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(meteorobs) [Very Juicy] Excerpts from "CCNet, 22/2000 - 17 February 2000"
This one's well worth reading over for meteor and comet afficianados!
Lew
------- Forwarded Message
From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet, 17 February 2000
Date: Thu, 17 Feb 2000 10:03:02 -0500 (EST)
CCNet, 22/2000 - 17 February 2000
---------------------------------
[...]
(3) NASA BEGINS BUILDING NEXT MISSION TO STUDY COMETS
NASANews@hq.nasadot gov=20
[...]
(7) RADAR OBSERVATIONS OF COMETS
J.K. Harmon et al., ARECIBO OBSERVATORY
(8) METEOROID STREAMS AT MARS
A.A. Christou & K. Beurle, UNIVERSITY OF LONDON=20
[...]
(11) HOW HARD IS EROS?
Mayo Greenberg <greenber@strw.leidenunivdot nl>=20
[...]
============================================================
(3) NASA BEGINS BUILDING NEXT MISSION TO STUDY COMETS
>From NASANews@hq.nasadot gov=20
=20
Donald Savage
Headquarters, Washington, DC February 15, 2000
(Phone: 202/358-1547)
RELEASE: 00-26
NASA BEGINS BUILDING NEXT MISSION TO STUDY COMETS
NASA's Comet Nucleus Tour, or CONTOUR, mission this month took a giant=20
step closer to its launch when the project received approval to begin=20
building the spacecraft.=20
Planned for a July 2002 launch, CONTOUR is expected to encounter Comet
Encke in November 2003 and Comet Schwassmann-Wachmann-3 in June 2006.
The mission has the flexibility to include a flyby of Comet d'Arrest in
2008 or an as-yet undiscovered comet, perhaps originating from beyond
the orbit of Pluto. Such an unforeseen cometary visitor to the inner
solar system, like Comet Hale-Bopp discovered in 1995, would present a
rare opportunity to conduct a close-up examination of these mysterious,
ancient objects which normally reside in the cold depths of
interstellar space.
The nucleus of a comet is its heart, believed by scientists to be a
tiny irregular chunk of ice and rock. To date only one comet nucleus
has ever been viewed by a spacecraft: Comet Halley in 1986. CONTOUR
will fly past at least two comets and take higher resolution images
than those of Halley. It will also collect and analyze gas and dust to
reveal the comet's makeup, greatly improving our knowledge of key
characteristics of comet nuclei and providing an assessment of their
diversity. CONTOUR also will clear up the many mysteries of how comets
evolve as they approach the Sun and their ices begin to evaporate.
The CONTOUR spacecraft will fly by each comet at the peak of its=20
activity when it's close to the Sun. During each encounter, the target =
comet will also be well situated in the night sky for astronomers=20
worldwide to make concurrent observations from the ground. The=20
spacecraft will fly by each comet at a distance of about 60 miles (100=20
kilometers).=20
After successful completion of both the Preliminary Design Review and=20
an independent Confirmation Assessment and the Confirmation Review at=20
NASA Headquarters, the comet flyby project is well on its way toward=20
completing the spacecraft design. The CONTOUR mission is managed for=20
NASA by the Johns Hopkins University Applied Physics Laboratory, in=20
Laurel, MD. The Principal Investigator is Dr. Joseph Veverka of=20
Cornell University, NY. More information on CONTOUR is available at:=20
http://www.contour2002.org and http://discovery.nasadot gov
============================================================
(7) RADAR OBSERVATIONS OF COMETS
J.K. Harmon*),D.B. Campbell, S.J. Ostro, M.C. Nolan: Radar observations
of comets. PLANETARY AND SPACE SCIENCE, 1999, Vol.47, No.12,=20
pp.1409-1422
*) ARECIBO OBSERVATORY,HC3 BOX 53995,ARECIBO,PR,00612
CORNELL UNIV,DEPT ASTRON,ITHACA,NY,14853
Seven comets have been detected by Earth-based radars during the period =
1980-1995. All but one of these gave a detectable echo fi om the=20
nucleus, while three of the comets also showed a broad-band echo from=20
large (similar to cm-size) grains in the inner coma. Although all=20
observations have been of the CW (continuous-wave) type, which=20
precludes direct size measurement, the radar cross sections are=20
consistent with nucleus diameters averaging a few kilometers and=20
varying over a range of ten. Comparisons with independent size=20
estimates indicate relatively low radar albedos, implying nucleus=20
surface densities of 0.5 to 1 g/cm(3), The surfaces of comet nuclei=20
appear to be as rough as typical asteroid surfaces, but are=20
considerably less dense. Analysis of coma echoes indicates that
some comets emit large grains at rates (similar to ton/s) which
are comparable with their gas and dust production rates, There=20
is also some indirect evidence for grain evaporation or fragmentation=20
within a few hundred to a few thousand kilometers of the nucleus. The=20
highest priority of future radar observations will be to obtain=20
delay-Doppler images of a nucleus, which would give direct size and=20
shape estimates as well as a more reliable albedo. Delay-Doppler or=20
interferometric imaging of the coma echo would also help to=20
better characterize the grain halo. Ten short-period comets are
potentially detectable during the next two decades, although=20
the best radar opportunities may well come from comets yet to=20
be discovered. (C) 1999 Elsevier Science Ltd. All rights=20
reserved.
============================================================
(8) METEOROID STREAMS AT MARS
A.A. Christou*) & K. Beurle: Meteoroid streams at Mars: possibilities=20
and implications. PLANETARY AND SPACE SCIENCE, 1999, Vol.47, No.12,=20
pp.1475-1485
*) UNIVERSITY OF LONDON QUEEN MARY & WESTFIELD COLL,ASTRON UNIT,SCH =
MATH SCI,MILE END RD,LONDON E1 4NS,ENGLAND
In order to assess the possibility of meteoroid streams detectable from =
the surface of Mars as meteor showers we have derived minimum distances =
and associated velocities for a large sample of small body orbits=20
relative to the orbits of Mars and the Earth. The population ratio for=20
objects approaching to within 0.2 AU of these two planets is found to=20
be approximately 2:1. The smaller relative velocities in the case of=20
Mars appears to be the main impediment to the detection of meteors in=20
the upper atmosphere of that planet. We identify five bodies, including =
the unusual object (5335) Damocles and periodic comet 1P/Halley, with=20
relative orbital parameters most suitable to produce prominent meteor=20
showers. We identify specific epochs at which showers related to these=20
bodies are expected to occur. An overview of possible detection methods =
taking into account the unique characteristics of the Martian=20
environment is presented. We pay particular attention on the effects of =
such streams on the dust rings believed to be present around Mars. (C)=20
1999 Elsevier Science Ltd. All rights reserved.
============================================================
*LETTERS TO THE MODERATOR *
============================================================
(11) HOW HARD IS EROS?
>From Mayo Greenberg <greenber@strw.leidenunivdot nl>=20
Dear Benny,
I have not heard any mention of obtaining the mean density of Eros By=20
NEAR. This to me seems one of the most important pieces of information=20
to be deduced from the orbit of the satellite and the size of Eros. Ths =
provides a basic data point on the composition.
Best regards =20
Mayo Greenberg
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