The L 98-59 planetary system contains two non-transiting planets and three transiting terrestrial planets, one of which is a warm rocky world with half the mass of Venus.
L 98-59 is a bright M3V-type dwarf located 34.6 light-years away in the southern constellation of Volans.
Also known as TOI-175 or TIC 307210830, the star is about one-third the mass of the Sun.
According to the new research, L 98-59 hosts five planets: L 98-59b, c, d, e and f.
“The fact that L 98-59 is an M-dwarf sets this system apart among multiplanetary systems,” said lead author Dr. Olivier Demangeon from the Instituto de Astrofísica e Ciências do Espaço at the University of Porto and his colleagues.
“According to the exoplanet archive and the recent literature, only seven multiplanetary systems are currently confirmed — including L-98-59 — around M-dwarfs for which the planetary masses and radius of at least two planets have been measured.”
“The other six are TRAPPIST-1, LTT-3780, TOI-1266, LHS-1140, K2-146, and Kepler-138.”
“With a V magnitude of 11.7 and a distance of 34.6 light-years, L 98-59 is the brightest and closest of these systems.”
The three inner planets, L 98-59b, c and d, were first discovered in 2019 using NASA’s Transiting Exoplanet Survey Satellite (TESS).
They range from 0.4 to 1.6 times the size of Earth and have orbital periods between 2.25 and 7.5 days.
“With a mass of 0.4 Earth masses (half the mass of Venus), L 98-59b is the lowest-mass exoplanet measured so far using radial velocities,” the astronomers said.
In the new study, they used the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) instrument on ESO’s Very Large Telescope (VLT) to study the L 98-59 system.
They were able to infer that L 98-59b, c and d may contain water in their interiors or atmospheres.
The two planets closest to the star are probably dry, but might have small amounts of water, while up to 30% of the third planet’s mass could be water, making it an ocean world.[embedded content]
“We also expand the view of this system with the discovery of a fourth planet and a planetary candidate,” the researchers said.
“These planets, L 98-59e and f, do not transit, but with minimum masses of 3.06 and 2.46 times that of the Earth, they are probably both rocky planets or water worlds (also called ocean worlds).”
“With an equilibrium temperature of 285 K, L 98-59f, if confirmed, would orbit in the habitable zone of its parent star.”
A paper describing the findings was published online in the journal Astronomy & Astrophysics.
O.D.S. Demangeon et al. 2021. Warm terrestrial planet with half the mass of Venus transiting a nearby star. A&A, in press; doi: 10.1051/0004-6361/202140728