Unraveling Cosmic Mysteries: Why Some Exoplanets Are Shrinking, Revealed by Kepler Space Telescope Data

In a groundbreaking study that delves into one of the enduring mysteries of space, scientists have utilized data from NASA’s retired Kepler Space Telescope to uncover evidence explaining why certain exoplanets are shrinking in size. Led by Caltech/IPAC scientist Jessie Christiansen, the research suggests a fascinating link between the cores of specific sub-Neptune planets and the reduction of their atmospheres.

Exoplanets, planetary bodies discovered beyond our solar system, number over 5000 so far. However, astronomers have long observed a peculiar “size gap” between rocky super-Earths and gaseous sub-Neptunes, with a scarcity of planets having diameters between 1.5 and 2 times that of Earth.

Published in The Astronomical Journal, the study proposes that atmospheric loss in less massive sub-Neptunes could be the key factor behind this size gap. Jessie Christiansen explains, “Our findings indicate there’s a significant factor preventing these planets from maintaining or achieving this size.”

The research introduces two primary mechanisms driving atmospheric loss: core-powered mass loss and photoevaporation. The evidence strongly supports core-powered mass loss, where radiation from a planet’s hot core gradually forces the atmosphere outwards.

Photoevaporation, akin to a hairdryer melting an ice cube, occurs when a star’s intense radiation strips away a planet’s atmosphere. While this process is believed to transpire within the first 100 million years of a planet’s existence, core-powered mass loss likely occurs around the 1 billion-year mark.

To substantiate their theories, the research team scrutinized data from the K2 mission, concentrating on the young star clusters Praesepe and Hyades. The findings revealed that nearly all stars in these clusters still harbor sub-Neptune planets, indicating that their atmospheres have not been eroded by photoevaporation. This observation strongly supports core-powered mass loss as the more plausible explanation for the observed size gap.

The implications of this study extend beyond solving a cosmic puzzle; they provide insights into the evolution of exoplanet atmospheres, offering potential clues about the habitability of distant worlds. As Christiansen notes, ongoing research and future studies will continue to test and refine these theories, unlocking further mysteries of the universe.