Papers › An extreme test case for planet formation: a close-in Neptune orbiting an ultracool star
An extreme test case for planet formation: a close-in Neptune orbiting an ultracool star
Gudmundur Stefansson, Suvrath Mahadevan, Yamila Miguel, Paul Robertson, Megan Delamer, Shubham Kanodia, Caleb Cañas, Joshua Winn, Joe Ninan, Ryan Terrien, Rae Holcomb, Eric Ford, Brianna Zawadzki, Brendan P. Bowler, Chad Bender, William Cochran, Scott Diddams, Michael Endl, Connor Fredrick, Samuel Halverson, Fred Hearty, Gary J. Hill, Andrea Lin, Andrew Metcalf, Andrew Monson, Lawrence Ramsey, Arpita Roy, Christian Schwab, Jason Wright, Gregory Zeimann
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In current theories of planet formation, close-orbiting planets as massive as Neptune are expected to be very rare around low-mass stars. We report the discovery of a Neptune-mass planet orbiting the `ultracool' star LHS 3154, which is nine times less massive than the Sun. The planet's orbital period is 3.7 days and its minimum mass is 13.2 Earth masses, giving it the largest known planet-to-star mass ratio among short-period planets (<\,100 days) orbiting ultracool stars. Both the core accretion and gravitational instability theories for planet formation struggle to account for this system. In the core-accretion scenario, in particular, the dust mass of the protoplanetary disk would need to be an order of magnitude higher than typically seen in protoplanetary disk observations of ultracool stars.
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