Nicknamed ‘Phoenix,’ the newly-discovered hot-Neptune exoplanet TIC 365102760b retained atmosphere despite relentless radiation from its parent star, according to a new paper published in the Astronomical Journal.
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An artist’s impression of the hot-Neptune exoplanet TIC 365102760b and its parent star. Image credit: Roberto Molar Candanosa / Johns Hopkins University.
TIC 365102760 is a red giant star located 555 parsecs (1,810 light-years) away in the constellation of Cygnus.
Also known as 2MASS J20232153+5423395 or Gaia DR2 2185044477033336064, the star is at least 6.3 billion years old.
Officially named TIC 365102760b, the newfound planet completes an orbit around the star every 4.2 days.
This alien world is surprisingly smaller, older, and hotter than astronomers thought possible.
It belongs to a category of rare exoplanets called hot Neptunes because they share many similarities with the Solar System’s outermost, frozen giant despite being far closer to their host stars and far hotter.
TIC 365102760b is 6.2 times bigger and 19.2 more massive than Earth, and is about 6 times closer to its star than Mercury is to the Sun.
Because of the planet’s age and scorching temperatures, coupled with its unexpectedly low density, the process of stripping its atmosphere must have occurred at a slower pace than scientists thought possible.
They also estimated that the planet is 60 times less dense than the densest hot Neptune discovered to date, and that it won’t survive more than 100 million years before it begins dying by spiraling into its giant star.
“This planet isn’t evolving the way we thought it would, it appears to have a much bigger, less dense atmosphere than we expected for these systems,” said Dr. Sam Grunblatt, an astrophysicist at Johns Hopkins University.
“How it held on to that atmosphere despite being so close to such a large host star is the big question.”
“TIC 365102760b is the smallest planet we’ve ever found around one of red giants, and probably the lowest mass planet orbiting a red giant star we’ve ever seen.”
“That’s why it looks really weird. 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.”
Dr. Grunblatt and his colleagues were able to gain such insights by devising a new method for fine-tuning data from NASA’s Transiting Exoplanet Survey Satellite (TESS).
The satellite’s telescope can spot low-density planets as they dim the brightness of their host stars when passing in front of them.
But the team filtered out unwanted light in the images and then combined them with additional measurements from the W.M. Keck Observatory, a facility that tracks the tiny wobbles of stars caused by their orbiting planets.
“The findings could help scientists better understand how atmospheres like Earth’s might evolve,” Dr. Grunblatt said.
“Scientists predict that in a few billion years the Sun will expand into a red giant star that will swell up and engulf Earth and the other inner planets.”
“We don’t understand the late-stage evolution of planetary systems very well.”
“This is telling us that maybe Earth’s atmosphere won’t evolve exactly how we thought it would.”
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Samuel K. Grunblatt et al. 2024. TESS Giants Transiting Giants. IV. A Low-density Hot Neptune Orbiting a Red Giant Star. AJ 168, 1; doi: 10.3847/1538-3881/ad4149
