Astronomers have broken yet another record, spotting a new gas giant with the shortest known orbit. The world takes just 16 hours to circle its star — but someday, the dance may come to an abrupt end.
The newly announced exoplanet belongs to a category scientists refer to as "hot Jupiters." These worlds are built more or less like our solar system's behemoth, but orbit much closer to their stars, hence the nickname. Although astronomers have identified more than 400 hot Jupiters to date, researchers say none are quite like the new discovery, which is designated TOI-2109b.
"Everything was consistent with it being a planet, and we realized we had something very interesting and relatively rare," Avi Shporer, an exoplanet scientist at the Massachusetts Institute of Technology (MIT) and co-author on the new research, said in a statement.
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Shporer and his colleagues made their discovery in data gathered by NASA's Transiting Exoplanet Survey Satellite (TESS), which has been orbiting Earth since April 2018.
TESS is honed to discover planets that orbit their stars very quickly, since the telescope stares at one patch of the sky for about a month before moving on. TESS doesn't see planets directly — instead, it watches for small, rhythmic dips in brightness that mark a planet coming between the telescope and the star.
In the case of TOI-2109b, those dips came every 16 hours, faster than for any gas giant scientists have spotted to date, according to the statement. The planet's star is located about 855 light-years away from Earth in the constellation Hercules, according to the statement. After the researchers spotted the signal, they recruited other telescopes to check in on the star, which is called TOI-2109. (TOI stands for "TESS Object of Interest.")
Combined, those observations didn't just confirm that there really is a planet orbiting the star; scientists were also able to measure a handful of key characteristics about TOI-2109b. It's about 1.5 million miles (2.4 million kilometers) away from its star, for example. (For comparison's sake, Mercury is about 24 times farther away from our sun.)
That's already pretty weird. "From the beginning of exoplanetary science, hot Jupiters have been seen as oddballs," Shporer said. "How does a planet as massive and large as Jupiter reach an orbit that is only a few days long? We don't have anything like this in our solar system, and we see this as an opportunity to study them and help explain their existence."
TOI-2109b is about five times as massive and one-third larger than our own Jupiter, and the star is about twice the size and mass of our sun. And the new planet also appears to be the second-hottest known exoplanet known, with dayside temperatures reaching nearly 6,000 degrees Fahrenheit (3,300 degrees Celsius), although the nightside is too faint for TESS to see. (Close-orbiting alien worlds are often "tidally locked," always showing the same face to their host star, just as the moon always shows its near side to Earth.)
That's reasonably interesting as well. "Is the temperature there very cold, or does the planet somehow take heat on the day side and transfer it to the night side?" Shporer said. "We're at the beginning of trying to answer this question for these ultrahot Jupiters."
But for scientists, the most intriguing characteristic of TOI-2109b may be the change in its orbit: The planet appears to be creeping closer to its star at the fastest rate astronomers have seen yet, between 10 and 750 milliseconds per year.
That's not fast enough to leave scientists hope that they could actually watch the planet's fate. But TESS is still working and will check back in on TOI-2109 in May and June 2022, and scientists hope those observations could allow them to study the orbital decay phenomenon in more detail.
"In one or two years, if we are lucky, we may be able to detect how the planet moves closer to its star," Ian Wong, lead author of the research who was a postdoc at MIT during the study and is now at NASA's Goddard Space Flight Center in Maryland, said in the statement.
"In our lifetime, we will not see the planet fall into its star," he said. "But give it another 10 million years, and this planet might not be there."
The research is described in a paper published Nov. 23 in The Astronomical Journal; a draft of the paper is available on the pre-print server arXiv.org.
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