TOI-174系

Imaginary Illustration of TOI-174 b

Imaginary Illustration of TOI-174

TOI-174 is a star located 127 light-years from Earth. This star, TOI-174, has five exoplanets, which are likely to be super-Earths and super-Mercuries.

The Transiting Exoplanet Survey Satellite (TESS) (a space telescope launched as part of NASA’s Explorer Program. Its mission is to search for exoplanets by observing an area 400 times larger than that of the Kepler Space Telescope using the transit method. (Launched in 2018) Observations using the transit method by TESS have indicated the possible existence of two exoplanet candidates, “TOI-174.01” and “TOI-174.02.”

Subsequently, in 2019, follow-up observations using Doppler spectroscopy were conducted with the High Accuracy Radial velocity Planet Searcher (HARPS) (an exoplanet observation instrument operated by the European Southern Observatory (ESO) since 2003), the existence of two planet candidates, TOI-174.01 and TOI-174.02, was confirmed through follow-up observations using Doppler spectroscopy, and they were named “TOI-174 b” and “TOI-174 c,” respectively.

Their orbital periods are approximately 17.7 days and 29.8 days, respectively, and the transit depths of these planets are 663 ± 48 ppm and 627 ± 61 ppm, respectively.

Following the confirmation of these planets, it was suggested in 2019 that “TOI-174.03,” “TOI-174.04,” and “TOI-174.05” might exist.

On September 27, 2022, follow-up observations using Doppler spectroscopy with ESPRESSO (the Echelle spectrograph mounted on the European Southern Observatory’s VLT) confirmed the existence of these three planets: “TOI-174.03,” “TOI-174.04,” and “TOI-174.05.” Starting with the planet having the shortest orbital period, TOI-174.04 was named “TOI-174 d,” TOI-174.05 was named “TOI-174 e,” and TOI-174.03 was named “TOI-174 f.”

Furthermore, research has indicated that b, c, and f are “super-Earths”—Earth-like planets with masses ranging from several to about ten times that of Earth. Additionally, it has been shown that d and e likely have compositions similar to Mercury in our solar system and are “super-Mercuries” with masses greater than that of Mercury.

Year of Discovery of the TOI-174 Series and Summary of the Project

Basic Information on the TOI-174 Series

References:

NASA, EXOPLANET CATALOG HD 23472b from https://exoplanets.nasa.gov/exoplanet-catalog/7338/hd-23472-b/

IAC, Astronomers discover a planetary system with three super-Earths and two super-Mercuries, from https://www.iac.es/en/outreach/news/astronomers-discover-planetary-system-three-super-earths-and-two-super-mercuries

Ia, Two rare super-mercuries discovered around the same star from https://divulgacao.iastro.pt/en/2022/09/27/hd23472-eng/

Weblio, TOI-174, from https://www.weblio.jp/wkpja/content/TOI-174_TOI-174%E3%81%AE%E6%A6%82%E8%A6%81

（文責：新原）

For detailed information on the TOI-174 system, click here (You can also access the detailed pages for each planet from the star’s detailed page.)

http://www.exoplanetkyoto.org/exohtml/TOI-174JP.html

K2-141 b

K2-141 b is an exoplanet orbiting the star K2-141, located 202.2 light-years (parsecs) from the Solar System, and was announced in 2018. The star K2-141 has an apparent magnitude of 11.5 and an absolute magnitude of 7.5. This star has 0.7 times the mass of the Sun, a radius of 0.7 times that of the Sun, a surface temperature of 4,599 K, and a spectral type of K4. In this star’s planetary system, K2-141 b orbits the star K2-141 with an orbital period of 0.3 days and a semi-major axis of 0.01 astronomical units (1,117,678.6 km).

K2-141 b is a Super Earth-sized exoplanet with a diameter approximately 1.5 times that of Earth and a mass approximately five times that of Earth. Its host star, K2-141, has a radius and mass both approximately 0.7 times that of the Sun and is located about 202 light-years from Earth. It has an orbital period of approximately 0.28 days and orbits at a semi-major axis of about 0.01 astronomical units. The inner boundary of the habitable zone around the host star K2-141 (the orbital radius where the planet receives Venus-like radiation) is 0.312 astronomical units, meaning that K2-141 b orbits well within the habitable zone.

According to a research group led by McGill University, K2-141 b is believed to be in a state of tidal locking, with its rotation and orbital periods synchronized. As a result, the temperature on the day side—which is constantly illuminated by the host star—is estimated to reach 3,000 degrees Celsius, while the temperature on the opposite night side is estimated to drop to minus 200 degrees Celsius; it is further estimated that a magma ocean approximately 100 kilometers deep covers the planet’s surface.

On the day side of this planet, temperatures are high enough to vaporize rock, so it is believed that substances that make up the rock—such as sodium, silicon monoxide, and silicon dioxide—vaporize and form the atmosphere. Simulations conducted by the research team predict that these substances are carried by the wind to the night side, where they cool and condense, falling as a “rock rain” into the magma ocean on the surface, thereby driving the rock cycle. However, the rate of this rock cycle is extremely slow, and as the planet’s composition changes over time, it may eventually develop a completely different atmosphere and surface. These simulation results are expected to be confirmed by the James Webb Space Telescope and may provide significant clues for understanding the temporal changes in rock composition on hot planets.

（文責：可児）

Click here for detailed information about K2-141 b

http://www.exoplanetkyoto.org/exohtml/K2-141_bJP.html