NASA scientists have discovered evidence of the mystery of planetary contraction

NASA scientists have been puzzling over the population of planets that appears to be shrinking. The culprit may be radiation.

There are all kinds of worlds outside our solar system. Distant alien planets, called exoplanets, could be gas giants like Jupiter, rocky balls roughly the size of our planet, or even “super-jets” as dense as cotton candy.

But there is a mysterious gap where there should be planets about 1.5 to 2 times the width of Earth.

A mysterious gap where there should be planets

Of the more than 5,000 exoplanets discovered by NASA, there are plenty of super-Earths (up to 1.6 times the width of our planet) and plenty of sub-Neptunian planets (about two to four times the diameter of Earth), but hardly any planets in between. .

“Exoplanet scientists have enough data now to say that this gap is not just a fluke. There is something going on that prevents planets from reaching and/or remaining at this size,” Jesse Christiansen, a research scientist at the California Institute of Technology and science lead for NASA’s exoplanet archive, said. In a press release on Wednesday.

Scientists believe this is because some of the sub-Neptunian planets are shrinking, losing their atmosphere and accelerating across the size gap until they become as small as giant Earths.

Christiansen’s latest research suggests that these worlds are shrinking because radiation from the planets’ cores pushes their atmospheres out into space.

The study, published in The Astronomical Journal on Wednesday, may solve the mystery of missing exoplanets.

The planets themselves may be pushing their atmospheres apart

Shrinking exoplanets may lack the mass (and thus gravity) to keep their atmospheres close.

However, the exact mechanism of atmospheric loss remains unclear.

The new study supports one hypothesis that scientists call “basic energy mass loss,” according to the release.

Losing mass with core energy is not a trendy new workout plan. This happens when the planet’s core emits radiation that pushes its atmosphere from below, causing it to separate from the planet over time, according to the release.

The other hypothesis, called photoevaporation, says that the planet’s atmosphere is dissipated by the radiation of its host star.

But photoevaporation is thought to occur when the planet is 100 million years old, and mass loss from fundamental energy could occur closer to the planet’s billionth birthday, according to the statement.

To test both hypotheses, Christiansen’s team looked at data from NASA’s retired Kepler space telescope.

They examined star clusters more than 100 million years old. Because planets are thought to be about the same age as their host stars, planets in these clusters will be large enough to undergo photoevaporation, but not large enough to lose mass with central energy.

Scientists found that most of the planets there retained their atmospheres, making mass loss from fundamental energy a more likely cause of eventual atmosphere loss.

“However, recent work points to an ongoing sequence of mass loss in which both processes are at work,” Christiansen wrote on X, the platform formerly known as Twitter, where he shared a link to a Harvard University assessment published online in July.

So the mystery has not been solved yet.

Her work is far from over, Christiansen said in the release, especially since our understanding of exoplanets will evolve over time.