Astronomers using NASA’s Transiting Exoplanet Survey Satellite, or TESS, have discovered three new exoplanets orbiting a quiet star 73 light-years from Earth. The team identified one super-Earth and two sub-Neptunes in the system, with one of these bigger planets being in the star’s temperate zone.
The discovery, reported in Nature Astronomy, is exciting for several reasons. The planets in the system, known as TOI-270, are unlike what we have seen in our own Solar System in more ways than one. The star is quiet and bright, making it a great place to study these objects and try to understand how they came to be.
"TOI-270 is a true Disneyland for exoplanet science, and one of the prime systems TESS was set out to discover," Maximilian Günther, a postdoc in MIT's Kavli Institute for Astrophysics and Space Research, said in a statement. "It is an exceptional laboratory for not one, but many reasons – it really ticks all the boxes."
The planets are very similar in size, unlike the planets in our Solar System, which range from tiny Mercury to gigantic Jupiter. The sizes of the system's planets are also different from those found in the Solar System. The sub-Neptunes, in particular, are often considered a missing link between the rocky planets and the icy giants like Uranus and, indeed, Neptune. Studying TOI-270 might explain if icy giants form just like rocky planets.
"There are a lot of little pieces of the puzzle that we can solve with this system," Günther added. "You can really do all the things you want to do in exoplanet science, with this system."
One particular advantage of the system is that the central star is an old M-dwarf with 40 percent of the mass of the Sun. The age is important because this stellar class is usually very active but as these stars grow old, they quieten down. This is great for observations. If the brightness of the star is steady, astronomers can better estimate the properties of the planets and gain insights into how they formed.
All three planets orbit very close to the star. The first one takes 3.36 Earth days, the second 5.66, and the third 11.38 days. They are so close to the star and to each other that they are synchronized in a resonance pattern. For every three full orbits of the furthest one, the middle one orbits six times, and the innermost one orbits exactly 10 times.
TESS is expected to discover a lot more of these objects. By the end of the primary mission, researchers expect 20,000 new exoplanets between candidates and confirmed objects.