469219 Kamoʻoalewa

469219 Kamooalewa (; provisional designation ) is a very small Apollo-type near-Earth asteroid approximately 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, second-closest, and second most stable known such quasi-satellite (after ).

Kamooalewa 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 arrived at the asteroid on July 4, 2026 and is intended to orbit the object for nine months before retrieving samples from the surface and returning them to Earth in 2027.

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.Castro-Cisneros, J. D., Malhotra, R., & Rosengren, A. J. (2023). Lunar ejecta origin of near-Earth asteroid Kamo'oalewa is compatible with rare orbital pathways. Commun Earth Environ, 4(1), 372. https://doi.org/10.1038/s43247-023-01031-w However, it might also be an S-type or L-type asteroid.Reddy, V., Kuhn, O., Thirouin, A., Conrad, A., Malhotra, R., Sanchez, J., & Veillet, C. (2017). Ground-based Characterization of Earth Quasi Satellite (469219) 2016 HO3 49th AAS-DPS Meeting, https://ui.adsabs.harvard.edu/abs/2017DPS....4920407R/abstractFenucci, M., & Novaković, B. (2021). The Role of the Yarkovsky Effect in the Long-term Dynamics of Asteroid (469219) Kamo'oalewa. The Astronomical Journal, 162(6). https://doi.org/10.3847/1538-3881/ac2902 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 Dermawan, B. (2019). Temporal Earth Coorbital Types of Asteroid 2016 HO3. Paper No. 012038 6th International Conference on Mathematics & Natural Sciences 2019. IOP Publishing. DOI: 10.1088/1742-6596/1127/1/012038 or a broken up set including the other NEOs , , and .

Discovery and naming

Kamooalewa 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, from the Hawaiian chant Kumulipo for an oscillating celestial object by A Hua He Inoa at the 'Imiloa Astronomy Center of Hawai'i.M.P.C. (2019). The MINOR PLANET CIRCULARS/MINOR PLANETS AND COMETS. In (Vol. 112435): International Astronomical Union. https://www.minorplanetcenter.net/iau/ECS/MPCArchive/2019/MPC_20190406.pdfImiloa. A Hua He Inoa Calling forth a name. https://imiloahawaii.org/a-hua-he-inoa

The name Kamooalewa is derived from the Hawaiian words 'the'; 'fragment', referring to it being a piece broken off a larger object; 'of'; and 'to oscillate', referring to its motion in the sky as viewed from Earth.ulukau HAWAIIAN ELECTRONIC LIBRARY The official was published by the Minor Planet Center on 6 April 2019 (M.P.C. 112435).

Orbit and classification

Kamooalewa 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. Kamooalewa 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 and Lagrange points, and a horseshoe orbit between the and Lagrange points.Qi, Y., & Qiao, D. (2022). Co-orbital transition of 2016 HO3. Astrodynamics, 7(1), 3-14. https://doi.org/10.1007/s42064-021-0122-0

Its orbit has an eccentricity of 0.10 and an inclination of 8° with respect to the ecliptic. In March 2024, it had an Earth minimum orbital intersection distance of or 12 lunar distances, well outside of Earth's Hill sphere of .

Quasi-satellite of Earth

In a rotating frame of reference Kamooalewa appears to circle elliptically around the Earth every ~45 years.Chodas, P. (2016). The Orbit and Future Motion of Earth Quasi-Satellite 2016 HO3 AAS-DPS 48th Meeting, https://ui.adsabs.harvard.edu/abs/2016DPS....4831104C/abstract 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 Kamooalewa as a quasi-satellite of Earth. Unlike asteroid , which previously followed a similar orbit, Kamooalewa 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, Kamooalewa continually dances around the Earth.

The closest Earth approach was on at . By late May 2369, the asteroid will be 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 Kamooalewa will probably hit the Earth in the next 100 million years.

Physical characteristics

The size of Kamooalewa has not yet been firmly established, but it is approximately in diameter.

Photometric observations in April 2017 revealed that Kamooalewa is a fast rotator. Lightcurve analysis gave a rotation period of 27.66 minutes and a brightness variation of magnitude (). 2024 inversion modeling was used to create a 100m x 81m x 46m (~72m diameter) 3D model from light curve data.Ren, J., Wu, B., Hesse, M. A., Li, H., Liu, Y., & Wang, X. (2024). Surface dynamics of small fast-rotating asteroids: Analysis of possible regolith on asteroid 2016 HO3. Astronomy & Astrophysics, 692. https://doi.org/10.1051/0004-6361/202451407 A new light curve model from 2026 has refined its dimensions to 68 × 46 × 39 m. However, thermal emission measurements with the James Webb Space Telescope (JWST) in 2026 indicate a much smaller mean diameter of 18 ± 2 m and a best‑fit visible albedo of pV = 0.59 +0.25/-0.17 (models with pV as low as 0.36 also fit adequately). JWST brightness variations independently confirm a rapid rotation period of about 27.9 minutes and an axis ratio of ~1.4, giving dimensions of roughly 15–21 m.

In 2021, a spectroscopic characterization of Kamooalewa 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. In 2026, JWST’s NIRSpec instrument and new LBT observations revealed a spectrum that is notably less red (more neutral) in the 1.0–2.5 μm range. The infrared colors are more similar to S‑, V‑, or E‑type asteroids than to weathered lunar silicates. A faint silicate absorption band is detected at 0.93 ± 0.01 μm, while no 2.0 μm absorption is seen. Together with the high albedo, these features point to an oldhamite‑bearing, enstatite‑rich composition rather than lunar mare soils. The temperature of the asteroid is estimated to be between 253.15 kelvin and 473.15 kelvin.

Lunar ejecta modeling shows some avenues that can achieve a stable Kamo'oalewa-style quasi-satellite orbit.Winter, O., Moraes, R., Gomes, L., Sfair, R., & Borderes-Motta, G. (2022). On the possibility that 2016 HO3 Kamo'oalewa was a piece of the Moon 44th COSPAR Scientific Assembly, https://ui.adsabs.harvard.edu/abs/2022cosp...44..274W/abstract

Exploration Tianwen-2

The China National Space Administration (CNSA) launched the Tianwen-2 mission in May 2025 to return samples from Kamooalewa. The spacecraft arrived at Kamoʻoalewa on July 4, 2026, and will spend several months surveying and imaging the asteroid, before collecting samples and departing in April 2027. The spacecraft has already performed relative position measurements of the asteroid, and when combined with ground-based spacecraft orbital tracking data, it has obtained ephemeris data for Kamooalewa during this period.

Proposed missions Numerous mission concepts targeting Kamoʻoalewa have been proposed, including a 2019 NASA solar-sail mission concept,Heiligers, J., Fernandez, J. M., Stohlman, O. R., & Wilkie, W. K. (2019). Trajectory design for a solar-sail mission to asteroid 2016 HO3. Astrodynamics, 3(3), 231-246. https://doi.org/10.1007/s42064-019-0061-1 a University of Colorado flyby and impact experiment,Venigalla, C., Baresi, N., Aziz, J. D., Bercovici, B., Brack, D. N., Dahir, A., De Smet, S., Fulton, J., Pellegrino, M. M., & Van wal, S. (2019). Near-Earth Asteroid Characterization and Observation (NEACO) Mission to Asteroid (469219) 2016 HO3. Journal of Spacecraft and Rockets, 56(4), 1121-1136. https://doi.org/10.2514/1.A34268 and was selected as a target for the Chinese ZhengHe project,Jin, W., Li, F., Yan, J., Yang, X., Ye, M., Andert, T., & Peytavi, G. (2019). Simulation of global GM estimate of Asteroid (469219) 2016 HO3 for China's future asteroid mission EPSC-DPS, Geneva, CH which has developed into the Tianwen-2 mission.Yan, J., Liu, L., Ye, M., Jin, W., Qiu, D., & Barriot, J.-P. (2022). A simulation of the joint estimation of the GM value and the ephemeris of the asteroid 2016 HO3. Icarus, 385. https://doi.org/10.1016/j.icarus.2022.115120 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.Zhang, X., Luo, Y., Xiao, Y., Liu, D., Guo, F., & Guo, Q. (2021). Developing Prototype Simulants for Surface Materials and Morphology of Near Earth Asteroid 2016 HO3. Space: Science & Technology, 2021. https://doi.org/10.34133/2021/9874929 In an ambitious proposal, Kamooalewa is even considered for use as a space station for Earth-to-Mars travel.Fargion, D. (2022). Mini-moon, Kamo'oalewa: The Future Space Station 44th COSPAR Scientific Assembly, https://ui.adsabs.harvard.edu/abs/2022cosp...44..215F/abstract

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) ", 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.

Gallery

469219 Kamoʻoalewa

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