Thermal fatigue as the origin of regolith on small asteroids.
Space missions and thermal infrared observations have shown that small asteroids (kilometre-sized or smaller) are covered by a layer of centimetre-sized or smaller particles, which constitute the regolith. Regolith generation has traditionally been attributed to the fall back of impact ejecta and by the break-up of boulders by micrometeoroid impact. Laboratory experiments and impact models, however, show that crater ejecta velocities are typically greater than several tens of centimetres per second, which corresponds to the gravitational escape velocity of kilometre-sized asteroids. Therefore, impact debris cannot be the main source of regolith on small asteroids. Here we report that thermal fatigue, a mechanism of rock weathering and fragmentation with no subsequent ejection, is the dominant process governing regolith generation on small asteroids. We find that thermal fragmentation induced by the diurnal temperature variations breaks up rocks larger than a few centimetres more quickly than do micrometeoroid impacts. Because thermal fragmentation is independent of asteroid size, this process can also contribute to regolith production on larger asteroids. Production of fresh regolith originating in thermal fatigue fragmentation may be an important process for the rejuvenation of the surfaces of near-Earth asteroids, and may explain the observed lack of low-perihelion, carbonaceous, near-Earth asteroids.
Laboratoire Lagrange, UNS-CNRS, Observatoire de la Côte d'Azur, Boulevard de l'Observatoire-CS 34229, 06304 Nice Cedex 4, France.
Marco
M
Delbo
1] Université de Lorraine, CRPG-CNRS, 15 Rue Notre-Dame des Pauvres, BP 20, 54501 Vandoeuvre les Nancy, France [2] Laboratoire Géoazur, UNS-CNRS, Observatoire de la Côte d'Azur, 250 rue Albert Einstein, Les Lucioles 1, Sophia-Antipolis, 06560 Valbonne, France.
Guy
G
Libourel
Hopkins Extreme Materials Institute, Johns Hopkins University, Latrobe 122, 3400 North Charles Street, Baltimore, Maryland 21218, USA.
Justin
J
Wilkerson
1] Laboratoire Lagrange, UNS-CNRS, Observatoire de la Côte d'Azur, Boulevard de l'Observatoire-CS 34229, 06304 Nice Cedex 4, France [2] Institut Supérieur de l'Aéronautique et de l'Espace, 10 avenue Edouard-Belin, BP 54032, 31055 Toulouse Cedex 4, France.
Naomi
N
Murdoch
Laboratoire Lagrange, UNS-CNRS, Observatoire de la Côte d'Azur, Boulevard de l'Observatoire-CS 34229, 06304 Nice Cedex 4, France.
Patrick
P
Michel
Hopkins Extreme Materials Institute, Johns Hopkins University, Latrobe 122, 3400 North Charles Street, Baltimore, Maryland 21218, USA.
K T
KT
Ramesh
Laboratoire Géoazur, UNS-CNRS, Observatoire de la Côte d'Azur, 250 rue Albert Einstein, Les Lucioles 1, Sophia-Antipolis, 06560 Valbonne, France.
Clément
C
Ganino
Laboratoire Géoazur, UNS-CNRS, Observatoire de la Côte d'Azur, 250 rue Albert Einstein, Les Lucioles 1, Sophia-Antipolis, 06560 Valbonne, France.
Chrystele
C
Verati
Solar System Exploration Research Virtual Institute, Institute for the Science of Exploration Targets, Southwest Research Institute, 1050 Walnut Street, Suite 300 Boulder, Colorado 80302, USA.
Simone
S
Marchi