# 469219 Kamoʻoalewa

469219 Kamoʻoalewa (/kəˌmoʊʔoʊəˈlɛvə/), provisionally designated 2016 HO$_3$, is a very small elongated asteroid, fast rotator and near-Earth object of the Apollo group, approximately 40–100 meters (130–330 feet) in diameter. At present it is a quasi-satellite of Earth, and currently the second-smallest, closest, and most stable known such quasi-satellite (after 2023 FW13).
The asteroid was discovered by Pan-STARRS at Haleakala Observatory on 27 April 2016. Numerous proposed missions have since targeted the object, including a NASA solar-sail mission, a University of Colorado flyby and impact experiment, and was selected as a target for the Chinese ZhengHe which has turned into the Tianwen-2 mission. The chondritic simulants QLS-1, 2, and 3 have been developed by the Qian Xuesen Laboratory of Space Technology to better prepare for these missions. In an ambitious proposal, 469219 Kamo’oalewa is even considered for use as a space station for Earth-to-Mars travel.
The object's Earth-like orbit, proximity to the Earth-Moon system, higher spectral reddening to other asteroids, and similarity to space weathered lunar materials indicate that it is likely lunar ejecta. However, it might also be an S-type or L-type asteroid. Despite being most similar to weathered Apollo 14 and Luna 24 Lunar Mare soils, it is suggested to be from the lunar far-side highland crust crater, Giordano Bruno.
Orbital similarities suggest it is likely a co-orbital pair with 2000 WN10 or a broken up set including the other NEOs 2020 KZ2, 2020 PN1, and 2020 PP1.

## Discovery and naming

Kamoʻoalewa was first spotted on 27 April 2016, by the Pan-STARRS 1 asteroid survey telescope on Haleakalā, Hawaii, that is operated by the University of Hawaii's Institute for Astronomy and funded by NASA's Planetary Defense Coordination Office. It was named in 2019 Ka moʻo a lewa, from the Hawaiian chant Kumulipo for an oscillating celestial object by A Hua He Ino at the ‘Imiloa Astronomy Center of Hawai’i.
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 naming citation was published by the Minor Planet Center on 6 April 2019 (M.P.C. 112435).

## Orbit and classification

Kamoʻoalewa orbits the Sun at a distance of 0.90–1.10 AU. Although the period as of 2022 is about 366 days, its longer-term average period is closer to 365 days. 469219 Kamoʻoalewa is a quasi-moon and not gravitationally bound to earth like a true satellite. It's orbit transfers between a Quasi satellite orbit type which resides in the L1 and L2 Lagrange points, and Horseshoe orbit between the L4 and L5 Lagrange points.
Its orbit has an eccentricity of 0.10 and an inclination of 8° with respect to the ecliptic. It presently has an Earth minimum orbital intersection distance of 0.031 AU (4.6 million km) or 12 lunar distances, well outside of Earth's Hill sphere of 1.5 million km (3.9 LD).

### Quasi-satellite of Earth

In a rotating frame of reference Kamoʻoalewa appears to circle elliptically around the Earth every ~45 years. 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. Orbital and Yarkovsky effect modeling suggest it will be stable for 0.3-0.5 million years.
Paul Chodas, manager of NASA's Center for Near-Earth Object Studies (CNEOS) at the Jet Propulsion Laboratory (JPL) in Pasadena, California described the orbit of 2016 HO$_3$ as a quasi-satellite of Earth. Unlike asteroid 2003 YN107, which previously followed a similar orbit, 2016 HO3 is more stable and has been Earth's companion for more than a century and will remain so for much longer. This asteroid spends half of its orbit closer to the Sun than Earth and the other half farther away, causing it to oscillate above and below Earth's orbit annually. Its orbit experiences slight drifts that Earth's gravity corrects, keeping it between 38 and 100 times the distance of the Moon. Thus, 2016 HO3 continually dances around the Earth.
The closest Earth approach was on 27 December 1923 (101 years ago) (1923-12-27) at 12.44 million km (0.0832 AU; 32.4 LD). By late May 2369, the asteroid will be 2.0 AU (780 LD; 300 million km) from Earth. The Earth-like orbit may be a result of it being lunar ejecta. Most objects in this kind of orbit are eventually perturbed out of being in an Earth-co-orbital state and hit the Earth, Venus, or the Sun or are ejected from the solar system, and Kamoʻoalewa will probably hit the Earth in the next 100 million years.

## Physical characteristics

The size of Kamoʻoalewa has not yet been firmly established, but it is approximately 40–100 m (130–330 ft). Based on an assumed standard albedo for stony S-type asteroids of 0.20, its absolute magnitude of 24.3 corresponds to a 41 meters (135 ft) diameter.
Photometric observations in April 2017 revealed that Kamoʻoalewa is a fast rotator. Lightcurve analysis gave a rotation period of 0.467 ± 0.008 hours (28.02 ± 0.48 minutes) and a brightness variation of 0.80±0.05 magnitude (U=2).. 2024 inversion modeling was used to create a 100m x 81m x 46m (~72m diameter) 3D model from light curve data.
In 2021, a spectroscopic characterization of Kamoʻoalewa was conducted using the Large Binocular Telescope and the Lowell Discovery Telescope, which found that the asteroid is likely silicate in origin. The object's Earth-like orbit, proximity to the Earth-Moon system, higher spectral reddening to other asteroids, and similarity to space weathered lunar materials indicate that it is likely lunar ejecta. However, it might also be an S-type or L-type asteroid. Despite being most similar to weathered Apollo 14 and Luna 24 Lunar Mare soils, it is suggested to be from the lunar far-side highland crust crater, Giordano Bruno for its required size and Copernican age.
Lunar ejecta modeling shows some avenues that can achieve a stable QS 469219 Kamo’oalewa-style orbit.

## Exploration
### Proposed missions

De la Fuente Marcos & de la Fuente Marcos first suggested in situ study of 2016 HO$_3$ because of its ideal orbital characteristics in their August 2016 paper.
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 HO$_3$", 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.
A 2019 NASA solar sail mission proposal selected it as a target.
The China National Space Administration (CNSA) is planning a robotic mission that would return samples from Kamoʻoalewa. This mission, Tianwen-2, is planned to launch in 2025.
469219 Kamo’oalewa has been considered for use as a space station for Earth-to-Mars travel.