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(meteorobs) Excerpts from "CCNet, 8 September 1999"
A major motherload of meteor-related material in this issue! :)
Lew
------- Forwarded Message
From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet, 8 September 1999
Date: Wed, 8 Sep 1999 11:41:28 -0400 (EDT)
CCNet, 8 September 1999
-----------------------
(1) NASA BUDGET BATTLE BEGINS AGAIN
SPACEVIEWS, 7 September 1999
(2) MAROCCAN METEORITE FOUND TO CONTAIN WATER
Andrew Yee <ayee@nova.astro.utorontodot ca>
[...]
(4) NEAR ENCOUNTER WITH ASTEROID 253 MATHILDE
J. Veverka et al., CORNELL UNIV
(5) MATHILDE: SIZE, SHAPE AND GEOLOGY
P.C. Thomas et al., CORNELL UNIV
[...]
(8) THE COLLISIONAL HISTORY OF MATHILDE
D.R. Davis, SJI
(9) NEAR PHOTOMETRY OF MATHILDE
B.E. Clark et al., CORNELL UNIV
(10) THE MULTISPECTRAL IMAGER ON NEAR
S. Murchie et al., JOHNS HOPKINS UNIV
=========
(1) NASA BUDGET BATTLE BEGINS AGAIN
>From SPACEVIEWS, 7 September 1999
http://www.spaceviews.com/1999/09/07b.html
The next round in the bruising battle over NASA's fiscal year 2000
budget will begin this week as both houses of Congress return from
summer recess and take action on the budget.
The full House of Representatives is expected to debate and vote on
H.R. 2684, the appropriations bill that includes a nearly $1-billion cut
in NASA's budget, on Wednesday, September 8, the first day the House is
in session.
The next day the Senate Appropriations Committee subcommittee that
deals with the Departments of Veterans Affairs, Housing and Urban
Development, and other independent agencies like NASA, was expected to
take action on the Senate version of the NASA budget. However, late
reports indicate that the markup session has been delayed.
While there are expected to be some efforts on the House floor to
restore some of the "devastating" cuts in the NASA budget, the Senate
subcommittee is expected to consider a similar cut in the NASA budget.
Sources report that Senator Christopher Bond (R-MO), chairman of the
subcommittee, has received little feedback from NASA and others on the
budget has no plans to meet with NASA or other officials regarding the
proposed cuts.
Public outcry on the cuts, however, has not diminished in the month
since the House Appropriations committee originally approved a $1.3
billion cut in NASA's 2000 budget, then restored $400 million in full
committee, largely in the hard-hit space sciences.
The science budget, though, is still in danger of major cuts. "The
House VA-HUD and Independent Agencies Subcommittee has recommended
gutting our nation's space science infrastructure", said JPL's Don
Yeomans, chairman of the American Astronomical Society's Division for
Planetary Sciences. "Their recommendation will deal a major blow to our
nation's leadership in space exploration from which we will not soon
recover."
NASA does have some support from the White House, where officials said
last week that President Clinton would consider vetoing any
appropriations bill that contains significant cuts in NASA's budget.
However, Congressmen fighting to restore NASA's budget will have to
work against two recent General Accounting Office reports. One stated
that a lack of contingency planning for station assembly and a high
cost overrun by Boeing, the station's prime contractor, were major
problems. The other noted that NASA's estimates of the cost to operate
the station once completed may not include all costs incurred, such as
the true cost of shuttle flights and contributions by international
partners.
There reports may be used as ammunition by space station opponents,
who see the proposed cuts as an opportunity to kill the space station
and use the funds to restore money to space science and other NASA
projects hit by cuts.
Copyright 1999, SpaceViews
===============
(2) MAROCCAN METEORITE FOUND TO CONTAIN WATER
>From Andrew Yee <ayee@nova.astro.utorontodot ca>
>From HOUSTON CHRONICLE, 6 September 1999
[http://www.chron.com/content/interactive/space/astronomy/news/1999/solarsys/990
907.html]
Monday, September 6, 1999, 10:33 p.m. CDT
Moroccan meteorite found to contain water
By ERIC BERGER
NASA scientists have found water preserved from the birth of our solar
system in a second meteorite, suggesting that it may be common in the
space rocks that fall to Earth.
A meteorite that fell in West Texas in 1998 created a splash last month
when researchers announced that it contained water, probably a remnant
of the solar system's fiery beginning and a possible clue to how the
sun and planets formed.
Tiny droplets of water about one-tenth the width of a human hair were
found in what was essentially purple table salt. Similar
water-containing salt crystals were recently found in a meteorite that
fell in Morocco in August 1998.
After finding water the first time, scientists were unsure whether
water was common in meteorites or if their find was an aberration.
"This suggests that it's fairly common," said Michael Zolensky, a NASA
researcher who found water in both meteorites. "I bet you that it's
going to be found to be a fairly common kind of phenomenon."
Zolensky said he announced the finding of water in the Moroccan
meteorite at a conference in South Africa last month.
Zolensky and his colleagues studied about a 1-pound chunk of the
so-called Zag meteorite, a 300-pound rock that broke into pieces when
it struck a remote area of Morocco.
The key, he said, is getting the specimens into a sealed lab as quickly
as possible. The Monahans meteorite was taken to a Johnson Space Center
laboratory within two days of impact. Zolensky said he got the Zag
meteorite from a dealer who had picked it up almost immediately.
The salt, or sodium chloride in which the water is trapped, is easily
washed out of a meteorite, even by a light rain. Scientists have
determined the water's age by dating the salt crystals back 4.5 billion
years.
Only two pieces of the Monahans meteorite were found, one of which is
preserved in a West Texas museum while the other one sold over the
Internet to a collector for $23,000.
At a gem show last weekend in Houston there was a buzz about the Zag
rocks, of which there are many pieces.
Dealer Jim Kunetka said the Zag meteorite was the most exciting piece
he owned.
"Zag was a fairly large chunk, and when they cut it open, they found
crystals," he said.
Word has slowly been spreading over the Internet, too, although it's
not widely known that the Zag rock also contains water.
On Mike Martinez's Web site, MARE Meteoritics, he is selling the Zag
meteorite for $5.50 per gram.
"The dealer that I traded for this said a researcher from NASA was
buying up pieces from him and seemed really excited about it. Why? I am
not sure," Martinez wrote.
Pieces of the Zag meteorite were also on sale at Web-based auction
sites such as ebay.com .
Zolensky said more people bidding for meteorites will mean that more
people will chase meteorites. That will help researchers get their
hands on more specimens soon after impact.
"Historically, it's been very difficult to get them pretty quickly," he
said.
Copyright 1999 Houston Chronicle
===================
(4) NEAR ENCOUNTER WITH ASTEROID 253 MATHILDE
J. Veverka*), P. Thomas, A. Harch, B. Clark, J.F. Bell, B. Carcich,
J. Joseph, S. Murchie, N. Izenberg, C. Chapman, W. Merline, M. Malin,
L. McFadden, M. Robinson: NEAR encounter with asteroid 253 Mathilde:
Overview. ICARUS, 1999, Vol.140, No.1, pp.3-16
*) CORNELL UNIV,DEPT ASTRON,SPACE SCI BLDG,ITHACA,NY,14853
On June 27, 1997, the NEAR spacecraft carried out the first-ever
encounter with a C-type asteroid, flying by 253 Mathilde at a distance
of 1212 km, We summarize findings derived from 330 images obtained by
NEAR's MSI camera which cover about 60% of the surface of the asteroid.
The highest resolution achieved was about 160 m/pixel, Mathilde is a
low-reflectance object (geometric albedo = 0.047) with principal
diameters of 66 x 48 x 44 km, The mean radius of 26.4 +/- 1.3 km is
somewhat smaller than the value of 30 km suggested by previous
telescopic data. Mathilde's surface morphology is dominated by large
craters, at least four of which have diameters comparable to the radius
of Mathilde. The two largest, Ishikari and Karoo, have diameters of 29.3
and 33.4 km, respectively. No evidence of layering is exposed in the
crater walls, but suggestions of downslope movement are present. The
surface density of craters in the diameter range from 0.5 to 5 km is
close to equilibrium saturation, a situation in which as many craters
are being destroyed as are being produced. Observed depth-to-diameter
ratios for craters in this size range are close to those observed on
the lunar surface. A disruption lifetime of about 4 billion years has
been estimated for Mathilde. Based on the mass determination obtained
from Doppler tracking (D. K. Yeomans et al., 1997, Science 278,
2106-2109) and the volume derived from MSI images, the average density
of Mathilde is remarkably low: 1.3 +/- 0.3 g/cm(3), a value consistent
with a rubble pile structure for the interior. Assuming that Mathilde's
rock type is similar to that found in CM meteorites, the porosity of
the interior must be some 50%. Shock and seismic disturbances
associated with major impacts are expected to be transmitted very
poorly by Mathilde's underdense interior, a fact which may explain the
remarkable degree to which surface morphology and topography have been
preserved in spite of later major collisional events, Except for the
lower geometric albedo (0.047 +/- 0.005), the photometric properties of
Mathilde are closely similar to those of Phobos, The surface is
extremely homogeneous in terms of both color or albedo: specifically,
no color or albedo variations associated with craters have been
identified. (C) 1999 Academic Press.
=============
(5) MATHILDE: SIZE, SHAPE AND GEOLOGY
P.C. Thomas*), J. Veverka, J.F. Bell, B.E. Clark, B. Carcich, J.
Joseph, M. Robinson, L.A. McFadden, M.C. Malin, C.R. Chapman, W.
Merline, S. Murchie: Mathilde: Size, shape, and geology. ICARUS, 1999,
Vol.140, No.1, pp.17-27
*) CORNELL UNIV,DEPT ASTRON,ITHACA,NY,14853
The Near Earth Asteroid Rendezvous (NEAR) spacecraft images of C-type
asteroid Mathilde show it to have a mean radius of 26.5 +/- 1.3 km, The
asteroid is geologically distinguished by its low mean density (1.3 +/-
0.2 g cm(-3)) and by at least four craters with diameters equal to or
greater than Mathilde's mean radius, The large craters and their
unremarkable appearance suggest formation without significant damage to
the asteroid outside the final crater volume and indicates the ability
of at least this type of asteroid to survive very large impacts without
disruption. There are suggestions of structures such as faults or
layers. Preservation of such structures would imply that objects that
are poor transmitters of impact seismic energy can still maintain some
mechanical fabric, and their surface exposure may imply inefficient
retention of ejecta from large craters. (C) 1999 Academic Press.
==============
(8) THE COLLISIONAL HISTORY OF MATHILDE
D.R. Davis: The collisional history of asteroid 253 Mathilde. ICARUS,
1999, Vol.140, No.1, pp.49-52
*) SJI,PLANETARY SCI INST,620 N 6TH AVE,TUCSON,AZ,85705
Asteroid 253 Mathilde is found to have a collisional lifetime of
approximately 4 billion years, essentially indistinguishable from the
age of the Solar System. However, uncertainties in our knowledge of
collisional physics of large bodies and the number of small asteroids
could allow an age as young as 2 billion years. This result is
consistent with general asteroid collisional evolution studies which
show that a Mathilde-sized asteroid has about equal probability of
being either an eroded primordial body or a more recently produced
collisional fragment from a larger parent body. Assuming a weak, porous
structure for Mathilde, projectiles 0.7-3.0 km in diameter are needed
to form the largest craters on Mathilde, significantly smaller than the
4- to 5-km projectile needed to fragment and disperse the asteroid. Ifa
3-km-diameter projectile is needed to form the largest crater, then
this collision could have despun Mathilde if it was initially a more
rapid rotator. If a smaller, < 1-km-diameter, projectile was
responsible for the largest crater, then it would likely have delivered
an angular momentum comparable to the present angular momentum of
Mathilde, too small to significantly despin the asteroid. (C) 1999
Academic Press.
==============
(9) NEAR PHOTOMETRY OF MATHILDE
B.E. Clark*), J. Veverka, P. Helfenstein, P.C. Thomas, J.F. Bell, A.
Harch, M.S. Robinson, S.L. Murchie, L.A. McFadden, C.R. Chapman: NEAR
photometry of asteroid 253 Mathilde. ICARUS, 1999, Vol.140, No.1,
pp.53-65
*) CORNELL UNIV,DEPT ASTRON,ITHACA,NY,14853
NEAR's Multispectral Imager (MSI) recorded over 300 images of asteroid
253 Mathilde during a flyby on June 27, 1997, Images were acquired at
0.70 mu m at solar phase angles from 40 degrees to 136 degrees. These
data, combined with telescopic observations at phase angles from 1
degrees to 16 degrees were used to derive a photometric model for
Mathilde, The photometric properties of Mathilde were then compared
with those of similar small bodies. We find that: (1) Mathilde has a
geometric albedo of 0.047 +/- 0.005 at 0.55 mu m, making it the darkest
minor planet yet observed by spacecraft. (2) Mathilde is remarkably
homogeneous in reflectance across the surface. Normal reflectance
ranges from 0.041 to 0.053, a distribution at the low end of the range
of reflectance measurements of carbonaceous chondrites (0.03-0.11) and
in the middle of the range of albedo measurements of C-type asteroids
(0.03-0.06), (3) Typical reflectance contrasts on Mathilde occur at the
level of +/-6% from the mean, as compared to Phobos which exhibits
variation at the level of +/-20% from the mean. (4) As a whole,
Mathilde is more backscattering than Phobos, and Mathilde may have a
less porous regolith or a different distribution of regolith grain
sizes than Phobos. (C) 1999 Academic Press.
=============
(10) THE MULTISPECTRAL IMAGER ON NEAR
S. Murchie*), M. Robinson, S.E. Hawkins, A. Harch, P. Helfenstein,
P. Thomas, K. Peacock, W. Owen, G. Heyler, P. Murphy,
E.H. Darlington, A. Keeney, R. Gold, B. Clark, N. Izenberg,
J.F. Bell, W. Merline, J. Veverka: Inflight calibration of the NEAR
multispectral imager. ICARUS, 1999, Vol.140, No.1, pp.66-91
*) JOHNS HOPKINS UNIV,APPL PHYS LAB,JOHNS HOPKINS RD,LAUREL,MD,20723
The multispectral imager on the Near-Earth Asteroid Rendezvous
spacecraft has been subjected to a comprehensive series of inflight
tests to validate its radiometric characteristics measured onground and
to characterize instrument stability, pointing, geometric distortion,
coalignment with other instruments, and light-scattering
characteristics under flight conditions. The results of these tests,
described herein, support the conversion of images of 253 Mathilde and
433 Eros into scientifically valid products with known geometric and
radiometric characteristics. Key results include stability of dark
current during cruise to within 1 data number; stability of the flat
field to within the limits of inflight detectability; absolute
radiometric accuracy of similar to 5%, with no evident systematic
change with time; validation of the focal length with an inflight
measurement of 166.85 mm, compared to 167.0 +/- 0.2 mm derived
onground; measurement of coalignment with the near-infrared
spectrometer under flight conditions; and quantification of the
intensity and distribution of scattered light. (C) 1999 Academic Press.
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