July 14, 2024
1 Solar System Way, Planet Earth, USA

Neptune-like planet 'Phoenix' baffles astronomers with its atmosphere

The discovery challenges conventional theories about how planets age in extreme radiation-filled environments.

Astronomers have discovered a planet beyond our solar system that is so welcoming to its host star that its highly swollen atmosphere should have been reduced to bare rock billions of years ago. However, the planet's dense air has withstood the immense radiation from its star for possibly billions of years, defying conventional theories about how planets age in extreme radiation-filled environments.

Just over six times larger than Earth, the newly discovered “hot Neptune” orbits close enough to its star that a year lasts just about four days. Neptune-sized bloated planets with such narrow orbits are rare finds, as models predict that radiation from stars strips planets of their atmospheres, often exposing bare rock surfaces. However, the 6 billion-year-old planet, which orbits its star six times closer than Mercury orbits our Sun, boasts a remarkably inflated atmosphere, rich in hydrogen and helium.

Although it is officially cataloged as TIC365102760 b, the discovery team has nicknamed it Phoenix for its persistence in surviving the star's immense radiation.

“This planet is not evolving as we thought,” the study's lead author, Samuel Grunblatt of Johns Hopkins University, said in a statement. statement. “We don't know why it still has an atmosphere when other hot Neptunes that are much smaller and much denser seem to be losing their atmospheres in much less extreme environments.”

Phoenix is ​​seen by TESS

Phoenix was discovered by NASA Transiting exoplanet study satellite (TESS) when the telescope recorded telltale dips in starlight each time Phoenix crossed the face of its star. Follow-up observations made with the Keck Observatory on Hawaii's Mauna Kea volcano helped confirm the finding.

The host star may be much less active than models predict, which would slow the rate at which Phoenix's atmosphere leaks into space, according to a paper published last week in The astronomical magazine reporting the discovery.

Alternatively, the researchers suggest that Phoenix may have been in a larger, farther orbit from the star a few billion years ago, when the star would have exploded more frequently than it does now. The planet could have preserved its atmosphere by avoiding the star's most active phase and migrating inward to its current four-day orbit. However, it is unknown what would have given Phoenix that push; There are no other known planets in the system nor is Phoenix's orbit highly elliptical, as would be expected for a planet that migrated, the researchers say.

Observations of other Neptune-sized puffy planets suggest Slowly rotating stars fail to evaporate the atmospheres of their planets. For example, late last year, a different team of astronomers studying LTT 9779 b, a similarly inflated planet that orbits its host star for less than a day, discovered that the star rotates at a rate of one kilometer per second, a snail's pace compared to 100 kilometers per second. -seconds (or about 62 miles per second) of spin of most hot stars. Fast-spinning stars are known to shine more frequently, causing an accelerated loss of atmospheres from nearby planets.

In another 100 million years, Phoenix will gradually spiral toward its star before finally being engulfed, a fate that awaits many worlds, including Earth. Our planet has about 4.5 billion years left before our Sun runs out of hydrogen fuel and becomes a red giant, swallowing up all the planets up to Mars (which will probably remain tied to the Sun after his death).

There are no signs that Phoenix has already begun to slide toward its star, according to the new study. Only two other planets have been found in the process of being condemned, including a world called Kepler-1658b, whose orbit astronomers estimate It is shrinking at a minuscule rate of 131 milliseconds per year.

“We don't understand the later stages of the evolution of planetary systems very well,” Grunblatt said. “This tells us that Earth's atmosphere may not evolve exactly as we thought it would.”

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