Discover How Some Exoplanets Are Shrinking
Researchers have used data from the Kepler Space Telescope to uncover a surprising trend: some exoplanets are actually shrinking due to the loss of their atmospheres, believed to be caused by radiation from their cores. This discovery has helped to shed light on the observed size gap in exoplanets and has revealed a significant atmospheric loss process unlike anything previously theorized.
A new study has brought forth an intriguing explanation for the ‘missing’ exoplanets that fall between super-Earths and sub-Neptunes. In this study, data collected from NASA’s retired Kepler Space Telescope revealed that certain exoplanets are losing their atmospheres and shrinking. The evidence also suggests that the cores of these planets are responsible for pushing away their atmospheres from the inside out.
Astronomers have known for quite some time that exoplanets come in a variety of sizes, ranging from small, rocky planets to colossal gas giants. However, there has always been a noticeable gap in the sizes of planets, with those that fall between 1.5 to 2 times the size of Earth puzzling scientists. According to Caltech/IPAC research scientist Jessie Christiansen, there are fewer planets than expected with a diameter between 1.5 and 2 times that of Earth. The newfound evidence from this study provides new insights into the observed planetary gap.
Furthermore, researchers think that the gap could be attributed to certain sub-Neptunes losing their atmospheres over time. The lack of enough mass and gravitational force to hold onto their atmospheres causes these sub-Neptunes to shrink down to about the size of super-Earths, leading to the observed size gap. Scientists have considered two potential mechanisms for how these planets are losing their atmospheres: core-powered mass loss and photoevaporation. However, the study has uncovered compelling new evidence that supports the former explanation.
Core-powered mass loss occurs when radiation emitted from a planet’s hot core pushes away its atmosphere over time. This discovery has caused researchers to reconsider the entire theory about how certain sub-Neptunes are losing their atmospheres.
The study utilized data from NASA’s K2, an extended mission of the Kepler Space Telescope, and observed star clusters Praesepe and Hyades. The observations found strong evidence that core-powered mass loss, rather than photoevaporation, is the leading explanation for what happens to the atmospheres of these planets. The research also points to the core-powered mass loss taking place much later in a planet’s life compared to photoevaporation.
While this new study led by Jessie Christiansen’s team is indeed significant, the research is still ongoing. The findings will likely be tested by future studies before there is a definitive conclusion to this perplexing planetary mystery.