What exactly is a “quasi-moon”?

“Quasi-moon” (or quasi-satellite) is the nickname for a small asteroid that shares Earth’s year-long trip around the sun in a 1:1 orbital resonance. In a frame of reference that moves with Earth, the object appears to trace a slow, bean‑shaped loop around our planet once per year. But unlike the real Moon, it isn’t gravitationally bound to Earth in a tight orbit; it’s primarily orbiting the sun, with Earth’s gravity gently corralling its path.

In simple terms, a quasi-moon is a fellow traveler: it keeps pace with Earth around the sun and, from our viewpoint, seems to orbit us on a vast, looping track spanning millions of kilometers.

• Primary master: the sun (not Earth)
• Relationship to Earth: 1:1 orbital resonance, near the same average distance from the sun
• Apparent motion: slow annual loops around Earth in the co-rotating frame
• Lifetime: months to millennia, depending on the object and perturbations

How scientists found it

Modern wide-field surveys scan the sky nightly for moving points of light. Once a new object is spotted in multiple images, astronomers fit its preliminary orbit and then run numerical simulations forward and backward in time. For this object, those integrations show it has been in the quasi-satellite state for about 60 years—likely captured into this configuration in the early 1960s as subtle gravitational nudges and resonances aligned.

Several lines of evidence support the classification:

• The orbital period around the sun closely matches Earth’s (about one year).
• The object’s relative motion with respect to Earth librates—oscillates—in a pattern characteristic of quasi-satellites.
• Simulations reveal the state persists over decades, indicating a genuine co-orbital resonance rather than a brief flyby.

Follow-up observations, including radar when geometry allows, refine the orbit, estimate size (often tens of meters across), and constrain the object’s reflectivity and spin.

Why “60 years” is interesting

Co-orbital states are delicate. Small gravitational tugs from Earth, the Moon, Venus, and Jupiter—plus tiny non‑gravitational forces like thermal recoil (the Yarkovsky effect)—can slide an asteroid into and out of the quasi-satellite phase. A residence time of roughly six decades means this object has been coherently looping with Earth for an appreciable fraction of a human lifetime, yet not so long that its state is permanent. It offers a live case study in how small bodies transition among co-orbital configurations (quasi-satellite, horseshoe, and passing orbits).

It’s not our first quasi-moon

Earth has hosted several co-orbital companions and temporary “mini-moons.” A few highlights:

• 469219 Kamoʻoalewa (2016 HO3): A persistent quasi-satellite discovered in 2016. It’s expected to remain in a stable Earth‑co‑orbital dance for centuries.
• 2023 FW13: Identified in 2023 as an Earth quasi-satellite that has likely accompanied us for millennia and should continue for many centuries to come.
• 2003 YN107 and 2004 GU9: Objects that have drifted in and out of quasi-satellite states on decadal timescales, illustrating how transient these arrangements can be.
• Temporary “mini-moons” (captured orbiters): Unlike quasi-moons, these are briefly gravitationally bound to Earth. Examples include 2006 RH120 (captured in 2006–2007) and 2020 CD3 (captured 2018–2020) before departing back into heliocentric orbits.

The new 60‑year resident fits this broader pattern: Earth’s co-orbital region is dynamic, and we are beginning to notice more of these subtle companions as our surveys improve.

The orbital dance: how quasi-satellites work

In a co-rotating frame where Earth is stationary, a quasi-satellite’s path looks like a slow loop that closes roughly once per year. In reality, both Earth and the asteroid are orbiting the sun. The object’s semimajor axis is very close to 1 astronomical unit, but its slight offset in eccentricity and inclination causes the characteristic looping motion relative to Earth.

Key drivers of the motion include:

• 1:1 resonance: The asteroid completes one solar orbit per Earth year on average.
• Libration: The object oscillates around a relative equilibrium, producing the looped track near Earth.
• Perturbations: Gravitational tugs from planets and the Moon, plus thermal forces, nudge the orbit and can eventually end the quasi-satellite phase.

Despite the dramatic name, quasi-moons typically stay far outside the Earth–Moon system’s tight confines—often many times farther away than the Moon. They pose no special tidal effects and, based on current solutions, no imminent collision risk.

Why this discovery matters

• Accessible targets for spacecraft: Because they move roughly with Earth, quasi-moons can be attractive destinations for technology demos, rendezvous missions, and even sample returns at relatively low fuel cost.
• Windows into near-Earth space: Studying these objects reveals how small bodies migrate, how resonances work, and how non‑gravitational forces reshape orbits over decades to millennia.
• Planetary defense: Characterizing nearby, slow‑moving objects improves our ability to predict and, if needed, mitigate potential impact hazards (even if a given quasi-moon is not a threat).
• Origins and materials: Spectroscopy can test whether some co‑orbitals are fragments from the inner solar system, remnants of ancient collisions, or even lunar ejecta.

Is it dangerous? Almost certainly not

Newly found quasi-moons are generally small—often a few to a few tens of meters across—and their current orbits keep them well away from Earth. Orbital solutions are continuously refined as more observations come in, but decades‑long quasi-satellite states are inconsistent with an imminent impact trajectory. As with all near‑Earth objects, astronomers will keep watch and update risk assessments as the data improve.

How many more are out there?

Probably quite a few. The night sky is vast, and the tiniest objects are faint. New survey facilities—especially the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST)—are poised to dramatically expand the census of co‑orbitals, temporary mini-moons, and other near‑Earth companions. As those discoveries roll in, we should expect more finds like this 60‑year quasi-moon and a clearer picture of how such objects come and go.

Quick Q&A

• Is a quasi-moon the same as a second Moon? No. It’s not bound like the Moon and doesn’t orbit Earth in a tight ellipse. It orbits the sun and only appears to loop around Earth.
• How close does it get? Typically far beyond the Moon’s distance. The exact range varies, but it remains well outside the Earth–Moon system’s immediate sphere.
• Will it stay for long? This one has already stayed about 60 years. It may exit the quasi-satellite state in the future as gravitational nudges accumulate.
• Can we visit it? Potentially. Co‑orbitals are compelling mission targets due to their relative accessibility.

The bigger picture

Earth’s co-orbital neighborhood isn’t empty; it’s just subtle. With better surveys and more sophisticated orbital modeling, we’re now able to spot small companions that have been traveling alongside us for years to centuries. The newly reported 60‑year quasi-moon underscores that what seems like a static solar system is, in fact, a constantly shifting interplay of gravity and sunlight—one that we’re only beginning to map in detail.