Astronomers have discovered an unusual exoplanet that has managed to retain its atmosphere despite intense nearby radiation from a giant red star.
Researchers at Johns Hopkins University found the rare planet, which should have been stripped to rock by the radiation emitted by its nearby host star, grew a puffy, less dense atmosphere instead.
The planet, nicknamed "Phoenix" because of its ability to survive, has sparked debate among scientists about how planets may adapt to extreme environments over time. In about 5 billion years, our own sun will turn into a red giant–a dying star in the final stages of stellar evolution–and expand and engulf Earth.
Sam Grunblatt, a Johns Hopkins University astrophysicist who led the research, told Newsweek: "Planets like Phoenix give us a glimpse into the final stages of a solar system that once may have looked similar to ours.
"Current understanding of the future evolution of the Earth's atmosphere suggests that when the sun evolves into a red giant, it will strip most, or all, of the planet's atmosphere just before finally engulfing the planet whole."
However, this study suggests that the Earth's atmosphere may be more resilient than previously thought.
"Earth may survive until, and even beyond, the start of planet engulfment, and may also puff up in the process," added Grunblatt. "This also suggests that the timing of other stages of Earth's atmospheric evolution may happen later than expected, or in a different sequence than models currently predict, which may have large implications for the longevity of life on Earth and beyond."
The newly discovered planet, which is officially called TIC 365102760 b, was found using the TESS space and W.M. Keck Observatory telescopes. It is around 6.2 times bigger than Earth and completes an orbit around its parent star—a giant red that gives off huge amounts of radiation—every 4.2 days.
According to the team who found Phoenix, the planet won't survive more than 100 million years before it begins dying by spiraling into its giant star.
Phoenix has been classified as a "hot Neptune" because it is similar to the planet—the most distant in our solar system from the sun, which therefore experiences freezing temperatures—despite being far hotter. It is about six times closer to its own star than Mercury is to the sun.
So-called "puffy" planets are less dense than others in the solar system and are made of gases, ice or other light materials. According to the study, these kinds of exoplanets are very rare and only 1 percent of stars have them.
They are harder to discover because of their small sizes, compared to larger, denser planets. The newly found Phoenix is smaller, older and hotter than scientists believed possible for this kind of exoplanet. It is 60 times less dense than the densest "hot Neptune" discovered to date.
However, the hot temperature and low density of the planet may have helped it survive the radiation emitted by its host star. According to the researchers, the process of stripping its atmosphere must have occurred at a slower pace than scientists believed to be possible.
Grunblatt said: "Hot Neptunes are believed to be rare because of the process of photoevaporation, or the stripping of a planetary atmosphere by high-energy radiation given off by the planet's host star.
"Hot Neptunes are difficult to discover because they're rare in general for the reason described above, and the signal from a hot Neptune isn't as large as a signal from a hot Jupiter," he explained.
"As the signals from all planets are smaller around giant stars, this means detecting a hot Neptune around a giant star is similar to detecting an Earth-sized planet around a sun-like star, and thus is right on the edge of detectability with current technology."
The full findings of the study were published in The Astronomical Journal.
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