HD 20794 d: new hopes for life on a nearby super-Earth
Astronomers have discovered another exoplanet that may have favourable conditions for the existence of liquid water. We are talking about HD 20794 d – a planet belonging to the group of so-called super-Earths. It is located in a star system less than 20 light-years away, making it one of the closest candidates for further research.
What distinguishes a super-Earth? As "National Geographic" explains, HD 20794 d is a planet significantly larger than Earth – its mass is more than five times greater, and its radius is twice as large.
It has been classified as a super-Earth, which means it is a rocky globe with a much larger mass than our planet but, at the same time, smaller than the gas giants.
The planetary system in which it is located consists of three celestial bodies orbiting a G-type star, which is a yellow dwarf similar to the Sun. Two of them move in orbits too close to their star, making them exposed to extreme temperatures. Meanwhile, HD 20794 d is located in an area that astronomers refer to as the habitable zone.
Orbit and conditions on the planet
The trajectory of this planet is not perfectly circular – it moves in an elongated elliptical orbit. According to "National Geographic," this means that it periodically enters the habitable zone and then exits it.
At the farthest point of its journey, it moves away from the star by approximately 300 million kilometres (186 million miles), while at the closest, it approaches roughly 112 million kilometres (70 million miles). For comparison, in the Solar System, a similar range covers Mars's orbit.
One complete orbit around the star takes 647 days, which is slightly shorter than a year on Mars. This means that at different points in the cycle, extreme conditions may prevail on the surface of HD 20794 d – from icy when it's farther from the star, to warmer when it approaches its inner edge.
Can life exist on HD 20794 d?
Scientists are still uncertain if water indeed exists on this super-Earth. If so, it could change its state depending on the planet's position in its orbit – remaining mostly frozen but melting and forming water bodies during periodic entry into the habitable zone.
"National Geographic" explains that such a cycle could favour the development of simple life forms, although much depends on the atmospheric composition and temperatures on the surface.
The discovery of HD 20794 d was described in the prestigious journal "Astronomy & Astrophysics." Scientists analysed data collected by advanced instruments, including the ESPRESSO and HARPS spectrographs.
For years, we analysed data, carefully eliminating sources of contamination – said Michael Cretignier from Oxford, co-author of the research and the planet's discoverer.
Future studies of super-Earth
The proximity of the HD 20794 planetary system and its relatively bright star make this object a subject of intensive future research. New telescopes, such as the Extremely Large Telescope (ELT) in Chile equipped with the ANDES spectrograph, will allow for even more precise analyses of this exoplanet's atmosphere. Thanks to this, astronomers may determine in the future whether HD 20794 d indeed has conditions conducive to life.
