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.

An artist’s impression of the ultra-short-period sub-Neptune exoplanet TOI-1634b. Image credit: Sci-News.com.

“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,” said Dr. Ryan Cloutier from the Harvard & Smithsonian Center for Astrophysics and his colleagues.

“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,” they said.

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 mass and radius of TOI-1634b are inconsistent with an Earth-like composition,” the astronomers noted.

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 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,” the researchers said.

“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,” they added.

“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.

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R. Cloutier et al. 2021. TOI-1634b: an Ultra-Short Period Keystone Planet Sitting Inside the M Dwarf Radius Valley. AAS journals, submitted for publication; arXiv: 2103.12790

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