PLEASE NOTE:
*
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.utoronto.ca>
(3) PERTH OBSERVATORY TO FOLLOW-UP NEOS
Michael Paine <mpaine@tpgi.com.au>
(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
(6) CRATERING ON MATHILDE
C.R. Chapman et al., SW RES INSTITUTE
(7) GIANT CRATERS ON MATHILDE
A.F. Cheng & O.S. Barnouin Jha, JOHNS
HOPKINS 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.utoronto.ca>
From HOUSTON CHRONICLE, 6 September 1999
[http://www.chron.com/content/interactive/space/astronomy/news/1999/solarsys/990907.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
================
(3) PERTH OBSERVATORY TO FOLLOW-UP NEOs
From Michael Paine <mpaine@tpgi.com.au>
Dear Benny
More news from Australia.
Regards
Michael Paine
http://www.abc.net.au/news/science/space/1999/09/item19990902110122_1.ht
Observatory devises new program to monitor space objects
There is concern that three years after the Australian Government
axed
a program to detect near earth objects, there is still no
comparable
project in the southern hemisphere.
Many research scientists and astronomers agree it is inevitable
that the
earth will be hit by a major asteroid and it is just a matter of
when.
Government astronomer James Biggs says the Perth Observatory is
devising
a program to monitor objects that have already been detected.
Dr Biggs says it is hoped that within six months the observatory
will be
able to track up to 40 positions a night.
But he says it is important that a detection system be set up to
avert
potential disasters.
"No one has been actually known to die from a collision from
outer
space, but the reason is it's a very low probability event, but a
very
high consequence if a one kilometre asteroid hits the
earth," Dr Biggs
said.
"It's going to be a major catastrophe, it will dwarf any of
the
earthquakes and what have you that we've experienced of
late."
Copyright 1999, ABC
PS The previous item, mentioned by Robert Clements is at
http://www.abc.net.au/news/science/space/1999/09/item19990906144940_1.htm
The Australian National University and University of Arizona are
jointly
funding (with help from NASA, I understand) a renewed NEO search
from
Siding Side by Rob McNaught. It is a welcome start and a very
good
example of international cooperation that governments should
follow!
===================
(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.
==============
(6) CRATERING ON MATHILDE
C.R. Chapman*), W.J. Merline, P. Thomas: Cratering on Mathilde.
ICARUS,
1999, Vol.140, No.1, pp.28-33
*) SW RES INST,SUITE 426,1050 WALNUT CREEK ST,BOULDER,CO,80302
Crater populations on Mathilde are assessed from NEAR flyby
images.
Small to intermediate-sized craters (1/2 to 5 km diameter)
approach
saturation equilibrium spatial densities and exhibit a range of
degradation states similar to the crater populations on Ida. They
probably represent a population in quasi-equilibrium between the
creation and the destruction of craters caused by saturated
impacts on
Mathilde. Very large craters, with diameters approaching or
exceeding
the average radius of Mathilde itself, dominate the shape of
Mathilde
and represent a uniquely high spatial density of craters on a
planetary
surface. Formation of these large craters were remarkably
ineffective
in modifying, let alone destroying, preexisting topography. We
speculate that Mathilde's retention of so many large, relatively
wed-preserved craters may be due to its bulk material properties
and/or
rubble-pile internal structure. The overall crater populations on
Mathilde are consistent with (although do not uniquely require)
the
same production function (i.e., same projectile power-law size
distribution) observed in the cratering records of the Moon,
Gaspra,
and (apparently) Ida. (C) 1999 Academic Press.
==============
(7) GIANT CRATERS ON MATHILDE
A.F. Cheng*), O.S. Barnouin Jha: Giant craters on Mathilde.
ICARUS,
1999, Vol.140, No.1, pp.34-48
*) JOHNS HOPKINS UNIV,APPL PHYS LAB,JOHNS HOPKINS
RD,LAUREL,MD,20723
Mathilde possesses at least five giant craters, where crater
diameters
are comparable to the mean radius of the body. Initially, it
seems
remarkable that this asteroid survived such an onslaught of
impacts
without disrupting. We consider implications of giant cratering
on
Mathilde, including effects of oblique impacts. Experimental
databases
and theory indicate that oblique impacts are (1) less likely to
disrupt
a target, (2) produce less ejecta relative to a normal impact,
and (3)
most often do not generate elongated craters. Moreover, oblique
impacts
reduce crater sizes and ejecta volumes particularly in the case
of
giant craters, where projectile fragments can miss the target.
The
morphology of giant craters on Mathilde and the lack of obvious
ejecta
are consistent with formation by oblique impacts,which could help
explain why Mathilde survived. The composition and low density of
Mathilde probably indicate a porous and volatile-rich body.
Target
porosity attenuates shock waves and enhances survival without
catastrophic disruption. It is not surprising that several giant
craters can be formed on a body without disrupting it. For a
realistic
projectile population, the probability of making a giant crater
on
Mathilde is 2.1 to 2.6 times greater than the probability of
disruption. The probability of Mathilde surviving the formation
of five giant craters is approximately 1 in 5 to 1 in 7.
(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.
----------------------------------------
THE CAMBRIDGE-CONFERENCE NETWORK (CCNet)
----------------------------------------
The CCNet is a scholarly electronic network. To
subscribe/unsubscribe,
please contact the moderator Benny J Peiser <b.j.peiser@livjm.ac.uk>.
Information circulated on this network is for scholarly and
educational use only. The attached information may not be copied
or
reproduced for any other purposes without prior permission of the
copyright holders. The fully indexed archive of the CCNet, from
February 1997 on, can be found at http://abob.libs.uga.edu/bobk/cccmenu.html