Back when asteroids 2019 PR2 and 2019 QR6 were born, humans in the 18th century were busy inventing the mercury thermometer, founding New Orleans and fighting wars across Europe. “The duo is exceptional because it is the youngest known ‘asteroid pair’ by at least a factor of 10, it passes close to Earth’s orbit, and it has properties that are hard to explain given its young age,” the Lowell Observatory in Arizona said in a statement on Friday.
First spotted in 2019, the asteroids attracted attention due to their similar orbits. Astronomers investigated and found they’re a pair that originated by separating from the same parent body. They have a notable size difference, on par with Arnold Schwarzenegger and Danny DeVito in Twins. The bigger is 1 kilometer (0.6 miles) in diameter and the other is half that.
The Lowell Discovery Telescope got in on follow-up observations of the asteroids, which showed they share the same surface properties. Researchers developed and ran models to better understand the pair’s formation and history. The team also dug into the archives of the Catalina Sky Survey to find some previously overlooked older observations of the asteroids.
“It’s very exciting to find such a young asteroid pair that was formed only about 300 years ago, which was like this morning — not even yesterday — in astronomical timescales,” said Petr Fatka of the Astronomical Institute of the Czech Academy of Sciences. Fatka is lead author of a paper on the pair published in the journal Monthly Notices of the Royal Astronomical Society this week.
The asteroids are currently separated from each other by about 1 million kilometers (620,000 miles). They’ve left scientists with a mystery to figure out. It’s possible they may have split off from a comet rather than a parent asteroid, but the researchers aren’t certain.
“In the present day, the bodies don’t display any signs of cometary activity,” said Lowell Observatory astronomer Nicholas Moskovitz. “So it remains a mystery how these objects could have gone from a single parent body, to individually active objects, to the inactive pair we see today in just 300 years.”
More observations and data could help clear up the asteroids’ origin story, but it’s going to take time. Fatka said the rocks won’t be back in view of the telescopes again until 2033. It will be worth the wait.