The small planet, named by scientists GJ 367b, is smaller than the Earth and has molten iron on its surface. The circumstances surrounding its genesis are still a mystery.
NASA’s TESS space telescope discovered this planet as part of its ongoing monitoring of nearby stars in the hope that possible terrestrial-type exoplanets pass in front of them and temporarily (and very slightly) decrease their light flow.
It is named GJ-367b because it rotates around GJ-367, a star that is 30.7 light years away from us – which is to say that it is in the suburbs of the Solar System when we consider that our galaxy, the Milky Way, extends for around 100,000 light years.
As a red dwarf, GJ-367 is half the size and mass of the Sun. Red dwarfs are the lightest, coldest and least bright stars in the galaxy, and they are also the most frequent in the galaxy.
According to Xavier Delfosse, one of the study’s co-authors from the Institute of Planetology and Astrophysics of Grenoble (CNRS-Université Grenoble-Alpes), when an exoplanet is discovered, it is referred to as a “single exoplanet”. Its mass and radius must be determined, and the density must be determined in order to obtain information on its composition.
Density is really a fundamental component in determining the composition of the planets: if we look to the stars of the Solar System, a rocky planet like the Earth has a density of 5.5 grams per cubic centimeter. With an ice core surrounded by a gaseous envelope, the density of Neptune-type planets is between 1.5 g/cm3 and 2 grams per cubic centimeter, whereas gas giants such as Jupiter and Saturn, which have a thick atmosphere of hydrogen and helium, have densities of approximately 1 g/cm3.
The radius of GJ-367b was determined using the transit approach, which was found to be 70% of the radius of the Earth. The mass of the planet was determined using the other way of finding exoplanets, known as “radial velocities,” which examines the minute oscillations in the position of the planet’s star caused by the mass of the planet.
In this way, the researchers were able to determine the density of GJ-367b and were not disappointed with the results: 8.1 grams per cubic centimeter, which is greater than the density of the planets in our Solar System and near to the density of iron.