Example Moon-forming Synestia Cases Created via Giant Impact¶

The various post-giant-impact synestias used throughout this document as examples are the same three potential Moon-forming impact cases used in (Lock et al., 2018). All three cases are Earth-mass synestias created shortly after (within 48 hours of) their respective giant impact. The synestia cases are all thermally equilibrated and have not yet begun to cool.

M$$_t$$ is the mass of the target body (body being impacted in the impact reference frame) and M$$_p$$ is the mass of the projectile (the impactor in the impact reference frame). Both masses are described in terms of the present-day mass of Earth. The velocity v is the relative velocity with which the projectile impacts the target. The angle of the impact is described in terms of b, where b = sin$$\theta$$ and $$\theta$$ is the angle between the centers of the target and projectile at first contact, such that b = 0 is a direct impact (at 0$$^\circ$$) and b = 1 is a glancing impact (at 90$$^\circ$$). Q$$_s$$ is the specific impact energy developed by (Leinhardt & Stewart, 2012); these three cases are high energy giant impacts. M$$_{bnd}$$ is the mass of the material gravitationally bound to the system in terms of the present-day mass of Earth. M$$_{seed}$$ is the mass of the lunar seed (in terms of the present-day mass of the Moon) created from the impact.

Synestia Case 1¶

This case is based on a giant impact proposed by (Canup, 2012), and is example A used in (Lock et al., 2018). Near two half-Earth-mass bodies collide near head on at a relative velocity close to that of the escape velocity for the system (11 km/s). The impact parameters are as follows:
M$$_t$$ = 0.572 M$$_{Earth}$$
M$$_p$$ = 0.468 M$$_{Earth}$$
v = 12.33 km s$$^{-1}$$
b = 0.4
Q$$_s$$ = 1.62 $$\times$$ 10$$^7$$ J kg$$^{-1}$$
M$$_{bnd}$$ = 0.895 M$$_{Earth}$$
M$$_{seed}$$ = 0.4 M$$_{Moon}$$

Synestia Case 2¶

This case is based on a giant impact proposed by (Ćuk & Stewart, 2012), and is example B used in (Lock et al., 2018). A relatively small impactor quickly collides with a rapidly rotating protoplanet at a near head on angle. The impact parameters are as follows:
M$$_t$$ = 0.99 M$$_{Earth}$$
M$$_p$$ = 0.1 M$$_{Earth}$$
v = 15 km s$$^{-1}$$
b = 0.4
Q$$_s$$ = 7.2 $$\times$$ 10$$^6$$ J kg$$^{-1}$$
M$$_{bnd}$$ = 0.9929 M$$_{Earth}$$
M$$_{seed}$$ = 0.5 M$$_{Moon}$$

Synestia Case 3¶

This case is based on a giant impact proposed by (Quintana et al., 2016), and is example C used in (Lock et al., 2018). A medium-size impactor collides with a proto-Earth (with twice the mass of the impactor) at a less-than-head-on angle and velocity near escape velocity of the system (11 km/s). The impact parameters are as follows:
M$$_t$$ = 0.75 M$$_{Earth}$$
M$$_p$$ = 0.3 M$$_{Earth}$$
v = 11.3 km s$$^{-1}$$
b = 0.6
Q$$_s$$ = 3.9 $$\times$$ 10$$^6$$ J kg$$^{-1}$$
M$$_{bnd}$$ = 0.9977 M$$_{Earth}$$
M$$_{seed}$$ = 0.8 M$$_{Moon}$$

References¶

Canup, R. M. (2012). Forming a Moon with an Earth-like Composition via a Giant Impact. Science (American Association for the Advancement of Science), 338 (6110), 1052-1055.

Ćuk, M., & Stewart, S. T. (2012). Making the Moon from a fast-spinning Earth: A giant impact followed by resonant despinning. Science (American Association for the Advancement of Science), 338 (6110), 1047-1052.

Leinhardt, Z. M., & Stewart, S. T. (2012). Collisions between gravity-dominated bodies. I. Outcome regimes and scaling laws. The Astrophysical Journal, 745 (79), 1-27.

Lock, S. J., Stewart, S. T., Petaev, M. I., Leinhardt, Z. M., Mace, M. T., Jacobsen, S. B., & Ćuk, M. (2018). The origin of the Moon within a terrestrial synestia. Journal of Geophysical Research: Planets (American Geophysical Union), 123 (4), 910-951.

Quintana, E. V., Barclay, T., Borucki, W. J., Rowe, J. F., & Chambers, J. E. (2016). The frequency of giant impacts on Earth-like worlds. The Astrophysical Journal, 821 (126), 1-13.