Evrim Yazgin
Cosmos science journalist
An Earth-like planet orbiting a red dwarf star, or ‘M dwarf,’ has been found to have had its atmosphere stripped away by intense radiation from its host star. The finding may help scientists narrow their search for extra-terrestrial life, as it suggests that planets orbiting other red dwarfs may also be rendered inhospitable by this star type.
That is, if we assume that aliens also need to breathe to metabolise. For the record, that is a fair assumption.
Red dwarfs are the most common star in the universe. They are about one tenth the diameter of our sun, but are still main sequence stars, meaning they fuse hydrogen atoms to form helium atoms in their cores. In fact, they are the smallest and coolest of the main sequence stars, reaching only around 2,000°C surface temperatures.
They are also, however, the universe’s most common star type. Red dwarfs are about 10 times more common than stars like our sun.
These little balls of gas don’t sound that impressive, but they are also known to have more solar activity like flares and intense radiation bursts than stars like our sun.
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Research on the rocky planet whose atmosphere was stripped by its red dwarf host star was published in the Astrophysical Journal Letters.
The planet, dubbed GJ 1252 b, was discovered in 2020 orbiting its red dwarf star 66 light years away. At 1.32 times Earth’s mass, this exoplanet is referred to as a ‘Super Earth’ but it orbits its star very closely – circling the red dwarf twice every Earth day.
GJ 1252 b’s fate appears similar to that of Mercury which has a tight orbit around our sun. Though Mercury retained its atmosphere, it is very thin.
Not only has GJ 1252 b’s atmosphere been stripped away by stellar radiation, it would also get very hot.
“The pressure from the star’s radiation is immense, enough to blow a planet’s atmosphere away,” says co-author Michelle Hill, an astrophysicist and PhD candidate at the University of California, Riverside (UCR). Day time temperatures on the planet are estimated to reach over 1,200°C – enough to melt many metals like gold, silver and copper.
It is this heat, plus presumed low surface pressure, which led the researchers to conclude that the planet’s atmosphere has been torn away. The researchers believe that even a huge amount of CO2 would not prevent the removal of the planet’s atmosphere.
“The planet could have 700 times more carbon than Earth has, and it still wouldn’t have an atmosphere. It would build up initially, but then taper off and erode away,” explains co-author Dr Stephen Kane, also an astrophysicist at UCR.
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Though GJ 1252 b is quite close to its star, the volatility of red dwarfs indicates that planets even further away may not be able to hold on to their atmospheres.
“It’s possible this planet’s condition could be a bad sign for planets even further away from this type of star,” Hill says. “This is something we’ll learn from the James Webb Space Telescope, which will be looking at planets like these.”
Of the 5,000 stars in the vicinity of our solar system, most are red dwarfs but around 1,000 stars are similar to our sun and could be host to hospitable planets. In addition, planets orbiting red dwarfs at a greater distance may still harbour life.
“If a planet is far enough away from an M dwarf, it could potentially retain an atmosphere. We cannot conclude yet that all rocky planets around these stars get reduced to Mercury’s fate,” Hill adds. “I remain optimistic.”