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Asteroid Kamo‘oalewa’s journey from the lunar Giordano Bruno crater to Earth 1:1 resonance

Nature Astronomy volume 8, pages 819–826 (2024)Cite this article

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Abstract

Among the nearly 30,000 known near-Earth asteroids (NEAs), only tens possess Earth co-orbital characteristics with semi-major axes ~1 au. In particular, 469219 Kamo‘oalewa (2016 HO3), an upcoming target of China’s Tianwen-2 asteroid sampling mission, exhibits a meta-stable 1:1 mean-motion resonance with Earth. Intriguingly, recent ground-based observations show that Kamo‘oalewa has spectroscopic characteristics similar to space-weathered lunar silicates, hinting at a lunar origin instead of an asteroidal one like the vast majority of NEAs. Here we use numerical simulations to demonstrate that Kamo‘oalewa’s physical and orbital properties are compatible with a fragment from a crater larger than 10–20 km formed on the Moon in the last few million years. The impact could have ejected sufficiently large fragments into heliocentric orbits, some of which could be transferred to Earth 1:1 resonance and persist today. This leads us to suggest the young lunar crater Giordano Bruno (22 km diameter, 1–10 Myr age) as the most likely source, linking a specific asteroid in space to its source crater on the Moon. The hypothesis will be tested by the Tianwen-2 mission when it returns a sample of Kamo‘oalewa. And the upcoming NEO Surveyor mission may help us to identify such a lunar-derived NEA population.

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Fig. 1: Kamo‘oalewa’s observed reflectance spectrum3 compared with typical asteroid taxonomies10, lunar samples7 and the lunar meteorite Yamato-791197,727.
Fig. 2: Simulated fragment SVD and escaping fragment cumulative size–frequency distribution for a 2.44-km-diameter asteroid striking the lunar crust at 18 km s−1 and 45°, creating a Kepler-sized (31 km) crater.
Fig. 3: N-body simulation results of GB ejecta.
Fig. 4: Source crater criterion to obtain at least one Earth co-orbit at the present day.

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Data availability

The raw simulation data are available from the corresponding authors upon reasonable request. Source data are provided with this paper.

Code availability

The spectral classification code classy is available via GitHub at https://github.com/maxmahlke/classy (ref. 65). The N-body code REBOUND is an open-source package available via GitHub at https://github.com/hannorein/rebound (ref. 66). The impact code SPHSOL is available from the corresponding authors on reasonable request.

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Acknowledgements

B.C. is supported by the National Natural Science Foundation of China (no. 12202227) and the Postdoctoral Innovative Talent Support Program of China (no. BX20220164). This work is also supported by the National Natural Science Foundation of China under grant 62227901. We thank W. F. Bottke and others for valuable discussions on this work at the Asteroids, Comets, Meteors Conference 2023. We thank M. Connors, T. Santana-Ros and F. Ferrari for providing helpful comments to improve and clarify the manuscript. We acknowledge the use of imagery from Lunar QuickMap (https://quickmap.lroc.asu.edu), a collaboration between NASA, Arizona State University and Applied Coherent Technology Corp.

Author information

Authors and Affiliations

  1. Tsinghua University, Beijing, China

    Yifei Jiao, Bin Cheng, Yukun Huang & Hexi Baoyin

  2. Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada

    Yukun Huang & Brett Gladman

  3. Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA

    Erik Asphaug & Renu Malhotra

  4. Laboratoire Lagrange, Observatoire de la Côte d’Azur, Université Côte d’Azur, CNRS, Nice, France

    Patrick Michel

  5. Beihang University, Beijing, China

    Yang Yu

  6. Inner Mongolia University of Technology, Inner Mongolia, China

    Hexi Baoyin

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Contributions

Y.J. performed the SPH and N-body numerical simulations and analysed the numerical results. B.C. and H.B. initiated the project, designed the simulations and led the research. Y.H., B.G. and R.M. contributed to the discussion of the dynamical evolution of lunar ejecta and the spectral comparison. E.A., P.M. and Y.Y. contributed to the discussion of the lunar impact ejection process. All authors contributed to interpretation of the results and preparation of the paper.

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Correspondence to Bin Cheng or Hexi Baoyin.

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Nature Astronomy thanks Martin Connors, Fabio Ferrari and Toni Santana-Ros for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Comparison of Kamo‘oalewa’s spectral slope with Bus-DeMeo asteroid taxonomies and lunar materials.

Due to errors in the infrared reflectance, Kamo‘oalewa’s slope possibly ranges from 76 to 101%/μm3. Typical asteroid slopes are plotted with the mean values and the standard deviations, based on 371 asteroid samples10. The slopes of lunar meteorite and samples, whose spectra have been shown in Fig. 1, are measured using the online Bus-DeMeo taxonomy tool10.

Source data

Extended Data Fig. 2 Spectral Comparison using the Mixture of Common Factor Analysers (MCFA) model.

The latent scores are computed as a lower-dimensional representation of the reflectance spectrum, using the classy package51. The MCFA results suggest that Kamo‘oalewa is spectrally similar to lunar materials, but incompatible with any typical asteroid spectrum in public repositories.

Source data

Extended Data Fig. 3 Simulated rotation distribution of escaping SPH particles with L\({}_{\max }\) larger than 36 m, for a Kepler-sized crater forming event.

Here we use the SPH particle vorticity to approximate the rotation state of the sub-resolution fragments. The upper panel presents the cumulative fraction of these high-velocity and low-shocked particles versus the rotation period. Note that about 65% of these particles, when ejected, are spinning faster than Kamo‘oalewa which has a period of 28.3 min3. The lower panel is a boxplot of the period distribution, suggesting a median of about 6 minutes and an interquartile range (IQR, the box range from the first quartile Q1 to the third quartile Q3) from a few to several tens of minutes. The whiskers are bounded at Q1-1.5*IQR and Q3+1.5*IQR, with the flier points removed. There are 466 and 94 SPH particles used for k=1030 m−3 and k=1033 m−3, respectively.

Source data

Extended Data Fig. 4 The location and topography of lunar crater Giordano Bruno.

Left is a map of the lunar farside using the Lunar QuickMap (https://bit.ly/45Ftwjh). Right is the topographic map of GB crater from the Lunar Reconnaissance Orbiter Camera (LROC) data69.

Extended Data Fig. 5 Initial condition of N-body simulations.

We start each set of simulation at a random lunar phase ϕ, which indicates the relative position of the Sun-Earth-Moon system, and launched 300 particles along a θ = 45∘ cone at random azimuths ζ and with a given velocity magnitude distribution v0 (following a power law distribution ranging from 2.38 to 6.0 km/s, and with the power of -4.0 according to Supplementary Fig. 7).

Extended Data Fig. 6 GB ejecta delivered to Earth, normalized with the background lunar meteorite flux.

It has been estimated that the GB ejecta is comparable to the total lunar ejecta produced by other craters over 10 Myr42, thus the background lunar ejecta per Myr is about one-tenth of the GB total ejecta. Assuming the same delivery efficiency (Earth collision fraction over time) as the GB ejecta, we can integrate the product of the ejecta volume and the delivery efficiency of all previous craters, to estimate the background flux delivered to Earth per Myr. The result shows a ten-fold spike of GB meteorites than the background flux in the first Myr after GB formation (several million years ago). However, this spike is currently unobservable due to the short terrestrial preservation period of lunar meteorites, which only lasts a few hundred thousand years8. Presently, GB ejecta contributes to roughly 10% of the background flux of lunar meteorites, implying that our current collection of lunar meteorites likely contains only a handful of GB ejecta, for example, the possible GB meteorites Yamato-82192/82193/8603242.

Source data

Supplementary information

Supplementary Information

Supplementary Text, Figs. 1–8 and Tables 1–5.

Supplementary Data

Source Data for Supplementary Figs. 1–8.

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Source Data Extended Data Fig. 1

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Jiao, Y., Cheng, B., Huang, Y. et al. Asteroid Kamo‘oalewa’s journey from the lunar Giordano Bruno crater to Earth 1:1 resonance. Nat Astron 8, 819–826 (2024). https://doi.org/10.1038/s41550-024-02258-z

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