For about a century, a small asteroid designated 2016 HO3, roughly the size of a Ferris wheel has been trailing Earth on its journey around the Sun. Discovered in 2016, it remained largely unnoticed until recent years, when studies revealed both its unusual orbit and surprising origin.
A Quasi-Satellite, Not a True Moon
Known formally as 469219 Kamoʻoalewa (designation 2016 HO3), this ~40–100 m asteroid is Earth’s most stable known quasi-satellite.
Unlike a conventional moon that orbits Earth directly, Kamoʻoalewa orbits the Sun in a 1:1 resonance with our planet. It completes one lap around the Sun in exactly the same time Earth does (365 days), but its slightly inclined and eccentric orbit makes it appear to loop around Earth from our perspective—tracing a slow, kidney-bean-shaped path in the sky.
It has been in this co-orbital configuration for roughly 100 years and is expected to remain so for several more centuries. At its closest, it never approaches nearer than about 38 lunar distances (~14 million km), posing no collision risk.
Discovery and Early Mystery
The asteroid was first detected in April 2016 by the Pan-STARRS 1 telescope in Hawaii. Because it spends much of its time near the Sun in the sky, it is difficult to observe and was only spotted once telescopes and search algorithms became sensitive enough.
Astronomers quickly recognized its unusual stable relationship with Earth. Paul Chodas, manager of NASA’s Center for Near-Earth Object Studies, noted at the time that objects in such quasi-satellite states rarely last more than a few decades—making Kamoʻoalewa’s century-long companionship remarkable.
A Piece of the Moon
What truly transformed our understanding came in 2021. Using large telescopes on Mauna Kea, a University of Arizona–led team obtained reflected sunlight spectra from the asteroid. The results were startling: its surface composition closely matches samples returned from the Moon by Apollo missions, particularly the silicate minerals found in lunar highlands.
Researchers concluded that Kamoʻoalewa is almost certainly a fragment ejected from the Moon by a meteoroid impact. Subsequent modeling published in 2024 suggests the likely source crater is Giordano Bruno, a relatively young (~1–10 million-year-old) 22-km crater on the lunar far side. In cosmic terms, this makes Kamoʻoalewa a very recent exile.
Rather than falling back to the Moon or escaping the Earth-Moon system entirely, the fragment received precisely the right velocity to enter a stable quasi-satellite orbit around Earth.
Tianwen-2: The Sample-Return Mission
In May 2025, China launched the Tianwen-2 mission specifically to visit Kamoʻoalewa. The spacecraft is scheduled to rendezvous with the asteroid. It will also perform detailed remote sensing, and execute a touch-and-go sample collection (possibly using an anchor-and-drill system). If successful, it will return the first samples from a quasi-satellite to Earth around 2027–2028.
Because Kamoʻoalewa has been exposed to space weathering for millions of years without an atmosphere or active geology to alter its surface (unlike the Moon itself), its samples are expected to preserve pristine records of:
- The Moon’s impact history
- Cosmic-ray exposure over millions of years
- Early solar system materials that may have been implanted in the lunar regolith
Broader Implications
Kamoʻoalewa is not unique in principle—Earth temporarily captures small “minimoons” every few years—but it is by far the most stable and longest-lasting example known. Its discovery highlights how dynamic near-Earth space truly is: rocks are routinely exchanged between planets, moons, and asteroids.
What began as an anonymous near-Earth object has become a scientific treasure: a accessible fragment of our own Moon drifting in solar orbit, now on its way to becoming humanity’s next sample-return target.
Far from a mysterious stalker, Kamoʻoalewa is a long-lost sibling—one we’re finally bringing home.
FAQ: Asteroid 2016 HO3 (Kamoʻoalewa)
What is the composition of 2016 HO3?
Asteroid 2016 HO3, also known as Kamoʻoalewa, has a surface composition dominated by lunar-like silicates, with a reddened infrared spectrum indicative of extensive space weathering. This matches the mineralogy of samples returned from the Moon's highlands by Apollo missions, such as Apollo 14. It is believed to be a fragment ejected from the Moon, likely from the Giordano Bruno crater on the lunar far side.
Can we see 2016 HO3 from Earth?
No, 2016 HO3 is not visible to the naked eye due to its small size (40–100 meters across) and faint apparent magnitude, typically around 21st magnitude or dimmer. About one-millionth as bright as the faintest visible stars. It requires a large professional telescope for observation, as it was first detected using the Pan-STARRS survey telescope. Amateur telescopes may occasionally spot it during closer approaches with precise coordinates, but it often lingers near the Sun in the sky, making it hard to view.
How far away is 2016 HO3?
As of November 21, 2025, 2016 HO3 is approximately 27.7 million kilometers (17.2 million miles) from Earth, or about 0.185 AU. Its distance varies between roughly 14 million km (38 lunar distances) at closest approach and 161 million km (100 lunar distances) at farthest, due to its quasi-satellite orbit. The next closest approach will occur on November 9, 2030, at about 16 million km.