Super-Earth: here are more than seven thousand extrasolar planets known to date, but there is something even more significant than this resounding number. It is their variety, determined by different characteristics, that, as far as we know at the moment, make these planets theoretically different from each other. In recent weeks, news has arrived about Hd 20794 d, a planet already known to scientists since 2011, which is 19.7 light-years from Earth. A distance that is technically enormous but scientifically much less distant, although to get an idea with our system of magnitude, we can consider that, after 50 years of travelling, the Voyager 1 probe is almost 1 light day away from our planet.

A starting point for future study

Discovered by Michael Cretignier, a scientist at the University of Oxford, Hd 20794 d represents the third planet (this is the meaning of the suffix d) orbiting Hd 20794, a Sun-like star that is, however, ‘not an ordinary star’. The words of Xavier Dumusque, professor at the University of Geneva and co-author of the study published in Astronomy & Astrophysics, confirm that it is a Super-Earth. This is a crucial step that opens up potentially unprecedented horizons for future studies of exoplanets with hypothetical conditions suitable for human life because, according to the researchers, ‘it is one of the closest analogues of Earth that we know of’.

‘Its brightness and proximity make it an ideal candidate for future telescopes whose mission will be to directly observe the atmospheres of exoplanets,’ reads the study carried out by an international team led by Nicola Nari of the Instituto de Astrofísica de Canarias. The importance and enthusiasm of the scientists comes from the peculiarities of Hd 20794 d, which is configured as a rocky planet larger than the Earth.

After all, we are talking about a celestial body in the constellation Eridanus that is less luminous and colder than the Sun but with a mass almost six times that of our planet. But there is more, as the orbit makes the movement of revolution around the planet in 647 days, drawing an elliptical path.

There can be life – super-Earth

Translating the scientific data into simple words, during its revolution, Hd 20794 d was very close to the star at one point and very far away at another. At the same time, precisely because of the shape of the path, the planet enters and leaves the habitable zone, which in astronomy means the region around a star where, theoretically, a planet can maintain liquid water on its surface. Which is one of the basic conditions for the eventual development of human life.

It must also be understood that the particular conditions of Hd 20794 d lead to opposite scenarios depending on the distance of the planet from the star. Imagine there was an expanse of water entering and leaving the habitable zone; Hd 20794 d could host an ocean that turns to ice during the seasons. For this reason, say researchers, it is one of the most interesting planets to study to determine whether there are, and if so, what the conditions for habitability would be.