Astronomers watch super-earths whose atmosphere has been destroyed by their stars


As the planets of our solar system demonstrate, understanding the solar dynamics of a system is a crucial aspect in determining habitability. Due to its protective magnetic field, the Earth has maintained a fluffy atmosphere for billions of years, ensuring a stable climate for the evolution of life. In contrast, other rocky planets that orbit our Sun are either airless, have a super dense atmosphere (Venus), or have very thin atmospheres (Mars) due to their interactions with the Sun.

In recent years, astronomers have been on the lookout for this same process when studying extrasolar planets. For example, an international team of astronomers led by the National Astronomical Observatory of Japan (NAOJ) recently carried out a follow-up observations of two Super-Earths which orbit very close to their respective stars. These planets, which do not have thick primordial atmospheres, represent a chance to study the evolution of atmospheres on hot rocky planets.

The study that described their findings, which were recently published in The Journal of Astrophysics, was led by Dr Teruyuki Hirano from NAOJ and The University of Higher Studies (SOKENDAI) in Tokyo, Japan. He was joined by researchers from the Instituto de Astrofísica de Canarias (IAC), SETI Institute at NASA’s Ames Research Center, the Harvard-Smithson Center for Astrophysics (CfA), the University of Tokyo and many other institutes.

Artist’s impression of the TOI-1634b and TOI-1685b Super-Earths. Credit: NASA Exoplanet Catalog

Dr Hirano and his team chose two planets originally identified by NASA Spaceship investigating exoplanets in transit (TRIAL) – TOI-1634b and TOI-1685b. These two super-Earth planets that orbit M-type stars (red dwarfs) located approximately 114 and 122 light years (respectively) in the constellation Perseus. Using the InfraRed Doppler (IRD) spectrograph mounted on the Subaru 8.5 m (~ 28 ft) telescope, the team made several confirmations about these two rocky exoplanets.

For starters, Dr Hirano and his colleagues confirmed that the candidates are rocky super-Earths that measure 1.7 and 1.79 Earth’s radii and are 4.91 and 3.78 times more massive. They also confirmed that they have ultra-short orbital periods, taking 24 hours and less than 17 hours to complete a single orbit around their stars. This makes TOI-1634b one of the largest and most massive ultra-short-lived rock exoplanets confirmed to date.

But more importantly, the spectra they obtained provided insight into the internal and atmospheric structures of these planets. What they found was that they were “naked,” meaning they lacked a primordial hydrogen-helium atmosphere, similar to what Earth had billions of years ago. . In all likelihood, this is due to the proximity of the planets to their host stars, which are prone to eruption activity.

Additionally, the “bare” nature of these rocky planets raises the possibility of a secondary atmosphere caused by volcanic outgassing. This is also what has happened on Earth billions of around. 2.5 billion years ago, which caused the Earth to change from a hydrogen-helium atmosphere to an atmosphere composed mainly of carbon dioxide, sulfur dioxide and other gases from our planet.

This artist’s impression shows the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star in the solar system. Credit: ESO / M. Kornmesser

Therefore, these planets are a major opportunity to study how atmospheres evolve on rocky planets, especially those that orbit red dwarf stars. In addition, the fact that these planets are “naked” means that astronomers will be able to test theories regarding the rocky planets that orbit near red dwarf stars. Compared to G-type yellow dwarfs (like the Sun), red dwarfs are known to be variable and prone to flare-ups.

Since the rocky planets that orbit a red dwarf’s habitable zone are likely to be tidal locked (with one side constantly facing the star), astronomers are understandably curious whether they can maintain their atmosphere for a long time. Red dwarfs make up about 75% of the stars in the Milky Way, and many rocky planets have been found in red dwarf systems (including Proxima b, which orbits the star closest to us).

For all these reasons, the study of these exoplanets could have important implications in the search for extraterrestrial life. At the same time, it will help astronomers learn more about how this particular class of planets (Super-Earths) forms and evolves. “Our project of intensively tracking the planetary candidates identified by TESS with the Subaru Telescope is still ongoing, and many unusual planets will be confirmed over the next few years,” said Dr Hirano.

In the near future, other observations will be possible using new generation telescopes, including the James Webb Space Telescope (JWST). In addition to several ground observatories, astronomers will have the necessary instruments to detect and characterize the atmospheres of these planets.

Further reading: Subaru Telescope, The astronomical journal

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