Two Rocky Exoplanets Found Orbiting Bright Red Dwarf

Astronomers using NASA’s Transiting Exoplanet Survey Satellite (TESS) have discovered a transiting multi-planetary system around a nearby red dwarf (M-dwarf) star called HD 260655.

An artist's impression of the two-planet system HD 260655. Image credit:

An artist’s impression of the two-planet system HD 260655. Image credit:

“Space missions devoted to exoplanet research via the transit technique are providing a wealth of discoveries and precisely measured parameters for planets with radii between 1 and 4 Earth radii,” said University of Chicago and Institute of Astrofísica de Andalucía astronomer Rafael Luque and his colleagues.

“These planets, with no counterpart in our Solar System, have been found to be very abundant around early M-dwarfs, more so than around solar-type stars.”

“M-dwarfs are interesting as planetary hosts because of their relative sizes and masses with respect to their planets, which make these systems more easily detectable by transit and radial velocity techniques.”

HD 260655 is a high proper motion star in the Gemini constellation located at a distance of approximately 10 parsecs (33 light-years).

Also known as Gliese 239, TOI-4599, LHS 1858, HIC 31635 and Wolf 287, the star is among the brightest early-type M dwarfs in the sky.

HD 260655 hosts two transiting exoplanets on orbits with periods of 2.8 and 5.7 days.

The inner planet, named HD 260655b, is 1.24 times the size of Earth, and has 2.14 times the mass.

Dubbed HD 260655c, the outer planet is 1.53 times larger than Earth and 3.1 times more massive.

“At a distance of 10 parsecs, HD 260655 becomes the fourth closest known multi-transiting planet system after HD 219134, LTT 1445Aand AU Micthe astronomers said.

HD 260655b and HD 260655c were detected by the TESS mission and confirmed independently with archival and new radial velocity data obtained with the HIRES high-resolution spectrograph on the 10-m Keck-I telescope on Mauna Kea, Hawai’i, and the CARMENES high-resolution spectrograph on the 3.5-m telescope at the Calar Alto Observatory in Spain since 1998 and 2016, respectively.

“The HD 260655 system presents a unique opportunity for comparative planetology studies of rocky worlds,” the researchers said.

“Both planets rank among the best targets for transmission and emission spectroscopy observations with the NASA/ESA/CSA James Webb Space Telescopewhich could detect secondary volatile-rich atmospheres or confirm the presence of water and carbon species in one or multiple visits, respectively.”

“Moreover, the radio emission arising from the interaction between the planets and its host could be measured in radio wavelengths.”

“These follow-up observations will improve our knowledge about the formation and evolution history of the system and open a new observational avenue to study the magnetic fields of low-mass stars and their imprint in planetary systems.”

The discovery is reported in a paper in the journal Astronomy & Astrophysics.


R. Luque and al. 2022. The HD 260655 system: Two rocky worlds transiting a bright M dwarf at 10 pc. A&Ain press arXiv: 2204.10261

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