Free Astronomy Magazine May-June 2022

40 MAY-JUNE 2022 ASTRO PUBLISHING E xoplanets come in shapes and sizes that are not found in our solar system. These include small gaseous planets called mini-Neptunes and rocky planets several times Earth’s mass called super-Earths. Now, astronomers have identified two different cases of “mini-Neptune” planets that are losing their puffy atmospheres and likely transforming into super-Earths. Radiation from the planets’ stars is stripping away their atmospheres, driving the hot gas to escape like steam from a pot of boiling water. The new findings help paint a pic- ture of how exotic worlds like these form and evolve, and help explain a curious gap in the size distribution of planets found around other stars. Mini-Neptunes are smaller, denser versions of the planet Neptune in our solar system, and are thought to consist of large rocky cores sur- rounded by thick blankets of gas. In the new studies, a team of astronomers used NASA’s Hub- ble Space Telescope to look at two mini-Nep- tunes orbiting HD 63433, a star located 73 light-years away. And they used the W. M. Keck Observatory in Hawaii to study one of two mini- by NASA/ESA Ray Villard Two mini-Neptunes that are transforming into super-Earths I n this artistic animation, the mini-Neptune TOI 560.01 is shown transforming into a super-Earth. The planet is about 2.8 times the size of Earth and has a puffy atmosphere, made up of mostly hydrogen and helium. Observations with the W. M. Keck Observatory in Hawaii revealed that helium is escaping from the planet. Scientists say that the planet could lose the vast ma- jority of its atmosphere after several hundred million years, leaving behind a type of large rocky planet called a super-Earth. [Adam Makarenko (Keck Observatory)]