Kamoʻoalewa was first spotted on 27 April 2016, by the Pan-STARRS 1 asteroid survey telescope on Haleakalā, Hawaii, operated by the University of Hawaii's Institute for Astronomy and funded by NASA's Planetary Defense Coordination Office. The name Kamoʻoalewa is derived from the Hawaiian words ka 'the', moʻo 'fragment', referring to it being a piece broken off a larger object, a 'of', and lewa 'to oscillate', referring to its motion in the sky as viewed from Earth. The official was published by the Minor Planet Center on 6 April 2019.
As it orbits the Sun, Kamoʻoalewa appears to circle 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. "Since 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", said Paul Chodas, manager of NASA's Center for Near-Earth Object Studies at the Jet Propulsion Laboratory in Pasadena, California. In its yearly trek around the Sun, asteroid spends about half of the time closer to the Sun than Earth is and passes ahead of our planet, and about half of the time farther away, causing it to fall behind. Its orbit is also 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. 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", said Chodas. "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." As of now, it is by far the most stable quasi-satellite of Earth discovered, in terms of orbit.
Physical characteristics
The size of Kamoʻoalewa has not yet been firmly established, but it is likely about. Based on an assumed standard albedo for stony S-type asteroids of 0.20 and an absolute magnitude of 24.3, it measures in diameter. Photometric observations in April 2017 revealed that Kamoʻoalewa is a fast rotator. Lightcurve analysis gave a rotation period of and a brightness variation of magnitude.
Proposed missions
During the 2017 Astrodynamics Specialist Conference held in Stevenson, Washington, a team composed by graduate research assistants from the University of Colorado Boulder and the São Paulo State University was awarded for presenting a project denominated "Near-Earth Asteroid Characterization and Observation Mission to Asteroid 2016 HO3", providing the first baselines for the investigation of this celestial object using a spacecraft. . Recently, another version of this work was presented adopting different constraints in the dynamics. The China National Space Administration is planning a robotic mission that would return samples from 2016 HO3. This mission, ZhengHe, is planned for launch in 2024.
