Scientists have found a new planet in our closest neighbouring planetary system.
The new alien world, named Proxima d, is the third found in the system. It is also one of the lightest exoplanets ever found, with just a quarter of the mass of the Earth.
The planet orbits around Proxima Centauri, the closest star to our own Sun. It is a relatively short four light-years away.
The first of its planets, named Proxima b, caused a stir when it was discovered in 2016. As well as being near to us, that Earth-sized planet was especially exciting because it could potentially be habitable: it has a temperature suitable for liquid water and a rocky surface.
The new planet is not quite so welcoming. It orbits between the star and the habitable area, too close to have liquid water and close enough to its star that a year lasts only five days on Earth.
Further research could reveal even more planets hiding inside the system, the researchers behind the new discovery suggest.
“The discovery shows that our closest stellar neighbour seems to be packed with interesting new worlds, within reach of further study and future exploration,” said João Faria, a researcher at the Instituto de Astrofísica e Ciências do Espaço, Portugal.
Faria is the lead author on a study describing the findings, titled ‘A candidate short-period sub-Earth orbiting Proxima Centauri’ and published today in Astronomy & Astrophysics.
Researchers were able to work out the size of the newly-discovered planet using the radial velocity technique. That watches for the tiny movements in stars caused by the gravity of the planets, and uses that to work out their mass.
It is the smallest planet to have been measured using that technique. Scientists using the Espresso instrument on the Very Large Telescope watched as the planet moved the star only a tiny amount: pulling it back and forth at about 40 centimetres per hour.
“This achievement is extremely important,” says Pedro Figueira, ESPRESSO instrument scientist at ESO in Chile.
“It shows that the radial velocity technique has the potential to unveil a population of light planets, like our own, that are expected to be the most abundant in our galaxy and that can potentially host life as we know it.”
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