two innermost planets to roughly twice Earth's radius for the two outermost planets. This architecture provides astronomers with a natural laboratory for investigating how planets with different compositions can emerge from the same protoplanetary environment.

HD 23472 e was also challenging to detect because of its proximity to the orbit of HD 23472 d. The two planets have orbital periods of approximately 3.98 and 7.91 days, placing them close to a 2:1 period relationship. The original study noted that HD 23472 e's small size, its proximity to the transit signal of planet d, and its near-resonant orbital relationship contributed to the difficulty of identifying it. The planet's eventual characterization highlights how signals from multiple worlds can overlap or complicate the interpretation of observations, particularly when astronomers are searching for planets only slightly smaller than Earth.

The system's compact architecture may also provide clues about how planetary systems evolve under intense stellar irradiation. The research team found a broad trend in which the estimated gas and water fractions of the planets increase with distance from the host star. The innermost worlds appear to be denser and more likely to be dominated by rocky and metallic material, while the outer planets may retain larger amounts of volatile material. This pattern is consistent with a scenario in which irradiation has played a major role in shaping the planets over billions of years, although the exact evolutionary history remains uncertain.

This makes HD 23472 e scientifically valuable beyond its own characteristics. Comparing it with its neighboring planets allows researchers to study planetary diversity while controlling for some of the variables that normally complicate exoplanet research. All five planets orbit the same star and therefore formed within the same broad protoplanetary disk. Their contrasting sizes, masses, and inferred compositions offer an opportunity to investigate why planets born in the same system can evolve into such different worlds.

The planet's estimated equilibrium temperature also emphasizes how different its environment is from Earth's. NASA's catalog lists an equilibrium temperature of approximately 723 K based on the adopted planetary parameters. This is not a direct measurement of the planet's actual surface temperature and should not be interpreted as a weather forecast or atmospheric temperature. Equilibrium temperature is a model-dependent quantity that generally assumes a simplified energy balance and does not capture the full effects of atmospheric circulation, greenhouse warming, or heat redistribution. Nevertheless, the value indicates that HD 23472 e receives substantially more stellar energy than Earth does.

Because HD 23472 e is relatively small and likely has a rocky composition, it is not an obvious target for atmospheric characterization in the same way as a large, inflated gas giant. Its small radius produces a comparatively weak transit signal, while its proximity to the host star places it in a challenging observational environment. Even so, the system could become increasingly important as observational techniques improve. Better measurements of the planet's mass and radius would directly refine its density and help determine whether the super-Mercury interpretation is robust.

One of the most important limitations in our current understanding of HD 23472 e is therefore the uncertainty surrounding its interior. The published estimate of approximately 0.76 Earth masses, later represented in the NASA Exoplanet Archive at around 0.72 Earth masses, carries an uncertainty of roughly 0.3 Earth masses. Its radius estimate of about 0.82 Earth radii also has significant uncertainty. Because density depends strongly on both mass and radius, these uncertainties propagate into the inferred interior composition. The evidence for a dense, Mercury-like interior is intriguing, but it should be regarded as a scientific hypothesis supported by current measurements rather than a definitive description of the planet's internal structure.

The discovery of HD 23472 e also illustrates the importance of combining different exoplanet detection techniques. Transit observations are particularly effective at measuring planetary radii, but they do not directly reveal mass. Radial-velocity observations provide the complementary information needed to estimate how strongly a planet gravitationally tugs on its star. For a small planet such as HD 23472 e, that stellar motion is extremely subtle. The ability of ESPRESSO to extract such a signal demonstrates the extraordinary precision now possible in exoplanet astronomy and represents an important step toward characterizing increasingly Earth-like worlds.

HD 23472 e is not considered a second Earth, despite its broadly Earth-sized dimensions. Its short orbital period, intense stellar irradiation, and potentially iron-rich interior make it a radically different world from our planet. Its scientific importance lies precisely in that contrast. By studying a planet that is similar to Earth in size but potentially very different in composition and environment, astronomers can test theories about how rocky planets form, lose volatile material, acquire their internal structures, and respond to the radiation of their host stars.

Ultimately, HD 23472 e is best understood as one piece of a much larger planetary puzzle. Its small size, high estimated density, close orbit, and position within a five-planet system make it an exceptional target for comparative exoplanet science. The possibility that it is a super-Mercury is particularly fascinating, but the most valuable feature of the system may be the opportunity to compare several planets that formed around the same star yet appear to have followed very different evolutionary paths. As future observations refine the masses and compositions of HD 23472 e and its neighboring worlds, this compact system could become an important benchmark for understanding why planetary systems produce such a remarkable diversity of worlds.

HD 23472 d: the tiny, ultra-dense exoplanet that may be a super-Mercury

HD 23472 d is a remarkable exoplanet for one simple reason: it is small, extremely dense, and located in a compact planetary system that gives astronomers an unusual laboratory for studying how rocky worlds form and evolve. Orbiting a K-type star roughly every four days, the planet has a radius of about 75% that of Earth but an estimated mass of only around half an Earth mass. Its measured density is therefore surprisingly high, leading researchers to identify it as a strong candidate for a so-called super-Mercury—a small, metal-rich planet with an unusually large iron core relative to its overall size.

HD 23472 d belongs to the five-planet system surrounding the star HD 23472, also known as TOI-174. The system is particularly interesting because its planets occupy tightly packed orbits, with orbital periods ranging from approximately 3.98 days for planet d to nearly 30 days for the outermost known planet, HD 23472 c. The system therefore contains several worlds that formed and evolved under different levels of stellar irradiation, providing astronomers with an opportunity to investigate how a planet's environment can influence its composition.

The discovery and characterization of HD 23472 d were part of a 2022 study led by astronomers using observations from the European Southern Observatory's ESPRESSO spectrograph. The planet was identified through a combination of transit observations and precise radial-velocity measurements. The transit method detects the tiny dip in a star's brightness that occurs when a planet passes across the stellar disk, allowing researchers to estimate the planet's radius. Radial-velocity observations measure the subtle gravitational tug that the planet exerts on its host star, providing information about its mass. Together, these techniques make it possible to estimate a planet's bulk density—one of the most valuable clues to its internal composition.

According to the NASA Exoplanet Archive, HD 23472 d has a radius of approximately 0.75 Earth radii and an estimated mass of about 0.55 Earth masses, although the uncertainties are substantial. It completes one orbit in about 3.9766 days and travels at an average orbital distance of roughly 0.043 astronomical units from its star. For comparison, Mercury orbits the Sun at an average distance of about 0.39 astronomical units. HD 23472 d is therefore extraordinarily close to its host star by Solar System standards.

That proximity has major consequences. The planet receives an estimated 117 times as much stellar energy as Earth receives from the Sun, and its calculated equilibrium temperature is approximately 909 kelvin, or about 636 degrees Celsius. An equilibrium temperature is not the same as a measured surface temperature—it is a theoretical temperature that depends on assumptions about how the planet absorbs and redistributes incoming energy—but it provides an important indication of the extreme environment in which HD 23472 d exists.

The most intriguing feature of HD 23472 d is its density. The current values listed by the NASA Exoplanet Archive give an estimated bulk density of approximately 7.5 grams per cubic centimeter, with large uncertainties. Earth's mean density is about 5.5 grams per cubic centimeter, while Mercury's is about 5.4 grams per cubic centimeter. HD 23472 d's central estimate is therefore unusually high for a planet of its size, although the uncertainty range is broad enough that its exact composition remains unresolved.

This is where the term "super-Mercury" becomes relevant. In exoplanet science, a super-Mercury is generally understood as a small rocky planet with an unusually high proportion of iron and other heavy elements, giving it a disproportionately large metallic core. The term does not mean that the planet is simply a larger version of Mercury. Rather, it describes a class of planets whose bulk composition appears to be more metal-rich than that of typical rocky planets. The 2022 study of HD 23472 proposed that planets d and e could be super-Mercuries based on their high inferred densities and internal-structure modelling.

The comparison with Mercury is especially interesting because both worlds are close to their respective stars, but the resemblance should not be overstated. Mercury is the innermost planet of our Solar System and has a large iron core relative to its size, while HD 23472 d is much smaller than Earth and orbits a different type of star under a radically different set of planetary-system conditions. The evidence for a super-Mercury interpretation comes primarily from the planet's inferred bulk density and models of its interior, not from direct observations of its core. Astronomers therefore cannot yet say with certainty exactly how much iron lies beneath its surface.

HD 23472 d's small size is itself significant. With a radius of only about three-quarters that of Earth, HD 23472 d lies firmly in the realm of small terrestrial-size exoplanets. Measuring the masses of such low-mass planets is technically difficult because their gravitational influence on their host stars is extremely weak. The 2022 research highlighted the ability of ESPRESSO to obtain radial-velocity measurements precise enough to characterize planets among the lowest-mass worlds for which such measurements had been obtained at the time.

HD 23472 d is also important because it is not an isolated planet. It is part of a tightly packed system containing at least five confirmed planets. The innermost three—HD 23472 d, e, and f—are approximately Earth-sized, while planets b and c are larger, with radii around two Earth radii and 1.85 to 1.9 Earth radii, respectively, according to the 2022 characterization and current NASA Exoplanet Archive data. Their orbital periods increase outward from about four days to nearly 30 days.

The architecture of this system may provide clues about how its planets formed. The 2022 study found a pattern in which the estimated gas and water fractions generally increase with distance from the host star. The researchers argued that this trend is consistent with a system shaped by irradiation: planets closer to the star would have experienced stronger heating, potentially losing volatile material more readily, while planets farther away could retain greater amounts of water or gaseous material. In that picture, HD 23472 d represents an especially extreme inner member of a planetary system whose composition changes systematically with distance from its star.

This interpretation also helps explain why HD 23472 d and its neighboring planet HD 23472 e attracted particular attention. Both are small, dense planets on very short-period orbits. The study estimated similar bulk densities for the two worlds and suggested that they could represent a rare pair of super-Mercuries. If that interpretation is confirmed, the system would be an exceptional test case for competing theories of how metal-rich rocky planets form.

One possible explanation for super-Mercury formation is that intense stellar irradiation and atmospheric loss stripped away lighter materials, leaving behind a relatively metal-rich remnant. Another possibility is that the planets formed with unusually large iron cores from the beginning, perhaps because of the conditions in the protoplanetary disk or through giant impacts that removed part of their rocky mantles. Determining which scenario is correct requires more than measuring density alone. Astronomers need better mass and radius measurements, improved models of planetary interiors, and a larger population of comparable planets for statistical comparison.

HD 23472 d is also a reminder of how much information astronomers can extract from tiny changes in starlight and stellar motion. The planet cannot be photographed directly with current instruments, and its physical surface has not been observed. Instead, researchers infer its properties from the way it affects its star. Its radius comes primarily from transit geometry, while its mass is inferred from the star's motion. From these measurements, scientists can estimate density and then test possible interior structures. It is an indirect process, but one that has transformed the study of planets beyond the Solar System.

There is, however, an important scientific caution when discussing HD 23472 d. Calling it a "super-Mercury" is a compelling interpretation, not a direct observation of its core. The mass and density measurements carry significant uncertainties, and different assumptions about a planet's interior can produce different compositional models. The NASA Exoplanet Archive currently lists a mass estimate of about 0.55 Earth masses with an uncertainty of roughly 0.2 Earth masses and a radius of about 0.75 Earth radii with an uncertainty of approximately 0.06 Earth radii. Those uncertainties propagate into the density estimate, which is itself correspondingly uncertain.

Even so, HD 23472 d remains scientifically valuable. Its combination of small size, short orbital period, high irradiation, and apparently high density makes it a particularly useful target for studying the boundary between ordinary rocky planets and metal-rich worlds. Its position within a five-planet system adds another layer of significance: instead of studying one unusual planet in isolation, astronomers can compare multiple worlds that formed around the same star but now experience very different environments.

For now, HD 23472 d is best described as a small, hot, high-density exoplanet and a strong candidate for a super-Mercury composition. Its estimated radius is around 75% that of Earth, its orbital period is just under four days, and its inferred density is high enough to make a metal-rich interior a plausible explanation. Yet the most important story may not be the planet itself, but the planetary system around it. By comparing HD 23472 d with its four known companions, astronomers can investigate how stellar irradiation, orbital architecture, volatile loss, and planetary composition interact over billions of years.

HD 23472 d therefore occupies an intriguing place in modern exoplanet science. It is neither an Earth twin nor a conventional super-Earth, and its extreme environment makes it an unlikely candidate for habitability. Its real importance lies elsewhere: it may preserve evidence of a radically different planetary formation history, encoded in an unusually dense interior. As observations improve and the population of known small exoplanets grows, worlds like HD 23472 d will help scientists determine whether super-Mercuries are rare cosmic oddities or a common outcome of planet formation around other stars.

CD-35 2722 b: the young, massive exoplanet companion challenging how we define a planet

CD-35 2722 b is one of the most unusual objects in the nearby exoplanet population. Discovered in 2011 through direct imaging, this enormous world orbits the young M-dwarf star CD-35 2722 at a projected distance of roughly 67 astronomical units, placing it far beyond the orbital region occupied by the giant planets of our Solar System. With a mass estimated at about 29.5 Jupiter masses and a radius of approximately 1.55 times that of Jupiter, it sits in the poorly defined territory between giant planets and brown dwarfs. Its remarkable properties make it valuable not only for studying how massive planetary companions form, but also for understanding the earliest stages of substellar evolution.

The system is located roughly 22 parsecs, or about 72 light-years, from Earth. Its host star, CD-35 2722 A, is a relatively cool M1-type dwarf with a mass of approximately 0.55 times that of the Sun and a radius of about 0.56 solar radii according to current NASA Exoplanet Archive parameters. The star is also young, with an estimated age of around 100 million years, although age estimates for young stellar systems can carry substantial uncertainty. The companion's youth is particularly important because young substellar objects retain heat from their formation and therefore remain much brighter in the infrared than comparable objects of the same mass would be after billions of years of cooling.

The object now cataloged as CD-35 2722 b was originally identified as CD-35 2722 B, a substellar companion to the nearby young M dwarf. The discovery came from the Gemini NICI Planet-Finding Campaign, which used high-contrast near-infrared imaging to search for faint companions around nearby stars. Astronomers detected the companion at a wide separation of about 67 AU and used observations at multiple epochs to establish that it was physically associated with the star rather than a distant background object. Near-infrared spectroscopy classified the companion as approximately an L4 dwarf, while its spectral characteristics and relatively low surface gravity were consistent with a young substellar object.

Direct imaging was crucial to the discovery. Unlike the transit method, which finds planets when they pass in front of their stars, or the radial-velocity method, which measures the gravitational wobble induced in a star, direct imaging attempts to detect the companion's own light. This is particularly effective for young, massive planets and brown dwarfs because they can still radiate substantial amounts of thermal energy left over from their formation. The challenge is that the host star is vastly brighter than its companion, so sophisticated coronagraphy, adaptive optics, image processing, and infrared observations are required to separate the two signals. CD-35 2722 b became an important example of what these techniques can reveal about young planetary systems.

The object's mass is where the terminology becomes especially interesting. Early evolutionary modeling based on the companion's luminosity and the estimated age of the system produced a mass of about 31 ± 8 Jupiter masses. More recent values listed by the NASA Exoplanet Archive give a mass of approximately 29.5 Jupiter masses, with uncertainties of roughly +5.1 and −4.3 Jupiter masses. These estimates place CD-35 2722 b well above the conventional deuterium-burning threshold often used as a rough dividing line between planets and brown dwarfs, although that threshold is not a universally accepted physical definition of a brown dwarf.

This distinction matters because mass alone does not necessarily tell the complete story of an object's origin. In astronomy, the difference between a planet and a brown dwarf is often discussed in terms of formation history as well as mass. A planet is generally expected to form within a circumstellar disk through processes such as core accretion or gravitational instability, while a brown dwarf can form more like a star through the collapse and fragmentation of a molecular cloud. At roughly 30 Jupiter masses, CD-35 2722 b is massive enough that its formation mechanism is a central scientific question.

Its enormous separation from its host star provides an important clue. At a projected distance of about 67 AU, the companion orbits much farther from its star than Jupiter does from the Sun. Recent studies of its atmospheric chemistry and the chemical relationship between the companion and its host star have suggested that gravitational instability may be a plausible formation pathway. The companion's mass, wide orbit, and estimated planet-to-host mass ratio of roughly 0.05 are consistent with a scenario in which the young circumstellar environment became unstable and fragmented, producing a massive substellar object at a large distance from the star. However, formation histories of individual objects are difficult to establish with absolute certainty, and alternative pathways cannot necessarily be excluded.

The physical appearance of CD-35 2722 b is equally fascinating. Its radius is estimated at about 1.55 times Jupiter's radius, while its mass is nearly 30 times greater than Jupiter's. That combination implies an object with much greater mass but only moderately larger size, reflecting the unusual physics of gas giants and brown dwarfs. As substellar objects become increasingly massive, their interiors become strongly compressed by gravity, so their radii do not increase proportionally with mass. In fact, objects spanning a broad range of brown-dwarf and giant-planet masses can have surprisingly similar physical dimensions.

The companion's atmosphere also offers a window into the physics of young L dwarfs. The original discovery study estimated an effective temperature in the range of approximately 1,700 to 1,900 kelvin and found evidence of relatively low surface gravity. These characteristics are consistent with a young object that has not yet contracted and cooled to the state expected of an old field brown dwarf. Its infrared spectrum showed similarities to dusty L dwarfs, while its colors and absolute magnitudes also resembled those of some much younger planetary-mass companions. This made CD-35 2722 b an especially useful benchmark for comparing the atmospheres of young brown dwarfs and directly imaged giant planets.

More recent atmospheric work has added another layer to the story. High-resolution spectroscopy has been used to investigate the chemical composition of CD-35 2722 b and compare it with that of its host star. The results indicate that, after accounting for systematic uncertainties, the atmospheric metallicity and carbon-isotope measurements of the companion are broadly compatible with the chemical composition of the star. This chemical similarity supports the idea that the two objects formed from the same original reservoir of material and is consistent with a formation scenario involving gravitational instability. The study also found no clear evidence for clouds in the analyzed data, despite the companion's red photometric appearance and its classification as a mid-L dwarf, illustrating how complex the relationship between observed colors and atmospheric cloud properties can be.

CD-35 2722 b also demonstrates why directly imaged companions are so important to exoplanet science. Most exoplanets discovered by transit and radial-velocity surveys are relatively close to their host stars, partly because those methods are much more sensitive to short-period systems. A massive companion separated by dozens of astronomical units would be extraordinarily difficult to detect through the small gravitational wobble of the host star or through a transit. Direct imaging, by contrast, is naturally suited to finding young, luminous objects on wide orbits. As a result, systems such as CD-35 2722 provide astronomers with rare opportunities to study planetary-mass and substellar companions in regions of planetary systems that remain largely inaccessible to conventional detection techniques.

The orbit itself is also extraordinarily long. NASA lists an orbital period of approximately 867.6 years for CD-35 2722 b, based on an orbital radius of about 67 AU. That means astronomers cannot simply watch the object complete an orbit within a human lifetime. Instead, orbital characterization depends on precise astrometric measurements accumulated over many years and on combining those observations with models of the system's dynamics. Continued monitoring will gradually improve estimates of the companion's orbit, inclination, and true separation, potentially helping researchers determine how its current configuration arose.

The system has become even more scientifically intriguing in 2026. A study published in Nature reported evidence for a planetary-mass object orbiting the brown-dwarf companion CD-35 2722 B itself. The researchers used radial-velocity measurements obtained from high-resolution spectra of the brown dwarf with the VLT/CRIRES+ instrument. Their best-fitting model indicated a satellite with a minimum mass of roughly 0.9 Jupiter masses and an orbital period of around 170 days. The result is potentially groundbreaking, but the authors emphasize that the terminology is complicated: the candidate orbits a brown dwarf rather than a conventional planet, and the criteria for calling such an object an exomoon are not formally settled.

If this signal is confirmed through independent observations, the CD-35 2722 system could become a uniquely important laboratory for studying hierarchical systems that do not fit neatly into the familiar categories of star, planet, and moon. The proposed companion is massive enough to resemble a planet, yet it appears to orbit a brown dwarf that itself circles a star. In other words, the system may contain a star, a brown dwarf, and a planetary-mass satellite-like object arranged in a configuration with no close analogue in our Solar System. The researchers' best-fitting model also included a second, less certain candidate with a minimum mass of about 0.28 Jupiter masses and an orbital period of approximately 87 days, although that signal is considerably less secure.

This possible discovery does not change the established properties of CD-35 2722 b itself, but it does make the system even more significant. The brown dwarf traditionally identified as CD-35 2722 B is now also cataloged as CD-35 2722 b in major exoplanet databases, reflecting the evolving conventions used to classify massive substellar companions. The underlying scientific reality, however, remains more nuanced than a simple label: with a mass around 30 Jupiter masses, the object lies firmly in the brown-dwarf regime under commonly used mass-based definitions, even though it is listed in exoplanet catalogs and was originally discovered as a substellar companion through direct imaging.

For researchers, that ambiguity is part of what makes CD-35 2722 b so valuable. It provides a natural test case for examining where the boundary between planets and brown dwarfs should be drawn, whether formation history should be given greater weight than mass, and how objects formed in different environments evolve atmospherically. Its youth makes it bright enough for detailed observations, its wide separation makes it accessible to direct-imaging techniques, and its high mass makes it an important benchmark for theories of substellar formation.

CD-35 2722 b is therefore much more than a distant giant world orbiting a small star. It is a massive, young, directly imaged substellar object whose properties sit at the intersection of planetary science and brown-dwarf astronomy. Its wide orbit challenges simple models of planet formation, its atmosphere offers a rare opportunity to study the evolution of young L dwarfs, and the possible presence of a planetary-mass satellite around its brown-dwarf host could make the broader system one of the most extraordinary known nearby substellar architectures. As astronomers continue to collect astrometric, spectroscopic, and high-resolution infrared observations, CD-35 2722 b is likely to remain an important reference point in the effort to understand how massive worlds form, how they evolve, and where the boundaries between planets, brown dwarfs, and moons truly lie.

K2-413 b: everything we know about the tiny scorching exoplanet orbiting its star in just 19 hours

K2-413 b is one of the smallest confirmed rocky exoplanets discovered by NASA's extended Kepler mission, K2. Although it is far too hot to support life, this remarkable world provides astronomers with valuable insights into the formation, evolution, and survival of terrestrial planets orbiting extremely close to their host stars. Its compact size, ultra-short orbital period, and membership in a multi-planet system make it an important target for researchers seeking to understand how planetary systems develop throughout the Milky Way.

The planet was officially announced in 2022 after being identified through the transit method, which detects the tiny decrease in a star's brightness when a planet passes in front of it. This technique has become one of the most successful methods for discovering exoplanets and was responsible for thousands of discoveries during NASA's Kepler and K2 missions. K2-413 b was identified alongside a second planet in the same system, K2-413 c, demonstrating that even relatively small stars can host multiple compact rocky worlds.

K2-413 b orbits a K-type star, which is cooler and smaller than the Sun. The host star has an estimated surface temperature of about 4,129 Kelvin and lies approximately 285 parsecs, or roughly 930 light-years, from Earth. K-type stars are particularly interesting for exoplanet studies because they combine long lifetimes with relatively stable energy output, making them attractive environments for planetary systems, even though K2-413 b itself is far too close to its star to be habitable.

One of the planet's most striking characteristics is its incredibly short year. K2-413 b completes a full orbit in only about 0.81 days, or approximately 19.5 hours. It circles its star at a distance of just 0.0117 astronomical units, placing it nearly one hundred times closer to its star than Earth is to the Sun. At such a tiny orbital distance, the planet is exposed to intense stellar radiation, producing surface temperatures that would make the existence of liquid water impossible.

Despite its extreme environment, K2-413 b is scientifically fascinating because of its size. The planet has a radius of approximately 0.76 times that of Earth, making it significantly smaller than our planet and one of the smallest confirmed exoplanets known. Current estimates place its mass at around 0.36 Earth masses, suggesting that it is a rocky terrestrial world rather than a gas-rich mini-Neptune or sub-Neptune. Its relatively low mass also indicates a weaker gravitational pull compared with Earth.

The existence of such a small planet so close to its host star raises important questions about planetary formation and survival. Astronomers continue to investigate whether planets like K2-413 b formed near their present locations or migrated inward after forming farther away in the protoplanetary disk. The intense radiation from the star could also have stripped away any primordial atmosphere over billions of years, leaving behind only the dense rocky core observed today. These processes are central to understanding how planetary systems evolve.

The K2-413 system itself offers additional scientific value because it contains at least two confirmed planets. The outer companion, K2-413 c, orbits every 5.33 days and is slightly larger than K2-413 b. Studying both planets within the same stellar environment allows astronomers to compare how orbital distance influences planetary composition, atmospheric evolution, and long-term stability. Such comparisons help refine theoretical models of compact planetary systems that have become increasingly common among Kepler and K2 discoveries.

Although K2-413 b has no realistic potential for habitability, its discovery contributes to the broader effort of understanding rocky planets throughout the galaxy. Every confirmed terrestrial exoplanet improves statistical models describing how frequently Earth-sized worlds occur around different types of stars. These data are essential for future missions that aim to identify planets located within habitable zones where liquid water could exist.

NASA's K2 mission, which continued after the original Kepler spacecraft lost two reaction wheels, demonstrated remarkable resilience by observing different regions of the sky along the ecliptic plane. Despite operating under significant engineering limitations, K2 successfully discovered hundreds of new exoplanets, including compact systems like K2-413. These discoveries continue to expand the catalog of known worlds and provide valuable targets for future observations with advanced observatories such as the James Webb Space Telescope and upcoming next-generation missions.

K2-413 b may never become one of the most famous exoplanets, but it represents an important piece of the growing puzzle of planetary diversity. Its tiny size, rocky composition, blistering orbit, and membership in a multi-planet system illustrate just how varied planetary systems can be across the galaxy. As astronomers continue to refine observational techniques and discover even smaller worlds, planets like K2-413 b help bridge the gap between theoretical models and the astonishing reality of the universe beyond our Solar System.