Patrick Michel, a global expert in asteroids, explains the scientific significance of China’s mission to return samples from the asteroid Kamoʻoalewa scheduled for 2025. This asteroid is intriguing due to its potential connection to the lunar crater Giordano Bruno. But that’s not all.
In 2025, China plans to launch Tianwen-2, an ambitious mission to return samples from the asteroid Kamoʻoalewa, a quasi-satellite of Earth. This means that it co-orbits with Earth around the Sun, following its own orbit, which, from our terrestrial perspective, appears to revolve around our planet. In reality, it is a companion of Earth evolving on an orbit in resonance with our planet in a 1:1 average motion.
This sample return mission presents major challenges due to the small size of the asteroid, measuring only 30 meters in diameter, and its rapid 28-minute rotation speed, suggesting a possible monolithic structure and a lack of information about its shape and topography. Operations near this asteroid to map it and locate a collection site will be complex. These operations are necessary because currently, the shape and surface characteristics of Kamoʻoalewa remain unknown. Unable to land on the equator due to the asteroid’s high rotation speed, the probe will have to target the poles to retrieve samples. Two methods are being considered: touch-and-go and anchoring.
This mission, which is also a technological demonstration, represents a major challenge and has aroused significant scientific interest as such a small, rapidly rotating object has never been explored before.
What makes the asteroid Kamoʻoalewa particularly interesting is “its possible connection to the lunar crater Giordano Bruno,” as explained by Patrick Michel, a CNRS research director at the Lagrange laboratory at the Côte d’Azur Observatory and co-investigator of several asteroid missions that have brought back samples to Earth.
According to recent observations from Earth, “which have revealed that Kamoʻoalewa shares spectroscopic characteristics similar to silicate material found on the Moon, subjected to space erosion,”It is possible that this asteroid “originated from the lunar surface rather than the main asteroid belt from which most asteroids, known as geocruisers, typically come”. To verify and support this hypothesis, a team of scientists, including Patrick Michel, conducted a study based on “numerical impact simulations on the Moon and the evolution of generated fragments.” These findings were presented in an article published in “Nature Astronomy” today, shedding light on the theory that “the asteroid Kamo’oalewa could be a fragment ejected from the Giordano Bruno lunar crater,” emphasized Patrick Michel, who is also a co-author of the article.
This study aims to determine if the “material ejected during a lunar impact could give rise to an asteroid like Kamo’oalewa.” The simulations suggest that a recent impact on the Moon could have “ejected fragments into heliocentric orbits, some of which ended up in a 1:1 resonance with Earth, leading to the current presence of quasi-satellites like Kamo’oalewa.” In other words, these simulations indicate that the asteroid could be “a fragment ejected from this lunar crater.”
The simulations also suggest that the Giordano Bruno lunar crater, with a diameter of 22 kilometers and a relatively young age estimated between 1 and 10 million years, located at the far end of the Moon’s dark side, “is the most likely crater to be the source of fragments producing quasi-satellites like Kamo’oalewa.”
This hypothesis will be tested by the Tianwen-2 mission when it brings back a sample of Kamo’oalewa to Earth for in-depth laboratory analysis. The analysis of this lunar sample “holds great scientific value, allowing a better understanding of ejection processes during impacts on the Moon, spatial erosion on our natural satellite over the past few million years, and the dynamic environment near Earth.” This information will help refine impact models, crucial for addressing various issues such as dating craters and collisions in the Solar System.
This analysis will also be interesting because Kamo’oalewa is an S-type asteroid, “similar to Itokawa from which samples have already been collected, originating in the asteroid belt, and whose properties can be compared, which should be different if the two objects do not share the same origin”.