The Instituto de Astrofísica de Canarias (IAC) and the Universidad de La Laguna (ULL) has confirmed the discovery of a super-Earth orbiting in the habitable zone of HD 20794, a nearby Sun-like star. This discovery, the result of over two decades of observations, opens a window to future studies of Earth-like planetary atmospheres.

The search for planets in the habitable zone of Sun-like stars is crucial for understanding the possibility of life beyond Earth and for studying conditions similar to those that enabled the development of life on our own planet. In this context, HD 20794, a star with a slightly lower mass than the Sun and located just 20 light-years away, has always been of great scientific interest. The newly discovered planet is the third planet identified in the system, following the discovery of two super-Earths published more than a decade ago. 

The name of the new planet is HD 20794 d and is a super-Earth with a mass six times that of Earth, taking 647 days to complete an orbit around its star, 40 days less than Mars. This orbit places it within the habitable zone of the system, meaning it is at the right distance from its star to sustain liquid water on its surface, one of the key ingredients for life as we know it.

It is precisely the combination of the planet's distance from its star and the proximity of the system that makes it particularly attractive, rendering it a perfect candidate for observations with the ELT, ESO's 40-meter telescope, or future space missions by ESA and NASA. “This is the perfect type of planet for characterizing terrestrial planet atmospheres with next-generation instruments and missions”, explains Nicola Nari, a researcher at Lightbridges S.L., a doctoral student at the Universidad de La Laguna and the study's lead author, published today in Astronomy & Astrophysics. “In fact, we know of very few similar planets”, notes Alejandro Suárez Mascareño, a researcher at the IAC and co-author of the work. “This will surely be one of the first we can study”, adds.

This discovery was made possible thanks to over 20 years of radial velocity measurements from the ESPRESSO and HARPS spectrographs, both installed at ESO observatories in Chile. These instruments, among the most advanced in the world, can measure the tiny variations in stellar velocity caused by the gravitational pull of planets in a system. “Very few instruments in the world can achieve the level of precision required for a discovery like this”, explains Nicola Nari.

To go even further, the team applied sophisticated processing techniques to the spectra obtained. “We worked on data analysis for years, gradually analyzing and eliminating all possible sources of contamination”, explains Michael Cretignier, a co-author of the study and researcher at the University of Oxford. This meticulous analysis revealed the presence of a candidate signal identified in 2022. The team immediately launched a new observation campaign to confirm it. “After two years of adding new measurements, we can confirm we have a robust detection”, adds Nathan Hara, a researcher at the Marseille Astrophysics Laboratory.

Although the planet is located in the system’s habitable zone, it is too early to say whether it could host life. Its high mass and eccentric orbit make it a very different world from ours. Unlike most planets in the Solar System, HD 20794 d’s orbit is not circular but elliptical. Its distance from its star changes significantly, causing the planet to move from the outer edge of the habitable zone to the inner edge throughout its year. “HD 20794 d is not a second home for humanity, but its position and peculiar orbit give us a unique opportunity to study how the conditions for habitability vary over time and how these variations may influence the evolution of the planet’s atmosphere”, says Alejandro Suárez Mascareño, researcher at the IAC and co-author of the work.

Researchers from the IAC, including Jonay I. González Hernández, Atanas K. Stefanov, Rafael Rebolo, Carlos Allende Prieto, and Enric Pallé, also contributed to this publication.

Contact: 

Jonay I. González Hernández jonay [at] iac.es (jonay[at]iac[dot]es)