Vol. 667
10. Planets and planetary techniques
Estimation of the area weathering timescale on (25143) Itokawa:
Implications on its rejuvenation course of
House weathering designates the ensemble of processes by which surfaces of airless our bodies are bodily and optically affected by their exposition to numerous sources of vitality from outer area. This may occasionally embrace the impacts of cosmic rays, irradiation by the photo voltaic wind, and meteoritic or micrometeoritic bombardment. House weathering is noticed to happen on lunar rocks, asteroid floor, and meteorite samples, however the dominant mechanism and its attribute timescale are sometimes troublesome to evaluate, with proposed timescales starting from ~10^3 to 10^8 years within the case of asteroids. Specializing in asteroid (25143) Itokawa, which was visited by the Hayabusa probe, Jin and Ishiguro suggest a novel technique that makes use of a statistical analysis of the intense mottles that happen on some boulder surfaces of the asteroid. These mottles are thought to include recent materials uncovered by impacts of millimeter- to centimeter-sized interplanetary mud particles (IDPs). Because the asteroid floor is completely darkened and reddened by area weathering, the quantity and dimension distribution of the intense mottles is managed by the stability between area weathering and the IDP affect frequency. The authors determine ~400 such mottles and decide their cumulative size-frequency distributions. The latter is then in comparison with expectations from an IDP flux mannequin. The slope of the dimensions distribution (with energy index q ~ -3.7) agrees with expectations from the IDP flux mannequin, lending confidence to the proposed mechanism, and absolutely the variety of vibrant mottles signifies an area weathering timescale of ~10^3 years, with a possible uncertainty of an element of 10 at most. In contrast with expectations from laboratory experiments, this timescale is according to area weathering by mild ions from the photo voltaic wind, versus irradiation by heavy ions (timescale ~ 10^6 years) or micrometeorite affect (~10^8 years). With such a brief timescale, the incidence of vibrant areas elsewhere on Itokawa implies the existence of one other rejuvenation course of, which the authors tentatively determine as seismic shaking triggered by a latest affect that created the Kamoi crater.
