Planets that boil away to turn into rocky super-Earths discovered by experts

Mini-Neptunes – gas-giant type planets that are smaller than those found in our own Solar System – are one of the most common types of planet detected elsewhere in the galaxy.

Now a new study reveals that the planets’ dense hydrogen and helium atmospheres can be “boiled away” by their parent star’ graduation – leaving a rocky ‘super-Earth’ planet in its place.

Astrophysicists from the California Institute of Technology, who have observed the process occurring in two different star systems, have published their findings in The Astronomical Journal.

A team led by the California Institute of Technology’s Michael Zhang observed two exoplanets in the TOI 560 system, which is roughly 103 light-years from Earth, and two others in the HD 63433 system, which lies just 73 light-years from us.

In both cases, the mini-Neptune lying closest to its parent star could be seen to be losing gas, which appeared to be pulled into the star. That phenomenon contradicts earlier predictions which said the gas would flow outwards awards the planets.

Over a period of hundreds of millions of years, the mini-Neptunes could lose their dense atmospheric cloak altogether and be left as rocky ‘super Earth’ planets.

Late last year University of Cambridge astronomers identified a new class of mini-Neptune planets that could potentially host life.

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These strange worlds were dubbed Hyceans by the researchers for their combination of hydrogen atmosphere and surface oceans.

Hyceans can be more than twice the radius of Earth, and around 10 times the mass. They’re significantly hotter too, with average atmospheric temperatures in the region of 200ºC.

“Hyceans are basically water worlds with hydrogen-rich atmospheres,” said Dr Nikku Madhusudhan, the lead author of the research from the University of Cambridge.

Because they’re so much larger than earth-type planets, they are a good deal easier to observe., and Dr Madhusudhan thinks they could well be the home of the first confirmed extraterrestrial lifeforms.

“We are saying that within two to three years we may see the first biosignature detection if these planets host life,” he told the Guardian.

“At the bare minimum,” he added, “microbial life should be possible”.

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