An article published in the journal “Astronomy & Astrophysics” describes the discovery of the exoplanet Ross 128 b, which might be similar to Earth with a mass of at least 35% higher than the Earth’s. A team of researchers used the HARPS instrument at the Silla Observatory in Chile to discover this planet about 11 light years from Earth. Its orbit might be in its system’s habitable zone making it the second exoplanet closest to the solar system with those characteristics after Proxima b.
The star Ross 128, also known as Proxima Virginis, Gliese 447 and HIP 57548, is a red dwarf with a mass which is only about 17% of the Sun’s, a radius that is only about 20% of the Sun’s and a temperature on its surface that is just over half of the Sun’s. The consequence is that the irradiation received from the planet Ross 128 b is 38% higher than the Earth receives from the Sun although it’s much closer to its star. In fact, the year of this exoplanet lasts only 9.9 Earth’s days since its distance from its star is about 5% of that of the Earth from the Sun.
It’s not certain that the Ross 128 b planet is in its system’s habitable zone but according to the authors of the research the combination of characteristics of its orbit and star is such that its surface may have temperatures similar to those on Earth. That, however, is true only if the planet has an atmosphere and it has a certain composition and this will have to be confirmed by further studies. That’s because this exoplanet doesn’t pass between its star and the Earth so it’s not possible to perform this verification with the current instruments.
The discovery of the planet Ross 128 b confirms that small stars can be really interesting, a great stimulus for new research, not just with the HARPS (High Accuracy Radial velocity planet searcher) instrument. The fact that red dwarfs are by far the most common stars and have a very long life due to the fact they consume their hydrogen very slowly is also an important factor. The Ross 128 system has an age just vaguely estimated, over 5 billion years old and therefore older than the solar system.
A problem with the discoveries of Proxima be of the seven rocky planets in the TRAPPIST-1 system is that their stars, respectively a red dwarf and an ultra-cool dwarf, despite their small size are very active with very violent flares that could devastate their planets with ultraviolet rays and even X-rays. Ross 128 is a much quieter star, with much less frequent flares, so from this point of view the conditions on the planet Ross 128 b might be similar to the Earth’s ones too.
The planet Ross 128 b will certainly be the subject of further studies. Xavier Bonfils of the Institut de Planétologie et d’Astrophysique de Grenoble – Université Grenoble-Alpes/Cnrs, Grenoble, France, first author of the article, stated that the observations will be better when the NIRPS (Near Infra Red Planet Searcher) instrument, which will complete HARPS at the La Silla observatory in August 2019, will enter service.
Another possibility for the future observations of the planet Ross 128 b will be with the Extremely Large Telescope (ELT) telescope, which is scheduled to be activated in 2024. That’s the new big ESO telescope that will help better understand the characteristics of the this and other potentially habitable exoplanets.