The European Space Agency’s (ESA) Gaia space telescope, renowned for its ability to track billions of stars in the Milky Way, has made a remarkable discovery closer to home. It has detected potential moons orbiting over 350 asteroids, previously thought to be solitary objects. This breakthrough showcases Gaia’s capability to conduct “blind searches” for entirely new asteroid-moon pairings.
Gaia had already been studying known binary asteroids, confirming the existence of their companions. However, this recent discovery signifies a significant leap forward. If these new observations are validated, the count of known binary asteroid systems in our solar system will nearly double.
“Binary asteroids are challenging to find as they are usually quite small and distant from us,” explained Luana Liberato, the leader of the team behind the discovery and a researcher at the Observatoire de la Côte d’Azur. “Despite our expectation that roughly one-sixth of asteroids have a companion, we have only identified 500 out of the one billion known asteroids to be in binary systems. This discovery demonstrates the abundance of asteroid moons waiting to be uncovered.”
Asteroids are remnants of the material that formed the sun and later gave birth to the planets in our solar system over 4.6 billion years ago. They primarily reside in the main asteroid belt between Mars and Jupiter, receiving minimal radiation from the sun. This means that the early solar system material found in asteroids remains largely “unspoiled.”
By studying asteroids, astronomers gain a deeper understanding of our solar system’s early stages. Furthermore, many scientists believe that water and complex organic molecules, crucial ingredients for life, were delivered to Earth through asteroid bombardment. Investigating asteroids could confirm or refute this theory.
However, studying binary asteroids offers even more profound insights into the infancy of our planetary system. The early solar system was a chaotic and violent environment where collisions between rocky bodies were frequent. Binary asteroids can reveal how these collisions unfolded and the outcomes of interactions between rocky bodies in the solar system.
Gaia has been making significant discoveries about asteroids since it commenced scanning our cosmic backyard and the wider Milky Way in 2013. Its Data Release 3 (DR3) saw the ESA satellite excel, precisely determining the orbits of over 156,000 asteroids. The quality of Gaia’s data is equally impressive. This data, estimated to be 20 times more precise as part of Gaia’s Focused Product Release, allowed Liberato and her colleagues to detect subtle “wobbles” in the orbits of asteroids, indicating the presence of a hidden moon companion exerting gravitational influence.
“Gaia has proven to be an exceptional asteroid explorer, tirelessly unveiling the secrets of the cosmos both within and beyond the solar system,” stated Timo Prusti, Project Scientist for Gaia at ESA. “This finding underscores the remarkable progress in data quality with each Gaia data release and highlights the incredible new science made possible by the mission.”
Excitingly, the fourth data release from Gaia, DR4, scheduled for mid-2026, will contain even more asteroid orbit data. This promises the discovery of even more asteroid-moon pairings.
While Gaia takes the lead in investigating binary asteroids, it’s not the only ESA mission dedicated to this research. This October, the space agency will launch Hera, a mission focused on studying the asteroid Didymos and its tiny moon Dimorphos. The familiarity of these names stems from Dimorphos being the space rock that NASA targeted with the Double Asteroid Redirection Test (DART) in September 2022. DART’s aim was to test whether a kinetic impact on an asteroid moon could alter its trajectory and that of its parent body, potentially diverting them from a collision course with Earth. Hera will conduct an in-depth investigation of DART’s impact and its aftermath to evaluate the feasibility of this method for planetary defense efforts.
The team’s research findings have been published in the journal Astronomy & Astrophysics.
