Biology
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p22b..09c&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P22B-09
Biology
[5220] Planetary Sciences: Astrobiology / Hydrothermal Systems And Weathering On Other Planets, [6020] Planetary Sciences: Comets And Small Bodies / Ices, [6040] Planetary Sciences: Comets And Small Bodies / Origin And Evolution
Scientific paper
Until recently, the interest generated by large wet asteroids was primarily due to their status of protoplanets, i.e., their intermediate stage between planetesimals and fully-developed planets [1]. This picture changed a few years ago, when it was suggested that these objects contain a lot of free water [2]. Such an idea was recently substantiated by the detection of ice and organics at the surface of large outer main belt asteroids (24 Themis and 65 Cybele) [3, 4]. This discovery sheds a new light on these asteroids, which now represent astrobiological targets accessible within NASA's Discovery program. Ceres' place in this picture is especially compelling as ground-based observations have shown that that object bears on its surface materials that are formed in alkaline hydrothermal environments [5], and it is the third planetary body on which carbonates have been detected. Large wet asteroids are akin to medium-sized outer planet satellites in terms of global internal structure and geophysical processes, but they benefit from far more heat [6]. Icy satellites are subject to tidal heating, supplied in the deep interior (in most cases), with an intensity function of the time-dependent dynamical state of these objects. The main heat source available at asteroids is solar energy, a permanent source that has been increasing with time. The contrast in surface temperature between the two classes of objects implies very different settings for endogenic and geological activity. Indeed the contrast in viscosity across icy satellite icy shells is at least ten orders of magnitude, while that contrast is only three to five orders of magnitude in the case of asteroids. This results preferentially in stagnant-lid convection in the former situation. On the other hand, we have demonstrated that Ceres could be subject to mobile-lid convection for at least part of its history [7]. Whether this regime is occurring nowadays depends on a number of unconstrained parameters. However, we believe that Ceres' smooth surface, homogeneous photometric properties, and unusual composition are the signatures of a relatively recent resurfacing event that would be logically associated to an episode of mobile-lid convection if the occurrence of such a process were a priori possible in that object. We will present the mechanism for emplacing Ceres' surface and discuss hypotheses to be tested by the Dawn Mission. We will also address the astrobiological implications of this outstanding situation. [1] Russell et al., ACM 2002; [2] McCord and Sotin, JGR 2005; [3] Rivkin and Emery, Nature Geoscience, 2010; [4] Licandro et al. ApJ 2011; [5] Milliken and Rivkin Nature Geoscience 2009; [6] Castillo-Rogez and Lunine, chapter in "Astrobiology: the Next Frontier," Cambridge University Press, submitted; [7] Castillo-Rogez et al. submitted to Nature Geoscience. Part of this work has been carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. Government sponsorship acknowledged.
Castillo Julie C.
Choukroun Mathieu
Hodyss R. P.
Johnson Paul V.
Raymond Carol A.
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