The discovery of exoplanets has opened up a whole new world of possibilities in our understanding of the universe. However, scientists at NASA have been puzzled by a strange phenomenon – a group of planets that seem to be shrinking. While there are plenty of super-Earths and sub-Neptunes among the over 5,000 exoplanets discovered, there is a mysterious gap where planets about 1.5 to two times the width of Earth should be. According to Jessie Christiansen, a research scientist at Caltech, there is something going on that prevents planets from reaching and staying at this size. But what could be the cause?
Christiansen’s latest research suggests that radiation from the planets’ cores may be the key to understanding the shrinking exoplanets. The study, published in The Astronomical Journal, proposes the hypothesis of “core-powered mass loss” as a potential explanation for the phenomenon. This hypothesis suggests that a planet’s core emits radiation, which pushes its atmosphere from underneath, leading to its separation from the planet over time.
While the core-powered mass loss hypothesis seems plausible, another hypothesis called photoevaporation also exists. This hypothesis proposes that a planet’s atmosphere is dissipated by the radiation of its host star. However, this process is thought to occur when a planet is around 100 million years old, whereas core-powered mass loss could occur closer to the planet’s one billionth birthday. To test these hypotheses, Christiansen’s team turned to data from NASA’s retired Kepler Space Telescope.
The scientists examined star clusters that were over 100 million years old, as planets in these clusters would be old enough to have experienced photoevaporation but not old enough for core-powered mass loss. Surprisingly, most of the planets in these clusters retained their atmosphere, suggesting that core-powered mass loss may be the more likely cause of eventual atmosphere loss. However, recent research indicates that both processes may operate simultaneously, adding to the complexity of the mystery.
While Christiansen’s research may shed some light on the shrinking exoplanet phenomenon, the mystery is far from being completely solved. The exact mechanism for the loss of atmospheres in these planets remains unclear, leaving scientists with more questions than answers. Christiansen herself acknowledges that her work is not over yet, especially considering how our understanding of exoplanets will continue to evolve with time.
As researchers delve deeper into the study of exoplanets, more intriguing discoveries are bound to happen. Exploring the vast expanse of the universe and uncovering the secrets held within distant planets will remain an exciting endeavor for scientists. While the mystery of shrinking exoplanets may still persist, it serves as a reminder of how much we have yet to learn about the universe and our place in it.