The centimeter-sized fragments and smaller particles that make up the regolith — the layer of loose, unconsolidated rock and dust — of small asteroids is formed by temperature cycling that breaks down rock in a process called thermal fatigue, according to a paper published today in the Nature Advance Online Publication.
Previous studies suggested that the regolith of asteroids one kilometer wide and smaller was made from material falling to the surface after impacts and from boulders that were pulverized by micrometeoroid impacts.
Recent laboratory experiments and impact modeling conducted by a team of researchers from Observatoire de la Côte d'Azur, Hopkins Extreme Materials Institute at Johns Hopkins University, Institut Supérieur de l'Aéronautique et de l'Espace and Southwest Research Institute (SwRI) have shown that the debris from large impacts reaches escape velocities and breaks free from the gravitational pull of these asteroids, indicating this mechanism is not the dominant process for regolith creation.
The team's research showed that thermal fragmentation, which is induced by mechanical stresses caused by temperature variations of the rapidly spinning asteroid's short night and day, to be the process primarily responsible for breaking up rocks larger than a few centimeters on asteroids.
"We took meteorites as the best analog of asteroid surface materials that we have on the Earth," said Dr. Marco Delbo of the Observatoire de la Côte d'Azur. "We then submitted these meteorites to temperature cycles similar to those that rocks experience on the surfaces of near-Earth asteroids and we found that microcracks grow inside these meteorites quickly enough to entirely break them on timescales much shorter than the typical lifetime of asteroids."
Model extrapolation of these experiments also showed that thermal fragmentation caused rocks to break down an order of magnitude faster than from micrometeoroid impacts, particularly at distances of 1 astronomical unit (about 93 million miles) with the speed of breakdown slowing at distances further from the Sun.
"Even asteroids significantly farther from the Sun showed thermal fatigue fragmentation to be a more relevant process for rock breakup than micrometeoroid impacts," said Dr. Simone Marchi, a scientist in the SwRI Space Science and Engineering Division.
The results of this study suggest that thermal fragmentation, combined with solar radiation pressures that sweep away surface particles, could completely erode small asteroids at distances closer to the Sun (about 28 million miles) in about 2 million years.
The French Agence National de la Recherche SHOCKS, BQR of the Observatoire de la Côte d'Azur, the University of Nice-Sophia Antipolis, the Laboratory GeoZur, the French National Program of Planetology, and NASA's Solar System Exploration Research Virtual Institute funded this research.
The paper "Thermal Fatigue as the Origin of Regolith on Small Asteroids," by Marco Delbo, Guy Libourel, Justin Wilkerson, Naomi Murdoch, Patrick Michel, K.T. Ramesh, Clement Ganino, Chrystele Verati, and Simone Marchi, (doi: 10.1038/nature13153) will be published in the April 10 print issue of Nature.
Maria Martinez Stothoff | EurekAlert!
Earth Day: Disease spread among species is predictable
24.04.2015 | National Science Foundation
Warming climate may release vast amounts of carbon from long-frozen Arctic soils
24.04.2015 | University of Georgia
KAIST researchers published an article on the development of a novel technique to precisely track the 3-D positions of optically-trapped particles having complicated geometry in high speed in the April 2015 issue of Optica.
Daejeon, Republic of Korea, April 23, 2015--Optical tweezers have been used as an invaluable tool for exerting micro-scale force on microscopic particles and...
A very small and rare species of shark is swimming its way through scientific literature. But don't worry, the chances of this inches-long vertebrate biting...
Ever since computers have been small enough to be fixtures on desks and laps, their central processing has functioned something like an atomic Etch A Sketch, with electromagnetic fields pushing data bits into place to encode data.
Unfortunately, the same drawbacks and perils of the mechanical sketch board have been just as pervasive in computing: making a change often requires starting...
How is lightning initiated in thunderclouds? This is difficult to answer - how do you measure electric fields inside large, dangerously charged clouds? It was discovered, more or less by coincidence, that cosmic rays provide suitable probes to measure electric fields within thunderclouds. This surprising finding is published in Physical Review Letters on April 24th. The measurements were performed with the LOFAR radio telescope located in the Netherlands.
How is lightning initiated in thunderclouds? This is difficult to answer - how do you measure electric fields inside large, dangerously charged clouds? It was...
Max Planck researcher Buhalqem Mamtimin determines how much nitrogen oxide is released into the atmosphere from agriculturally used oases.
In order to make statements about current and future air pollution, scientists use models which simulate the Earth’s atmosphere. A lot of information such as...
23.04.2015 | Event News
23.04.2015 | Event News
13.04.2015 | Event News
24.04.2015 | Materials Sciences
24.04.2015 | Materials Sciences
24.04.2015 | Health and Medicine