NASA's findings suggest a potential explanation for the shrinking of certain exoplanets

On Wednesday, November 15th, astronomers made an intriguing discovery regarding certain planets beyond our solar system. It appears that these worlds are gradually losing their atmospheres, causing them to shrink in size. Interestingly, this phenomenon is not a result of forceful winds from their stars, but rather a consequence of their own actions. A recent study conducted with NASA's retired Kepler Space Telescope suggests that the cause of this phenomenon may be due to the planets' cores pushing their atmospheres outwards from the inside.

In the vast expanse of the universe, exoplanets exhibit a remarkable diversity in size. Ranging from small, rocky planets to colossal gas giants, they captivate scientists' curiosity. However, a peculiar phenomenon known as the "size gap" has caught the attention of researchers. This gap refers to the absence of planets that fall between 1.5 to 2 times the size of Earth, lying between the rocky super-Earths and the larger sub-Neptunes with their expansive atmospheres. Scientists have been diligently working to shed light on the mysteries surrounding this intriguing gap.

Caltech/IPAC research scientist Jessie Christiansen, the science lead for the NASA Exoplanet Archive and lead author of a recent study in The Astronomical Journal, has confirmed that scientists have detected over 5,000 exoplanets. However, it is surprising to note that there are fewer planets with a diameter between 1.5 and 2 times that of Earth than initially expected. Christiansen suggests that there may be some underlying factors preventing planets from reaching or maintaining this particular size range. The explanation for this gap in the sizes of sub-Neptunes and super-Earths lies in the possibility of certain sub-Neptunes gradually losing their atmospheres. This occurs when these planets lack sufficient mass and gravitational force to retain their atmospheres. Consequently, sub-Neptunes that are not massive enough would diminish in size, resembling super-Earths, thus creating the observed gap. However, the precise mechanisms behind the atmospheric loss of these planets have remained enigmatic. Scientists have identified two probable mechanisms: core-powered mass loss and photoevaporation. The latest study has revealed new evidence that supports the former mechanism.

Core-powered mass loss refers to the phenomenon where the radiation emitted from a planet's hot core gradually pushes its atmosphere away. It is worth mentioning that this radiation exerts pressure on the atmosphere from below and the phenomenon of photoevaporation takes place when a planet's atmosphere is essentially stripped away by the scorching radiation emitted by its host star. In this analogy, the star's high-energy radiation acts as a hair dryer, causing the planet's atmosphere to dissipate like an ice cube, This is believed to take place within the initial 100 million years of a planet's formation, whereas core-powered mass loss is expected to occur much later, around 1 billion years into the planet's life. Christiansen explained that in either scenario, the lack of sufficient mass would result in the inability to retain an atmosphere, causing a shrinkage.

In exploring the fascinating phenomena of core-powered mass loss and photoevaporation, we gain valuable insights into the dynamic and intricate processes shaping exoplanets. As we unravel the mysteries of these celestial bodies, it's a testament to the continuous advancements in our understanding of the cosmos. The journey of discovery is marked by these extraordinary findings, propelling us further into the frontiers of space exploration. Together, these revelations not only deepen our knowledge of exoplanets but also underscore the incredible achievements made in the quest to comprehend the vast and awe-inspiring universe that surrounds us.