469219 Kamoʻoalewa

As it orbits the Sun, Kamoʻoalewa appears to circle (highly elliptically) around Earth as well. The object is beyond the Hill sphere of Earth and the Sun exerts a much stronger pull on it than Earth does. Although it is too distant to be considered a true natural satellite of Earth, it is the best and most stable example to date of a near-Earth companion, or quasi-satellite.[3]

Paul Chodas, manager of NASA's Center for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory in Pasadena, California, commented on the orbit:

Since 2016 HO₃ loops around our planet, but never ventures very far away as we both go around the Sun, we refer to it as a quasi-satellite of Earth. One other asteroid – 2003 YN107 – followed a similar orbital pattern for a while over 10 years ago, but it has since departed our vicinity. This new asteroid is much more locked onto us. Our calculations indicate 2016 HO₃ has been a stable quasi-satellite of Earth for almost a century, and it will continue to follow this pattern as Earth's companion for centuries to come.[4]

In its yearly trek around the Sun, Kamoʻoalewa spends approximately half of the time closer to the Sun than Earth is (that is, the asteroid is inside the Earth's orbit) and passes ahead of our planet, and approximately half of the time farther away (crosses outside Earth's orbit), causing it to fall behind. Also, its orbit is tilted a little, causing it to bob up and then down once each year through Earth's orbital plane. In effect, this small asteroid is caught in a game of leap frog with Earth that will last for hundreds of years.[4]

Chodas explained how the asteroid's orbit also undergoes a slow, back-and-forth twist over multiple decades:

The asteroid's loops around Earth drift a little ahead or behind from year to year, but when they drift too far forward or backward, Earth's gravity is just strong enough to reverse the drift and hold onto the asteroid so that it never wanders farther away than about 100 times the distance of the moon.[lower-alpha 3] The same effect also prevents the asteroid from approaching much closer than about 38 times the distance of the moon. In effect, this small asteroid is caught in a little dance with Earth.[4]

In terms of orbit, it currently is the most stable among the quasi-satellites of Earth that have been discovered and will remain in that orbit for about the next 300 years.[7] The closest Earth approach was on 27 December 1923 at 12.4 million km (32 LD).[2] By late May 2369 the asteroid will be 2.0 AU (300 million km) from Earth.[11] The Earth-like orbit may be a result of it being lunar ejecta.[7]

During the 2017 Astrodynamics Specialist Conference held in Stevenson in the U.S. state of Washington, a team composed of graduate research assistants from the University of Colorado Boulder and the São Paulo State University (UNESP) was awarded for presenting a project denominated "Near-Earth Asteroid Characterization and Observation (NEACO) Mission to Asteroid (469219) 2016 HO₃", providing the first baselines for the investigation of this celestial object using a spacecraft.[13][14][15] Recently, another version of this work was presented adopting different constraints in the dynamics.[16]

The China National Space Administration (CNSA) is planning a robotic mission that would return samples from Kamoʻoalewa.[17][18] This mission, Tianwen-2, is planned to launch in 2025.[19]