Orbital Evolution of Impact Ejecta from Ganymede

Alvarellos, J. L.; Zahnle, Kevin; Dobrovolskis, Anthony R.; Hamill, Patrick

doi:10.1006/icar.2002.6950

Cited by 24 publications

(11 citation statements)

References 32 publications

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“…Although the actual value could differ for the Saturnian satellites, the general trends described here would not change. Alvarellos et al (2002Alvarellos et al ( , 2005 clarified that the relevant velocity to escape a moon in orbit around a planet isn't the classical escape velocity appropriate for an isolated body, but rather the velocity required to reach the moon's Hill Radius, which is:…”

Section: Making An Impact: V Minmentioning

confidence: 99%

“…When an ejectum is launched at a speed faster than the escape velocity of a moon, it can go into orbit about the planet. Most escaped ejecta are eventually swept up by the source moon, but the orbits of some escaped ejecta can be sufficiently perturbed, or the original ejection velocity so high, that the ejecta will impact another satellite (Alvarellos et al, 2005(Alvarellos et al, , 2002. In either case, craters formed by ejecta that initially escape their parent object are called sesquinary ("1 1 2 -ary"; formerly "poltorary") craters (Dobrovolskis and Lissauer, 2004;.…”

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confidence: 99%

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The role of ejecta in the small crater populations on the mid-sized saturnian satellites

Bierhaus

Dones

Alvarellos³

et al. 2012

Icarus

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We find evidence, by both observation and analysis, that crater ejecta play an important role in the small crater (less than a few km) populations on the Saturnian satellites, and more broadly, on cratered surfaces throughout the Solar System. We measure crater populations in Cassini images of Enceladus, Rhea, and Mimas, focusing on image data with scales less than 500 m/pixel.(slope index of ∼ 2 for a differential power-law) for comets a few kilometers diameter and smaller.

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Section: Making An Impact: V Minmentioning

confidence: 99%

mentioning

confidence: 99%

The role of ejecta in the small crater populations on the mid-sized saturnian satellites

Bierhaus

Dones

Alvarellos³

et al. 2012

Icarus

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“…Subsequently, we use an iterative algorithm to find the bounded mass to that specific cluster. The algorithm uses the initial guess and classifies particles as bounded to the moonlet if they are within the Hill radius of the moonlet ( r i < R Hill, i , where r i is the distance of the particle to moonlet i , R Hill, i = a i ( M i /3( M ⊕ + M i )) 1/3 is the Hill radius of moonlet i and a i its semimajor axis) and have a velocity smaller than that required to reach the Hill sphere of the moonlet (Alvarellos, ; Bierhaus et al, ):

V_{Hill}^{2} = \frac{2 G M_{i}}{r_{i}} ((), \frac{R_{Hill, i}^{2} - R_{Hill, i} \cdot r_{i}}{R_{Hill, i}^{2} - r_{i}^{2} \sin^{2} ζ_{i}})

where G is the gravitational constant, M i is the mass of the moonlet i , and ζ is the angle of the particle relative to the moonlet (following Bierhaus et al, , we assume that

\sin^{2} ζ \approx 0.5

). The moonlet's mass, Hill radius, and center of mass are adjusted and bounded particles are recalculated until convergence is achieved (typically a few iterations).…”

Section: Methodsmentioning

confidence: 99%

Impact Dynamics of Moons Within a Planetary Potential

Rufu

Aharonson

2019

JGR Planets

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Current lunar origin scenarios suggest that Earth's Moon may have resulted from the merger of two (or more) smaller moonlets. Dynamical studies of multiple moons find that these satellite systems are not stable, resulting in moonlet collision or loss of one or more of the moonlets. We perform Smoothed Particle Hydrodynamic (SPH) impact simulations of two orbiting moonlets inside the planetary gravitational potential and find that the classical outcome of two bodies impacting in free space is altered as erosive mass loss is more significant with decreasing distance to the planet. Depending on the conditions of accretion, each moonlet could have a distinct isotopic signature; therefore, we assess the initial mixing during their merger, in order to estimate whether future measurements of surface variations could distinguish between lunar origin scenarios (single vs. multiple moonlets). We find that for comparable‐size impacting bodies in the accretionary regime, surface mixing is efficient, but in the hit‐and‐run regime, only small amount of material is transferred between the bodies. However, sequences of hit‐and‐run impacts are expected, which will enhance the surface mixing. Overall, our results show that large‐scale heterogeneities can arise only from the merger of drastically different component masses. Surfaces of moons resulting from merger of comparable‐sized components have little material heterogeneities, and such impacts are preferred, as the relatively massive impactor generates more melt, extending the lunar magma ocean phase.

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“…But because of three-body effects, a particle ejected from a moon may be considered to escape if it reaches the satellite's Hill sphere. The escape criterion then becomes V 0 ≥ V * e = γV e (Alvarellos et al 2002(Alvarellos et al , 2005, where the dimensionless correction factor…”

Section: The Dynamical Environmentmentioning

confidence: 99%

Exchange of ejecta between Telesto and Calypso: Tadpoles, horseshoes, and passing orbits

Dobrovolskis

Alvarellos²,

Zahnle

et al. 2010

Icarus

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We have numerically integrated the orbits of ejecta from Telesto and Calypso, the two small Trojan companions of Saturn's major satellite Tethys. Ejecta were launched with speeds comparable to or exceeding their parent's escape velocity, consistent with impacts into regolith surfaces. We find that the fates of ejecta fall into several distinct categories, depending on both the speed and direction of launch.The slowest ejecta follow sub-orbital trajectories and re-impact their source moon in less than one day. Slightly faster debris barely escape their parent's Hill sphere and are confined to tadpole orbits, librating about Tethys' triangular Lagrange points L 4 (leading, near Telesto) or L 5 (trailing, near Calypso) with nearly the same orbital semi-major axis as Tethys, Telesto, and Calypso. These ejecta too eventually re-impact their source moon, but with a median lifetime of a few dozen years. Those which re-impact within the first ten years or so have lifetimes near integer multiples of 348.6 days (half the tadpole period).Still faster debris with azimuthal velocity components ∼ > 10 m/s enter horseshoe orbits which enclose both L 4 and L 5 as well as L 3 , but which avoid Tethys and its Hill sphere. These ejecta impact either Telesto or Calypso at comparable rates, with median lifetimes of several thousand years. However, they cannot reach Tethys itself; only the fastest ejecta, with azimuthal velocites ∼ > 40 m/s, achieve "passing orbits" which are able to encounter Tethys. Tethys accretes most of these ejecta within several years, but some 1% of them are scattered either inward to hit Enceladus or outward to strike Dione, over timescales on the order of a few hundred years.

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Orbital Evolution of Impact Ejecta from Ganymede

Cited by 24 publications

References 32 publications

The role of ejecta in the small crater populations on the mid-sized saturnian satellites

The role of ejecta in the small crater populations on the mid-sized saturnian satellites

Impact Dynamics of Moons Within a Planetary Potential

Exchange of ejecta between Telesto and Calypso: Tadpoles, horseshoes, and passing orbits

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