India’s Chandrayaan-2 lunar orbiter performed a manoeuvre in September to prevent a close encounter with the Korea Pathfinder Lunar Orbiter (KPLO), officially known as Danuri, according to the Indian Space Research Organisation (ISRO). The adjustment carried out on September 19, 2024, was necessary to avoid a potential collision between the two orbiters, which was projected for two weeks later if no changes were made to Chandrayaan-2’s trajectory.

Following this, on October 1, 2024, another orbital modification was implemented to maintain separation from other lunar orbiters, including NASA‘s Lunar Reconnaissance Orbiter (LRO), as per an ISRO report.

Frequent Collision Risks Among Lunar Orbiters

Around the lunar poles, orbiters such as Chandrayaan-2, Danuri, and LRO share a similar near-polar path, increasing the likelihood of close approaches. Over the past 18 months, the Korea Aerospace Research Institute (KARI), which operates Danuri, reported having received over 40 collision alerts for interactions among Danuri, Chandrayaan-2, and LRO. These alerts, referred to as “red alarms,” underscore the growing risk of accidental collisions as multiple international agencies operate missions in close proximity around the Moon.

Previously, in 2021, Chandrayaan-2 reportedly avoided a similar situation by shifting its path, preventing a close pass by LRO that would have brought the two within just three kilometres. Danuri itself has performed at least three orbital adjustments since it entered lunar orbit in December 2022, including avoiding both LRO and Japan’s Smart Lander for Investigating Moon (SLIM).

Lack of Unified Collision Protocols in Lunar Operations

At present, no globally coordinated protocol exists for managing collision risks around the Moon. Space agencies like ISRO, KARI, and NASA rely on direct communication, sharing spacecraft position data through email and teleconferences. However, according to Soyoung Chung, a senior researcher with KARI’s strategy and planning team, difficulties such as network security barriers and a lack of personnel contact information have, at times, complicated communication.

NASA’s Jet Propulsion Laboratory provides the Multimission Automated Deep-Space Conjunction Assessment Process (MADCAP) software, which estimates and warns of collision risks. Still, experts like Chung have suggested the need for a formal international framework for managing close approaches around the Moon.

The Moon is gradually moving farther from Earth, a phenomenon explained by NASA scientists as a result of complex gravitational interactions. Currently, the Moon drifts away at a rate of approximately 4 centimetres per year, a process influenced by tidal forces between the Earth and its satellite. This steady separation, though imperceptible on a human timescale, has profound implications for the Earth-Moon system and its long-term evolution, as per the space agency.

The Role of Tidal Forces in the Moon’s Drift

Earth’s gravitational pull creates bulges in the Moon’s shape, while the Moon’s gravity exerts similar forces on Earth, most notably on its oceans. However, the tidal bulges on Earth lag slightly behind the Moon’s position due to the time it takes for water to respond to gravitational changes, says NASA. This lag generates friction, slowing Earth’s rotation and transferring energy to the Moon, pushing it into a higher orbit.

NASA explains that this interaction causes the Moon to drift and lengthens Earth’s day by about 2 milliseconds per century. Over billions of years, this dynamic exchange of energy has significantly shaped the relationship between the two celestial bodies.

Implications for the Distant Future

If the process continues for another 50 billion years, the Moon’s orbit will become so vast that Earth itself could become tidally locked to the Moon. This would mean that only one hemisphere of Earth would ever see the Moon in the sky. A similar phenomenon is already observed in the Pluto-Charon system, where the two bodies are mutually tidally locked.

While such changes occur on timescales far beyond human experience, they highlight the ongoing evolution of the Earth-Moon system, which began when the Moon formed around 4.5 billion years ago. NASA’s research continues to unravel the complexities of these tidal interactions, offering insights into planetary systems within and beyond our solar system.