Scientists find possible reasons why exoplanets are “shrinking”. The picture shows a schematic diagram of the exoplanet TOI-421 b. (NASA)
Text/Reporter Chen Juncun
Scientists from the National Aeronautics and Space Administration (NASA) have discovered that the mass of some exoplanets is getting smaller and smaller, seemingly “shrinking”, which may be caused by radiation emitted from the planet’s interior.
NASA points out that some exoplanets appear to be losing their atmospheres and shrinking. Astronomers using data from NASA’s retired Kepler space telescope found that it may be radiation emitted from the cores of these planets that pushes the atmosphere into space. The research results have been published in the Astronomical Journal.
Planets outside our solar system are called exoplanets and range in size from small rocky planets to massive gas giants. In the middle are super-Earth (1.6 times the diameter of the Earth) and sub-Neptune (2~4 times the diameter of the Earth).
NASA has discovered more than 5,000 exoplanets so far, but there are very few exoplanets with a diameter between 1.5 and 2 times that of the Earth. Scientists say there is enough data to prove that it is not accidental that there are so few exoplanets of this size (mass), but that there are some factors that prevent exoplanets from developing or maintaining this size.
Researchers believe that there are not many exoplanets of this mass, possibly because some sub-Neptunes have lost their atmospheres over time. If these planets don’t have enough mass, there won’t be enough gravity to hold on to their atmospheres, so the planets will lose their atmosphere and shrink to the size of a super-Earth.
Researchers have proposed two theories, one is mass loss caused by the planet’s core, and the other is photoevaporation (high-energy radiation ionizes gas), and this study also found evidence to support the first theory.
Jessie Christiansen, a scientist at the California Institute of Technology (Caltech) and NASA and the lead author of the research report, said that the mass loss caused by the planet’s core refers to the radiation emitted by the planet’s hot core pushing the atmosphere away from the inside out, resulting in a reduction in mass. .
She said that the research team spent five years looking for exoplanets suitable for study, but the research is not over yet because people’s understanding of the above two theories may change over time.
The Kepler Space Telescope used by this research ended its mission on October 30, 2018 after nine years of service. Scientists have used its data to discover more than 2,600 confirmed exoplanets, with thousands more yet to be confirmed. ◇
