Shape shifter

Look: "Puffy" planets could solve a longstanding exoplanet mystery

Are Mini-Neptunes just giant Super-Earths?

W. M. Keck Observatory/Adam Makarenko

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To get a grasp on the size of exoplanets, researchers often compare them to familiar bodies in the Solar System.

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Mini-Neptunes, for example, describe bodies that are larger than Earth but smaller than Neptune.

They typically contain rocky cores and puffy, gaseous atmospheres — not unlike actual Neptune itself.

But some Mini-Neptunes might be shape-shifters.

Researchers observed two losing their atmospheres — suggesting that they may eventually morph into a different type of planet.

W. M. Keck Observatory/Adam Makarenko

Writing in a pair of reports for The Astronomical Journal, researchers documented the shifting atmospheres of exoplanets HD 63433c and TOI 560.01.

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Both planets are actively losing mass, as evidenced by the detection of gas flowing off the planets.

W. M. Keck Observatory/Adam Makarenko

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Radiation from their stars strips away the puffy outer layers of gas, which will cause the planets to transform over the next few million years.

The result may be a planet that looks similar to another type we’ve seen elsewhere: Super-Earths.

These rocky bodies are smaller than Mini-Neptunes and common among exoplanets found in the Milky Way.

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Without their gaseous atmospheres, the cores of the two Mini-Neptunes could become rocky planets, not unlike Earth and Mars.

Mini-Neptunes and Super-Earths have been observed orbiting in the same star systems before — such as the TOI 270 system, which was discovered in 2019.

NASA’s Goddard Space Flight Center/Scott Wiessinger

W. M. Keck Observatory/Adam Makarenko

But more evidence is needed to confirm if Mini-Neptunes actually transform into Super-Earths.

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If confirmed, this discovery could help explain why there aren’t many exoplanets that fall between Mini-Neptune and Super-Earth size.

It could simply be due to the fact that smaller Mini-Neptunes are just transitioning into Super-Earths.