Astronomers have found more than 350 possible moons around asteroids by analyzing data from the European Space Agency’s Gaia space telescope. While asteroids known to have moons, also known as binary asteroids, have been studied by Gaia before, this is the first time the telescope has been used to discover new binary asteroids.
“Binary asteroids are difficult to find as they are mostly so small and far away from us,” said lead author Luana Liberato of Observatoire de la Côte d’Azur, France. “Despite us expecting just under one-sixth of asteroids to have a companion, so far we have only found 500 of the million known asteroids to be in binary systems. But this discovery shows that there are many asteroid moons out there just waiting to be found.”
Previously, astronomers have discovered binary asteroids using various techniques that all have their own limitations. Radar measurements are only limited to asteroids relatively close to Earth, while direct observation through high-resolution telescope imagery works best for binary asteroids with a large distance between the two bodies.
Space probes have also discovered asteroid moons. In November 2023, NASA’s Lucy spacecraft imaged asteroid Dinikesh during a flyby and surprised astronomers by showing that it had a moon. Subsequent images showed that Dinikesh’s moon consisted of two smaller objects touching each other and was a so-called contact binary.
Graphic summarizing how binary asteroids are detected using Gaia’s observations. (Credit: ESA)
For this study, Liberato et al. used Gaia’s third release of data collected with the spacecraft’s astrometry instrument. The purpose of this instrument is to precisely measure the positions and movements of stars and other objects.
This instrument is precise enough to measure slight variations, or a “wobble”, in the light signals from binary asteroids. This wobble is caused by the gravitational pull the two bodies exert on each other, which slightly alters the path the pair traces across the sky. The same effect has also been used to detect binary stars or even exoplanets.
An earlier attempt at detecting binary asteroids using this method in Gaia’s second data release did not result in any detections. However, the new study uses the third release, which is of better quality and contains more data than the second release. With this data, the team was able to detect 352 potential binary asteroids.
Like the other methods used to discover asteroid moons, this method using astrometric data is not without limitations. The wobble in the signal that this method relies on could also be caused by a single rotating irregularly shaped asteroid, an effect that would be especially pronounced for larger objects with a diameter approaching 100 km.
Visualization of asteroids included in Gaia’s Focused Product Release. (Credit: ESA/Gaia/DPAC)
While further observations are needed to confirm the 352 asteroids are binary asteroids, the study does show that this method and Gaia’s observations could become powerful tools in the discovery of binary asteroids. The authors suggest that future studies could apply the same method to Gaia’s more recent and more precise Focused Product Release, or to the upcoming fourth full data release that marks the end of the spacecraft’s primary mission in 2026.
Gaia was launched in 2013 to build a precise three-dimensional map of our galaxy. Throughout its ongoing mission, it has shown to be capable of much more and contributed to many studies beyond its primary objective. The telescope has discovered many new asteroids and helped track asteroids more accurately than before.
“Gaia has proven to be an outstanding asteroid explorer and is hard at work revealing the secrets of the cosmos both within and beyond the Solar System,” said Gaia Project Scientist Timo Prusti of ESA. “This finding highlights how each Gaia data release is a major step up in data quality, and demonstrates the amazing new science made possible by the mission.”
Liberato et al.’s results were published in the journal Astronomy & Astrophysics on Aug. 8.
(Lead image: Visualization of the 156,801 asteroids included in Gaia’s Data Release 3. The position of each asteroid is displayed as it was on June 13, 2022, with a trail visualizing the asteroid’s motion over the prior 10 days. Credit: ESA/Gaia/DPAC)
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