By Iain Todd

Published: Thursday, 08 August 2024 at 07:09 AM


The Europeans Space Agency’s Gaia mission has found potential moons around over 350 asteroids.

Gaia had previously studied asteroids already known to have moons orbiting them, and confirmed those moons’ existence, but this time the spacecraft searched asteroids not known to have moons, and found 352 candidates.

Artist’s impression of the Gaia spacecraft. Credit: ESA–D. Ducros, 2013

“Binary asteroids are difficult to find as they are mostly so small and far away from us,” says Luana Liberato of Observatoire de la Côte d’Azur, France, lead author of the new study.

“Despite us expecting just under one-sixth of asteroids to have a companion, so far we have only found 500 of the one billion known asteroids to be in binary systems. But this discovery shows that there are many asteroid moons out there just waiting to be found.”

Infographic showing Gaia's discovery of 352 potential asteroids with moons orbiting them. Credit: ESA
Click to expand. Credit: ESA

Why study asteroids?

Asteroids are spacerocks left over from the formation of our Solar System; remnants of the dusty disc of material that surrounded our young Sun in its infancy.

The material in this circumstellar disc coalesced over time to form the planets and moons we see today across our Solar System.

And remnants of that disc are seen in asteroids; particularly the Asteroid Belt between Mars and Jupiter.

As such, asteroids can be studied to learn more about what our early Solar System was like and how it evolved over time.

And binary asteroids can give astronomers insight into how different bodies form, collide and interact in space.

If Gaia’s data is confirmed, 
it will add 352 known binary asteroids to the total, nearly doubling the known number of asteroids with moons. 

Gaia's all-sky view of the Milky Way based on the measurements of almost 1.7 billion stars. Credit: ESA
Gaia’s all-sky view of the Milky Way based on the measurements of almost 1.7 billion stars. Credit: ESA – ESA/Gaia/DPAC, CC BY-SA 3.0 IGO

Gaia’s asteroid discoveries

ESA’s Gaia space telescope launched on 19 December 2013, tasked with surveying over a billion stars to create the most precise 3D map of our Milky Way ever made.

In its data release 3, Gaia revealed the positions and motions of over 150,000 asteroids, and astronomers were able to use this data to look for asteroids ‘wobbling’ as a result of the gravitational tug of a moon in orbit around them.

This is the same method used to detect binary stars or even exoplanets orbiting stars.

150,000 asteroids detected by Gaia Gaia space observatory, 13 June 2022 Credit: ESA/Gaia/DPAC; CC BY-SA 3.0 IGO, CC BY-SA 3.0 IGO. Acknowledgements: P. Tanga (Observatoire de la Côte d'Azur)
150,000 asteroids detected by GaiaGaia space observatory, 13 June 2022Credit: ESA/Gaia/DPAC; CC BY-SA 3.0 IGO, CC BY-SA 3.0 IGO. Acknowledgements: P. Tanga (Observatoire de la Côte d’Azur)

Gaia was also able to unlock the characteristics of the asteroids’ chemistry, gathering data known as asteroid ‘reflectance spectra’, which relates to how light from a celestial object can reveal information about that object’s colour and composition.

“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,” says Timo Prusti, Project Scientist for Gaia at 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.”

Asteroid Didymos (top left) and moonlet Dimorphos, 2.5 minutes before the impact of NASA’s DART spacecraft. Credit: NASA/Johns Hopkins APL
Asteroid Didymos (top left) and moonlet Dimorphos, 2.5 minutes before the impact of NASA’s DART spacecraft. Credit: NASA/Johns Hopkins APL

Gaia and DART

The Gaia mission lent its assistance to the DART mission in 2022, which purposely collided with Dimorphos, a moon orbiting asteroid Didymos.

The aim of the DART mission was to study how the collision affected the asteroid moon’s orbital path.

Gaia observed the shadow cast by Didymos as it passed in front of distant stars, known as stellar occultation.

ESA’s Hera mission is due to launch in October 2024 and will follow up on the DART mission to produce a post-impact survey of Dimorphos.

‘Binary asteroid candidates in Gaia DR3 astrometry’ by Liberato et al. (2024) is accepted for publication on 8 August 2024 in Astronomy & Astrophysics. Read it at doi.org/10.1051/0004-6361/202349122.