469219 Kamoʻoalewa

469219 Kamoʻoalewa (/kəˌmoʊʔoʊəˈlɛvə/)^[6] (provisional designation 2016 HO₃) is a very small Apollo-type near-Earth asteroid approximately 40–100 meters (130–330 feet) in diameter. It is an elongated object that rapidly rotates every 28 minutes. 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).

Kamoʻoalewa was discovered by Pan-STARRS at Haleakala Observatory on 27 April 2016. It is the target of the China National Space Administration's Tianwen-2 mission, which is scheduled to visit the asteroid sometime in July 2026.^[7][8] Tianwen-2 will retrieve samples from the surface of Kamoʻoalewa and is planned to return them to Earth in 2027.^[7]

The object's Earth-like orbit, proximity to the Earth–Moon system, higher spectral reddening relative to other asteroids, and similarity to space weathered lunar materials indicate that it is likely lunar ejecta.^{[9][10][11][12]} However, it might also be an S-type or L-type asteroid.^[13][9][14] 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.^[12]

Orbital similarities suggest it is likely a co-orbital pair with 2000 WN10^[15] or a broken up set including the other NEOs 2020 KZ2, 2020 PN1, and 2020 PP1.^[9]

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.^[1][4] It was named Ka moʻo a lewa in 2019, from the Hawaiian chant Kumulipo for an oscillating celestial object by A Hua He Inoa at the 'Imiloa Astronomy Center of Hawai'i.^[16][17]

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.^[18][19] The official naming citation was published by the Minor Planet Center on 6 April 2019 (M.P.C. 112435).^[20]

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. Kamoʻoalewa is a quasi-moon and not gravitationally bound to Earth like a true satellite. Its orbit transfers between a quasi satellite orbit type which resides in the L₁ and L₂ Lagrange points, and a horseshoe orbit between the L₄ and L₅ Lagrange points.^[11][21]

Its orbit has an eccentricity of 0.10 and an inclination of 8° with respect to the ecliptic.^[2] In March 2024, it had an Earth minimum orbital intersection distance of 0.031 AU (4.6 million km) or 12 lunar distances,^[2] well outside of Earth's Hill sphere of 1.5 million km (3.9 LD).

In a rotating frame of reference Kamoʻoalewa appears to circle elliptically around the Earth every ~45 years.^[22] 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] Orbital and Yarkovsky effect modeling suggest it will be stable for 0.3–0.5 million years.^[15][14][21]

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 Kamoʻoalewa as a quasi-satellite of Earth. Unlike asteroid 2003 YN107, which previously followed a similar orbit, Kamoʻoalewa 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, Kamoʻoalewa continually dances around the Earth.^[4]

The closest Earth approach was on 27 December 1923 (1923-12-27) at 12.44 million km (0.0832 AU; 32.4 LD).^[2] By late May 2369, the asteroid will be 2.0 AU (780 LD; 300 million km) from Earth.^[23] The Earth-like orbit may be a result of it being lunar ejecta.^[9] 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.^[12]

The size of Kamoʻoalewa has not yet been firmly established, but it is approximately 40–100 m (130–330 ft).^[4] Based on an assumed standard albedo for stony S-type asteroids of 0.20, its absolute magnitude of 24.3 corresponds to 41 meters (135 ft) in diameter.^[5]

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).^[5][b] 2024 inversion modeling was used to create a 100m x 81m x 46m (~72m diameter) 3D model from light curve data.^[24]

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.^{[9][10][11][12]} However, it might also be an S-type or L-type asteroid.^[13][9][14] 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.^[12]

Lunar ejecta modeling shows some avenues that can achieve a stable Kamo'oalewa-style quasi-satellite orbit.^[25][11][12]

The China National Space Administration (CNSA) launched the Tianwen-2 mission in May 2025 to return samples from Kamoʻoalewa.^[26][27][28] The spacecraft is scheduled to arrive at Kamoʻoalewa sometime in July 2026, and will depart it in April 2027.^[7][8]

Numerous mission concepts targeting Kamoʻoalewa have been proposed, including a 2019 NASA solar-sail mission concept,^[29] a University of Colorado flyby and impact experiment,^[30] and was selected as a target for the Chinese ZhengHe project,^[31] which has developed into the Tianwen-2 mission.^[32] 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.^[33] In an ambitious proposal, Kamoʻoalewa is even considered for use as a space station for Earth-to-Mars travel.^[34]

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.^[35][36][37] Recently, another version of this work was presented adopting different constraints in the dynamics.^[38]

• Asteroid 2016 HO3 - Earth's Constant Companion NASA Jet Propulsion Laboratory, 23 June 2016
• 469219 Kamoʻoalewa at NeoDyS-2, Near Earth Objects—Dynamic Site
  • Ephemerides · Observation prediction · Orbital info · MOID · Proper elements · Observational info · Close approaches · Physical info · Orbit animation
• 469219 Kamoʻoalewa at ESA–space situational awareness
  • Ephemerides · Observations · Orbit · Physical properties · Summary
• 469219 Kamoʻoalewa at the JPL Small-Body Database