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(meteorobs) Excerpt from "CCNet 65/2001 - 9 May 2001"
------- Forwarded Message
From: Peiser Benny <B.J.Peiser@livjm.acdot uk>
To: cambridge-conference <cambridge-conference@livjm.acdot uk>
Subject: CCNet 65/2001 - 9 May 2001
Date: Wed, 9 May 2001 10:02:42 +0100
CCNet 65/2001 - 9 May 2001
--------------------------
[...]
(4) SPACECRAFT MEASURES ASTEROIDAL MAGNETIC FIELD
Harvey Leifert <hleifert@agu.org>
[...]
(6) LUNAR NON-IMPACT
Michael Paine <mpaine@tpgi.com.au>
[...]
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(4) SPACECRAFT MEASURES ASTEROIDAL MAGNETIC FIELD
>From Harvey Leifert <hleifert@agu.org>
The irregular asteroid Braille (also known as 1992 KD) was discovered in May
1992. Deep Space 1 (DS1) performed a successful flyby at the asteroid in
July 1999, passing Braille on the nightside with a relative velocity of 15
kilometers [nine miles] per second and allowing, for the first time, a
direct measurement of an asteroidal magnetic field. Richter et al. ["First
direct magnetic field measurements of an asteroidal magnetic field: DS1 at
Braille"] conclude that the measured field is simply the unperturbed dipole
field of the asteroid, and estimate the upper limit of Braille's magnetic
moment to be about 2.1 X 10^11 ampere meter-squared (A-m^2).
Authors: I. Richter, K.-H. Glassmeier, F. Kuhnke, G. Musmann, C. Othmer,
Inst. for Geophysics and Meteorology, Technical U. of Braunschweig,
Braunschweig, Germany; D. E. Brinza, B. T. Tsurutani, JPL, Caltech,
Pasadena, California; M. Cassel, Inst. for computer and Communication
Network Engineering, Technical U. of Braunschweig, Braunschweig, Germany; K.
Schwingenschuh, Ins. For Space Research, Technical U. of Graz, Graz,
Austria.
============================
* LETTERS TO THE MODERATOR *
============================
(6) LUNAR NON-IMPACT
>From Michael Paine <mpaine@tpgi.com.au>
Dear Benny
The following statement from CCNet 4 May doesn't show a very good
understanding of events randomly distributed in time (if impacts are indeed
random):
"An impact this size on the Moon is predicted to happen once every
15 million years or so," Paul Withers told BBC News Online. "Having one
happen in the past 1,000 years would suggest that the predictions might
be dangerously incorrect and the Earth might be in more danger from
colliding space rocks than is currently thought."
In any, case LPL's Crater Calculator
(http://www.lpl.arizonadot edu/tekton/crater.html ) gives a predicted impactor
diameter of 850m (assuming a stony asteroid generated the 22km crater on the
Moon), not the 3km quoted in the article. Therefore the odds of such an
impact in the last 1000 years are very roughly 1 in 1000 (assuming such
Lunar impacts occur with an average interval of one million years but are
randomly distributed). Therefore a large crater that young on the Moon would
be unusual but not surprising.
Nevertheless, the evidence seems to be building up against crater Giordano
Bruno being linked to the 1178AD account.
Regards,
Michael Paine
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