PLEASE NOTE:
*
CCNet DIGEST, 1 October 1998
----------------------------------------------
(1) TREMENDOUS GAMMA-RAY FLARE BLASTS EARTH
NASANews@hq.nasa.gov
(2) SPACE ELEVATOR
Scott Manley <spm@star.arm.ac.uk>
(3) METEORITE PICTURE?
Paolo Farinella <paolof@keplero.dm.unipi.it>
(4) FIRST GRADUATE PROGRAMME IN ASTROBIOLOGY
Andrew Yee <ayee@nova.astro.utoronto.ca>
(5) ASTEROID 4 VESTA
A. Ghosh & H.Y. McSween, UNIVERSITY
OF TENNESSEE
(6) THE CHANGING SPECTRUM OF VESTA
A.L. Cochran*) & F.
Vilas, UNIVERSITY OF TEXAS
(7) ANALYSING CENTAURS
J.K. Davies et al., JOINT ASTRONOMY CTR
(8) COMETARY SODIUM IN HALE-BOPP
M.E. Brown et al., CALTECH
(9) THE DEATH OF COMET TABUR 1996 Q1
M. Fulle et al., ASTRONOMICAL
OBSERVATORY TRIESTE
(10) RADAR DETECTABILITY OF A SUBSURFACE OCEAN ON EUROPA
C.F. Chyba*), S.J.
Ostro, B.C. Edwards, SETI INSTITUTE
(11) DYNAMICS OF COSMIC DUST NEAR THE SUN
A. Krivov et al., MAX
PLANCK INSTITUTE
(12) SIZE & ORBIT DEPENDENT TRENDS IN THE REFLECTANCE COLORS
OF
EARTH-APPROACHING
ASTEROIDS
D.L. Rabinowitz,
CALTECH, JET PROP LAB
=========================
(1) TREMENDOUS GAMMA-RAY FLARE BLASTS EARTH
From NASANews@hq.nasa.gov
Donald Savage
Headquarters, Washington,
DC
Sept. 29, 1998
(Phone: 202/358-1547)
Tim Tyson
Marshall Space Flight Center, Huntsville, AL
(Phone: 256/544-0994)
RELEASE: 98-172
TREMENDOUS GAMMA-RAY FLARE BLASTS EARTH
An intense wave of gamma rays, emanating from a catastrophic
magnetic flare on a mysterious star 20,000 light years away,
struck the Earth's atmosphere on August 27, 1998, providing
important clues about some of the most unusual stars in the
Universe. Scientists said the gamma radiation posed no
health
risk to humans.
The wave hit the night side of the Earth
and ionized (or
knocked electrons out of) the atoms in the upper atmosphere to a
level usually seen only during daytime. This astonishing
blast of
ionization was detected by Prof. Umran Inan of Stanford
University. "It is extremely rare for an event
occurring outside
the solar system to have any measurable effect on the
Earth," Inan
said. It was so powerful that it blasted sensitive
detectors to
maximum or off-scale on at least seven scientific spacecraft in
Earth orbit and around the solar system.
The wave of radiation
emanated from a newly discovered type
of star called a magnetar. Magnetars are dense balls of
super-
heavy matter, no larger than a city but weighing more than the
Sun. They have the greatest magnetic field known in the
Universe,
so intense that it powers a steady glow of X-rays from the star's
surface, often punctuated by brief, intense gamma-ray flashes,
and
occasionally by cataclysmic flares like the one observed on
August
27. Astronomers think that all these effects are caused by
an
out-of-control magnetic field -- a field capable of heating,
mixing, and sometimes cracking the star's rigid surface to bits.
In June a team of scientists
led by Dr. Chryssa Kouveliotou
of NASA's Marshall Space Flight Center in Huntsville, AL, used
NASA's Compton Gamma Ray Observatory to detect a series of about
50 flashes from the star, a type called a Soft Gamma Repeater
(SGR), known as "SGR1900+14" in the constellation
Aquila. During
the flashing episode, Kouveliotou's team, in collaboration with
Dr. Tod Strohmayer and his colleagues at NASA's Goddard Space
Flight Center, Greenbelt, MD, pointed sensitive X-ray detectors
aboard NASA's Rossi X-ray Timing Explorer satellite toward the
star. They found faint X-rays coming from the star, which
pulsed
regularly in intensity every 5.16 seconds.
These 5.16-second pulses already had been
detected in April,
when Dr. Kevin Hurley, University of California, Berkeley, aimed
the Japanese/NASA Advanced Satellite for Cosmology and
Astrophysics (ASCA) at the star. Comparisons of the ASCA
and RXTE
data showed that the X-ray pulses were gradually slowing down.
The finding implies that the
Soft Gamma Repeater has a
magnetic field about 800 trillion times stronger than Earth's
magnetic field, and about 100 times stronger than any found
anywhere in the Universe. Kouveliotou and her team had
earlier
found that another SGR was also a magnetar. This was
exactly what
Dr. Robert Duncan, University of Texas, Austin, and Dr.
Christopher Thompson, University of North Carolina, Chapel Hill,
predicted in 1992 when they originated the "magnetar"
theory.
Before the NASA team could
announce these conclusions,
SGR1900+14 emitted the tremendous flare of August 27, which was
observed by almost every spacecraft with a high-energy radiation
detector in space.
"Magnetars seem to
answer several mysteries about the
structure and evolution of stars," said Kouveliotou.
"We think
magnetars spend their first 10,000 years as Soft Gamma
Repeaters.
As they weaken with age and slow their rotation, they become
Anomalous X-ray Pulsars -- stars that do not have enough 'juice'
to flash anymore, but which emit a steady flow of X-rays for
perhaps another 30,000 years. After that, they fade to
black and
drift for eternity through the heavens. The absence of
observable
pulsars in some supernova remnants just means that the pulsar's
lights have gone out sooner than we expected."
A magnetar forms from the
explosion, or supernova, of a
very large, ordinary star. The star's heavy center
collapses
under its own gravity into a dense ball of super-compressed
matter
12 miles across. This "neutron star" consists
mostly of neutrons
in a dense fluid, but the outer layers solidify into a rigid
crust
of atoms about 1 mile deep, with a surface of iron.
Even with this solid crust,
a magnetar is incredibly
unstable. Almost unimaginable magnetic fields, about 800
trillion
times that of Earth's, cause the crust to crack and ripple in
powerful starquakes. The energy released in these explosive
starquakes streams out into space as intense flashes of gamma-
rays. In the August 27 flare, pure magnetic energy was also
released, as the star's entire crust was broken to bits.
"A magnet this strong
could erase the magnetic strip on the
credit cards in your wallet or pull the keys out of your pocket
from a distance halfway to the Moon," said Duncan.
========================
(2) SPACE ELEVATOR
From Scott Manley <spm@star.arm.ac.uk>
> I think it is time NOW to consider WHICH asteroid to use for
a future
> space elevator. Once the job is under way I guess it's too
late to
> reconsider. Even with the best of techniques it's bound to
be fraught
> with danger to extend a base by 'docking' another asteroid
to it.
There are plenty of candidates out there.
If we are to Follow Sir Arthur's suggestion of carbon Nanotubes
as an ideal
candidate for constructing an orbital tower then we can estimate
just how
large an asteroid is needed. I don't have the precise strength to
mass ratio
of carbon nanotube cables (if anyone has this and other physical
data please
tell me and I'll do this by more than dead reckoning) but some
guesstimation
for a tower capable of supporting a few million tons of tension
would require
a cable massing several million tons. If you have some magical
machine capable
of processing raw asteroid material and weaving the carbon into
perfect
nanotube cables then you can make do with an asteroid a few
hundred metres
across - with all the unused materials being used as the
counterweight.
Such a machine would have it's work cut out - growing
cables which are metres
across at very high speeds - if you wanted to build a 100,000km
tower in a
year you'd need to produce the cable at about 10 miles per hour,
24 hours a
day.
Then we have a minor problem with rotation, the completed
structure must
rotate at the same speed as earth, and the cable is by no means
rigid. As the
cable is extended if the parent body is rotating then the
tendency is for the
cable to begin to spiral round as the moment of inertia of the
whole system
changes. OTOH how do you go about spinning up a 100,000
kilometer cable - I'd
guess that the space engineering techniques required for this are
somewhat
more sophisticated than those required to park a small asteroid
in earth orbit.
It may one day be done - in fact the only reason I can see for
not creating
something like this would be if some radical new method of space
launching
became possible (e.g. good old sci-fi antigravity).
Think Big!
Scott Manley (aka Szyzyg)
=====================
(3) METEORITE PICTURE?
From Paolo Farinella <paolof@keplero.dm.unipi.it>
I have recently visited the Melk Monastery, not far from Vienna,
which has been
completely restored some a few years ago and is now a magnificent
(mainly early
XVIII century) complex of buildings, overtowering the village and
the Danube. In
the small museum inside the Monastery there are several XV
century paintings,
including one on the martyrdom of St. Catherine by a painter
called Hans Egkel.
Now, the painting shows a strange scene, with a kind of dark
opening in the sky
from which angels throw many stones toward the ground, aiming (I
suppose) at the
evil characters who are putting the Saint to death. Now, the
museum catalogue gives
`um 1470' for the painting's date, but I don't know which
uncertainty does `um'
imply. Might it be possible that the painting was done after the
1492 Ensisheim
fall, given the wide circulation of the news about it in central
Europe (see the
beautiful article by Marvin 1992, "Meteoritics" 27,
28-72)? Or that is there some
other connection to real meteorite falls? Please send me
any information or
suggestion on this matter at: paolof@dm.unipi.it
Paolo Farinella
=========================
(4) FIRST GRADUATE PROGRAMME IN ASTROBIOLOGY
From Andrew Yee <ayee@nova.astro.utoronto.ca>
University of Washington
FROM: Vince Stricherz, 206-935-7430, vinces@u.washington.edu
Contacts:
James Staley: (206) 543-0461 or (206) 543-6646 or e-mail at
jstaley@u.washington.edu.
Woodruff Sullivan: (206) 543-7773 or (206) 543-2888 or e-mail at
woody@astro.washington.edu.
Conway Leovy: (206) 543-4952 or e-mail at leovy@atmos.washington.edu.
Richard Gammon: (206) 543-1609 or (206) 543-4301 or e-mail at
gammon@u.washington.edu.
UW prepares for first graduate program in astrobiology to train
those who
will hunt for life in outer space
The University of Washington is poised to become the first
institution
anywhere to launch a doctoral program specifically geared to
train
scientists to search for life on celestial bodies such as Mars or
Europa,
an icy moon of Jupiter.
The astrobiology program will be financed by a 5-year, $2 million
grant
announced today by the National Science Foundation and
supplemented by
$500,000 from the university.
The highly interdisciplinary curriculum will involve 11 UW degree
programs --
Oceanography, Astronomy, Aeronautics & Astronautics,
Genetics, Chemistry,
Biochemistry, Microbiology, Atmospheric Sciences, Geophysics,
Geological
Sciences and History. Graduates can receive degrees in any of
those areas,
with an endorsement noting an emphasis in astrobiology.
The School of Oceanography will provide dedicated laboratory
space for
students to study organisms that live in extreme conditions.
Oceanography
professors John Delaney and Jody Deming and associate professor
John Baross
have closely studied organisms living in high-temperature,
high-pressure
conditions in ocean environments where little light penetrates.
Baross is
trying to relate the conditions in which those organisms live now
to
conditions when life began on Earth 3.5 billion years ago.
Two entities outside the university also are participating. The
Pacific
Northwest National Laboratory in Richland will offer students a
chance to
study microbial life in the subterranean basalt formations in
Eastern
Washington. ZymoGenetics Inc. of Seattle, a subsidiary of Novo
Nordisk A/S
of Denmark that is interested in enzymes from unusual bacteria,
is offering
summer internships so students can pursue that work.
"We recognize that there is a good possibility that life
exists in the solar
system outside Earth, but if that life does exist it would be
microbial, not
the higher forms," said James Staley, a UW microbiology
professor who is the
principal investigator for astrobiology.
Likely sites for such life are Mars, where there is evidence of
water, or
the ice-clad moon Europa.. The key to finding life in such
forbidding
environments is understanding how life exists in extreme
conditions on Earth
-- such as hot springs in Yellowstone National Park, undersea
vents where no
sunlight penetrates and temperatures reach several hundred
degrees, pools of
brine within polar sea ice, and volcanic basalt formations.
"We have microbial systems on Earth that are good models for
those on Mars
or Europa, and those systems are poorly studied," Staley
said. He added that
such life forms were the precursor to advanced life on Earth, so
their
presence on other planets could signal the eventual evolution of
advanced
life there, as well.
The idea for an astrobiology program grew out of a special
seminar, Planets
and Life, offered at the university in 1996 shortly after the
discovery of
planets orbiting nearby stars and an announcement that NASA
scientists
possibly had found microbial fossils inside a Martian rock. That
claim since
has drawn much scientific skepticism, but the success of the
seminar -- it
was attended by 30 graduate students and 20 post-doctoral
researchers and
faculty, and it sparked much campus excitement -- laid a
foundation for a
program in astrobiology.
Woodruff Sullivan, a UW astronomy professor and adjunct history
professor,
spearheaded the seminar and is an astrobiology co-investigator.
He expects
about a dozen students when the program begins in the fall
quarter of 1999.
But there is much to be done before then. Five new courses must
be designed
to complement existing courses that will be included in the
curriculum,
Sullivan said. Departments involved will have to devise different
ways of
testing and grading students involved in astrobiology, since an
astrobiology
student pursuing a degree in astronomy, for instance, will have
significantly different course demands than other astronomy
students.
One-third of astrobiology course work will be in areas not
closely related
to the student's home department, so an astronomy astrobiology
student might
spend a great deal of time studying microbiology.
Students also must take part in an annual workshop, three days of
work in
the field. It could be looking for microbes at the Hanford
Nuclear
Reservation, Sullivan said, or using an electron microscope to
study comet
dust. "Everyone will have to get their hands dirty."
Conway Leovy, a UW atmospheric sciences professor and also a
co-investigator,
expects the program to be an education for faculty members as
well as
students. But he said the students will be particularly
challenged as they
blaze a new path, and it will be some time before the first
doctoral degrees
in astrobiology are awarded.
"Astrobiology students will have to learn rigorously as well
as more broadly
than most other science graduate students," Leovy said.
"We probably can't
expect to see the fruits of our efforts in the form of many Ph.
D. graduates
sooner than five years from now."
Richard Gammon, who is a UW chemistry and oceanography professor
and also is
an adjunct professor of atmospheric sciences, helped write a
financing
proposal for the astrobiology degree program. He believes the
approach of
breaching traditional barriers between different science
disciplines was a
key to National Science Foundation support.
"All of these efforts are to meet the needs of students of
the future, who
are going to need training across fields," Gammon said.
The UW is one of 17 universities sharing in $40.5 million in
National
Science Foundation graduate education and research training
grants. For more
information about the NSF program, visit http://www.nsf.gov/igert/ on
the
World Wide Web.
================
(5) ASTEROID 4 VESTA
A. Ghosh & H.Y. McSween: A thermal model for the
differentiation of Asteroid 4
Vesta, based on radiogenic heating. ICARUS, 1998, Vol.134, No.2,
pp.187-206
UNIVERSITY OF TENNESSEE, DEPT GEOL SCI, KNOXVILLE, TN, 37996
A finite element code has been developed to model the thermal
history of Asteroid 4
Vesta. This is the first attempt to model the thermal history of
a differentiated
asteroid through core and crust formation and subsequent cooling
until geochemical
closure is attained. The results of the simulation are consistent
with
chronological measurements and other constraints provided by
cumulate and
noncumulate eucrites believed to have been derived from Vesta.
The work solves two
major problems with the hypothesis of heating by decay of Al-26,
an extinct
radionuclide, postulated to be a plausible heat source in the
early Solar System.
First, the model demonstrates that it is possible to keep the
mantle of Vesta hot
for similar to 100 Ma, thereby explaining the observed difference
in ages
between cumulate and noncumulate eucrites. Second, the simulation
offers a possible
explanation of why detectable excesses of Mg-26 (the decay
product of Al-26) are
not observed in noncumulate eucrites. The simulation draws a
model
chronology of Vesta and predicts times (relative to CAI
formation) for accretion at
2.85 Myr, core formation at 4.58 Myr, crust formation at 4.58
Myr, and geochemical
closure at similar to 100 Myr for a H-chondrite asteroidal bulk
composition. Decay
of Fe-60 is found to cause no perceptible difference in the
thermal history of
Vesta, even when sequestered into a central core. Although
chondritic xenoliths
have not been described in HED igneous lithologies, the thermal
model suggests the
possibility that a veneer of unmelted near-surface material
should remain. (C) 1998
Academic Press.
==================
(6) THE CHANGING SPECTRUM OF VESTA
A.L. Cochran*) & F. Vilas: The changing spectrum of Vesta:
Rotationally resolved
spectroscopy of pyroxene on the surface. ICARUS, 1998, Vol.134,
No.2, pp.207-212
*) UNIVERSITY OF TEXAS, AUSTIN,TX,78712
Moderate spectral resolution observations of the 505-nm Fe2+
pyroxene feature in
the reflectance spectrum of Vesta were acquired across the
complete surface of the
asteroid. The feature is consistently centered at 506.54 nm,
suggesting an augite
(high-calcium) composition. Variations in the equivalent width of
the feature
correlate with topographically high terrain on Vesta's surface,
and could be due to
the presence of another material (possibly olivine), or particle
size variations,
or both. (C) 1998 Academic Press.
==================
(7) ANALYSING CENTAURS
J.K. Davies*), N. McBride, S.L. Ellison, S.F. Green, D.R.
Ballantyne: Visible and
infrared photometry of six Centaurs. ICARUS, 1998, Vol.134, No.2,
pp.213-227
*) JOINT ASTRONOMY CTR, 660 N AOHOKU PL, HILO, HI, 96720
We present infrared (JHK) and visible (VRI) observations of the
Centaurs 2060
Chiron, 5145 Pholus, 7066 Nessus, 1995 DW2, 1995 GO, and 1997
CU26. These are
combined whenever possible to derive relative reflectance spectra
between 0.55 acid
2.2 mu m. The extreme visible to infrared color of Pholus found
in 1992
is confirmed, as is the redness of 7066 Nessus, We refine the
rotation period and
lightcurve of 1995 GO and resolve ambiguous determinations of its
V-R color. We
find that 1997 CU26 has V-JHK colors very similar to 1995 GO. Our
data imply
changes in the visible-IR color of 2060 Chiron with level of
cometary
activity and, aware of the difficulties of combining
nonsimultaneous data, we
comment on the likely reality of these. We find a wide range of
reflectances within
the Centaur population with no obvious correlations with
heliocentric distance. (C)
1998 Academic Press.
=================
(8) COMETARY SODIUM IN HALE-BOPP
M.E. Brown*), A.Z. Bouchez, H. Spinrad, A. Misch: Sodium
velocities and sources in
Hale-Bopp. ICARUS, 1998, Vol.134, No.2, pp.228-234
*) CALTECH, DIV GEOL & PLANETARY SCI, PASADENA, CA, 91125
We use spatially resolved high-resolution spectra of the 5890 and
5896 Angstrom
sodium D lines in the nuclear regions of Comet Hale-Bopp to
determine the sources
of cometary sodium. Comparison of the data to a Monte Carlo model
of sodium
dynamics suggests that the intensities and velocities of sodium
in HaleBopp can be
explained if 55% of the observed sodium is produced at the
nucleus, the remaining
45% is produced in an extended source, and the sodium is
accelerated by solar
radiation pressure. Observations of H2O+ in Hale-Bopp and
subsequent modeling of a
plasma-derived sodium source show that this source produces
sodium at higher
velocities than those observed; any contribution from such a
source must be small.
The combined nucleus and extended sources of sodium which fit our
data best would
create a sodium tail at a scale 100 times larger than that of
these observations
identical in morphology and velocity to that observed in
Hale-Bopp. (C) 1998
Academic Press.
===============
(9) THE DEATH OF COMET TABUR 1996 Q1
M. Fulle*), H. Mikuz, M. Nonino, S. Bosio: The death of comet
tabur 1996 Q1: The
tail without the comet. ICARUS, 1998, Vol.134, No.2, pp.235-248
*) ASTRONOMICAL OBSERVATORY TRIESTE, VIA TIEPOLO 11, I-34131
TRIESTE, ITALY
After a normal brightness increase, Comet Tabur 1996 Q1 showed a
remarkable
photometric behavior by rapidly fading in late October 1996. In
this paper we
analyze three CCD images of the remnant dust tail observed during
the fading of the
comet around perihelion and model them by means of the inverse
dust tail model (M.
Fulle, 1989, Astron. Astrophys. 217, 283-297). Assuming
hemispherical sunward dust
emission from the nucleus, satisfactory fits of the observed tail
brightness
distribution, turning axis and temporal fading allow us to
conclude that only dust
was observed, and contamination by gas and/or ions in the images
is negligible. The
model results include the temporal variation of the dust ejection
velocity, the
size distribution and dust mass loss rate. These values show a
strong correlation
during fading with strong drops consistent with the comet's
deactivation. In
particular, the slow increase of the dust mass loss rate in
September and its low
absolute values allow us to exclude outbursts preceding fading
and to exclude that
the disappearance was due to a complete nucleus disruption. In
this case, the
nucleus mean radius should have been no more than 350 m (for a
nucleus bulk density
of 100 kg m(-3)), which seems inconsistent with the observed
water loss rate. A
probable explanation of the comet fading is that the comet
nucleus deactivation was
due either to seasonal effects, putting all active areas in
permanently night
sides, or to the complete end of the whole nucleus surface
activity (possibly due
either to nucleus mantling or to the end of the ice reservoirs).
(C) 1998 Academic
Press.
==================
(10) RADAR DETECTABILITY OF A SUBSURFACE OCEAN ON EUROPA
C.F. Chyba*), S.J. Ostro, B.C. Edwards: Radar detectability of a
subsurface ocean
on Europa. ICARUS, 1998, Vol.134, No.2, pp.292-302
*) SETI INST, 2035 LANDINGS DR, MT VIEW, CA, 94043
A spacecraft in orbit around Jupiter's moon Europa can use ice
penetrating radar to
probe for a possible liquid water ocean beneath Europe's surface
ice and to
characterize other important subsurface structure. Consideration
of available
constraints on the properties of Europa's ice, possible
subsurface temperature
gradients, and possible impurities in the ice places an upper
limit of about 10 km
on the depth to which an ocean might be detectable with an
orbiting radar. (C)
1998 Academic Press.
=================
(11) DYNAMICS OF COSMIC DUST NEAR THE SUN
A. Krivov*), H. Kimura, I. Mann: Dynamics of dust near the sun.
ICARUS, 1998,
Vol.134, No.2, pp.311-327
*) MAX PLANCK INST AERON,KATLENBURG DUHM,GERMANY
In an effort to shed some light on the main features of the
innermost part of the
zodiacal cloud, the solar F-corona region, for which both
observational and
theoretical studies still give controversial results, we model
the dynamics and
physical evolution of dust grains at several solar radii (Ro)
from the Sun. We take
into account solar gravity, direct solar radiation pressure,
Poynting-Robertson
force, sublimation, and the Lorentz force. The latter is computed
on the base of
(i) the grain surface potentials derived from elaborate model
calculations and
shown to vary from +3 to +12 V; (ii) a multipole radial model of
the actual solar
magnetic field for the period 1976-1996. The dust particles are
assumed to be
porous and compact spherical grains, made of two types of
material: dielectric
(silicate) grains and absorbing (carbon) ones. Our main results
can be summarized
as follows. The decrease of grains' sizes and the dynamics of
particles in the
orbital plane are well described by taking into account solar
gravity and radiative
forces together with the sublimation process, being relatively
insensitive to the
electromagnetic force. The silicate grains typically move inward
in near-circular
spirals until intensive sublimation starts and they disappear at
heliocentric
distances from 2 to 3 R.. The carbon grains intensively sublimate
near 4R.. After
several radial oscillations, they are eventually ejected out as
beta-meteoroids,
when they approach a critical radius of approximate to 2.4 mu m
(for porous grains)
or approximate to 0.5 mu m (for solid spheres), which corresponds
to the radiation
pressure to solar gravity ratio beta equal to unity. The
orientation of the orbital
planes of the particles is dictated by the Lorentz force. Both
porous and compact
carbon grains possess high beta ratios and must be larger than
respectively 2.4 and
0.5 mu m to reach the near-solar region. For these sizes, the
Lorentz force is
relatively weak, comes basically from the dipole zonal component
of the field, and
leads to low-amplitude oscillations of orbital inclinations and a
precession of the
lines of nodes. The same behavior is predicted for silicate
porous (compact)
grains larger than 2 mu m (1 mu m) and 1 mu m (0.5 mu m) for the
periods of quiet
and active Sun, respectively. From these sizes to smaller ones,
the Lorentz force
effectively broadens the initial distribution of inclinations of
silicate grains.
Submicrometer-sized particles easily get in polar and retrograde
orbits well before
the evaporation. On the whole, we find that the dynamics of
near-solar grains
depend radically on their sizes, chemical composition, and
structure and, in cases
of relatively small dielectric grains, may be severely correlated
to the solar
activity cycle. (C) 1998 Academic Press.
===================
(12) SIZE & ORBIT DEPENDENT TRENDS IN THE REFLECTANCE COLORS
OF
EARTH-APPROACHING
ASTEROIDS
D.L. Rabinowitz: Size and orbit dependent trends in the
reflectance colors of
earth-approaching asteroids. ICARUS, 1998, Vol.134, No.2,
pp.342-346
CALTECH, JET PROP LAB, 4800 OAK GROVE DR, PASADENA, CA, 91109
New observations show that reflectance colors of
Earth-approaching asteroids depend
on their sizes and orbits. Most bodies larger than similar to 2
lan have reddish
colors similar to common main-belt asteroids of spectral type S.
Smaller
bodies, and those that may have recently migrated from the main
belt, have
relatively neutral spectra in the 0.5- to 0.8-mu m wavelength
range, These trends
may result from the action of ''space-weathering,'' recently
proposed to explain
similar spectral variations on the surfaces of S-type asteroids
and the disparity
between the colors of ordinary chondrite meteorites and their
probable main-belt
parents. (C) 1998 Academic Press.
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CCNet DEBATE, 1 October 1998
------------------------------------------------
SUPPOSE THEY HAD A MEDIA OPPORTUNITY AND NO ONE SHOWED UP;
THE DEEP SPACE 1 BRIEFING;
NEWT SMELLS BLOOD, BEGINS ATTACK ON NASA
From E.P. Grondine <epgrondine@hotmail.com>
Benny -
I went up to Washington last Tuesday to attend the briefing on
Deep Space 1. My day actually started the night before, as
I
gathered together some of my late mother's papers for the family
accountant, and I started my day Tuesday with a visit to his
office.
This matter delayed my arrival at the day's first NASA event,
which
was the donation by Dan Goldin of used computers from NASA to
Kramer
Junior High School. Kramer Junior High School is in
Anacostia,
one of the "bad sections of town", and I really have to
give Goldin
credit for being one of the few federal officials with guts
enough to go
there. When I arrived he was posing for a photo with the
best
students, and he was really enjoying it, and the kids were too.
It's sad no one saw it, as none of the mass media came out to the
presentation. Everyone seemed to be completely devoting
their entire
resources to the Tripp Affair.
I struck up a conversation with one Thomas Gore, who has been
working for years to keep area kids in the system. We
reflected on how
crack cocaine had devasted the neighborhood, and the sight of the
boarded up houses across from Kramer made me shudder. It
was not
how I remembered it; by the way, did I mention that I attended
Kramer Junior High?
Of course, while the neighborhood was a little rough then, it was
nowhere near the state it is in today, and Mr. Gore and I
reflected that
it had been the crack cocaine, starting about 1983-1984, that had
caused
the real decline. I also spoke with the principle of
Kramer, who was
bitter that while the Republican Congressmen and Starr would
spend $40
million investigating the President, they would not spend 4
dollars on
her kids.
I wouldn't normally bring this up. but I just want to put the
Deep
Space 1 funding numbers in a little perspective. Of course,
when the
next big one comes the folks in Anacostia will be just as dead as
the rest of us, unless we take steps now, so here goes...
The total cost of Deep Space 1 is estimated at $152.3 million
dollars. Of this $94.8 million dollars went to pre-launch
development, $43.5 million dollars for launch on a Boeing Delta
II
launcher, $10.3 million dollars will go for mission operations,
and
$3.7 million dollars for science. The Delta II is also
going to be used
to place in orbit a student Earth resources satellite, whose
images will
be delivered free daily over the internet, and which also has an
amateur
radio transponder, so NASA is really going to be getting a lot
out of
this one rocket launch.
What are the key points of Deep Space 1 in terms of planetary
defense? First, DS-1 is going to test a new optical system
capable both
of navigating it to asteroid 1992 KD (discovered by Eleanor Helin
-
congratulations Eleanor), as well as controling it during its
fly-by.
During the flight the optical system will calculate DS-1's
position by
examining which stars are obscured by the 250 asteroids in its
computer's database. As it approaches 1992 KD the same
system will
build a model of 1992 KD by combining images of the rotating
asteroid;
during fly-by it will take action by comparing information from
its CCDs
with the stored model. Pretty impressive stuff if it works!
This optical navigation system did not come from the military,
but
was developed by JPL itself. But it is heartening to note
that there
was co-operation between the military and JPL in the development
of the
probe, as BMDO contributed solar panels for DS-1, and the Air
Force's
Phillips Laboratory contributed the probe's multifunctional
structure.
So the technology tested will definetly be available for use for
planetary defense when it is needed.
Relative speed at closest encounter with 1992 KD is estimated at
15
kilometers per second, and the science array will be active for
around 1,000 seconds either side of this, for a total time of
around
2,000 seconds. The same camera that is used for navigation
will then be
taking multi-spectral images, and DS-1 is also equipped
with
ultra-violet and infra-red spectrometers. These should
return
excellent data on 1992 KD's composition, which is so important in
figueing out how to stop these things. As a bonus, it is
hoped that
DS-1 will then be able to continue on and get similar data from
both
asteroid Wilson-Herrington (suspected to be a comet transitioning
to an
asteroid) and Comet Borrelly.
I'm sorry I did not get this to the Conference earlier, but
Thursday Republican leader (and $4 million dollar friend of
Rupert
Murdoch) Newt Gingrich began his attack on NASA. Due to the
collapse of
Russia's economy Russia had been having trouble meeting its
commitments
for the International Space Station, and Newt had been sending
out his
colleagues to test the waters as to whether this could be used to
launch
an attack on President Clinton, and to further weaken Clinton by
taking
away this important tie to Russia.
The trigger for Newt's attack was news that has been trickling
out
of NASA that the director of the Russian Space Agency, Yuri
Koptev, had
promised to give Kazakhstan $115 million dollars a year for the
use of
the Baykonur launch facility, and now Koptev was trying to get
this
money from NASA to pay them.
Newt's attack was so out of touch with reality that it is
difficult
to describe it, but I'll try. Newt accused NASA of slowing
down the US
space program, and claimed that over the last 30 years the US
would have
settled the Moon if NASA had just not gotten in the way.
Newt called the International Space Station an absolute disaster,
which
he blamed entirely on Clinton.
Now I'm sure that everybody on this list is perfectly aware that
Earth impactors are not going to be found and stopped by private
efforts. Maybe some of the more delusional space
fantasists, think
this, but I'm sure that no one on this list shares in their
insanity.
We all know that NASA is essential if we are going to have a
planetary
defense.
So what I'd like everyone on the list to consider what they can
do
to stop Newt now, and to stop him cold, before he can do any more
damage. The way I see it, the first step in planetary
defense is no
longer getting NASA to devote more resources to the problem, but
instead
to preserve NASA itself.
Best wishes -
Ed