An article published in the journal “Astronomy & Astrophysics” reports the identification of the exoplanet that was cataloged as HD 20794 d. A team of researchers used data collected in more than twenty years with two spectrographs: ESPRESSO, mounted on the VLT, and HARPS, at the La Silla Observatory, both of ESO in Chile, to identify HD 20794 d and define its orbit and characteristics. The analysis indicates that it’s a super-Earth with a mass almost six times the Earth’s with a highly elliptical orbit that brings it into the habitable zone of its star system for part of its year.

The star HD 20794, also known as 82 Eridani and with other designations connected to various catalogs, is a bit smaller and less massive than the Sun. Despite the distance of almost 20 light-years, which places this system in the cosmic neighborhood, searches for planets orbiting it have been complex because their positions don’t seem to lead them to pass in front of the star from the Earth’s point of view. For this reason, searches have been based on the radial velocity method with the uncertainties that especially in the last decade led to results that weren’t always reliable.

The consequence is that over the years, several exoplanet candidates were proposed in the HD 20794 system but only two were confirmed. Now, however, a sophisticated examination of over twenty years of data collection using the ESPRESSO (Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations) and HARPS (High Accuracy Radial velocity Planet Searcher) spectrographs has offered confirmation to one of the candidates.

The researchers attempted to find direct traces of the exoplanet HD 20794 d in observations from NASA’s TESS space telescope but to no avail. Even when the inclination of a system favors direct observations from Earth, they’re much easier with exoplanets with a very short year, as they frequently transit in front of their star from the Earth’s point of view.

Without direct observations of the exoplanet HD 20794 d, it’s impossible to say if it has an atmosphere, so any possibilities that are examined are based on assumptions. A planet of that mass has a good chance of retaining an atmosphere, but there’s no certainty. The variability in conditions due to its orbit could also have influenced the evolution of its atmosphere.

Despite the lack of direct observations, the exoplanet HD 20794 d is interesting because of the orbit that emerges from the data analysis. Its year lasts about 647 Earth days in a highly elliptical orbit that is partly inside the habitable zone of its system and partly outside it. This means that at least in theory the conditions on its surface could be suitable to support life forms similar to those on Earth but only during part of this exoplanet’s year. The seasons on that exoplanet are greatly influenced by the distance from its star while on Earth they depend on the inclination of its axis.

Being able to directly observe HD 20794 d would allow to study a planet with peculiar conditions that have already led to it being defined as a sort of natural laboratory to test hypotheses connected to the search for extraterrestrial life. For this reason, its discovery has aroused interest and other researchers could try to observe it directly to study its real characteristics.