Mathematics – Logic
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsa12b..03c&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SA12B-03
Mathematics
Logic
[6022] Planetary Sciences: Comets And Small Bodies / Impact Phenomena, [6205] Planetary Sciences: Solar System Objects / Asteroids, [6245] Planetary Sciences: Solar System Objects / Meteors
Scientific paper
Historically, the study of asteroids has been separate from meteor science because of an observational gap: meteoroids larger than a few meters in size strike the Earth very rarely, and telescopic observations generally are of bodies tens of meters in size or larger. But bolide observations (from both Earth and space) are becoming more synoptic and telescopic searches will soon push down to ever smaller Near-Earth Objects (NEOs). So, instead of a gap between NEOs and meteoroids, there is now overlap. Already, last year, there was the first-ever discovery of an NEO that was predicted to - and did - strike Earth’s atmosphere, just 20 hours later. Before atmospheric entry, 2008 TC3 was well characterized for physical properties by telescopic observation. Despite ground-zero being very remote, observations were made of the atmospheric entry and explosion, and hundreds of rare ureilite meteorites were recovered during ensuing months. It is not widely appreciated that prospects are excellent that the Catalina Sky Survey (and other existing and proposed telescopic search programs) should detect a significant fraction of asteroids/meteoroids > 1 m diameter on their final plunge to Earth, providing hours to days of advance notice so that the NEO can be characterized telecopically, so that the bolide can be observed, and so that associated meteorites can be recovered. An NEO hazard issue concerns the smallest body that is dangerous. The 2003 SDT study considered that bodies < 50 m diameter would not cause significant damage on the ground. Since then, theoretical work suggests that downward momentum of smaller bodies (down to 20-30 m diameter) disintegrating in the atmosphere could be damaging. Moreover, the 2007 impact in Carancas, Peru, shows that metallic meteoroids (which are a few percent of the total) are not the only ones that can strike the ground at hypervelocity. Furthermore, even if nothing more than a rain of meteorites were expected, a prudent public official could well respond to advanced warning of an impact at a specific time and place, even for a meteoroid just a few meters across, by advising people to stay indoors. Is any size truly safe? What is the smallest meteoroid meriting evacuation? Are there other effects (e.g. EMP) of comparatively small impacts that might be dangerous? Asteroid science is rapidly evolving in ways that have profound implications for meteor science and meteoritics. It is now recognized that small NEOs (and presumably their similar-sized cousins in the main asteroid belt) may be constantly evolving in shape and form, as YORP forces spin them up, avalanches and landslides move rubble from pole to equator and into orbit, satellites form, some satellites escape onto heliocentric orbit (to become meteoroids and meteorites if they strike Earth), and other satellites decay and form contact binary shapes, as seen in Arecibo radar images, or head-and-body shapes, like that of Itokawa. Depending on mineralogical composition, NEAs may go through several generations of such evolving form during their few-million-year lifetimes in planet-crossing orbits. Since these kinds of processes, more than hypervelocity cratering and fragmentation, may dominate the liberation of meteoroids, it is important that these developments be followed by the meteor/meteoroid community.
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