[meteorite-list] POP QUIZ FRIDAYS ANSWER

From: Shawn Alan <photophlow_at_meteoritecentral.com>
Date: Sun, 27 Mar 2011 10:04:55 -0700 (PDT)
Message-ID: <519820.72183.qm_at_web35405.mail.mud.yahoo.com>

Hello Listers,

I would like to thank everyone that sent in their answers and I enjoyed the feedback on this POP QUIZ question. I would like to congratulate Andre b being the 10th Lister to email the correct answer. Andre will receive a? free 115mg Saratov meteorite fragment which fell on?Sept. 6th, 1918 in Russia.
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Question
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True or False
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The absorption and reemission of electromagnetic radiation on?small size?asteroids in the range of 1-10km can have a tiny force that leads to large, long-term effects in the orbits of the small bodies?
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Answer
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True
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If you would like to learn more about this process which in the meteoritcal science community is know as the Yarkovsky effect , discovered by a Russian civil engineer Ivan Osipovich Yarkovsky (1844?1902) click on these links below.
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http://www.jpl.nasa.gov/releases/2003/163.cfm
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http://impact.arc.nasa.gov/news_detail.cfm?ID=132
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http://www.boulder.swri.edu/~davidn/papers/kyarko.pdf
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Detection of the Yarkovsky effect for main-belt asteroids
by
David Nesvorn? ?, William F. Bottke

Abstract

The Yarkovsky effect, a non-gravitational acceleration produced by the anisotropic emission of thermal energy (?pik, 1951, Proc. Roy.
Irish Acad. 54, 165?199), plays an important role in the dynamical evolution of asteroids. Current theoretical models of the Yarkovsky effect,
however, rely on a number of poorly known parameters that can only approximate how real asteroids respond to solar heating. To improve
this situation, we investigated whether the orbital distribution of the Karin cluster, a 5.8 ? 0.2 Myr old S-type asteroid family (Nesvorn?
et al., 2002a, Nature 417, 720?722), could be used to determine the rate at which multikilometer main-belt asteroids spread in semimajor
axis due to the Yarkovsky effect. Our results indicate that the orbital histories of individual Karin cluster members bear clear signatures of
having drifted in semimajor axis drift since their formation. Using numerical methods, we determined the drift speed of ? 70 Karin cluster
members (asteroids 1?6 km in diameter). This is the first time the speed that main-belt asteroids evolve in the semimajor axis due to the
non-gravitational effects have been measured. The magnitude of measured speeds is similar to those predicted by theoretical models of the
Yarkovsky force. Taken together, our results represent the first direct detection of the Yarkovsky effect for main-belt asteroids, and they
validate in significant ways the asteroid thermal models described in the recent literature (e.g., Vokrouhlick?, 1999, Astron. Astrophys. 344,
362?366). By comparing the measured drift speeds to those calculated from theoretical models of the Yarkovsky effect, we determined that
Karin cluster members do not have surface thermal conductivities K in excess of ? 0.1Wm?1 K?1. Instead, their derived K values are
consistent with the presence of regolith over most/all of their ? 5.8 Myr lifetimes. This low-conductive regolith layer may be thin because
the penetration depth of the diurnal thermal wave is
5 cm. The regolith material may have been deposited in the immediate aftermath
of the Karin cluster formation event or was produced over time by impacts. Our method also allows us to estimate spin obliquity values
for Karin cluster members. We find that members with diameters  3.5-km are predominantly retrograde rotators, while those < 3.5-km
have obliquities more equally distributed between 0? and 180?. These data may be used to study the spin states of asteroids produced by
catastrophic disruption events. Interestingly, we find that a few Karin members have drifted further than predicted by our standard Yarkovsky
model. We hypothesize these objects may have: (i) faster drift speeds than predicted by theoretical models, (ii) high albedos ( 0.3), and/or
(iii) densities
2 gcm?3.
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Shawn Alan
IMCA 1633
eBaystore
http://shop.ebay.com/photophlow/m.html


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Received on Sun 27 Mar 2011 01:04:55 PM PDT