Astronauts using NASA’s Satellite Survey Transiting Exoplanet and the Echelle High Resolution Spectrometer on the WM Keck Observatory’s Keck I telescope have discovered a system with three transmission exoplanets – including a short-lived super Earth – around TOI-561, one of the oldest stars in our Galaxy Milky Way.
How an artist presents the TOI-561 planetary system. Image credit: Adam Makarenko / WM Keck Theater.
TOI-561 is a bright star located 280.5 light-years away in the constellation Sextans.
The star is about 10 billion years old, and is about 80% the size of the sun.
Also known as TYC 243-1528-1, it belongs to a rare population of stars called Galactic thick disk.
“Stars in this region are chemically different, with fewer heavy elements like iron or magnesium associated with planetary construction,” said Lauren Weiss, a graduate researcher at the University of Hawaii and her colleagues.
TOI-561 hosts at least three small transmission planets, named TOI-561b, c, and d, and is one of the oldest, poorest metal planetary systems found still in the Milky Way.
The inner planet, TOI-561b, is a so-called super-Earth with an orbital time of just 0.44 days.
“For every day you’re on Earth, this planet revolves around the star twice,” said co-author Dr. Stephen Kane, a planetary astronaut at the University of California, Riverside .
“Part of the reason for the short orbit is as close to the planet as its star, which also creates incredible heat.”
“Its average surface temperature is above 1,727 degrees Celsius (2,000 degrees Kelvin) – too busy to sustain life as we know it today, although it may be possible at some point. ”
TOI-561b has a mass and radius of 3.2 and 1.45 times that of Earth, and a density of 5.5 g / cm3, compatible with rocky outcrops.
“We figured out that its density was equal to that of our planet,” Dr. Kane said.
“This is surprising because you would expect the density to be higher. This is based on the idea that the planet is very old. ”
“TOI-561b is one of the oldest rocky planets yet to be discovered,” Weiss said.
“Its existence shows that the Universe has formed of almost rocky planets since its inception 14 billion years ago.”
The two outer planets, TOI-561c and d, have 7 and 3 times the masses, on the radii of 2.9 and 2.3 radii of the Earth, respectively.
They rotate their host star once every 10.8 and 16.3 days.
“Thanks to the bright host star, this multi-device system is capable of sensing space-based telescopes,” said the astronauts.
“TOI-561b is expected to be a good eclipse target, while TOI-561c and its planets are promising targets for transmission spectroscopy.”
“Relatively atmospheric buildings would give the planets in this poor metal system a unique test for planetary formation conditions.”
The find is reported in a paper in the Astronomical Iris.
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Lauren M. Weiss et al. 2021. TESS-Keck study. II. Ultra-short-lived Rocky Planet and its sisters move over Galactic thick disk star TOI-561. AJ 161, 56; doi: 10.3847 / 1538-3881 / abd409