Air around a few planets beyond our solar system is escaping into space, making those worlds smaller, astronomers reported Nov. 15. And the atmospheres of these planets don’t get blown away by the strong winds from their stars like you might. wait, but rather by their own action.
It is known that about 90 tons of air from the Earth’s protective cover, responsible for sheltering life, escapes into space every day because our atmosphere is heated by the sun. However, at this extremely slow rate, scientists believe it would take at least 15 trillion years for our planet to be completely stripped of its atmosphere. So there’s nothing to worry about in that regard.
But a few exoplanets, particularly some larger than Earth but smaller than Neptune, actually push out their atmospheres from the inside through a process known as “core-powered mass loss,” according to a new study . This mechanism is thought to be capable of shrinking a bloated, sub-Neptune planet down to a rocky super-Earth. With this information, astronomers say they now have enough data to explain why they don’t see many exoplanets that are about 1.5 to twice the size of Earth. It’s the happy medium between a super-Earth and a sub-Neptune.
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“Exoplanet scientists now have enough data to say that this gap is not a coincidence,” study lead author Jessie Christiansen, a scientist at Caltech, said in a statement. “Something is happening that prevents planets from reaching and/or staying at this size.”
The team suspects that “something” is radiation coming from the depths of these sub-Neptune planets, particularly from their hot cores, pushing back atmospheres. “This radiation pushes the atmosphere from below,” Christiansen said.
An alternative (but unlikely) theory for these sub-Neptunes is a phenomenon called photoevaporation, in which a planet’s atmosphere is destroyed by a star’s radiation, like “a hairdryer on an ice cube.” This is probably not the solution to this mystery, as the process is thought to occur within the first 100 million years after a planet’s birth, whereas the new study analyzed much older sub-Neptunes .
Christiansen and his colleagues analyzed exoplanet data collected by NASA’s Kepler 2 mission, a revised exoplanet-hunting effort after the Kepler spacecraft faced some technical setbacks. The team searched for stars orbiting beneath Neptune in two star clusters: the Praesepe or Beehive cluster, which hosts about 1,000 stars, and the Hyades cluster, which hosts about 500 stars and forms the head of “Taurus » in the constellation Taurus. They are 600 and 800 million years old, respectively.
In this age range, scientists found that almost all stars had sub-Neptunes with atmospheres orbiting them, suggesting that photoevaporation did not occur (or that they would have already completely lost their atmosphere).
On the planets around the stars more over 800 million years in the K2 database, however, only 25 percent exhibited sub-Neptune orbits. Since the older age of these stars is close to the billion years mark during which core-driven mass loss is expected to occur, the core-pushing mechanism is likely the reason for atmospheric escape on these stars. planets, says the new study. .
Either way, “if you don’t have enough mass, you can’t hold on, you lose your atmosphere and you shrink,” Christiansen said.
This research is described in an article published November 15 in The Astronomical Journal.
Originally published on Espace.com.