Exoplanets like Neptune losing atmosphere: Explaining the Fulton gap

Neptun-like exoplanets that are slightly larger than Earth could lose their atmosphere as radiation from their core pushes it from the inside out, according to a recent analysis. This is one possible explanation for the phenomenon known as the Fulton gap, as suggested by the analysis. The Fulton gap describes the absence of exoplanets between the largest super-Earths and the smallest mini-Neptunes. Benjamin Fulton from the California Institute of Technology (Caltech) has found that this type of exoplanet is underrepresented. A possible explanatory model is now being presented by a team led by Jessie Christiansen from the Exoplanet Archive at NASA.

The term Fulton gap was used to describe the striking absence of exoplanets that are more than 75 percent larger than Earth but less than two and a half times its size. Such exoplanets are found less frequently than expected based on current theories of planet formation. Christiansen’s team has proposed two different explanations for the gap between the largest rocky planets and the smallest ice giants. Either the dense atmospheres around the solid cores are pushed away relatively early by their respective stars, or the radiation from the interior of the celestial bodies removes them much later in the life cycle of the exoplanets.

To test these hypotheses, the research team has created two catalogs of stars discovered to have exoplanets by the Kepler space telescope, which are in different age groups, in painstaking detail over many years. The investigations revealed that almost all stars in the younger group had a mini-Neptune, while this was only the case for about 25 percent of the stars in the older group. This suggests that it is not the stars themselves, but rather the exoplanets themselves, that push away the atmospheres and shrink only in a very late stage.

However, the research team emphasizes that further investigations are necessary to confirm whether the findings published in the Astronomical Journal actually solve the mystery of the Fulton gap. Nevertheless, there is now a promising hypothesis to focus on. This work was only possible thanks to the NASA Exoplanet Archive. The information from the archive is publicly accessible and currently includes over 5,500 confirmed exoplanets as well as thousands of unconfirmed candidates. The research also relies on the extensive data collection of the Kepler space telescope, whose nine-year mission ended in 2018. This instrument alone discovered about half of all known exoplanets.

Schlagwörter: Neptunähnliche Exoplaneten + FultonLücke + Strahlung aus den Kernen

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