Like the mythical half-human, half-horse creatures, centaurs in the solar system are hybrids between asteroids and comets.
Now, astronomers have caught one morphing from one type of space rock to the other, potentially giving scientists an unprecedented chance to watch a comet form in real-time in the decades to come.
The object, called P-2019 LD2, was discovered by the ATLAS telescope in Hawaii in May. Its orbit suggests that it's a centaur, a class of rocky and icy objects with unstable orbits.
Because of that mixed composition and potential to move around the solar system, astronomers have long suspected that centaurs are a missing link between small icy bodies in the Kuiper Belt beyond Neptune and comets that regularly visit the inner solar system.
In a report on the Science News website, lead author and planetary scientist Kat Volk of the University of Arizona said: "We have an opportunity here to see the birth of a comet as it starts to become active. Our projections suggest that this object should be becoming a comet when I'm retiring."
In 2019, a study found that there's a region of space just beyond Jupiter that they call the "Gateway". In this area, small planetary objects hang out while warming up and transitioning from outer solar system ice balls to inner solar system comets with their long tails. It's like a comet incubator.
All previously found short-period comets were spotted only after they had transitioned into comets. But LD2 just came in from the Kuiper Belt recently and will become a comet in as little as 43 years, said a report by arXiv website on August 10.
"Our study found that P - 2019 LD2 orbit probably took it near Saturn around 1850, and it entered its current orbit past Jupiter after a close encounter with the gas giant in 2017. The object will leave its present orbit and move in toward the sun in 2063, where heat from the sun will probably sublimate LD2's volatile elements, giving it a bright cometary tail," said co-author and planetary scientist Gal Sarid of the SETI Institute in the same report.
"This will be the first-ever comet that we know its history, because we've seen it before being a comet," Sarid said.