64 research outputs found
ON THE INTERACTION OF SUBLIMATING GAS WITH COMETARY BODIES
Sublimation of volatiles is a defining process of comet nuclei, and profoundly affects their dynamics, structure, and appearance. Central to understanding the processes by which comets formed and subsequently evolved is a careful computation of this sublimation pressure as a function of heliocentric distance. Unlike previous efforts, I develop a thermodynamic method to numerically compute the sublimation pressure of any species from limited knowledge of its physical properties. I then describe a novel cometary disruption mechanism in which this sublimation pressure induces differential stresses within the body of the nucleus that exceed its material strength, resulting in structural failure and breakup of the nucleus. I show that this mechanism is consistent with the behavior of Comet ISON (C/2012 S1), and use it to estimate the cohesive strength of ISON’s nucleus, a first for a Long-Period Comet
Thermal Alteration of Labile Elements in Carbonaceous Chondrites
Carbonaceous chondrite meteorites are some of the oldest Solar System
planetary materials available for study. The CI group has bulk abundances of
elements similar to those of the solar photosphere. Of particular interest in
carbonaceous chondrite compositions are labile elements, which vaporize and
mobilize efficiently during post-accretionary parent-body heating events. Thus,
they can record low-temperature alteration events throughout asteroid
evolution. However, the precise nature of labile-element mobilization in
planetary materials is unknown. Here we characterize the thermally induced
movements of the labile elements S, As, Se, Te, Cd, Sb, and Hg in carbonaceous
chondrites by conducting experimental simulations of volatile-element
mobilization during thermal metamorphism. This process results in appreciable
loss of some elements at temperatures as low as 500 K. This work builds on
previous laboratory heating experiments on primitive meteorites and shows the
sensitivity of chondrite compositions to excursions in temperature. Elements
such as S and Hg have the most active response to temperature across different
meteorite groups. Labile element mobilization in primitive meteorites is
essential for quantifying elemental fractionation that occurred on asteroids
early in Solar System history. This work is relevant to maintaining a pristine
sample from asteroid (101955) Bennu from the OSIRIS-REx mission and
constraining the past orbital history of Bennu. Additionally, we discuss
thermal effects on surface processes of near-Earth asteroids, including the
thermal history of "rock comets" such as (3200) Phaethon. This work is also
critical for constraining the concentrations of contaminants in vaporized water
extracted from asteroid regolith as part of future in situ resource utilization
for sustained robotic and human space exploration.Comment: 12 pages of text, 3 tables, 7 figures, accepted by Icaru
Semi-major Axis Jumps as the Activity Trigger in Centaurs and High-Perihelion Jupiter Family Comets
We present a dynamical study of 39 active Centaurs and 17 high-perihelion
(q4.5 au) JFCs with a focus on investigating recent orbital changes as
potential triggers for comet-like activity. We have identified a common feature
in the recent dynamical histories of all active Centaurs and JFC in our sample
that is not present in the history of the majority of inactive population
members: a sharp decrease in semi-major axis and eccentricity occurring within
the last several hundred years prior to observed activity. We define these
rapid orbital changes as `a-jumps'. Our results indicate that these orbital
reshaping events lead to shorter orbital periods and subsequently greater
average per-orbit heating of Centaur nuclei. We suggest the a-jumps could
therefore be a major trigger of cometary activity on Centaurs and JFCs. Our
results further imply that analyses of the recent dynamical histories could be
used to identify objects that are currently active or may become active soon,
where we have identified three such Centaurs with recent a-jumps that should be
considered high-priority targets for observational monitoring to search for
activity.Comment: 19 pages, 4 figures, 1 table, accepted for publication in ApJ
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