A super-Earth laboratory for the search for life in the Universe 🧪

An international team of researchers has discovered a super-Earth that will allow astronomers to test new hypotheses in the quest for life in the Universe.


Thirty years after the discovery of the first exoplanet, more than 7,000 such planets have been detected in our Galaxy. But there could still be billions more to discover! At the same time, exoplanetologists have begun to focus on their characteristics with the goal of searching for life elsewhere in the Universe.

It is in this context that the discovery of the super-Earth HD 20794 d by an international team including the University of Geneva (UNIGE) and the PRN PlanetS fits. The new planet is on an eccentric orbit, so that it is sometimes in the habitable zone of its star, and sometimes outside of it. This discovery is the result of 20 years of observations with the best telescopes in the world. The results are published in the journal Astronomy & Astrophysics.


"Are we alone in the Universe?" The question has been confined to philosophy for millennia and it is only very recently that modern science has begun to provide solid hypotheses and evidence to answer it. Astronomers, however, are advancing in small steps.

Each new discovery, theoretical or observational, adds its stone to the edifice by pushing the boundaries of knowledge. This was the case with the discovery in 1995 of the first planet orbiting a star other than the Sun, which earned the two UNIGE researchers, Michel Mayor and Didier Queloz, the Nobel Prize in Physics in 2019.

Its brightness and proximity make it an ideal candidate for future telescopes observing the atmospheres of exoplanets.

Almost thirty years later, astronomers have multiplied advances allowing the detection of more than 7,000 of these exoplanetes. The current scientific consensus points to the existence of a planetary system for each star in our galaxy.

Astronomers are now looking for exoplanets that are easy to study or have interesting features to test their hypotheses and consolidate their knowledge on the subject. This is the case of the planet HD 20794 d, which has just been detected by a team including members of the Department of Astronomy at UNIGE.

In the habitable zone of its star

This promising planet is a super-Earth, a terrestrial planet larger than Earth. It is part of a planetary system that contains two other planets. It orbits a G-type star, similar to the Sun, which is located at a distance of only 19.7 light-years, or, on the scale of the Universe, in the very close neighborhood of Earth. This "proximity" makes it easier to study, as its light signals are more visible and more significant.

"HD 20794, around which HD 20794 d orbits, is not a star like the others," explains Xavier Dumusque, teaching and research associate at the Department of Astronomy at UNIGE and co-author of the study. "Its brightness and proximity make it an ideal candidate for future telescopes whose mission will be to directly observe the atmospheres of exoplanets."



The interest in the planet HD 20794 d lies in its position in the habitable zone of its star, the zone that defines where liquid water can exist, one of the necessary conditions for the development of life as we know it. This zone depends on several factors, including the type of star.

For stars like the Sun or HD 20794, it can extend from 0.7 to 1.5 astronomical units (AU) and thus includes, in addition to the orbit of Earth, that of the planet Mars in the case of the Sun. The exoplanet HD 20794 d thus takes 647 days to orbit its star, about forty days less than Mars.

Instead of following a relatively circular orbit, like Earth or Mars, HD 20794 d follows an elliptical trajectory with large changes in the distance to its star during its revolution. The planet is thus at the inner edge of the habitable zone when it is closest to its star (at 0.75 AU) and outside the zone when it is farthest from its star (at 2 AU).

This configuration is particularly interesting for astronomers because it allows them to adjust theoretical models and test their understanding of the notion of a planet's habitability. If there is water on HD 20794 d, it would go from the state of ice to the state of liquid, conducive to the emergence of life, during the planet's revolution around the star.

Many years of observation

The detection of this super-Earth was not easy and the process was iterative. The team analyzed more than twenty years of data from leading instruments such as ESPRESSO and HARPS. For the latter, scientists were able to rely on YARARA, a data reduction algorithm recently developed at UNIGE.

For years, planetary signals were drowned in noise, making it difficult to discern whether the planets really existed. "We worked on data analysis for years, carefully eliminating sources of contamination," explains Michael Cretignier, postdoctoral researcher at the University of Oxford, co-author of the study and developer of YARARA during his PhD at UNIGE.


The discovery of HD 20794 d provides scientists with an interesting laboratory to model and test new hypotheses in their quest for life in the Universe. The proximity of this planetary system and its bright star also makes it a prime target for next-generation instruments such as the ANDES spectrograph for ESO's Extremely Large Telescope (ELT).

Determining whether this planet harbors life will still require many scientific milestones and a transdisciplinary approach. Its habitability conditions are already being studied by the new Center for Life in the Universe (CVU) at the Faculty of Science at UNIGE.