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Unusual new exoplanet ‘a true Disneyland’ for astrophysicists

Image credit: pa

Nasa’s planet hunting satellite has discovered three new exoplanets, one of which is unlike anything in our solar system.

The planets are orbiting the TOI-270 star which is 73 light years from Earth; one is rocky and slightly larger than Earth, while the two others are gaseous and roughly twice Earth’s size.

The smaller planet is located in the habitable zone: the range of distances from a star that are warm enough to allow liquid-water oceans on a planet. TOI-270 is classified as a “quiet” star in that it has very few flares emanating from it.

“We’ve found very few planets like this in the habitable zone, and many fewer around a quiet star, so this is rare,” said astrophysics professor Stephen Kane. “We don’t have a planet quite like this in our solar system.”

In our own solar system, there are either small, rocky planets (Earth, Mercury, Venus, and Mars) or much larger planets (Saturn, Jupiter, Uranus, and Neptune) composed mostly of gas rather than rock. This solar system does not have any planets approximately half the size of Neptune, although these are common around other stars.

“TOI-270 will soon allow us to study this “missing link” between rocky Earth-like planets and gas-dominant mini-Neptunes, because here all of these types formed in the same system,” said lead researcher Maximilian Gunther.

The trio of planets are among the smallest and nearest exoplanets known so far. They were discovered using data gleaned from Nasa’s Transiting Exoplanet Survey Satellite (TESS), which was sent into space in 2018 with the aim of finding new worlds around neighbouring stars that could support life. 

TESS discovered its first two planets last September when it made an early discovery of “super-Earth” and “hot-Earth” planets in solar systems at least 49 light years away.

Follow-up observations on the TOI-270 system have been planned for 2021, when the James Webb Space Telescope launches. It will be able to measure the composition of the TOI-270 planets’ atmospheres for oxygen, hydrogen, and carbon monoxide. These observations will help scientists to determine whether a planet has ever had a liquid water ocean, and whether any of the planets has conditions which could sustain life.

The closest of the three planets (TOI-270b) takes little over three days to orbit its star, with TOI-270c taking 5.7 days, and TOI-270d at 11.4 days.

The satellite looks for dips in light that might betray the presence of a planet passing in front of its host star.

“TOI-270 is a true Disneyland for exoplanet science, and one of the prime systems TESS was set out to discover,” Gunther said. “It is an exceptional laboratory for not one, but many reasons - it really ticks all the boxes.”

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