Ultra Short Period Sub-Neptune Found Orbiting TOI-1634

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Using data from NASA’s Transiting Exoplanet Survey Satellite (TESS) and the HARPS-N spectrograph at the 3.6-m Telescopio Nazionale Galileo, astronomers have discovered and confirmed an ultra-short period keystone planet orbiting an M2 dwarf (red dwarf star) called TOI-1634.

Dr. Ryan Cloutier from the Harvard & Smithsonian Center for Astrophysics and his colleagues said, since its science operations began in July 2018, TESS has uncovered a wealth of transiting planet candidates whose orbital periods and radii lie within the radius valley, including three planets transiting early M-dwarfs: TOI-1235b, TOI-776b, and TOI-1685b. Radius valley planets, which we refer to as keystone planets, are valuable targets to conduct tests of the competing radius valley emergence models across a range of stellar masses. Doing so requires that we characterize the bulk compositions of a sample of keystone planets using precise radial velocity measurements. We present the confirmation and characterization of one such keystone planet from TESS: TOI-1634b. The mass and radius of TOI-1634b are inconsistent with an Earth-like composition.

TOI-1634b is a sub-Neptune planet with a radius of 1.8 times that of Earth and a mass of 4.8 Earth masses.

The alien world has an orbital period of 1 day and lies 0.015 AU (astronomical units) from its host star, the M2 dwarf TOI-1634. Also known as TIC 201186294 or 2MASS J03453363+3706438, the system is located 115 light-years away in the constellation of Perseus.

The researchers said, the bulk composition of TOI-1634b is inconsistent with models of thermally-driven mass loss (i.e. photoevaporation and core-powered mass loss) and with gas-poor formation. Instead, TOI-1634b favors the gas-depleted formation model and suggests that this formation mechanism may start to dominate the close-in planet population around M dwarfs with masses equal or less than 0.5 solar masses. Emission spectroscopy observations will help to establish the chemical and physical properties that make the atmosphere of TOI-1634b resistant to hydrodynamic escape. Atmospheric models of solar composition, water-dominated, and carbon dioxide-dominated may be distinguished with 2-5 eclipse observations with instruments on the upcoming James Webb Space Telescope.

A paper on the findings will be published in one of the AAS journals.