Astronomers using NASA’s Transiting Exoplanet Survey Satellite (TESS) and the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) instrument on ESO’s Very Large Telescope have revisited the planetary system LHS 1140 with its two known Earth-like planets. Their results show strong evidence for the signal of a third planet in the LHS 1140 system.
LHS 1140 is a cool low-mass star approximately 39 light-years away in the constellation of Cetus.
Also known as Gliese 3053, GJ 3053 and 2MASS J00445930-1516166, the star is about one-fifth the size of the Sun and approximately 5 billion years old.
LHS 1140 is known to host two transiting planets at orbital periods of 3.77 and 24.7 days.
The external planet, LHS 1140b, is a super-Earth with a mass of 6.5 Earth masses. It possesses a rocky composition and lies within the habitable zone of the star.
The inner planet, LHS 1140c, is a rocky word with a mass of 1.8 Earth masses.
“We further characterized this system by improving the physical and orbital properties of the known planets, searched for additional planetary-mass components in the system, and explored the possibility of co-orbitals,” lead author Dr. Jorge Lillo-Box of CSIC-INTA and colleagues wrote in their paper.
The astronomers collected 113 high-precision radial velocity observations of the LHS 1140 system with the ESPRESSO spectrograph and analyzed additional data from TESS.
“Although both planets have Earth-like bulk compositions, the internal structure analysis suggests that LHS 1140b might be iron-enriched and LHS 1140c might be a true Earth twin,” they wrote.
“In both cases, the water content is compatible to a maximum fraction of 10-12% in mass, which is equivalent to a deep ocean layer of 650-779 km (404-484 miles) for the habitable-zone planet LHS 1140b.”
The team’s results also provide evidence for a new planet candidate in the system on a 78.9-day orbit.
Named LHS 1140d, the third planet has a minimum mass of 4.8 Earth masses and is likely a world in the rocky-gaseous frontier beyond the habitable zone.
“The possible presence of a third rocky planet in the system that may be transiting the host star at periods beyond the habitable zone makes this system a key target for understanding atmospheric properties of rocky worlds at different stellar irradiations,” the researchers concluded.
The team’s paper was published in October 2020 in the journal Astronomy & Astrophysics.
J. Lillo-Box et al. 2020. Planetary system LHS 1140 revisited with ESPRESSO and TESS. A&A 642, A121; doi: 10.1051/0004-6361/202038922