Centaur spotted: Astronomers find space rock near Jupiter that might transform into a comet by 2063

The rare sighting is an opportunity to see the birth of a comet as it starts to become active, researchers say.

Many of the mythical creatures we know are unlikely to ever turn up in the real world, and that's probably for the best. However, a half-horse, half-human hybrid – a centaur, appears to have wiggled its way into the universe in the form of a whole new kind of astrophysical phenomenon.

Centaurs in the solar system are space rock hybrids – a cross between asteroids and comets. Researchers have spotted a centaur in the early days of its several-decade-long transformation into a comet. The space rock was caught in action near Jupiter by astronomers using the ATLAS telescope in Hawaii in May 2020.

Dubbed 'P/2019 LD2', the orbit of the space rock indicates to researchers that it falls under a class of rocky, icy asteroids that have unstable orbits. This class of asteroids, called 'Jupiter Trojans', are also called 'Trojan asteroids' or simply 'Trojans'. They are a huge band of asteroids that follow Jupiter's orbit around the Sun.

P/2019 LD2, specifically, seems to have a composition resembling both asteroid and comet [are you reminded of a certain interstellar visitor our solar system hosted last year, too?]. Since the comet also happens to move around in our solar system, astronomers have a unique opportunity to study Trojans, centaurs, and how comets form.

After crunching some numbers of the object's orbit and likely temperature over the past 3000 years, astronomers have found that P/2019 LD2 was a centaur even before it got into its current orbit joining other Jupiter Trojans in July 2018. After a brief warming up period, they expect that the space rock will return to being a Centaur by February 2028. Eventually, the centaur is going to become a comet by February 2063, and possibly a bright one, researchers said.

 Centaur spotted: Astronomers find space rock near Jupiter that might transform into a comet by 2063

The interstellar comet C/2019 Q4 in action. Image:
Gemini Observatory/NSF/AURA

"We have an opportunity here to see the birth of a comet as it starts to become active," Kat Volk, says planetary scientist from the University of Arizona, Tucson, told Science News.

Researchers suspect that centaurs are the missing link between the icy, tiny space rocks at the edge of our solar system (called the Kuiper Belt) beyond Neptune, and the comets that frequently make their way towards the inner planets. These comets, also known as "short-period" comets, come from the sea of icy space rocks in the Kuiper Belt, orbit the sun once a decade or longer, and show up predictably in Earth’s skies, according to a Science News report. In contrast, there are also "long-period" comets that visit the inner solar system once a century or longer, which might originate from regions even farther away from the Sun, with orbits that carry them to the very edges of the solar system.

Astronomers think the space rock P/2019 LD2 is morphing from one kind of space rock to a whole other kind, with very different features. This presents an opportunity to watch a comet form in real time over decades to come, the study pre-published in arXivreads

“What we really need to do is study many of these,” says lead author Henry Hsieh, a planetary astronomer at Planetary Science Institute but not involved in the study, is quoted as saying by Science News.

"Study this one first, and then study more of them, and figure out whether this object is an outlier or whether we see a consistent picture."

But we may not have to wait till 2063 to find out what happens to space rocks like P/2019 LD2. With new telescopes like the Vera Rubin Observatory going online in the decade to come, along will come more opportunity to watch these centaurs be born, transform, and interact with the solar system.

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