A giant water ice shell under the surface of the asteroid (90) Antiope ?
Publiée le 2010-06-30
A giant water ice shell under the surface of the asteroid (90) Antiope ?
Several recent studies on the asteroid (24) Themis led to the detection of water ice under the form of a very thin layer of just 1/20th of a micron thick coating surface grains with a diameter of 30 microns. The incident solar flux is sufficient to completely sublimate the ice water. Therefore the presence of water ice may be due to the existence of an internal reservoir, source of outgazing of water vapor which turns into ice once in the surface (Rivkin and Emery, Nature, 464, 2010 , Campins et al, Nature, 464, 2010).

These convergent results are now completed by geophysical models of the evolution of asteroid parent body of the family of Themis. This family of objects has 550 members who are believed to come from the disruption of a parent body of approximately 450km in diameter. This body would have been differentiated with a solid core in the center inserted within a shell of dirty water ice (Castillo-Rogez and Schmidt, 2010). The double asteroid (90) Antiope, a member of the Themis family, whose components fit perfectly to the shape they would if they were like giant rotating fluid masses of 90 km in diameter, may actually house a large quantity of ice water under a solid surface layer.

Figure shows the infrared reflectance spectra of 24 Themis which are well fitted by a mixture of ice-coated pyroxene grains and amorphous carbon (Rivkin & Emery, Nature, 464). All spectra show an absorption band near 3,1 microns attibuted to fine-grained water ice as a frost deposited on regolith grains.

Puce Water ice and organics on the surface of the asteroid 24 Themis, Campins et al, Nature 464, 1320-1321 (29 April 2010)
Puce Detection of ice and organics on an asteroidal surface, Andrew S. Rivkin1 & Joshua P. Emery, Nature 464, 1322-1323 (29 April 2010)
Puce Geophysical evolution of the Themis family parent body, Castillo-Rogez and Schmidt, GEOPHYSICAL RESEARCH LETTERS, VOL. 37 (29 mai 2010)
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