In preparation for the launch of Destiny+, a new study reveals that two near-Earth asteroids may share the same parent.

Asteroid illustration
Artist's illustration of the near-Earth asteroid 3200 Phaethon, one target of an upcoming fly-by mission.
Heather Roper / University of Arizona

Over their lifetimes, the millions of minor rocky bodies of our solar system — asteroids — are subject to extreme conditions. Some experience dramatic collisions, some are spun up to such high rotation speeds that they fly apart, and some venture so close to the Sun that our star’s heat cracks them into pieces.

Asteroid breaking apart
Illustration of an asteroid breaking apart into smaller fragments.

Over time, these violent processes create families of asteroids that dance around our solar system on similar paths. Where one rock once orbited, there might now be a group of genetically linked asteroids that follow similar trajectories — all produced by the splitting of one parent rock.

In a new study, scientists have explored two especially nearby asteroids to determine whether they might be linked.

A Visit to a “Potentially Hazardous” Neighbor

Asteroids whose orbits bring them close to the Earth are of particular interest to us: we like to keep an eye on those bodies that might threaten our planet.

The highly elongated orbit of asteroid 3200 Phaethon
The orbital path of the near-Earth asteroid Phaethon.
Sky & Telescope diagram

Perhaps 22,000 near-Earth asteroids are currently known, with just over 2,000 that are large enough and swing close enough to Earth’s orbit to be considered “potentially hazardous” — though it should be noted that the vast majority of these have been ruled out as being an impact threat in at least the next 100 years.

To learn more about these nearby bodies, the Japanese Aerospace Exploration Agency is sending a spacecraft, Destiny+, to fly by a large (~5-km) near-Earth asteroid. The target is 3200 Phaethon — an unusual blue-toned, dust-producing asteroid thought to be the source of the Geminid meteor stream — and other minor bodies that might be associated with it.

Artist’s illustration of the Destiny+ spacecraft.

As Destiny+ is currently scheduled to launch in 2022, scientists are currently preparing by learning all they can about the possible mission targets using ground- and space-based observatories. In a new study led by Maxime Devogèle (Lowell Observatory), a team of scientists presents detailed observations of (155140) 2005 UD, another near-Earth object and potential Destiny+ target that might be related to Phaethon.

Signs Point to a Linked Pair

Devogèle and collaborators gathered an impressive array of observations of 2005 UD, using dozens of telescopes to obtain photometry, polarimetry, and spectroscopy, and also reanalyzing thermal imaging.

A graph comparing the spectra of 2005 UD and 3200 Phaethon.
2005 UD and Phaethon exhibit very similar spectra, including rare spectroscopic (B-type) signatures.
Devogèle et al. 2020

By combining new observations with archival data and detailed modeling, the team constrained 2005 UD’s size (just over 1 km across) and rotation rate (it spins roughly once every 5.2 hours), as well as many other properties like its albedo, spectroscopic class, and even the size of the grains on its surface — knowledge that will all help with mission planning for Destiny+.

But what about 2005 UD’s potential link to Phaethon? Based on Devogèle and collaborators’ observations, 2005 UD and Phaethon appear to share more than just orbital characteristics. They also have very similar — and rare, among asteroids — physical properties as shown by their spectroscopy and polarimetry.

More study is needed, but the data suggest that the two are, indeed, genetically linked — perhaps 2005 UD and Phaethon both split from the same parent thousands of years ago. With any luck, Destiny+ will soon reveal more about these close-swinging rocky bodies!


“New Evidence for a Physical Link between Asteroids (155140) 2005 UD and (3200) Phaethon,” Maxime Devogèle et al 2020 Planet. Sci. J. 1 15. doi:10.3847/PSJ/ab8e45

This post by Susanna Kohler originally appeared on AAS Nova, which features research highlights from the journals of the American Astronomical Society.


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