View from Mars Hill: detection of the youngest pair of asteroids in the solar system | Columnists

KEVIN SCHINDLER

An international team of astronomers has discovered a pair of asteroids that separated from their parent body just 300 years ago. The pair is exceptional because it is the youngest known “pair of asteroids” by at least a factor of 10, it passes close to Earth’s orbit and it has properties that are difficult to explain given its young age.

The majority of asteroids in our solar system reside in the area between the orbits of Mars and Jupiter, known as the Main Asteroid Belt. Closer to home, scientists have identified other asteroids known as near-Earth asteroids (NEAs), whose orbits bring them close to Earth.

In 2019, scientists using the Pan-STARRS1 telescope in Hawaii and the Catalina Sky Survey in southern Arizona each discovered a new NEA, identified as 2019 PR2 and 2019 QR6. The larger of the two is about a kilometer in diameter and the other half that size, and they have been found to have very similar orbits around the sun.

Further study involved a team led by Petr Fatka of the Astronomical Institute of the Czech Academy of Sciences and including Nick Moskovitz and Brian Skiff of Lowell Observatory and NAU graduate Annika Gustafsson. They confirmed it to be a pair of asteroids – two asteroids that split from a single parent asteroid over the past few million years – currently about a million kilometers apart.

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Several telescopes were used for follow-up observations, including the 4.3-meter Lowell Discovery Telescope (LDT) in northern Arizona. These observations revealed very similar surface properties of the two asteroids, further supporting the hypothesis of their common origin.

Fatka says: “Thanks to the measurements made with the LDT, it is clear that 2019 PR2 and 2019 QR6 originate from the same parent object and that their high orbital similarity is no coincidence.”

The majority of asteroid pairs probably form by spinning fission, when a spinning asteroid (which is essentially a pile of rubble) reaches a critical velocity at which the debris flies off and forms one or more new bodies, now orbits very similar to those of the parent body.

Based on several modeling techniques and additional observations — including retrieving previously unnoticed detections made with the Catalina Sky Survey 14 years before the 2019 discovery — the team determined that the pair separated there. is only 300 years old, making them the youngest known pair of asteroid pairs.

Fatka says: “It’s very exciting to find such a young pair of asteroids that only formed about 300 years ago, which was like this morning – not even yesterday – on astronomical timescales.” Former record holders were at least 10 times older.

This young age led to difficulties in reconciling the history of the couple’s formation. Standard models of asteroid pair formation by rotational fission could not fully explain the properties of 2019 PR2 and 2019 QR6; something else had to be going on to explain their current separation.

The team then developed new models that assume the original body was a comet, whose gas jets could push their orbits into the configuration seen today. This provided a viable origin story for these objects, but as Moskovitz explains, “The bodies today show no 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.

To answer this question, further observations will have to come. However, that will have to wait more than a decade. Fatka explains: “To get a better idea of ​​the process that caused the disruption of the parent body, we have to wait until 2033, when both objects will again be within reach of our telescopes.

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