'Very Exciting' 300-Year-Old Baby Asteroids Are Youngest Pair Ever Found

Astronomers have discovered a pair of asteroids passing close to Earth's orbit is the youngest duo of such objects ever discovered.

Identified as 2019 PR2 and 2019 QR6, the "baby" Near-Earth Asteroids (NEAs) split from their parent body just 300 years ago, a blink of an eye in our around 4.6-billion-year-old solar system. It makes the pair ten times younger than its nearest challengers for the record of youngest asteroid pair.

Petr Fatka, an astronomer at the Astronomical Institute of the Czech Academy of Sciences, said in a press release: "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."

The largest of the asteroids has a diameter of around 3,280 feet, while its smaller companion is about half this size. The duo is separated by about 600,000 miles and share similar orbits around the sun.

The pair was initially spotted in 2019, one by a team using the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1) instrument located at the Haleakala Observatory in Hawai'i. The other NEA was discovered by astronomers conducting the NASA-funded Catalina Sky Survey (CSS) at the University of Arizona's Lunar and Planetary Lab in Tucson, Arizona.

The mission of the CSS is to discover and track asteroids close to Earth greater than around 460 feet in diameter that could potentially pose a threat to our planet, collectively known as Potentially Hazardous Asteroids.

A further investigation conducted by a team of scientists led by Fatka, using the 4.3-meter Lowell Discovery Telescope (LDT) in northern Arizona followed. This revealed that the two asteroids had separated from a single-parent body within the last million years, with additional evidence of this common origin provided by the fact that the surface properties of both asteroids are both very similar and rare for NEAs.

Fatka, who is the lead author of a paper discussing the asteroids published in the Monthly Notices of the Royal Astronomical Society, said: "Thanks to the measurements performed with the LDT, it is clear that 2019 PR2 and 2019 QR6 come from the same parent object and their high orbital similarity is not coincidental."

Using multiple modeling techniques and through the recovery of previously unnoticed detections made with the Catalina Sky Survey in 2005, the team determined that the pair separated only 300 years ago.

This makes the duo of 2019 PR2 and 2019 QR6 the youngest known asteroid pair ever discovered, with the next youngest pair at least ten times older.

How Did This Young Asteroid Pair Form?

Because many asteroids are little more than gravitationally bound rubble-piles when they spin at a critical speed, debris flies away from them forming new bodies that tend to share the orbits of the parent body.

While this young age made the pair of asteroids an exciting discovery, it also presented difficulty in assessing how they formed. The usual theory of rotational fission couldn't account for the properties of 2019 PR2 and 2019 QR6.

The team addressed this mystery by creating formation models that assume the parent body of the duo was a comet, rather than a larger asteroid.

With a comet—icy bodies usually found at the cold outer edges of the solar system—it would be possible for jets of material created as solids at the surface to be transformed into gas in a process triggered as they pass closer to the sun. These jets could have pushed the asteroids into their current orbits.

Lowell Observatory researcher and team member Nicholas Moskovitz said that while a viable origin story for this asteroid pairing, there are still flaws in this cometary formation theory.

He said: "In the present day, the bodies don't display any signs of cometary activity. 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."

Astronomers will seek to answer these questions by further investigating 2019 PR2 and 2019 QR6, but these observations will have to wait a while. Fatka explains: "To have a better idea about what process caused the disruption of the parent body, we have to wait until 2033 when both objects will be within the reach of our telescopes again."

Baby Asteroid
An illustration of two newly discovered "baby" asteroids. Though around 300 years old, the asteroids split off from their parent body recently in cosmic terms. SETI Institute/UC Berkeley