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(meteorobs) Excerpts from "CCNet 42/2001 - 16 March 2001"
------- Forwarded Message
From: Peiser Benny <B.J.Peiser@livjm.acdot uk>
To: cambridge-conference <cambridge-conference@livjm.acdot uk>
Subject: CCNet, 16 March 2001
Date: Fri, 16 Mar 2001 10:13:58 -0000
CCNet 42/2001 - 16 March 2001
-----------------------------
[...]
(2) A NUTTY EFFECT ON EROS
Ron Baalke <baalke@jpl.nasadot gov>
(3) ALL ABOARD THE METEOR EXPRESS OF LIFE
SpaceDaily, 16 March 2001
[...]
(6) UK NATIONAL ASTRONOMY MEETING 2001 AT THE UNIVERSITY OF CAMBRIDGE
Jacqueline Mitton <aco01@dial.pipex.com>
(7) METEOR SHOWER [sic] OVER THE CHANNEL?
Benny J Peiser <b.j.peiser@livjm.acdot uk>
[...]
* ABSTRACTS *
(11) UPDATED IMPACT PROBABILITIES OF MINOR BODY POPULATIONS
Dell'Oro A, et al.
(12) ON THE ATMOSPHERIC FRAGMENTATION OF SMALL ASTEROIDS
Foschini L
[...]
(16) SIZE DETERMINATION OF THE CENTAUR CHARIKLO
Altenhoff WJ, et al.
========================================================================
(2) A NUTTY EFFECT ON EROS
>From Ron Baalke <baalke@jpl.nasadot gov>
Astronomy.com, 15 March 2001
http://www2.astronomy.com/Content/Dynamic/Articles/000/000/000/352xcmcd.asp
A report from this year's Lunar and Planetary Science Conference in Houston
on the mysterious surface of the now-famous asteroid.
by Vanessa Thomas
High-resolution images of asteroid 433 Eros taken by the Near Earth Asteroid
Rendezvous (NEAR) Shoemaker spacecraft reveal a surface strewn with large
boulders. Where these boulders came from is an interesting topic for debate.
At the Lunar and Planetary Science Conference in Houston on Tuesday, a group
of scientists suggested that these boulders might have been shaken to the
surface from inside Eros.
A logical explanation for the presence of these boulders is that they are
blocks of material ejected by impacts. If this is the case, planetary
scientists expect to see craters near boulder groupings, and do see this
association on another large asteroid, 243 Ida. On Eros, however, no such
correlation exists.
"When you look at the surface, you see all these blocks littering the
surface and there are very few craters," University of California (Santa
Cruz) planetary scientist Eric Asphaug pointed out on Tuesday. Either
something wiped out the craters, or some other mechanism transported these
boulders to their present positions on the surface.
At the conference, Asphaug described a problem common in the pharmaceutical
sciences. "Whenever you try to mix powders, they don't mix," he said. "They
segregate according to grain properties." Asphaug and his team think a
similar situation might be taking effect on Eros, "sifting" the largest
rocks to the surface.
Asphaug's group likens the process to shaking a can of mixed nuts. In a
typical can of mixed nuts, Brazil nuts are the largest. When the can is
shaken, the Brazil nuts eventually rise to the surface and the small peanuts
end up at the bottom. Repeated shaking of Eros caused by impacts could cause
the grains and rocks of the asteroid's regolith to sort themselves according
to size.
Like the Brazil nuts, Eros's large boulders rise to the top when the
asteroid is shaken by impacts, and like the peanuts, the fine grains of
Eros's regolith falls through the fractures, grooves, and other crevasses on
the asteroid's surface.
"Everything's undergoing random motions during shaking, and a small grain
can find its way underneath a big grain," Asphaug explained. But, he said,
the opposite will never happen. "The big grain's never going to find a big
enough hole to fall back into." Several small grains would have to all move
out of the way at the same time to allow room for a large grain to move
down. "So statistically, the big grain works its way to the top," Asphaug
concluded.
But how often would Eros need to be shaken to raise all of the boulders seen
on the surface? According to Asphaug's team, that statistic is hard to pin
down. They do know, however, that it is easier for material to move around
in a low-gravity environment. "Asteroids with very low gravity are more
prone to particle size segregation," Asphaug said. The "Brazil Nut Effect"
would have a more difficult time on a larger body such as Earth or the moon.
If Eros's boulders actually have been shaken to the surface like Brazil nuts
in a can, Asphaug's team suggests that scientists could predict the original
depth of the boulders. "You could make a prediction, if you were bold
enough, to say how deep the asteroid's regolith is by looking at the size
distribution of the crowded surface," Asphaug said. If this is the case, the
boulders sitting on Eros could provide a window to the secrets of the
asteroid's interior.
Copyright ) 1996-2001 Kalmbach Publishing Co.
========================================================================
(3) ALL ABOARD THE METEOR EXPRESS OF LIFE
>From SpaceDaily, 16 March 2001
http://www.spacedaily.com/news/life-01i.html
by Jeff Hecht
Houston - March 17, 2001
Don't worry about contact with aliens from other solar systems-they may be
our distant cousins. According to an American astronomer, there is a slim
chance that microbes could be carried from one solar system to another on
rocks blasted from terrestrial planets by asteroid impacts, spreading life
across the Galaxy.
"About one meteorite ejected from a planet belonging to our Solar System is
captured by another stellar system every 100 million years," Jay Melosh of
the University of Arizona told the Lunar and Planetary Science Conference in
Houston this week.
Although radiation would threaten stowaway microbes, Russell Vreeland of
West Chester University of Pennsylvania says it would be quite possible for
meteorites to carry well-protected organisms over interstellar distances.
In the 1970s, astronomers Fred Hoyle and Chandra Wickramasinghe put forward
the still controversial theory, dubbed "panspermia". This says that comets
bombarding the Earth brought the bacteria and viruses from interstellar
space that started life here 4 billion years ago, and continue to bring in
new biological material today. Melosh argues that alien organisms might also
come from a distant planet similar to our own.
He is part of a group that earlier showed microbes could hitch a ride on
meteorites travelling between planets in our Solar System (New Scientist, 15
January 2000, p 19). At the time, he didn't think any microbes could survive
the millions of years a meteorite would take to travel between stars.
That view changed, however, after Vreeland successfully cultured bacterial
spores from a 250-million-year-old salt deposit in New Mexico (New
Scientist, 21 October 2000, p 12). The longer survival time makes the
transfer of life conceivable, Melosh says.
Transfers between solar systems depend on gravitational interactions between
meteorites and other planets. As a starting point, Melosh considered rocks
blasted off the surface of Mars by impacts.
His simulations show that Jupiter can act as a slingshot, flinging roughly
500 kilograms of Martian rocks each year right out of our Solar System in
all directions. Their velocity averages 5 kilometres per second, so in a
million years they would travel about 17 light years-far enough to reach
nearby stars.
Most ejected meteorites would continue to drift in the interstellar void,
but a few would eventually pass near other planetary systems. "The
probability of direct capture by an Earth-sized planet is very, very tiny,"
says Melosh.
However, the gravity of a Jupiter-sized giant planet can capture meteorites
passing within a hundred million kilometres of it, if the two are moving at
similar velocities in the same direction. The meteorite would then fall into
an eccentric orbit about the star.
It is still far from certain whether the meteorite would go on to collide
with a terrestrial planet, and Melosh's calculations suggest that the
likelihood of such an event is low for a solar system like our own. The
chances would be higher, he says, if terrestrial planets orbited near to a
Jupiter-sized planet.
"The probabilities are pretty low," acknowledges Melosh. But they aren't
impossibilities, he adds. Wickramasinghe believes that his panspermia
theory, in which bacteria can drift on their own between solar systems,
propelled by radiation pressure, is a more likely scenario. "The only
advantage that you might have [with] huge chunks of rock [is that] the
interior is shielded totally from any damaging radiation," he says.
This article will appear in the March 17 edition of News Scientist
Copyright 2001, Space Daily
========================================================================
(6) UK NATIONAL ASTRONOMY MEETING 2001 AT THE UNIVERSITY OF CAMBRIDGE
>From Jacqueline Mitton <aco01@dial.pipex.com>
ROYAL ASTRONOMICAL SOCIETY PRESS NOTICE
Date: 15 March 2001 Ref. PN 01/08 (NAM2)
Issued by: RAS Press Officers
Peter Bond
Phone: +44 (0)1483 268672
Fax: +44 (0)1483 274047
E-mail: 100604.1111@compuserve.com
Dr Jacqueline Mitton [NB. Jacqueline Mitton not available 17 - 31 March]
Phone: +44 ((0)1223) 564914
Fax: +44 ((0)1223) 572892
E-mail: jmitton@dial.pipex.com
UK NATIONAL ASTRONOMY MEETING 2001
AT THE UNIVERSITY OF CAMBRIDGE
Between Tuesday 3rd and Friday 6th April about 300 professional astronomers
will gather in Cambridge for the National Astronomy Meeting (NAM), one of
the most important astronomy meetings held regularly in the UK which is
hosted this year by the University of Cambridge. The UK Solar Physics
Meeting will also take place in Cambridge in parallel with the NAM.
Media representatives are cordially invited and press room facilities will
be available from 8.30 a.m. on Tuesday 3rd April through to 12.30 p.m. on
Friday 6th April. Scientific sessions are in the Law Faculty Building and
the Lady Mitchell Hall on the University's Sidgwick Site.
To pre-register, contact Peter Bond but advance registration is not
essential. The main registration desk for the meeting will be in the Law
Faculty foyer. Media registration is free. Directions to the press room will
be posted from the registration area.
PRESS ROOM & CONTACT NUMBERS
The press room will be the Lyttleton Room, in nearby Selwyn College. The
phone numbers are:
(0)1223 313724
(0)1223 313754
(0)1223 315553
Press officers' mobile phones will be:
07770 386133 (Jacqueline Mitton) and 07711 213486 (Peter Bond).
The programme and more information about the NAM (including location maps)
can be found at
http://www.astdot cam.acdot uk/~nam2001/
Abstracts are expected to be available on this web site from 23rd March.
More on the UK Solar Physics Meeting can be found at
http://www.shef.acdot uk/~uksp01
THE CASE FOR HUMAN SPACEFLIGHT
A highlight of the week will be a one-day symposium on Thursday 5th April,
entitled 'The Scientific Case for Human Spaceflight'. It marks the 40th
anniversary of the first human space flight by Yuri Gagarin on 12 April
1961. NASA astronaut Jeff Hoffman is one of the speakers. The full programme
for the symposium can be found at
http://www.star.ucl.acdot uk/~iac/nam_space_meeting.html
TACKLING THE ASTEROID HAZARD
Dr Duncan Steel, author of the recent Time-Life book 'Target Earth' will
give a public lecture with the title 'The Spaceguard Project: Tackling the
Impact Hazard' on Thursday 5 April at 8.15 p.m. in the Lady Mitchell Hall.
FROM EARTH TO THE EDGE OF THE UNIVERSE
Topics to be covered in the science sessions include: extra-solar planets,
galaxies, black holes, X-rays from the universe, cosmology, star formation,
meteorites, first results from Cassini at Jupiter, astronomy from the
International Space Station, sunspots, future space missions and new
observatories. See the web site for details.
VISIT THE MULLARD RADIO ASTRONOMY OBSERVATORY
There will be an opportunity to visit the Mullard Radio Astronomy
Observatory at Lord's Bridge, just outside Cambridge, between 2.00 and 4.00
p.m. on the afternoon of Friday 6 April.
=============================================================================
(7) METEOR SHOWER OVER THE CHANNEL?
>From Benny J Peiser <b.j.peiser@livjm.acdot uk>
The press officer of the Royal Astronomical Society has had a couple of
enquiries by local papers in Kent and Bedfordshire about what appeared to be
unusually bright meteors reported by public during the evening of Tuesday 13
March. Kent coastguard was alerted as witnesses thought they were flares.
Reporters from the 'Bedfordshire on Sunday' were saying that they too have
had reports of bright lights falling from the sky on Tuesday evening.
=============
* ABSTRACTS *
=============
(11) UPDATED IMPACT PROBABILITIES OF MINOR BODY POPULATIONS
Dell'Oro A, Marzari F, Paolicchi P, Vanzani V: Updated collisional
probabilities of minor body populations ASTRONOMY AND ASTROPHYSICS 366: (3)
1053-1060 FEB 2001
The consistent increase in the discovery rate of new asteroids and Trans
Neptunian Objects (TNOs) in these last years has urged an update of the
values of intrinsic probability of collision and impact Velocity for some
minor body populations. With the statistical method of Dell'Oro & Paolicchi
(1998) we have recomputed tl-le values of impact probability and velocity
for Hilda asteroids, for Trojans vs. Short Period Comets (SPC), and for
TNOs. The algorithm of Dell'Oro and Paolicchi is particularly suited for the
task since it can account for resonant behaviour (Dell'Oro et al. 1998) and
for the clustering of the perihelion longitude of Main Belt asteroids and
Hildas, caused by the presence of a forced component in the eccentricity.
The Hilda population turns out to be well sampled ill the orbital parameter
space since no significant changes are found for the collision frequency
among Hildas, and of Hildas with Main Belt asteroids, although a much larger
sample of orbits has been used in our computations (232 objects) vs. the
smaller group used in previous computation by Dahlgren (1998) (40 objects).
We also computed the impact rate of SPCs vs. Trojans that turned out to be
an order of magnitude lower respect to the Trojans vs. Trojans impact rate.
The relative velocity is instead about 30% higher. Using reasonable
estimates of SPC and Trojan number densities, we find that approximately 1
every 100 collisions involving Trojans may be with all SPC. In the case of
TNOs there is a consistent discrepancy between our values of the collision
probability and impact speed, and those computed by Davis & Farinella
(1997). The consistent increase in the number of known TNOs (186 at present,
only 16 at the time of the Davis and Farinella's work) has led to a better
knowledge of their distribution in the phase space and, consequently, to
more reliable estimates of the collisional probability and impact velocity.
Addresses:
Dell'Oro A, Univ Pisa, Dipartimento Fis, Piazza Torricelli 2, I-56127 Pisa,
Italy.
Univ Pisa, Dipartimento Fis, I-56127 Pisa, Italy.
Univ Padua, Dipartimento Fis, I-35131 Padua, Italy.
Copyright ) 2001 Institute for Scientific Information
=============================================================================
(12) ON THE ATMOSPHERIC FRAGMENTATION OF SMALL ASTEROIDS
Foschini L: On the atmospheric fragmentation of small asteroids
ASTRONOMY AND ASTROPHYSICS 365: (3) 612-621 JAN 2001
It is known, from observational data recorded from airbursts, that small
asteroids breakup at dynamical pressures lower than their mechanical
strength. This means that actual theoretical models are inconsistent with
observations. In this paper, we present a detailed discussion about data
recorded from airbursts and about several theoretical models. We extend and
improve a theory previously outlined for the fragmentation of small
asteroids in the Earth atmosphere. The new condition for fragmentation is
given by the shock wave-turbulence interaction, which results in sudden
outburst of the dynamical pressure.
Addresses:
Foschini L, CNR, Ins TeSRE, Via Gobetti 101, I-40129 Bologna, Italy.
CNR, Ins TeSRE, I-40129 Bologna, Italy.
Copyright ) 2001 Institute for Scientific Information
=============================================================================
(16) SIZE DETERMINATION OF THE CENTAUR CHARIKLO
Altenhoff WJ, Menten KM, Bertoldi F: Size determination of the Centaur
Chariklo from millimeter-wavelength bolometer observations ASTRONOMY AND
ASTROPHYSICS 366: (2) L9-L12 FEB 2001
Using the Max-Planck Millimeter Bolometer Array (MAMBO) at the IRAM 30 m
telescope we detected emission at 250 GHz from the Centaur Chariklo (1997
CU26). The observed continuum flux density implies a photometric diameter.
of 273 km. The resulting geometric albedo is 0.055, somewhat higher than
expected from a comparison with mast of the other few Centaurs and cometary
nuclei for which such data are available.
Addresses:
Altenhoff WJ, Max Planck Inst Radioastron, Hugel 69, D-53121 Bonn, Germany.
Max Planck Inst Radioastron, D-53121 Bonn, Germany.
Copyright ) 2001 Institute for Scientific Information
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