Astronomers Look at Super-Earths That had Their Atmospheres Stripped Away by Their Stars

Understanding the solar dynamics of a system can help determine if it is habitable, as the planets in our Solar System show. Earth's protective magnetic field has kept it a warm, fluffy atmosphere over billions of years. This allows for the development of life. Contrary to this, other rocky planets orbiting our Sun are either completely airless (Venus), super-dense (Venus), and have extremely thin atmospheres (Mars). This is due to their interactions.
Astronomers have been looking for the same phenomenon in extrasolar planet studies over the past few years. An international team of astronomers, led by the National Astronomical Observatory of Japan(NAOJ), recently observed two Super-Earths orbiting very close to their stars. These planets have no thick primordial atmospheres and offer an opportunity to study the evolution of atmospheres in hot rocky planets.

The research that led to their findings was conducted by Dr. Teruyuki hirano, of The NAOJ and The Graduate University for Advanced Studies, (SOKENDAI), in Tokyo, Japan. He was joined by researchers at the Instituto de Astrofsica de Canarias, the SETI Institute of NASAs Ames Research Center and the Harvard-Smithson Center for Astrophysics, as well as many other institutes.

Artists impression of Super Earths TOI-1634b & TOI-1685b. Credit: NASA Exoplanet Catalog

Dr. Hirano's team selected two planets that were originally identified by NASAs Transiting Exoplanet Survey Spacecraft, (TESS), TOI-1634b or TOI-1685b. These Super-Earth planets orbit M-type (red dwarf), stars that are approximately 114 and 120 light-years apart (respectively). They are located in Perseus constellation. The team confirmed multiple exoplanets by using the InfraRed Doppler spectrograph mounted on Subaru Telescope (8.5m, 28ft).

Dr. Hirano and colleagues first confirmed that the candidates were rocky super-Earths with 1.7 and 1.79 Earth radiuses and are 4.91 to 3.78 times more massive. They also confirmed that their orbital periods are extremely short, with 24 and 17 hours respectively to complete one orbit around their stars. This makes TOI-1634b the largest and most massive of all known ultra-short-period rock exoplanets.

The most important thing was that the spectra provided information about these planets' internal and atmospheric structures. They discovered that the planets were barred, which means that they lack a primordial hydrogen-helium atmosphere similar to that of Earth billions of years back. This is most likely due to the planets' proximity to their host stars which are susceptible to flare activity.

These rocky planets are also bare, which raises the possibility that there is a secondary atmosphere from volcanic outgassing. This is what also happened on Earth billions of years ago. Earth's transition from a hydrogen-helium environment to one that is dominated by carbon dioxide, sulfur dioxide and other gases occurred 2.5 billion years ago.

This artist's impression shows Proxima B orbiting the red dwarf star Proxima Centauri. It is the nearest star in the Solar System. Credit: ESO/M. Kornmesser

These planets offer a great opportunity to study how atmospheres develop on rocky planets that orbit red dwarf star. Astronomers will also be able test theories about rocky planets orbiting close to red dwarf stars because these planets are barred. Red dwarfs, unlike G-type yellow dimers (like the Sun), are more variable and more prone to flare ups than G-type yellow dimers.

Astronomers are naturally interested in the ability of rocky planets to maintain their atmospheres, as they are likely to be tidally bound (with one side always facing towards the star). Red dwarfs account for 75% of the Milky Way's stars, and many rocky planets have also been discovered in red dwarf systems, including Proxima B, which orbits the nearest star to ours.

All of these reasons mean that studying exoplanets can have important implications for the search for extraterrestrial human life. It will also help astronomers to learn more about the formation and evolution of this specific class of planets (Super-Earths). Dr. Hirano said that our ongoing project to closely follow-up candidates for planetary spectra identified by TESS using the Subaru Telescope is still underway. Many unusual planets will also be confirmed over the next few years.

Future observations with next-generation telescopes such as the James Webb Space Telescope will allow for further observations. Astronomers will be able to use several ground-based observatories as well as the necessary instruments to characterize these planets' atmospheres.

Additional Reading: Subaru Telescope, The Astronomical Journal