Planets are mysteriously shrinking: NASA scientists explained why

Researchers are studying a group of planets that appear to be collapsing. Radiation may be the cause.

Artist's impression of the sub-Neptunian exoplanet TOI-421 b/photo by NASA, ESA, CSA, and D. Player (STScI)

There are a variety of worlds outside our solar system. Distant alien planets, called exoplanets, could be gas giants like Jupiter, rocky balls the size of our planet, or even “super plump” ones with the density of cotton candy.

But there is a mysterious gap in which there should be planets about 1.5-2 times wider than Earth, writes Business Insider. A study published in The Astronomical Journal may solve the mystery of missing exoplanets.

Mysterious hole where planets should be

Among the more than 5,000 exoplanets discovered by NASA, there are many super-Earths (which are 1.6 times wider than our planet) and many sub-Neptunes (about two to four times the diameter of Earth), but there are almost no planets in between.

“Scientists who study exoplanets now have enough data to say that this gap is not a fluke. Something is going on that prevents planets from reaching and/or staying that size,” said Jesse Christiansen, a Caltech postdoctoral fellow and scientist. Director of the NASA Exoplanet Archive.

Scientists believe this happens because some sub-Neptunes contract – lose their atmosphere and quickly overcome the size difference until they become as small as a super-Earth.

Christiansen’s latest research suggests that these worlds are collapsing because radiation from the planets’ cores is pushing their atmospheres into space.

The planets themselves may be pushing away their atmospheres

Collapsing exoplanets may lack enough mass (and therefore gravity) to keep their atmospheres dense. However, the exact mechanism of atmospheric loss remains unclear.

The new study supports one hypothesis, which scientists call “mass loss due to nuclear energy.”

Core mass loss is when a planet’s core emits radiation that pushes its atmosphere from below, causing it to separate from the planet over time.

Another hypothesis, called photoevaporation, states that the planet’s atmosphere is dissipated by radiation from its host star.

But photoevaporation is thought to occur by the time the planet is 100 million years old, and mass loss from core energy could occur closer to the planet’s billionth birthday, the study says.

To test these two hypotheses, Christiansen’s team examined data from the former Kepler space telescope.

They examined star clusters that are more than 100 million years old. Because planets are thought to be about the same age as their parent stars, planets in these clusters must be old enough to undergo photoevaporation but not old enough to lose mass through core energy.

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Scientists have found that most of the planets there have retained their atmospheres, making mass loss caused by core energy a more likely cause of eventual atmospheric loss.

“However, recent work suggests an ongoing sequence of mass losses in which both processes are at work,” Christiansen said.

Other space news

As UNIAN reported, earlier, during observations of the Orion Nebula, dozens of planet-sized objects were discovered, which may mark the existence of a new astronomical category.

The free-floating objects are called Jupiter-mass binaries, or Jumbos. They are too small to be stars, but they defy the generally accepted definition of a planet because they do not orbit a parent star.

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