Impact evolution of asteroid shapes 1. Random mass redistribution

D. G. Korycansky, Erik Asphaug

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

We explore whether the cumulative effect of small-scale meteoroid bombardment can drive asteroids into nonaxisymmetric shapes comparable to those of known objects (elongated prolate forms, twin-lobed binaries, etc). We simulate impact cratering as an excavation followed by the launch, orbit, and reimpact of ejecta. Orbits are determined by the gravity and rotation of the evolving asteroid, whose shape and spin change as cratering occurs repeatedly. For simplicity we consider an end-member evolution where impactors are all much smaller than the asteroid and where all ejecta remain bound. Given those assumptions, we find that cumulative small impacts on rotating asteroids lead to oblate shapes, irrespective of the chosen value for angle of repose or for initial angular momentum. The more rapidly a body is spinning, the more flattened the outcome, but oblateness prevails. Most actual asteroids, by contrast, appear spherical to prolate. We also evaluate the timescale for reshaping by small impacts and compare it to the timescale for catastrophic disruption. For all but the steepest size distributions of impactors, reshaping from small impacts takes more than an order of magnitude longer than catastrophic disruption. We conclude that small-scale cratering is probably not dominant in shaping asteroids, unless our assumptions are naive. We believe we have ruled out the end-member scenario; future modeling shall include angular momentum evolution from impacts, mass loss in the strength regime, and craters with diameters up to the disruption threshold. The ultimate goal is to find out how asteroids get their shapes and spins and whether tidal encounters in fact play a dominant role.

Original languageEnglish (US)
Pages (from-to)374-388
Number of pages15
JournalIcarus
Volume163
Issue number2
DOIs
StatePublished - Jun 1 2003
Externally publishedYes

Fingerprint

asteroids
asteroid
cratering
impactors
ejecta
angular momentum
timescale
orbits
excavation
meteoroids
craters
encounters
metal spinning
crater
bombardment
gravity
gravitation
thresholds
modeling

Keywords

  • Asteroids
  • Dynamics

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Impact evolution of asteroid shapes 1. Random mass redistribution. / Korycansky, D. G.; Asphaug, Erik.

In: Icarus, Vol. 163, No. 2, 01.06.2003, p. 374-388.

Research output: Contribution to journalArticle

Korycansky, D. G. ; Asphaug, Erik. / Impact evolution of asteroid shapes 1. Random mass redistribution. In: Icarus. 2003 ; Vol. 163, No. 2. pp. 374-388.
@article{ae2348b25fcc425ba586a97763603be9,
title = "Impact evolution of asteroid shapes 1. Random mass redistribution",
abstract = "We explore whether the cumulative effect of small-scale meteoroid bombardment can drive asteroids into nonaxisymmetric shapes comparable to those of known objects (elongated prolate forms, twin-lobed binaries, etc). We simulate impact cratering as an excavation followed by the launch, orbit, and reimpact of ejecta. Orbits are determined by the gravity and rotation of the evolving asteroid, whose shape and spin change as cratering occurs repeatedly. For simplicity we consider an end-member evolution where impactors are all much smaller than the asteroid and where all ejecta remain bound. Given those assumptions, we find that cumulative small impacts on rotating asteroids lead to oblate shapes, irrespective of the chosen value for angle of repose or for initial angular momentum. The more rapidly a body is spinning, the more flattened the outcome, but oblateness prevails. Most actual asteroids, by contrast, appear spherical to prolate. We also evaluate the timescale for reshaping by small impacts and compare it to the timescale for catastrophic disruption. For all but the steepest size distributions of impactors, reshaping from small impacts takes more than an order of magnitude longer than catastrophic disruption. We conclude that small-scale cratering is probably not dominant in shaping asteroids, unless our assumptions are naive. We believe we have ruled out the end-member scenario; future modeling shall include angular momentum evolution from impacts, mass loss in the strength regime, and craters with diameters up to the disruption threshold. The ultimate goal is to find out how asteroids get their shapes and spins and whether tidal encounters in fact play a dominant role.",
keywords = "Asteroids, Dynamics",
author = "Korycansky, {D. G.} and Erik Asphaug",
year = "2003",
month = "6",
day = "1",
doi = "10.1016/S0019-1035(03)00079-4",
language = "English (US)",
volume = "163",
pages = "374--388",
journal = "Icarus",
issn = "0019-1035",
publisher = "Academic Press Inc.",
number = "2",

}

TY - JOUR

T1 - Impact evolution of asteroid shapes 1. Random mass redistribution

AU - Korycansky, D. G.

AU - Asphaug, Erik

PY - 2003/6/1

Y1 - 2003/6/1

N2 - We explore whether the cumulative effect of small-scale meteoroid bombardment can drive asteroids into nonaxisymmetric shapes comparable to those of known objects (elongated prolate forms, twin-lobed binaries, etc). We simulate impact cratering as an excavation followed by the launch, orbit, and reimpact of ejecta. Orbits are determined by the gravity and rotation of the evolving asteroid, whose shape and spin change as cratering occurs repeatedly. For simplicity we consider an end-member evolution where impactors are all much smaller than the asteroid and where all ejecta remain bound. Given those assumptions, we find that cumulative small impacts on rotating asteroids lead to oblate shapes, irrespective of the chosen value for angle of repose or for initial angular momentum. The more rapidly a body is spinning, the more flattened the outcome, but oblateness prevails. Most actual asteroids, by contrast, appear spherical to prolate. We also evaluate the timescale for reshaping by small impacts and compare it to the timescale for catastrophic disruption. For all but the steepest size distributions of impactors, reshaping from small impacts takes more than an order of magnitude longer than catastrophic disruption. We conclude that small-scale cratering is probably not dominant in shaping asteroids, unless our assumptions are naive. We believe we have ruled out the end-member scenario; future modeling shall include angular momentum evolution from impacts, mass loss in the strength regime, and craters with diameters up to the disruption threshold. The ultimate goal is to find out how asteroids get their shapes and spins and whether tidal encounters in fact play a dominant role.

AB - We explore whether the cumulative effect of small-scale meteoroid bombardment can drive asteroids into nonaxisymmetric shapes comparable to those of known objects (elongated prolate forms, twin-lobed binaries, etc). We simulate impact cratering as an excavation followed by the launch, orbit, and reimpact of ejecta. Orbits are determined by the gravity and rotation of the evolving asteroid, whose shape and spin change as cratering occurs repeatedly. For simplicity we consider an end-member evolution where impactors are all much smaller than the asteroid and where all ejecta remain bound. Given those assumptions, we find that cumulative small impacts on rotating asteroids lead to oblate shapes, irrespective of the chosen value for angle of repose or for initial angular momentum. The more rapidly a body is spinning, the more flattened the outcome, but oblateness prevails. Most actual asteroids, by contrast, appear spherical to prolate. We also evaluate the timescale for reshaping by small impacts and compare it to the timescale for catastrophic disruption. For all but the steepest size distributions of impactors, reshaping from small impacts takes more than an order of magnitude longer than catastrophic disruption. We conclude that small-scale cratering is probably not dominant in shaping asteroids, unless our assumptions are naive. We believe we have ruled out the end-member scenario; future modeling shall include angular momentum evolution from impacts, mass loss in the strength regime, and craters with diameters up to the disruption threshold. The ultimate goal is to find out how asteroids get their shapes and spins and whether tidal encounters in fact play a dominant role.

KW - Asteroids

KW - Dynamics

UR - http://www.scopus.com/inward/record.url?scp=0038442161&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0038442161&partnerID=8YFLogxK

U2 - 10.1016/S0019-1035(03)00079-4

DO - 10.1016/S0019-1035(03)00079-4

M3 - Article

VL - 163

SP - 374

EP - 388

JO - Icarus

JF - Icarus

SN - 0019-1035

IS - 2

ER -