Earth hosts natural satellites that slip into and out of our planet’s gravitational grasp. Often called minimoons or semimoons, these tiny asteroids briefly loop around Earth before drifting away again. Scientists see them as potential stepping stones on humanity’s journey to becoming a truly spacefaring species, offering practical lessons in small-scale autonomous operations and in-situ resource use that could shape future missions beyond the Moon.
The first clear detection of a minimoon came from the Catalina Sky Survey in 2006. This object proved to be a rock only a few meters across and was designated RH120. It spent roughly twelve months in a roughly Earth-bound orbit, wandering around our planet before finally escaping the gravitational pull and resuming a solar trajectory. The encounter underscored how dynamic the population of near-Earth objects can be and how readily small bodies can become temporary companions of our planet.
In 2020, researchers at the Catalina Sky Survey identified another transient satellite, known as CD3, about the size of a compact car. It remained in near-Earth space for only a short period, finally departing as spring arrived. Each discovery added a data point to the evolving picture of how minimoons form, behave, and disperse, enriching our understanding of how Earth interacts with the broader asteroid belt and the inner solar system.
Some scientists argue that these ephemeral satellites could accelerate humanity’s capabilities for deep-space exploration, potentially shortening travel times to destinations like Mars. According to planetary scientist Richard Binzel, a professor at the Massachusetts Institute of Technology, minimoons might eventually serve as convenient staging grounds for launches, landing operations, or autonomous refueling and maintenance hubs. The idea is rooted in their low gravity, which could reduce the energy required to launch payloads into higher orbits or on interplanetary trajectories. Research on this concept continues, with emphasis on robust mission architectures and reliable capture and release mechanisms that can handle the fast-paced dynamics of small-body orbits.
One of the main challenges is the inherently fleeting nature of minimoons. Because these objects are only temporarily bound to Earth, any plan to utilize them as transit points must be built around rapid detection, precise tracking, and agile mission planning. Engineers must develop systems capable of extending the usable window, coordinating rendezvous with spacecraft, and ensuring safe maneuvering in the vicinity of Earth and the Moon. The field relies on advances in small-body dynamics, autonomous navigation, and lightweight propulsion to realize practical, repeatable operations rather than single, one-off demonstrations.
Binzel noted that the discovery of moon-like moons has accelerated only in recent years, driven by improvements in telescope sensitivity and faster data processing. The growing catalog of minimoons is gradually revealing how these bodies move relative to Earth, how long they stay in Earth’s neighborhood, and what resources they might bring if captured for brief periods. The science community continues to refine detection methods and orbit determinations so that future missions can plan with higher confidence. As our catalog expands, so too does the potential for using minimoons to test propulsion concepts, on-orbit assembly ideas, and other technologies that could support longer, more complex journeys beyond the near-term lunar environment.