Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2012 Nov 23;338(6110):1052-5.
doi: 10.1126/science.1226073. Epub 2012 Oct 17.

Forming a Moon with an Earth-like composition via a giant impact

Robin M Canup  1
Affiliations

Forming a Moon with an Earth-like composition via a giant impact

Robin M Canup. Science. .

Abstract

In the giant impact theory, the Moon formed from debris ejected into an Earth-orbiting disk by the collision of a large planet with the early Earth. Prior impact simulations predict that much of the disk material originates from the colliding planet. However, Earth and the Moon have essentially identical oxygen isotope compositions. This has been a challenge for the impact theory, because the impactor's composition would have likely differed from that of Earth. We simulated impacts involving larger impactors than previously considered. We show that these can produce a disk with the same composition as the planet's mantle, consistent with Earth-Moon compositional similarities. Such impacts require subsequent removal of angular momentum from the Earth-Moon system through a resonance with the Sun as recently proposed.

PubMed Disclaimer

Figures

Figure 1.
Figure 1.
An SPH simulation of a moderately oblique, low-velocity (v∞ = 4 km/sec) collision between an impactor and target with similar masses (run 31 from Table 1). Color scales with particle temperature in Kelvin, per color bar, with red indicating temperatures > 6440 K. All particles in the 3D simulation are overplotted. Time is shown in hours, and distances are shown in units of 103 km. After the initial impact, the planets re-collided, merged, and spun rapidly. Their iron cores migrated to the center, while the merged structure developed a bar-type mode and spiral arms (24). The arms wrapped up and finally dispersed to form a disk containing about 3 lunar masses whose silicate composition differed from that of the final planet by less than 1%. Due to the near symmetry of the collision, impactor and target material are distributed approximately proportionately throughout the final disk, so that the disk’s δfT value does not vary appreciably with distance from the planet.
Figure 2.
Figure 2.
Compositional difference between the disk and final planet (δfT, eqn. 2) produced by simulations with γ = 0.3 (left) and γ = 0.4 (right, triangles) and 0.45 (right, squares) versus the predicted mass of the moon that would accrete from each disk (MM, eqn. 1) scaled to the final planet’s mass (MP). Note the change in y-axis scales between the two plots. Grey, purple, dark blue, light blue, green, yellow, orange, and red points correspond to vimp/vesc = 1.0, 1.1, 1.2, 1.3, 1.4, 1.6, 1.8, and 2.0, respectively. The open square is run 60* from Table 1 that includes pre-impact rotation. Forming an appropriate mass Moon mass requires MM/MP > 0.012, the region to the right of the vertical solid line. Constraints on δfT needed to satisfy Earth-Moon compositional similarities are shown by horizontal lines for oxygen (solid), titanium (dotted), and chromium (dot-dashed), assuming a Mars-composition impactor.
See this image and copyright information in PMC

Comment in

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Canup RM, Asphaug E, Nature 412, 708 (2001). - PubMed
    1. Canup RM, Icarus 168, 433 (2004).
    1. Canup RM, Icarus 196, 518 (2008).
    1. Wiechert U, Halliday AN, Lee D–C, Synder GA, Taylor LA, Rumble D, Science 294, 345–348 (2001). - PubMed
    1. Lugmair GW, Shukolyukov A, Geochimica et Cosmochem. Acta 62, 2863 (1998).

Publication types