The University of Leiden has participated in an international study carried out by the CARMENES consortium, which has discovered two small, terrestrial planets around Teegarden's Star. The planets have masses similar to Earth and their temperatures could be mild enough to sustain liquid water on their surfaces.
At a distance of only 12.5 light years, Teegarden's Star is the 24 the nearest star system to ours, and one of the smallest red dwarf stars known. Despite its proximity and due to its faintness, Teegarden's Star was only identified in 2003. The Doppler measurements of Teegarden's Star showed the presence of at least two signals, now reported as the two new exoplanets, Teegarden's Star b and c. Obtaining a robust detection with a new instrument required the collection of over 200 measurements over 3 years. Based on the measured motion, the researchers can deduce that Teegarden's Star b has a mass similar to that of the Earth, it orbits the star every 4.9 days at about 2,5% the Earth-Sun distance. Teegarden's Star c is also similar to the Earth in terms of mass, completes its orbit in 11.4 days and is located at 4,5% the Earth-Sun distance. Since Teegarden's Star radiates much less energy than our Sun, the temperatures on these planets should be mild and they could, in principle, hold liquid water on their surfaces, especially the outer one, Teegarden's Star c. This kind of planets is the primary target for future searches for life beyond our Solar System.
Although planetary systems around similar stars are known, they have always been detected using the transit method – the planets have to pass visibly in front of the star and darken it for a moment, which only happens in a very small fraction of all planetary systems. Such transits have not yet been found for the new planets. But the system is located at a special place in the sky: From Teegarden's star, you can see the planets of the solar system passing in front of the sun.
Original publication: Mathias Zechmeister et al. "The CARMENES search for exoplanets around M dwarfs - Two temperate Earth-mass planet candidates around Teegarden's Star. Astronomy & Astrophysics 2019."