Astronomers find a new planetary system close to Earth and are ‘optimistic’ there will be habitable worlds

The star is only 33 light-years from our own planet, although the two worlds discovered so far are too hot to live on

Astronomers have found a new multiplanetary system just 33 light-years from our own planet.

The system, now the closest known one to Earth, has two terrestrial planets orbiting a cool M-dwarf star, named HD 260655.

The inner planet, HD 260655b, orbits the star every 2.8 days and is about 1.2 times as big as the Earth but is slightly denser, while the outer planet, HD 260655c, orbits every 5.7 days and is 1.5 times as big as the Earth, but is less dense.

These planets are, unfortunately, not habitable; the planets orbit their star at too close a range, exposing them to temperatures too high to maintain liquid water on their surfaces. Based on their short orbits, it is estimated that the surface of the inner planet is 436 degrees Celsius, while the outer planet is around 286 degrees Celsius.

“We consider that range outside the habitable zone, too hot for liquid water to exist on the surface,” Michelle Kunimoto, a postdoc in MIT’s Kavli Institute for Astrophysics and Space Research and one of the discovery’s lead scientists, says.

But there could be more planets to be discovered, as many multiplanetary systems have five or six planets and this is especially common around small stars. It is possible that one could be in the habitable zone, although MIT scientist Avi Shporer said that such a possibility was “optimistic thinking”.

Until then, the proximity and brightness of HD 260655 means that scientists can closely examine the properties of the planets and study their atmospheres.

“Both planets in this system are each considered among the best targets for atmospheric study because of the brightness of their star,” says Michelle Kunimoto, a postdoc in MIT’s Kavli Institute for Astrophysics and Space Research and one of the discovery’s lead scientists.

“Is there a volatile-rich atmosphere around these planets? And are there signs of water or carbon-based species? These planets are fantastic test beds for those explorations.”

The system was first spotted by Nasa’s Transiting Exoplanet Survey Satellite (TESS), which detected periodic dips in the light from HD 260655 – indicative of a planet passing in front of the star.

HD 260655 was also in a survey of stars taken by the High Resolution Echelle Spectrometer (HIRES), an instrument that operates as part of the Keck Observatory in Hawaii.

HIRES had been monitoring the star since 1998, so the researchers had access to the survey’s publicly available data which shortened the time it took to confirm the system.

The scientists used data from other surveys to measure the star’s radial velocity – the movement it experiences from gravity when another planet is near it. “Every planet orbiting a star is going to have a little gravitational pull on its star,” Michelle Kunimoto said.

“What we’re looking for is any slight movement of that star that could indicate a planetary-mass object is tugging on it.”

Scientists have now discovered over 5,000 exoplanets orbiting distant suns. “It’s not just a number,” Jessie Christiansen, science lead for the Exoplanet Archive and a scientist with the Nasa Exoplanet Science Institute at Caltech said.

“Each one of them is a new world, a brand-new planet. I get excited about every one because we don’t know anything about them.”