Tour: NASA's Chandra Finds Baby Exoplanet is Shrinking

A baby planet is shrinking from the size of Jupiter with a thick atmosphere to a small, barren world, according to a new study from NASA’s Chandra X-ray Observatory.

This devastating transformation is happening as the host star is unleashing a barrage of X-rays that is tearing the young planet’s atmosphere away at an enormous rate.

The planet, named TOI 1227 b, is in an orbit around a red dwarf star about 330 light-years from Earth. TOI 1227 b orbits very close to its star — less than a fifth the distance that Mercury orbits the Sun — and the new study shows this exoplanet is a “baby” at a mere 8 million years old. By comparison, the Sun is about 5 billion years old, or nearly a thousand times older.

A research team found that X-rays from its star are blasting TOI 1227 b and tearing away its atmosphere at such a rate that the planet will entirely lose it in about a billion years. At that point the planet will have lost a total mass equal to about two Earth masses, down from about 17 times the mass of the Earth now.

The planet’s atmosphere simply cannot withstand the high X-ray dose it’s receiving from its star.

Indeed, it is probably impossible for anything or anyone to live on TOI 1227 b, either now or in the future. The planet is too close to its star to fit into any definition of a ‘habitable zone,’ a term astronomers use to determine if planets around other stars could sustain liquid water on their surface.

The star that hosts TOI 1227 b, which is called TOI 1227, is only about a tenth the mass of the sun and is much cooler and fainter in optical light. In X-rays, however, TOI 1227 is brighter than the sun and is subjecting this planet, in its very close orbit, to a withering assault. The mass of TOI 1227 b, while poorly determined, is likely similar to that of Neptune, but its diameter is three times larger than Neptune’s, making it similar in size to Jupiter.

This is the latest example of Chandra helping scientists get a better handle of the high-energy radiation like X-rays that planets outside our solar system receive. If we are going to understand how habitable or even viable a planet is — or not — this kind of information is crucial.