TESS – aka NASA’s Transiting Exoplanet Survey Satellite – has discovered three new exoplanets that are among the smallest and nearest found to date.
They orbit a star just 73 light-years away and include a small, rocky super-Earth and two sub-Neptunes, which astronomers say may be a “missing link” in planetary formation.
They are of an intermediate size and could help determine whether small rocky planets like Earth and larger icy worlds like Neptune formed in a similar or very different way.
The system has been dubbed TOI-270 – for the 270th “TESS Object of Interest” – and it has a lot to offer, say Maximilian Günther, from the Massachusetts Institute of Technology, US, and the lead author of a paper published in the journal Nature Astronomy.
“You can really do all the things you want to do in exoplanet science with this system,” he says.
The system has a number of curious qualities, he adds, not the least being that all three planets appear to be relatively close in size.
The star itself is an M-dwarf, a type that is normally extremely active, with frequent flares and solar storms. However, TOI-270 appears to be older and to have gone a little quiet. It is giving off a steady brightness, against which scientists can measure many properties of the orbiting planets, such as their mass and atmospheric composition.
Günther notes that the planets seem to line up in what astronomers refer to as a “resonant chain”, meaning the ratios of their orbits are close to whole integers – in this case, 3:5 for the inner pair and 2:1 for the outer pair – and that the planets are therefore in “resonance” with each other.
“For TOI-270, these planets line up like pearls on a string,” Günther says. “That’s a very interesting thing, because it lets us study their dynamical behaviour.
“And you can almost expect, if there are more planets, the next one would be somewhere further out, at another integer ratio.”
The sub-Neptune furthest out appears to be within a “temperate” zone, meaning that the very top of the planet’s atmosphere is within a temperature range that could support some forms of life.
However, scientists say the planet’s atmosphere is likely a thick, ultra-dense heat trap that would render the planet’s surface too hot to host water or life.