Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p23c1728r&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P23C-1728
Physics
[6017] Planetary Sciences: Comets And Small Bodies / Erosion And Weathering, [6055] Planetary Sciences: Comets And Small Bodies / Surfaces, [6205] Planetary Sciences: Solar System Objects / Asteroids, [6210] Planetary Sciences: Solar System Objects / Comets
Scientific paper
In November 2010, the Deep Impact spacecraft flew by comet Hartley 2 as part of its extended (EPOXI) mission. The flyby revealed a nucleus comprised of two, relatively coarse-terrained lobes connected by a smooth, neck region (A'Hearn et al., Science, 2011). If we assume that this smooth neck formed via some type of fluidized particulate flow, then it should lie roughly coincident with an equipotential surface with respect to the combined forces of gravity and rotation. Utilizing a Hartley 2 shape model and measured rotation state, we tested this idea by varying the model bulk density to find the gravity field wherein the potential variation across the neck region was at a minimum, yielding a best-fit bulk density of 220 (140-520) kg/m^3. Curiously, this same potential variance minimization technique applied to the entire shape model yields a bulk density of 200 (140-350) kg/m^3. At first glance, this similar global result seems to invalidate the regional result. However, the same global exercise performed for asteroids 243 Ida and 433 Eros does yield densities close to the measured densities for those objects. For 433 Eros, the technique yields a best-fit density of 2200 (1400-4000) kg/m^3, within 18% of the measured density of 2670 +/- 30 kg/m^3. For 243 Ida, the technique yields a best-fit density of 2300 (1500-4800) kg/m^3, within 12% of the measured density of 2600 +/- 500 kg/m^3. Clearly, there is some mechanism that causes the topography of some small, rotating bodies to move toward as small a potential energy variance over the surface as possible. We hypothesize that the above phenomena can be explained by the effect that disturbance-driven slope degradation processes have on the topography of a small body, given a mobile regolith layer on its surface. The first key factor in this explanation involves the exponential increase in the downslope flow/creep rate that occurs when the slope is increased toward the critical angle for that material (Roerring, Water Resources Res., 35, 1999). The second key factor occurs when rotational forces on the surface of a body represent a significant fraction of the total force, such that the rotational force has a significant effect on surface slope magnitude (what direction is "up") at a given location. Initially, it would seem that if the rotation rate of a body is changed, some slopes will increase and some decrease, with an overall rough cancellation. However, when 433 Eros is considered, either increasing or decreasing the rotation rate will cause an increase in the slope distribution. That is, the current surface shape of 433 Eros appears to rest in an 'erosional saddle-point', wherein changing the rotation rate of the body in either direction will cause an overall increase in surface slopes, with a corresponding, non-linear increase in downslope erosion rates, which push the surface back towards a low overall slope distribution again. This dynamic thus creates a self-correcting system in which disturbance-driven slope degradation is constantly working to push the topography towards that of a flat, equipotential surface. In this work, we explore this phenomena within a study that includes seven small objects for which detailed shape models exist (four asteroids, two comets, and one small martian moon).
Bowling Timothy J.
Richardson James E.
No associations
LandOfFree
Investigating the Combined Effects of Gravity and Rotation on Small-Body Surface Terrains does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Investigating the Combined Effects of Gravity and Rotation on Small-Body Surface Terrains, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Investigating the Combined Effects of Gravity and Rotation on Small-Body Surface Terrains will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-869861