Forming a Moon with an Earth-like Composition via a Giant Impact

Canup, R. M.

doi:10.1126/science.1226073

Cited by 570 publications

(550 citation statements)

References 29 publications

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“…Some have invoked the evection resonance to permit the Moon to be created with collision parameters that are quite different to the Canonical model, satisfying both the dynamical and isotopic constraints (e.g. Canup 2012;Ćuk and Stewart 2012;Reufer et al 2012), while others have argued that the Canonical model parameters still satisfy the isotopic constraints, e.g., if some equilibration of the accreted material occurs in the protolunar disk (Pahlevan and Stevenson 2007;Salmon and Canup 2012) or if the impactor formed sufficiently close to the Earth (Mastrobuono-Battisti et al 2015), but the basic idea of the origin of the Moon in a giant impact does not seem to be in doubt.…”

Section: Earth-moon Systemmentioning

confidence: 99%

Insights into Planet Formation from Debris Disks

Wyatt

Jackson

2016

Space Sci Rev

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Giant impacts refer to collisions between two objects each of which is massive enough to be considered at least a planetary embryo. The putative collision suffered by the proto-Earth that created the Moon is a prime example, though most Solar System bodies bear signatures of such collisions. Current planet formation models predict that an epoch of giant impacts may be inevitable, and observations of debris around other stars are providing mounting evidence that giant impacts feature in the evolution of many planetary systems. This chapter reviews giant impacts, focussing on what we can learn about planet formation by studying debris around other stars. Giant impact debris evolves through mutual collisions and dynamical interactions with planets. General aspects of this evolution are outlined, noting the importance of the collision-point geometry. The detectability of the debris is discussed using the example of the Moon-forming impact. Such debris could be detectable around another star up to 10 Myr post-impact, but model uncertainties could reduce detectability to a few 100 yr window. Nevertheless the 3 % of young stars with debris at levels expected during terrestrial planet formation provide valuable constraints on formation models; implications for super-Earth formation are also discussed. Variability recently observed in some bright disks promises to illuminate the evolution during the earliest phases when vapour condensates may be optically thick and acutely affected by the collision-point geometry. The outer reaches of planetary systems may also exhibit signatures of giant impacts, such as the clumpy debris structures seen around some stars.

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Section: Earth-moon Systemmentioning

confidence: 99%

Insights into Planet Formation from Debris Disks

Wyatt

Jackson

2016

Space Sci Rev

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“…To date, most numerical simulations of impacts between rock/metal protoplanets have been performed with the goal of reproducing the mass, angular momentum, and composition of the Earth-Moon system (e.g., [15,16,19,20,24,[65][66][67][68]). Early simulations of the Moon-forming impact were forced, due to computational constraints, to use low numerical resolution, or to use simplified equations of state, leading to unphysical behaviors for rock and metal at high temperatures and pressures.…”

Section: Impact Simulationsmentioning

confidence: 99%

“…Large impact-generated disks can form in collisions with higher velocities, a few×v esc , but this phenomenon has been explored for only a limited range of impactor-to-target mass ratios, and impact angles [19,20].…”

Section: Impact Simulationsmentioning

confidence: 99%

“…Earth's Moon and Charon are thought to have formed from planet-scale collisions [13][14][15][16][17]. Numerical simulations of the collisions and the subsequent accretion of impact-generated debris show that systems with the proper masses, angular momenta, and compositions of each system are consistent with a collision with a body 10% to 50% the mass of the precursor planet [16][17][18][19][20]. In the inner Solar System, collisions between planetary embryos are common during the late stages of terrestrial planet accretion [1,2,21].…”

Section: Introductionmentioning

confidence: 99%

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Formation of exomoons: a solar system perspective

Barr

2016

Astronomical Review

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Satellite formation is a natural by-product of planet formation. With the discovery of numerous extrasolar planets, it is likely that moons of extrasolar planets (exomoons) will soon be discovered. Some of the most promising techniques can yield both the mass and radius of the moon. Here, I review recent ideas about the formation of moons in our Solar System, and discuss the prospects of extrapolating these theories to predict the sizes of moons that may be discovered around extrasolar planets. It seems likely that planet-planet collisions could create satellites around rocky or icy planets which are large enough to be detected by currently available techniques. Detectable exomoons around gas giants may be able to form by co-accretion or capture, but determining the upper limit on likely moon masses at gas giant planets requires more detailed, modern simulations of these processes.

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“…The change in angular momentum corresponding to modern inclination excitation of ~5 degrees is likely a few tens of percent or less. Hence, the standard giant impact scenario 4 followed by little subsequent dynamical modification is compatible with the dynamical state of the modern system, while a high angular momentum impact scenario 3,5 would require another dynamical mechanism such as the evection resonance 3,12,16 to be reconciled with the modern EM system. Each suite of simulations is composed of two subsets: one with late accretion delivered via 1 body (greater excitation), the other 4 (lesser excitation).…”

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confidence: 99%

Collisionless encounters and the origin of the lunar inclination

Pahlevan

Morbidelli

2015

Nature

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The Moon-forming impact is thought to have generated a compact circumplanetary disk (within < 10 Earth radii) from which the Moon rapidly accreted. Like Saturn's rings, the proto-lunar disk is expected to become equatorial on a timescale rapid relative to its evolutionary timescale. Hence, so long as the proto-lunar material disaggregated into a disk following the giant impact, the Moon is expected to have accreted within ~1° of the Earth's equator plane 6 . Tidal evolution calculations suggest that for every degree of inclination of the lunar orbit plane relative to the Earth's equator plane at an Earth-Moon (EM) separation of 10 Earth radii (R E ), the current lunar orbit would exhibit ~1/2° of inclination relative to Earth's orbital plane [7][8][9] . The modern ~5° lunar inclination wouldwithout external influences -translate to a ~10° inclination to Earth's equator plane at 10 R E shortly after lunar accretion. This ~10x difference between theoretical expectations of lunar accretion and the EM system has become known as the lunar inclination problem.Previous work on this problem has sought to identify mechanisms such as a gravitational resonance between the newly formed Moon and the Sun 12 or the remnant proto-lunar disk 13 that can excite the lunar inclination to a level consistent with its current value.Neither of these scenarios is satisfactory, however, as the former requires particular values of the tidal dissipation parameters while the latter has only been shown to be viable in an idealized system where a single, fully-formed Moon interacts with a single pair of resonances in the proto-lunar disk. Moreover, prior works have all assumed that the excitation of the lunar orbit was determined during interactions essentially coinciding with lunar origin. Here, we propose that the lunar inclination arose much later as a consequence of the sweep-up of remnant planetesimals in the inner Solar System. After the giant impact and at most ~10 3 years 14,15 , the Moon has accreted, interacted with 13 and caused the collapse of the remnant proto-lunar disk onto the Earth 6 , passed the evection resonance with the Sun 3,12,16 , and begun a steady outward tidal evolution. On a timescale (~10 6 -10 7 years) rapid relative to that characterizing depletion of planetesimals in the final post-Moon formation stage of planetary accretion 17 (called "late accretion"), the lunar orbit expands through the action of tides to an EM separation of ~20-40 R E . In this time, the lunar orbit transitions from precession around the spin-axis of Earth to precession around the heliocentric orbit normal vector 8 , and its inclination becomes insensitive to the shifting of the Earth's equatorial plane via subsequent accretion 18 .However, as we show below, lunar inclination becomes more sensitive to gravitational interactions with passing planetesimals as the tidal evolution of the system proceeds. The sensitivity is such as to render the lunar orbital excitation a natural outcome of the sweepup of the leftovers of accretion and to yield ...

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Forming a Moon with an Earth-like Composition via a Giant Impact

Cited by 570 publications

References 29 publications

Insights into Planet Formation from Debris Disks

Insights into Planet Formation from Debris Disks

Formation of exomoons: a solar system perspective

Collisionless encounters and the origin of the lunar inclination

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