An article published in the journal “Nature Astronomy” reports the discovery of three exoplanets in the system of the red dwarf indicated in the research as TOI (Tess Object of Interest) 270 because it was studied using NASA’s TESS space telescope. They’re a super-Earth and two mini-Neptunes, all with orbits very close to their star. A team of researchers used observations made by TESS and follow-up observations with other telescopes to confirm the existence of the three exoplanets and provide some estimates of their characteristics, useful also because the two mini-Neptunes could provide information to understand the mechanisms of formation of planets of that type but also of rocky ones.
About 73 light-years from Earth, the red dwarf examined during this research is known only with various catalog names such as TIC 259377017, UCAC4 191-004642 and others so it’s more practical to use the short abbreviation TOI 270 which identifies it among the targets of the TESS space telescope, launched on April 18, 2018. It has a mass and size about 40% of the Sun’s and its small system has at least for now turned out to be very compact given that the three confirmed planets are only a few million kilometres away from it.
The nearest exoplanet, TOI 270b, is about 4.5 million kilometers away from its star for a year lasting about 3.4 Earth days. It’s most likely a super-Earth with an estimated diameter about 1.25 times the Earth’s. The estimated temperature on its surface without taking into account the greenhouse effect in a possible atmosphere is about 250° Celsius (near 490° Fahrenheit) but if it were a super-Venus with an atmosphere in which a runaway greenhouse effect occurred the temperature could be even twice as much.
The second exoplanet, TOI 270c, is about 7.5 million kilometers away from its star for a year lasting about 5.7 Earth days. It’s a mini-Neptune with an estimated diameter about 2.4 times the Earth’s and an estimated mass about 7 times the Earth’s. Its dense gaseous atmosphere has an estimated temperature based only on the energy received from its star of about 150° Celsius (about 300° Fahrenheit).
The outermost exoplanet, TOI 270d, is about 10.5 million kilometers away from its star for a year lasting about 11.4 Earth days. Like its neighbor it’s a mini-Neptune but a little smaller since its diameter is estimated at about 2.1 times the Earth’s and its mass is estimated at about 5 times the Earth’s. The estimated temperature in its dense gaseous atmosphere based only on the energy received from its star is about 66° Celsius (about 150° Fahrenheit). This would allow the presence of liquid water in that atmosphere but there’s probably a greenhouse effect that makes it much higher with the consequence that any presence of water is in the form of steam.
The discovery of these exoplanets is interesting for various reasons, in particular those related to studies on planetary formation. The two mini-Neptunes are not much larger than the super-Earth and could be a sort of missing link in the mechanisms that lead to the formation of these sub-Neptunian gaseous planets but perhaps also of rocky planets. According to one of the models developed by astronomers, mini-Neptunes close to their star could lose their atmosphere leaving only the rocky nucleus or almost only that.
The three exoplanets of the TOI 270 system are among the smallest discovered within 100 light years away so follow-up observations are less difficult. Some have already been completed but it will certainly be the targets of further studies to better understand the characteristics of the exoplanets discovered but also to verify if there are more of them. Maximilian Günther of the Kavli Institute for Astrophysics & Space Research at MIT, lead author of the research, explained that this red dwarf is particularly quiet unlike other younger ones that emit powerful flares so it would be interesting to find a planet in the habitable zone, which in this case could start at about 15 million kilometers from the star.
The TESS space telescope has just completed its first year of scientific activity, which began in July 2018 after the test phase, with great success. There are 24 confirmed exoplanets but there are 993 candidates still to be verified and the observations continue to find more of them. In the TOI 270 system’s case, it proved the possibility of discovering relatively small and very interesting exoplanets to improve our planetary formation models.