CCNet 132/2000 - 14 December 2000

"The asteroid belt between Mars and Jupiter may not be alone in
harbouring debris left over from the formation of the planets. New
calculations hint there could be similar asteroid hoards associated
with planets nearer the Sun. This lends added urgency to scientists'
eager scrutiny of the belt once regarded as the trash heap of the solar
system, now deemed a potential source of rare minerals or of bodies on
a collision course with Earth."
     --Philip Ball, Nature, 12 December 2000

    Ron Baalke <>

    Andrew Yee <>

    Geochimica Et Cosmochimica Acta Vol. 64 (23) pp. 4049-4081

    NASA Astrobiology Institute, 12 December 2000

    Scientific American, January 2001

    Andrew Yee <>


    Ron Baalke <>

    G.H. Stokes et al.

     D. Vokrouhlicky & A. Milani

     H. Ishimoto


From Ron Baalke <>

From Nature Science Update, 12 December 2000

More asteroids caught in Trojan force traps

The asteroid belt between Mars and Jupiter may not be alone in harbouring
debris left over from the formation of the planets. New calculations hint
there could be similar asteroid hoards associated with planets nearer the
Sun. This lends added urgency to scientists' eager scrutiny of the belt once
regarded as the trash heap of the solar system, now deemed a potential
source of rare minerals or of bodies on a collision course with Earth.

Wyn Evans and Serge Tabachnik of the University of Oxford, UK, have worked
out that there are probably other asteroid pockets in the inner Solar
System, which are being shepherded by Mars, Earth, Venus and Mercury. And
the duo suggests where, when and how astrophysicists should look for them.

The asteroids associated with the giant planet Jupiter are known as 'the
Trojans'. They owe their existence to a peculiarity of gravitational
interactions. Isaac Newton showed in the seventeenth century how gravity
holds a planet in orbit around the Sun. But the equations to describe the
motion of three mutually gravitating bodies, rather than just two, are
fiendishly difficult to solve.

In the eighteenth century, the French mathematician Joseph Louis Lagrange
simplified things. He showed that if one of the bodies orbits around
another, like a planet around the Sun, a third small body can get trapped at
any of five specific points -- Lagrange points -- relative to the orbiting

In 1906, astrophysicists detected the first of Jupiter's Trojan asteroids at
one of its Lagrange points. Now, 470 Trojans are known and there may be as
many as 2,500, some with diameters that could exceed 15 kilometres.

Saturn too has some small moons captured at its Lagrange points. And in
1990, a Trojan-like asteroid called '5261 Eureka' was discovered on Mars'
orbit, showing that you don't have to be a giant planet to secure your own

But in the Monthly Notices of the Royal Astronomical Society 1,2, Evans and
Tabachnik ask: how many asteroids are associated with the inner planets, and
how easy would it be to spot them, given that they'd be proportionately
smaller than those of Jupiter?

These questions can only be answered through computer simulations of the
planetary motions. This involves scattering 'candidate Trojans' around the
orbits of the inner planets and then seeing whether the simulations trap
them at Lagrange points or send them hurtling off elsewhere.

The confidence in the results depends on sampling enough possibilities and
on running the simulations for long enough compared with the age of the
Solar System. Evans and Tabachnik ran their simulations to cover up to 100
million years -- ten times longer than most previous studies, but still
quite short relative to the Solar System's 4.6 billion-year age.

The simulations reveal that, like Mars, Venus and Earth can shepherd Trojans
at their Lagrange points. For Mercury, very few candidate Trojans survive in
the traps because the planet is small and has a rather unusual orbit.

Astrophysicists have already scanned the Lagrange points of Mars and Earth
and found nothing, aside from Eureka and one other martian Trojan. But Evans
and Tabachnik have used their results to propose optimal search strategies
that could be conducted with existing telescopes and might prove more

1. Tabachnik, S. A. & Evans, N. W. Asteroids in the inner solar system - I.
Existence. Monthly Notices of the Royal Astronomical Society 319, 63-79

2. Evans, N. W. & Tabachnik, S. A. Asteroids in the inner solar system - II.
Observable properties. Monthly Notices of the Royal Astronomical Society
319, 80-94 (2000).

Macmillan Magazines Ltd 2000 - NATURE NEWS SERVICE


From Andrew Yee <>

Iowa State University

Dennis Bazylinski, Microbiology, (515) 294-2561
Teddi Barron, News Service, (515) 294-4778



AMES, Iowa -- An Iowa State University professor is part of a research team
that has found compelling evidence that Mars once supported primitive life.

The researchers discovered evidence of bacteria in a Martian meteorite. Tiny
magnetite crystals -- so called magnetofossils -- embedded in the meteorite
were confirmed to be the type produced only by a biological process unique
to magnetotactic bacteria.

Dennis Bazylinski, associate professor of microbiology, was one of nine
researchers conducting the four-year investigation, which was funded by
NASA's Astrobiology Institute. A report of their research is in the December
issue of the scientific journal, "Geochimica et Cosmochimica Acta."
[ ]

"Finding these type of magnetic crystals in any material from another planet
is an amazing and important finding," said Bazylinski. He leads one of the
few labs capable of culturing these magnet-producing bacteria, which are
common in many freshwater and marine environments on Earth.

The researchers studied the magnetite crystals that were located in
carbonates in the Martian meteorite. The 4.5 billion year-old meteorite was
found in Antarctica in 1984. Earlier research has confirmed that the
carbonates formed on Mars, signaling that the magnetite crystals also were
formed on Mars.

Magnetite crystals produced by magnetotactic bacteria are chemically pure
and generally defect free and have a distinctive size and shape. Their
properties are so unusual that they have only been seen in magnetite
crystals produced through biological processes by organisms.

The researchers discovered that about one-fourth of the magnetites in the
meteorite are identical to the magnetites produced by a strain of
magnetotactic bacteria called MV-1, which have been isolated and studied
extensively by Bazylinski.

"There is currently no known chemical means of producing these magnetite
crystals with their unique morphologies," Bazylinski said. "The significance
to astrobiology and geobiology is that many scientists have been searching
for 'biomarkers' for life, that is, chemical, isotopic, and/or mineral
indications that life was present, either in extreme habitats or in ancient
materials on Earth and, of course, now in extraterrestrial materials. The
need for biomarkers is obvious and these magnetite crystals might prove to
be an excellent biomarker."

Since the team began the research in 1996, observations from the Mars Global
Surveyor have indicated that Mars had a strong magnetic field at about time
that the carbonate containing the unique magnetites was formed.

"Now we are trying to answer the question of whether magnetotactic bacteria
could have actually lived on Mars," Bazylinski said. "And we have found
certain aspects of their metabolism which suggest that they might have been
able to do so."

The journal "Science" recently published research showing evidence of
widespread sediment layers on Mars, which the researchers interpret to be
the product of many lakes. Because these lakes may have provided a habitat
for magnetotactic bacteria, this finding supports the possibility that the
bacteria may have existed on Mars, Bazylinski said.

In addition to Bazylinski, the scientists are Kathie Thomas-Keprta, Simon
Clemett, and Susan Wentworth, Lockheed Martin at Johnson Space Center; David
McKay and Everett Gibson, NASA/JSC; Joseph Kirschvink, California Institute
of Technology; H. Vali, McGill University, Montreal; and Christopher
Romanek, Savannah River Ecology Laboratory.

Note to Editors: A jpeg photo of Bazylinksi is available by e-mailing .


From Geochimica Et Cosmochimica Acta Vol. 64 (23) pp. 4049-4081

Elongated prismatic magnetite crystals in ALH84001 carbonate globules:
Potential Martian magnetofossils

a Kathie L. Thomas-Keprta
b Dennis A. Bazylinski
c Joseph L. Kirschvink
a Simon J. Clemett
d David S. McKay
a Susan J. Wentworth
e Hojatollah Vali
f Everett K. Gibson, Jr.
g Christopher S. Romanek

a Lockheed Martin, 2400 NASA Rd. 1, Mail Code C23, , Houston, TX 77058, USA
b Iowa State University, Dept. of Microbiology, 207 Science I, , Ames, IA
50011, USA
c California Institute of Technology, Div. of Geological and Planetary
Sciences, 1200 E. California Blvd., Pasadena, CA 91125, USA
d NASA/Johnson Space Center, Mail Code SN, , Houston, TX 77058, USA
e McGill University, Dept. of Earth and Planetary Sciences, 3450 University
St., , Montreal, PQ H3A 2A7, Canada
f NASA/Johnson Space Center, Mail Code SN2, , Houston, TX 77058, USA
g Savannah River Ecology Laboratory, Drawer E, University of Georgia, ,
Aiken, SC 29802, USA

Received 7 December 1999; Revised 30 May 2000; Accepted 30 May 2000

Using transmission electron microscopy (TEM), we have analyzed magnetite
(Fe3O4) crystals acid-extracted from carbonate globules in Martian meteorite
ALH84001. We studied 594 magnetites from ALH84001 and grouped them into
three populations on the basis of morphology: 389 were irregularly shaped,
164 were elongated prisms, and 41 were whisker-like. As a possible
terrestrial analog for the ALH84001 elongated prisms, we compared these
magnetites with those produced by the terrestrial magnetotactic bacteria
strain MV-1. By TEM again, we examined 206 magnetites recovered from strain
MV-1 cells. Natural (Darwinian) selection in terrestrial magnetotactic
bacteria appears to have resulted in the formation of intracellular
magnetite crystals having the physical and chemical properties that optimize
their magnetic moment. In this study, we describe six properties of
magnetite produced by biologically controlled mechanisms (e.g.,
magnetotactic bacteria), properties that, collectively, are not observed in
any known population of inorganic magnetites. These criteria can be used to
distinguish one of the modes of origin for magnetites from samples with
complex or unknown histories. Of the ALH84001 magnetites that we have
examined, the elongated prismatic magnetite particles (~27% of the total)
are indistinguishable from the MV-1 magnetites in five of these six
characteristics observed for biogenically controlled mineralization of
magnetite crystals.

Full text available online (PDF 3085 Kbytes)

Copyright 1999-2000, Elsevier Science, All rights reserved.


From NASA Astrobiology Institute, 12 December 2000

In what could turn out to be a landmark discovery in the history of Mars
exploration, imaging scientists using data from NASA's Mars Global Surveyor
spacecraft have observed features that suggest there may be current sources
of liquid water at or near the surface of the red planet.

The images show the smallest features ever observed from martian orbit --
the size of an SUV. NASA scientists compare the features to those left by
flash floods on Earth.

Gullies on Mars are divided into three parts: the alcove, the channel, and
the apron. Water seeps from between layers of rock on the wall of a cliff,
crater, or other type of depression. The alcove forms above the site of
seepage as water comes out of the ground and undermines the material from
which it is seeping. The channel forms from water and debris running down
the slope from the seepage area. The aprons are the down-slope deposits of
ice and debris that were moved down the slope and through the channel.
"We see features that look like gullies formed by flowing water and the
deposits of soil and rocks transported by these flows. The features appear
to be so young that they might be forming today. We think we are seeing
evidence of a ground water supply, similar to an aquifer," said Dr. Michael
Malin, principal investigator for the Mars Orbiter Camera on the Mars Global
Surveyor spacecraft at Malin Space Science Systems (MSSS), San Diego, CA.
"These are new landforms that have never been seen before on Mars."



From Scientific American, January 2001

Evidence for the maverick view that extrasolar planets are really small

PASADENA, CALIF.--"It's not even wrong" was physicist Wolfgang Pauli's
famous putdown for a theory he regarded as implausible and inconsequential.
For the past several years, it has been most astronomers' response to the
ideas of David C. Black. The researcher from the Lunar and Planetary
Institute in Houston is the most outspoken skeptic of the discovery of
planets around other sunlike stars. He thinks the planets are actually
misidentified stars, and he has stuck to that position despite the failure
of his predictions, the weight of scientific opinion and an almost total
lack of observational support. His colleagues whisper that his planet
doesn't go all the way around his star.
POSSIBLE PROTOPLANET, hanging on at the lower left from a star system in
Taurus, has several times Jupiter's mass. Such direct, infrared views are
needed to determine whether, in other systems, massive planets are really
brown dwarf stars.[S. TEREBEY Extrasolar Research Corp. AND NASA] Now, for
the first time, some evidence for Black's view has emerged. At the Division
for Planetary Sciences conference in Pasadena last October, veteran planet
hunter George D. Gatewood of the University of Pittsburgh Allegheny
Observatory presented the results of a study he conducted with Black and
then graduate student Inwoo Han. They checked whether the parent stars of
the purported planets swayed from side to side, the sign of a cosmic
do-si-do with partners too small to be seen directly. In many cases, the
team concluded, the swaying motion was strong enough that the partners must
be fairly heavy--brown dwarfs or other smallish stars, it would seem. At the
least, the group has stirred a debate over selection biases in the planet
searches and spiced up the broader discussion over what exactly a planet is.

In the 1980s the name of David Black was practically synonymous with
extrasolar planets. He was once the head of the National Aeronautics and
Space Administration's search. But his reputation started to slide in 1995
when planet hunting became planet finding. None of the new worlds resembled
anything in our solar system. Black took this as a sign that they weren't
planets after all. Their mass distribution and orbital characteristics, he
asserted, look rather like those of stars. But most astronomers--including
ones who used to share his views, such as William D. Heacox of the
University of Hawaii at Hilo--now say Black is clinging to outmoded ideas.
If nature created odd planets, even ones with starlike orbits, so be it.
Accept it and move on.

To be fair, there was always a loophole in the observations. The swaying
motion of the parent stars has two components, one along the line of sight
(the radial velocity) and the other across the sky (the astrometric motion).
Today's instruments can spot the latter only if the partner is fairly
massive, like a star, so nearly all planet discoveries rely on the former.
But radial velocity alone can merely put a lower limit on the planet masses,
and if the orientation is just right, the true mass might be much greater.

Han, Gatewood and Black have extended previous work that merged radial
velocities with astrometric data from the Hipparcos satellite. They found
that out of 30 stars with companions, 15 showed astrometric motion, which
implies that the partners are brown dwarfs or stars. "If that's right, it
sure does make life interesting," Heacox says. The response from other
planet people has been swift and vigorous. "The claim by David Black is
completely incorrect," says famed planet finder Geoffrey W. Marcy of the
University of California at Berkeley. He and others argue that the inferred
orientations are incredibly improbable. Four of the partners were said to
orbit within one degree of perfect alignment with the line of sight. Yet the
chance of any single partner of a given mass having that orientation is
about 1 in 5,000. Conversely, for every partner with that orientation, there
should be 5,000 or so with less extreme orientations. No such bodies are
seen. Marcy is so convinced that he says Scientific American "will be doing
science a bum steer" simply by mentioning Black's work.

Two independent groups have weighed in. Tsevi Mazeh and Shay Zucker of Tel
Aviv University suggest that the truth lies somewhere in the middle. They
confirm that two of the bodies indeed have the heft of a star--but only two.
They see no astrometric motions for the other bodies. Hipparcos expert
Dimitri Pourbaix of the Free University of Brussels initially got similar
results but now suspects that the analyses have fallen prey to subtle
computational biases that overestimate the mass and underestimate the error
bar. To resolve the dispute, astronomers will need higher-precision
astrometry (as at least two teams now intend) and direct searches for
infrared light from the stellar companions (as Mazeh plans this month at the
Keck Observatory on Mauna Kea in Hawaii).

Although it looks as if Black is wrong, planet hunters can't go scot-free
just yet. Even two stellar interlopers would be two too many. Brown-dwarf
expert Gibor Basri of Berkeley and others say it is quite plausible that
searchers have unwittingly skewed their sample. No matter what, the
theorists still have their work cut out for them. What could possibly
account for the amazing diversity of worlds, from the mannerly ones in our
solar system to the errants traipsing through interstellar space? Do they
all deserve the label "planet"? Basri quotes from Lewis Carroll: "'When I
make a word do a lot of work like that,'" said Humpty-Dumpty, 'I always pay
it extra.'"

--George Musser

Copyright 2000, Scientific American


From Andrew Yee <>

ESA Science News

11 Dec 2000

766 Days to Launch ... And Counting!

Representatives of the Rosetta science instrument teams came together from
all over Europe and the United States this week for the 7th meeting of the
Rosetta Science Working Team.

The purpose of the gathering at the premises of Alenia Spazio in Turin was
to familiarise everyone with the latest status of the programme. However,
the primary consideration for everyone was the limited time remaining to
complete the spacecraft Assembly, Test and Verification programme -- 766
days to launch ... and counting.

Members of the ESA project team for Rosetta explained to the 80-strong
audience that the Electrical Qualification Model (EQM) test programme on the
Orbiter and Lander is now half completed, although considerable work remains
to be done.

All of the Orbiter's EQM instruments have been delivered and are currently
undergoing functional testing. This phase of the intensive EQM programme is
scheduled for completion by the end of January 2001, after which the
instrument compatibility tests will begin.

"Progress is being made, but not quite as fast as we originally hoped," said
ESA Project Manager John Ellwood. "However, engineers at Alenia are working
double shifts and we are confident that we will be able to catch up with our
tight schedule."

Meanwhile, all of the experiments on the Orbiter have passed their Final
Design Reviews after several months of discussions about the results of
tests on prototype instruments that have been carried out at the various
institutes. This is an important step towards the Mission Critical Design
Review in April 2001.

The meeting was also informed that the Assembly, Integration and
Verification programme for the Rosetta Orbiter Flight Model will take place
in parallel to the EQM tests. The first step will be the delivery of the
Flight Model structure from Finland to Italy in mid-January, followed
immediately by the delivery of key subsystems such as the harness and the
Reaction Control System.

The scientists were able to see for themselves the current state of play in
the EQM programme during a visit to the giant clean room at Alenia, where
they could inspect at close quarters the Rosetta Orbiter and Lander EQMs (as
well as the Flight Model of ESA's Integral gamma ray observatory which is
scheduled for launch in 2002).

However, the main message for the gathered assembly was pronounced early on
the first day by John Ellwood.

"No major technological risks are outstanding, but we must all continue to
make every effort to meet our deadlines," he said.

"We are 'Go' for launch on 12 January 2003 -- but Comet Wirtanen will not


* More about Rosetta


[Image 1: ]
The faint, moving image of the nucleus of Comet Wirtanen (in the circles),
as observed by the 8.2-m VLT KUEYEN telescope (formerly UT2) and the VLT
Test Camera on 17 May 1999, during the commissioning phase. Photograph
courtesy ESO.

[Image 2: ]
Rosetta Orbiter EQM at Alenia Spazio in Turin, Italy, 11 October 2000.

[image 3: ]
Rosetta rises to meet the challenge. A three colour image of Comet Wirtanen,
taken from observations on Pik Tersko, which shows the three cometary
components -- dust, neutral gas and ions. Using different filters on the
telescope, the cometary water (H2O) ions appear red, the dust is green and
neutral CN gas is blue.

This shows Wirtanen's ion tail (here H2O+) for the first time. It appears as
a straight, red diffuse band to the left side (anti-sunward direction). The
blue sphere is the very extended neutral CN coma. In contrast to this, the
dust is much more concentrated and dominates the near nucleus region, here
seen as a yellowish green colour. This image illustrates that 46P/Wirtanen
is dust poor and about 2-3 times less dusty than Comet Halley.

Photo Max-Planck-Institut fur Aeronomie, courtesy T. Credner, J. Jockers,


The International Rosetta Mission was approved in November 1993 by ESA's
Science Programme Committee as the Planetary Cornerstone Mission in ESA's
long-term space science programme. The mission goal is a rendezvous with
comet 46 P/Wirtanen. On its eight-year journey to the comet, the spacecraft
will pass close to two asteroids, (Otawara and Siwa are now the planned

Rosetta will study the nucleus of comet Wirtanen and its environment in
great detail for a period of nearly two years, the near-nucleus phase
starting at a heliocentric distance of about 3.25 AU, with far-observation
activities leading ultimately to close observation (from about one km

Rosetta operations will be carried out from ESA's Operations Centre (ESOC)
in Darmstadt. Orbit determination for all mission phases will also be
performed by ESOC.

Rosetta will be launched in January 2003 by an Ariane-5 from Kourou, French
Guiana. To gain enough orbital energy to reach its target, one Mars and two
Earth gravity assists will be required. The long mission duration required
the introduction of extended hibernation periods. The mission falls into
several distinct phases:

Major event Nominal date
Launch 12 January 2003
Mars gravity assist 26 August 2005
First Earth gravity assist 21 November 2005
Otawara flyby 11 July 2006
Second Earth gravity assist 28 November 2007
Siwa flyby 24 July 2008
Rendezvous manoeuvre 29 November 2011


From Ron Baalke <>

NEAR Shoemaker Engine Burn Puts Spacecraft on Track for Final Months in

December 13, 2000

An engine burn at 3:15 p.m. (EST) today put the NEAR Shoemaker spacecraft in
orbit just 22 miles (35 kilometers) above Eros' center of mass in
preparation for low altitude operations in January and February, just prior
to the mission's end. The orbit correction maneuver lasted a minute and a
half and pushed the spacecraft from an elliptical orbit approximately 120
miles (200 kilometers) above Eros at its farthest point, into its current
circular orbit around the tumbling space rock.

The maneuver is the latest in the mission's five-year history that has taken
the NEAR Shoemaker spacecraft on a 2-billion-mile journey and provided a
unique 150,000-image photo-op since it began its orbital approach in

"The next two months will be the most challenging time of the entire mission
for the operations team," says Dr. Robert W. Farquhar, mission director for
NASA's Near Earth Asteroid Rendezvous (NEAR) program at The Johns Hopkins
University Applied Physics Laboratory (APL), Laurel, Md. "We're working very
closely with the navigation team at the Jet Propulsion Laboratory to ensure
the success of each maneuver. The final controlled descent on Feb. 12 is one
of the most complicated maneuvers to date, but the return will be worth it.
We expect to get images that are 10 times better in resolution than anything
we've taken so far."

NEAR Shoemaker will stay in a 22-mile (35-kilometer) orbit until Jan. 24,
when three more engine burns will push it first to within 12 miles (19
kilometers) and then back to a circular 22-mile orbit, by the end of the
month. During the lower orbits the spacecraft will come within 1.9 miles (3
kilometers) of the asteroid's ends.

The mission team will use the progressively lower orbits and low flyovers to
collect valuable data. "This will give us an excellent opportunity for the
gamma ray spectrometer to measure element abundances at low altitudes," says
Project Scientist Dr. Andrew F. Cheng of the Applied Physics Laboratory.
"These measurements will help us clear up some questions we have regarding
how closely Eros' composition fits the pattern of ordinary chondrites. The
spectrometer will also give us composition measurements from 10 centimeters
below the surface and will give us a reading of natural radioactivity on the
asteroid. At the same time the imager and laser rangefinder will be giving
us additional low-altitude, high-resolution data to complete a global
mapping of Eros."

On the final day of the mission, Feb. 12, 2001, the spacecraft will execute
a series of maneuvers that will enable NEAR Shoemaker to gather
high-resolution images from only 1,640 feet (500 meters) above the
asteroid's surface.

NEAR Shoemaker has been in orbit around Eros since Feb. 14, 2000, conducting
the first in-depth study of an asteroid. APL manages the NEAR mission and
built the spacecraft. For more information on the mission, and for daily
images of Eros, visit Web site: (
Media contact:

             JHU Applied Physics Laboratory:
             Helen Worth            Michael Buckley
             Laurel, MD 20723       Laurel, MD 20723
             Phone: 240-228-5113    Phone: 240-228-7536
             E-mail:                E-mail:


G.H. Stokes, J.B. Evans, H.E.M. Viggh, F.C. Shelly, E.C. Pearce: Lincoln
Near-Earth Asteroid Program (LINEAR). ICARUS 148: (1) 21-28 NOV 2000

The Lincoln Near-Earth Asteroid Research (LINEAR) program has applied
electro-optical technology developed for Air Force Space Surveillance
applications to the problem of discovering near-Earth asteroids (NEAs) and
comets. This application is natural due to the commonality between the
surveillance of the sky for man-made satellites and the search for
near-Earth objects (NEOs). Both require the efficient search of broad swaths
of sky to detect faint, moving objects. Currently, the Air Force
Ground-based Electro-Optic Deep Space Surveillance (GEODSS) systems, which
operate as part of the worldwide U.S. space surveillance network, are being
upgraded to state-of-the-art charge-coupled device (CCD) detectors. These
detectors are based on recent advances made by MIT Lincoln Laboratory in the
fabrication of large format, highly sensitive CCDs. In addition,
state-of-the-art data processing algorithms have been developed to employ
the new detectors for search operations. In order to address stressing space
surveillance requirements, the Lincoln CCDs have a unique combination of
features, including large format, high quantum efficiency, frame transfer,
high readout rate, and low noise, not found on any commercially available
CCD. Systems development for the GEODSS upgrades has been accomplished at
the Lincoln Laboratory Experimental Test Site (ETS) located near Socorro,
New Mexico, over the past several years. Starring in 1996, the Air Force
funded a small effort to demonstrate the effectiveness of the CCD and broad
area search technology when applied to the problem of finding asteroids and
comets. This program evolved into the current LINEAR program, which is
jointly funded by the Air Force Office of Scientific Research and NASA.
LINEAR, which started full operations in March of 1998, has discovered
through September of 1999, 257 NEAs (of 797 known to date), 11 unusual
objects (of 44 known), and 32 comets. Currently, LINEAR is contributing
similar to 70% of the worldwide NEA discovery rate and has single-handedly
increased the observations submitted to the Minor Planet Center by a factor
of 10. This paper covers the technology used by the program, the operations,
and the detailed results of the search efforts.

Stokes GH, MIT, Lincoln Lab, 244 Wood St, Lexington, MA 02420 USA.
MIT, Lincoln Lab, Lexington, MA 02420 USA.

Copyright 2000 Institute for Scientific Information

D. Vokrouhlicky, A. Milani: Direct solar radiation pressure on the orbits of
small near-Earth asteroids: observable effects? ASTRONOMY AND ASTROPHYSICS
362: (2) 746-755 OCT 2000

We consider the perturbations of Near-Earth Asteroid orbits due to direct
solar radiation pressure (both the absorption and the reflection
components). When the body is spherical and the surface albedo homogeneous
the effect is small (and only short-periodic). However, when at least one of
these restrictive and unrealistic assumptions is relaxed,long-term orbital
effects appear and they may potentially lead to observable displacement of
the orbit. We illustrate this conclusion by computing the orbital
perturbations due to radiation pressure for objects with an odd-zonal
distribution of albedo and for objects with ellipsoidal shape. Especially in
the first case the effects are large, due to the long-term perturbations of
the semimajor axis. For high-eccentricity orbits observed over a long
interval of time, the (v/c)-correction of the direct radiation pressure,
known as Poynting-Robertson effect, should be also considered. As an example
we demonstrate that for the asteroid 1566 Icarus, during its next close
approach to the Earth, the orbit displacement due to the direct solar
radiation forces might be, under reasonable assumptions. comparable to the
orbit determination uncertainty, thus potentially observable.

Vokrouhlicky D, Charles Univ, Astron Inst, V Holescovickach 2, CR-18000
Prague 8, Czech Republic.
Charles Univ, Astron Inst, CR-18000 Prague 8, Czech Republic.
Univ Pisa, Dipartimento Matemat, I-56127 Pisa, Italy.

Copyright 2000 Institute for Scientific Information


H. Ishimoto: Modeling the number density distribution of interplanetary dust
on the ecliptic plane within 5AU of the Sun. ASTRONOMY AND ASTROPHYSICS 362:
(3) 1158-1173 OCT 2000

We have used the relationship, consistent with observational data, between
the radial dependence of the dust supply and the mass dependence of the
number density distribution, to consider the parent bodies of interplanetary
dust. We examine the number density distribution of the interplanetary dust
within 5AU of the Sun on the ecliptic plane.

For the model calculations, the number density equations for the ecliptic
plane are solved directly by taking into account collisional destruction
between particles and the Poynting-Robertson effect, and by assuming a state
of equilibrium and axial symmetry in the interplanetary dust cloud. Typical
models for the radial dependence of the dust input on the ecliptic plane are
considered. For three typical dust groups that are characterized by their
orbits-i.e., bound particles, hyperbolic particles of collisional origin,
and interstellar particles-a variety of simple models of the physical
parameters are considered. These include the particles' optical properties,
the mean sweep-out velocities of the dust clouds, the power law distribution
of mass in the collisional fragments, the maximum size of particles, and the
inner/outer boundaries.

From the model calculations, the existence of the three characteristic
particle groups and their input radial dependencies are found to play
important roles in determining the environmental conditions of
interplanetary dust and the number density distribution of the particles.
The roles played by comets and asteroids are estimated by analyzing the
relationship between the radial dependence of the dust input and the
resultant number density distribution at 1AU. To simulate the flux curve of
interplanetary meteoroids at 1AU (e.g., Grun et al. 1985), a source that
directly supplies the interplanetary dust is required. It is found that the
simulated number density distribution fits that observed at 1AU well, if the
mass production rate of dust sources outside 1AU increases with a radial
index of -3 similar to -4 as the solar distance decreases. Such dust sources
are more likely to be comets rather than asteroids.

The numerical results indicate that, at 1AU, cometary dust is the major
component of particles with masses m greater than or equal to 10(-6) g, and
almost comparable in number to asteroidal particles with masses 10(-12) g
less than or equal to m less than or equal to 10(-7) g. Furthermore, we can
expect that within IAU the contribution of cometary particles increases as
the solar distance decreases, due to the direct input of cometary particles.

In order for the results to be consistent with the observed r(-1 similar to
-1.3) radial dependence in the number density distribution of the zodiacal
cloud inside IAU, the mass production rate by the dust source should be
almost constant or decreasing as the solar distance decreases.

Using a possible model for the dust sources and for the radial dependence of
dust input, the number density of hyperbolic particles of collisional origin
at 1AU is estimated to be similar to 1.8 x 10(-4) m(-2)sec(-1).

Hyperbolic particles and the influx of interstellar particles (m similar to
10(-13) g) inside 5AU increase the number density of interplanetary dust
particles in the medium-sized range (10(-15) g less than or equal to m
greater than or equal to 10(-6) g). Interplanetary dust beyond 3AU of the
Sun will, therefore, maintain a flat radial distribution of medium mass
particles if the interstellar flux is significant.

Ishimoto H, Japan Meteorol Agcy, Meteorol Res Inst, Nagamine 1-1, Tsukuba,
Ibaraki 3050052, Japan.
Japan Meteorol Agcy, Meteorol Res Inst, Tsukuba, Ibaraki 3050052, Japan.

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