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Dying planet is spiraling into its sun, giving a glimpse of Earth’s fate

The exoplanet is spending the next 3 million years inching towards its final goodbye.

(CN) — In 2019, recent post-grad Shreyas Vissapragada attended a science conference where his now colleague Ashley Chontos talked about an exoplanet that flew under the radar for ten years — Kepler-1658b. Vissapragada was interested in exoplanet transits and decided that Kepler-1658b would be interesting to look into — just to discover the Jupiter-sized world spiraling to its death. 

"This is one of the first looks that we get at the ultimate fate of these planets," said Vissapragada, now a 51 Pegasi b Fellow at the Center for Astrophysics Harvard & Smithsonian, in an interview.

Kepler-1658b was the first unidentified exoplanet candidate found by the NASA Kepler telescope in 2009 — a space telescope designed specifically for exoplanet discovery. However, scientists at the time wrote it off as a false positive and moved on to other findings. Finally, in 2019, when Chontos and her team characterized the planet's star in intense detail, Kepler-1658b's true identity was revealed. 

"Maybe it could have been Kepler-1, but it ended up being Kepler-1658 after one decade of work," Vissapragada noted. 

Published on Monday in The Astrophysical Journal Letters, Vissapragada proves the exoplanet is going through orbital decay.

Similar to Earth's ocean, tides are the main culprit for Kepler-1658b's ultimate demise. As the planet and its star work to be in alignment, immense amounts of energy are lost. The energy expended is being taken from the planet's orbit, causing the orbit to shrink. In layperson's terms, Kepler-1658b is spiraling closer and closer to its star. The "death by star" theory isn't new but this is the first observation of it occurring between a planet and an evolved star.

"We're only seeing a snapshot of this planet's life, but if it continues on this trajectory, in 3 million years, it will no longer be here. It will have crashed into the star," explained Vissapragada. "I think 3 million years sounds like a long time. But if you were to convert the age of the star to 100 years or a human lifetime, it's like a month — it's in the last month of its life." 

The planet is roughly 2.3 billion years old and has given scientists more to think about than its death. Kepler-1658b is an extremely bright planet, a characteristic that contributed to its false positive status in 2009. At first, researchers thought the brightness could be chalked up to reflecting its star's light. However, after looking at energy scales, Vissapragada and his team found that the planet could have been "superheated" by its tides. 

"I think it's really interesting and new that planets in this very end stage of their life glow — glow hotter than they did before. I feel like it's pretty cool," Vissapragada said.

These observations give scientists and civilians a glimpse at what Earth's final millions of years will look like when the Sun gets several billion years older and evolves. The findings also allow for more refined tidal physics models. Related research in the field has scientists looking at the spectra of stars they suspect have recently engulfed a planet and the chemical signatures of those planets.

"I find it really amazing that we can watch the orbit of the planet change on timescales that are accessible to humans. We're actually able to point at the telescope and say, 'Hey, that looks different than it did ten years ago,' even though these things are on such titanic timescales. It's cool that it's accessible to us for once," Vissapragada said. 

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