Researchers have discovered rocky exoplanets as hot as 1,700 degrees C, twice as large as the Sun.
The exoplanet called TOI-561b is about 50% larger than Earth and has 3 times the mass, so it is classified as a “super-Earth”. However, TOI-561b only took half a day to complete an orbital loop around the host star. “For each day that you are on Earth, this planet revolves around its host star,” said Stephen Kane, an astrophysicist at the University of California at Riverside, co-author of the study. Kane and his colleagues announced the discovery on Jan. 11 at the 237th meeting of the American Astronomical Association.
The close distance between the super-Earth and its host star causes the average temperature of the planet’s surface to exceed 1,700 degrees Celsius. The planet was discovered thanks to NASA’s Transitional Exoplanet Survey Satellite (TESS), launched in space 2018. TESS has regularly studied the sky and observed nearby stars to determine whether the exoplanets are in orbit or not. Astronomers have found TOI-561b in the Milky Way galactic disk. This population of rare stars contains few heavy elements such as iron or magnesium.
To confirm the discovery, the team used the W.M. Keck Observatory in Hawaii to learn the mass, radius and density of the planet. However, they were very surprised to find that despite the large mass, the density of TOI-561b is equivalent to that of Earth, according to the very old hypothesis of the planet.
The old planets are less dense because there aren’t many heavy elements in the universe when they formed. Heavy elements are created when stars reach the end of their lifespan and explode, providing material for the formation of new stars and planets throughout the universe. TOI-561b is one of the oldest rocky planets ever discovered, according to team leader Lauren Weiss, postdoctoral fellow at the University of Hawaii.
In addition to the TOI-561, there are two larger planets orbiting the star, probably gas planets. The Milky Way was formed about 12 billion years ago. The TOI-561 star system is around 10 billion years old, while the Sun is only 4.5 billion years old. TOI-561 appears as most of the stars in the Milky Way start to glow. Knowing the mass and radius of the planet will allow astronomers to explore its internal structure.