On the Origin of Asteroid (469219) Kamo'oalewa: Main-Belt Asteroid or Lunar Ejecta?

Asteroid (469219) Kamo'oalewa, discovered by Pan-STARRS in 2016 as 2016 HO3, has attracted significant attention because of both its unusual orbit and its peculiar spectral properties. In addition to being a long-term quasi-satellite of Earth [1,2], its spectrum led to the hypothesis that it may have originated from the Moon as impact ejecta [3], possibly from the Giordano Bruno crater [4]. Kamo'oalewa is also the target of the Tianwen-2 sample-return mission by the China National Space Administration, further increasing interest in its origin and evolution [5,6,7].

In this work, we investigate the relative contribution of two possible sources of Kamo'oalewa-like objects: the general near-Earth asteroid (NEA) population originating from the main asteroid belt, and lunar ejecta from the Giordano Bruno impact. We first used NEA population models to estimate the expected number of Earth co-orbitals in the same size range as Kamo'oalewa. We then performed numerical simulations to determine the fraction of Earth's co-orbital population occupying quasi-satellite states, allowing us to estimate the expected number of Kamo'oalewa-like objects originating from the main belt. An analogous approach was applied to estimate the contribution from the ejecta of Giordano Bruno crater. In addition, we simulated the detection efficiencies of the Catalina Sky Survey and Pan-STARRS for Kamo'oalewa-like objects.

Our simulations show that, on average, 1.4% of the Earth's co-orbital phase space is occupied by quasi-satellite orbits. Combined with current NEA population models, this implies an average of 1.23 ± 0.13 Kamo'oalewa-like objects originating from the main belt. In contrast, the expected number of Kamo'oalewa-like objects produced as Giordano Bruno ejecta is only 0.042, more than an order of magnitude lower. We also find that the detection efficiency of Earth quasi-satellites by Pan-STARRS ranges from about 95% to 70% for objects with absolute magnitudes between 22 and 25, whereas CSS showed a slightly lower efficiency, both in good agreement with the currently known quasi-satellite population.

These results show that current NEA population models based on migration from the main asteroid belt can naturally account for Kamo'oalewa-like objects. In contrast, lunar ejecta do not appear capable of producing a sufficient number of Earth quasi-satellites in the Kamo'oalewa size range, making a lunar origin less likely. Future observations, together with in situ exploration and sample return by Tianwen-2, will provide important new constraints on the origin of this remarkable asteroid.

For more details, see our paper [8]:    https://doi.org/10.1051/0004-6361/202558680

References:

1. de la Fuente Marcos, C., de la Fuente Marcos, R. 2016. Asteroid (469219) 2016 HO3, the smallest and closest Earth quasi-satellite. Monthly Notices of the Royal Astronomical Society 462, 3441–3456

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3. Sharkey, B.~N.~L. and 9 colleagues 2021. Lunar-like silicate material forms the Earth quasi-satellite (469219) 2016 HO3 Kamoʻoalewa. Communications Earth and Environment 2, id.231

4. Jiao, Y. and 8 colleagues 2024. Asteroid Kamo`oalewa's journey from the lunar Giordano Bruno crater to Earth 1:1 resonance. Nature Astronomy 8, p. 819-826

5. Zhang, R. and 7 colleagues 2026. Tianwen-2 Mission of China's Planetary Exploration Program. Space Science Reviews 222, id.11

6. Fenucci, M. and 11 colleagues 2025. Astrometry, orbit determination, and thermal inertia of the Tianwen-2 target asteroid (469219) Kamo'oalewa. Astronomy and Astrophysics 695, id.A196

7. Ren, J., Wu, B., Liu, W., Yu, T., Li, H. 2026. Thin regolith layer anticipated on the surface of the Tianwen-2 target asteroid (469219) Kamo'oalewa. Astronomy and Astrophysics 708, id.A142

8. Fenucci, M., Novakovic, B., Granvik, M., Zhang, P. 2026. Origin of asteroid (469219) Kamo'oalewa: The main asteroid belt or the Giordano Bruno crater on the Moon?. Astronomy and Astrophysics 706, id.A276