One of these exoplanets, HD 20794d, is likely to be a rocky planet in the habitable zone of its parent star, the G-dwarf HD 20794.
This image shows the habitable zone around HD 20794 (green) and the trajectory of the three planets in the system. Image credit: Gabriel Pérez Díaz / SMM / IAC.
“HD 20794, around which HD 20794d orbits, is not an ordinary star,” said UNIGE astronomer Xavier Dumusque.
“Its luminosity and proximity makes it an ideal candidate for future telescopes whose mission will be to observe the atmospheres of exoplanets directly.”
HD 20794 is a bright G6V star located 6.04 parsecs (19.7 light-years) away in the constellation of Eridanus.
Also known as LHS 19 or e Eri, the star hosts at least three massive exoplanets: HD 20794b, c, and d.
They have orbital periods of 18.3, 89.7, and 647.6 days, along with masses of 2.2, 3, and 5.8 Earth masses, respectively.
“The interest in the super-Earth planet HD 20794d lies in its position in the habitable zone of its star, the zone that delimits the place where liquid water can exist, one of the conditions necessary for the development of life as we know it,” Dr. Dumusque and colleagues said.
“Instead of following a relatively circular orbit, like the Earth or Mars, HD 20794d follows an elliptical trajectory with large changes in the distance to its star during its revolution.”
“The planet thus oscillates between the inner edge of its star habitable zone (0.75 AU) and outside of it (2 AU) along its orbit.”
“If there is water on HD 20794d, it would pass from the state of ice to the liquid state, conducive to the appearance of life, during the planet’s revolution around the star.”
The astronomers monitored the HD 20794 system with the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) instrument, which is installed at ESO’s Very Large Telescope (VLT) in Paranal, Chile.
They joined ESPRESSO data with the data from the High Accuracy Radial velocity Planet Searcher (HARPS) instrument, which is installed at the 3.6-m telescope in La Silla, Chile, including archival data and new measurements from a recent program.
“The HD 20794 system is a high-priority target for future atmospheric characterization with direct imaging facilities,” the researchers said.
Their paper was published in the journal Astronomy & Astrophysics.
_____
N. Nari et al. 2025. Revisiting the multi-planetary system of the nearby star HD 20794. Confirmation of a low-mass planet in the habitable zone of a nearby G-dwarf. A&A 693, A297; doi: 10.1051/0004-6361/202451769
