[Prev][Next][Index][Thread]

(meteorobs) (Intriguing) Excerpts from "CCNet, 29/2000 - 8 March 2000"


This issue is a gold mine for those interested in interplanetary dust,
and especially those intrigued by the Delta Leonids, Geminids and other
meteoroid streams which appear to originate from "asteroidal" bodies!

Lew Gramer

------- Forwarded Message

From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet, 8 March 2000
Date: Wed, 8 Mar 2000 13:03:06 -0500 (EST)

CCNet, 29/2000 - 8 March 2000
-----------------------------


     A Delta Air Lines jet was traversing Arizona on a clear day. The
     copilot was bombarding passengers with remarks about landmarks
     over the PA system. "Coming up on the right side of our cabin, you
     can see Meteor Crater. A major tourist attraction in northern
     Arizona, it was formed when a lump of nickel and iron weighing
     300,000 tons, 150 feet across, struck the earth at 40,000 miles an
     hour, scattering white-hot debris for miles in every direction.
     The hole measures nearly a mile across and is 570 feet deep." From
     the cabin, a passenger was heard to exclaim: "Wow! It just missed
     the highway!"


(1) FAST-SPINNING ASTEROID STUDIED
    Andrew Yee <ayee@nova.astro.utorontodot ca>

(2) INTERESTING STRUCTURAL FEATURES ON EROS
    Ron Baalke <baalke@jpl.nasadot gov>

(3) FUTURE ESA PROJECTS
    ESA <sciweb@estec.esadot nl>

[...]

(9) PERSPECTIVES ON THE COMET-ASTEROID-METEORITE LINK
    K. Lodders, WASHINGTON UNIVERSITY

(10) POLARISATION OF LIGHT SCATTERED BY COMETARY DUST
     A.C. Levasseur Regourd, UNIVERSITY OF PARIS

(11) DYNAMICAL LIFETIMES & FINAL FATE OF SMALL BODIES
     L. Dones et al., SW RES INSTITUTE

(12) TIDAL SPLITTING & ROTATIONAL BREAKUP OF COMETS
     B.J.R. Davidsson, UPPSALA ASTRONOMICAL OBSERVATORY


====================================================

(1) FAST-SPINNING ASTEROID STUDIED

>From Andrew Yee <ayee@nova.astro.utorontodot ca>

[From Fall 1999/Number 87 issue of Lunar and Planetary Information,
http://www.lpi.usradot edu/publications/newsletters/lpib/lpib87/lpib87.pdf=
]

FAST-SPINNING ASTEROID STUDIED

Spinning faster than any object ever observed in the solar system, a
lumpy, water-rich sphere known as 1998 KY26, measuring about the=20
diameter of a baseball diamond, is rotating so swiftly that its day=20
ends almost as soon as it begins, NASA scientists report.

Asteroid 1998 KY26, where the Sun rises or sets every five minutes,=20
was observed June 2=AD8, 1998, shortly after it was discovered and as=20
it passed 800,000 kilometers (half a million miles) from Earth, or=20
about twice the distance between Earth and the Moon. Publishing their=20
findings in a recent issue of Science magazine, Dr. Steven J. Ostro=20
of NASA's Jet Propulsion Laboratory, Pasadena, California, and an=20
international team of astronomers used a radar telescope in=20
California and optical telescopes in the Czech Republic, Hawai'i,=20
Arizona, and California to image the 30-meter, water-rich ball as it=20
twirled through space. It is the smallest solar system object ever=20
studied in detail.

"Enormous numbers of objects this small are thought to exist very=20
close to Earth, but this is the first time we've been able to study=20
one in detail. Ironically, this asteroid is smaller than the radar=20
instruments we used to observe it," Ostro said.

The asteroid's rotation period was calculated at just 10.7 minutes,=20
compared to 24 hours for Earth and at least several hours for the=20
approximately 1000 asteroids measured to date. In addition, the=20
minerals in 1998 KY26 probably contain about a million gallons of=20
water, enough to fill two or three olympic-sized swimming pools,=20
Ostro said.

"This asteroid is quite literally an oasis for future space=20
explorers," he said. "Its optical and radar properties suggest a=20
composition like carbonaceous chondrite meteorites, which contain 
complex organic compounds that have been shown to have nutrient=20
value. These could be used as soil to grow food for future human=20
outposts. And among the 25,000 or so asteroids with very reliably=20
known orbits, 1998 KY26 is in an orbit that makes it the most=20
accessible to a spacecraft."

The solar system is thought to contain about 10 million asteroids=20
this small in orbits that cross Earth's, and about 1 billion in the=20
main asteroid belt between Mars and Jupiter. However, only a few=20
dozen of these tiny asteroids have ever been found and, until now,=20
hardly anything was known about the nature of these objects.

Ostro and his colleagues used the 70-meter-diameter Goldstone,=20
California, antenna of NASA's Deep Space Network to transmit radar=20
signals continuously to the asteroid and turned a 34-meter-diameter=20
antenna on it to collect echoes bouncing back from the object.

1998 KY26's color and radar reflectivity showed similarities to=20
carbonaceous chondrites, primordial meteorites that formed during the=20
origin of the solar system and are unlike any rocks formed on Earth.
They contain complex organic compounds as well as 10=AD20% water. Some
carbonaceous chondrites contain amino acids and nucleic acids, which
are the building blocks of proteins and DNA, and hence are of interest
to scientists trying to unravel the origins of life.

A second team of astronomers used optical telescopes to track 1998=20
KY26, which was discovered by the University of Arizona's Spacewatch
telescope, the world's first instrument dedicated to searching for=20
near-Earth asteroids. Dr. Petr Pravec of the Czech Republic's Academy=20
of Sciences said collisions likely gave 1998 KY26 its rapid spin.

But one way or another, Pravec said, this object's 10.7-minute "day" is
the shortest of any known object in the solar system.

"The motion of the sky would be 135 times faster than it is on=20
Earth," he said. "Sunrises and sunsets take about two minutes on=20
Earth, but on 1998 KY26, they would take less than one second. You'd=20
see a sunrise or sunset every five minutes."

Dr. Scott Hudson of Washington State University in Pullman found the=20
asteroid's shape particularly surprising. Asteroids thousands of times
larger have spherical shapes as a result of their large masses and=20
strong gravitational fields, he said. 1998 KY26 is very unusual,
however, because gravity and mass play no significant role in its=20
shape. Instead, the spheroid shape is the result of collisions with=20
other asteroids.

====================================================

(2) INTERESTING STRUCTURAL FEATURES ON EROS

>From Ron Baalke <baalke@jpl.nasadot gov>

NEAR image of the day for 2000 Mar 7
http://near.jhuapldot edu/iod/20000307/index.html

Interesting Structural Features on Eros

This image of the interior of Eros' saddle area, taken at a range of=20
204 km (127 miles), displays a paucity of craters compared to the=20
surface on the right hand side of the image. The saddle displays many=20
interesting structural features. Visible on the left wall are a
series of closely spaced grooves that follow the terrain downslope.=20
Opposite, on the upper right wall, trending towards the back of the=20
saddle is a prominent ridge. Boulders are visible throughout this=20
image. Features as small as 20 meters (65 feet) are discernable in this
image.
- --------------------------------------------------------

NEAR image of the day for 2000 Mar 6
http://near.jhuapldot edu/iod/20000306/index.html
Large Crater on Eros

This mosaic image of the large crater at Eros' center was taken during=20
an optical navigation imaging sequence from a range of 127 miles (204=20
km). This same area was imaged following orbit insertion at a range of
approximately 210 miles (330 km) on February 14th (Feb 14 G). This=20
picture resolves features as small as 65 feet (20 meters) compared to=20
the resolution of 100 feet (30 meter) in the earlier image. The shadow=20
cast by the boulder near the floor of the crater (the sun is from
the northeast) is now visible. The walls of the crater display some=20
distinctive variations in their albedo or reflectivity. The upper part=20
of the walls tend to be bright, while the lower portions of the walls=20
and the crater floor show patches of darker or less reflective=20
materials. These albedo patterns are also visible on other crater=20
walls. To the right of the large crater two sets of closely spaced=20
orthogonal grooves are visible.
- --------------------------------------------------------
Built and managed by The Johns Hopkins University Applied Physics=20
Laboratory, Laurel, Maryland, NEAR was the first spacecraft launched in =

NASA's Discovery Program of low-cost, small-scale planetary missions.=20
See the NEAR web page at http://near.jhuapldot edu for more details.

====================================================

(3) FUTURE ESA PROJECTS

>From ESA <sciweb@estec.esadot nl>

Six proposals, ranging from a visit to the Asteroid Belt to amazingly =20
sensitive gyroscopes, will undergo close examination during the next=20
six months, as the European Space Agency's science advisors move=20
towards the selection of Flexi-missions for launch between 2005 and=20
2009. Science working groups and the Space Science Advisory Committee=20
have chosen them from 50 ideas submitted after a call for proposals=20
last October.=20

More at:
http://sci.esa.int/newsitem.cfm?TypeID=3D1&ContentID=3D9611&Storytype=3D=
7

====================================================

(9) PERSPECTIVES ON THE COMET-ASTEROID-METEORITE LINK

K. Lodders*) & R. Osborne: Perspectives on the comet-asteroid-meteorite =

link. SPACE SCIENCE REVIEWS, 1999, Vol.90, No.1-2, pp.289-297
     =20
*) WASHINGTON UNIVERSITY,DEPT EARTH & PLANETARY SCI,PLANETARY  =20
   CHEM LAB,CAMPUS BOX 1169,ST LOUIS,MO,63130

We discuss the possibility that CI and CM carbonaceous chondrites are=20
fragments of extinct cometary nuclei. Theoretical and observational=20
work suggests that comets evolve into asteroids, and several extinct=20
cometary nuclei are now suspected to he among the near Earth object=20
population. This population is the most likely source of meteorites and =
consequently, we may expect that some meteorites are from extinct=20
comets in this population. The mineralogy and chemistry of CI and CM=20
chondrites is consistent with the view that they originate from=20
asteroidal objects of carbonaceous spectral classes, and these objects=20
in turn may have a cometary origin. We do not suggest that CI or CM=20
chondrites are directly delivered by active comets during perihelion=20
passage or that these chondrites come from cometary debris in meteor=20
streams. Instead, we summarize arguments suggesting that CI and CM=20
chondrites represent fragments of cometary nuclei which evolved
into near Earth asteroids after losing their volatiles. Copyright 2000,
Institute for Scientific Information Inc.

====================================================

(10) POLARISATION OF LIGHT SCATTERED BY COMETARY DUST

A.C. Levasseur Regourd: Polarization of light scattered by cometary=20
dust particles: Observations and tentative interpretations. SPACE=20
SCIENCE REVIEWS, 1999, Vol.90, No.1-2, pp.163-168

*) UNIVERSITY OF PARIS 06,BP 3,F-91371 VERRIERES BUISSON,FRANCE

Analysis of the polarization of light scattered by cometary particles
reveals similarities amongst the phase curves. together with some clear
differences: i) comets with a strong silicate emission feature present
a high maximum in polarization, ii) the polarization is always slightly
lower than the average in inner comae and stronger in jet-like
structures. These results are in excellent agreement with the Greenberg
model of dust particles built up of fluffy aggregates of much smaller
grains. Also, they suggest the existence of different regions of
formation, and of different stages of evolution for the scattering
particles inside a given cometary coma. Copyright 2000, Institute for
Scientific Information Inc.

====================================================

(11) DYNAMICAL LIFETIMES & FINAL FATE OF SMALL BODIES

L. Dones*), B. Gladman, H.J. Melosh, W.B. Tonks, H.F. Levison,=20
M. Duncan: Dynamical lifetimes and final fates of small bodies: Orbit=20
integrations vs Opik calculations. ICARUS, 1999, Vol.142, No.2,=20
pp.509-524

*) SW RES INST,SPACE STUDIES DEPT,1050 WALNUT ST,SUITE=20
   426,BOULDER,CO,80302

The dynamical lifetimes of small bodies against ejection from the=20
Solar System or collision with the Sun or a planet are often=20
estimated by Monte Carlo codes based on the equations of Opik and=20
using a method implemented by Arnold. Such algorithms assume that=20
orbital changes are dominated by close encounters, and that=20
successive encounters are uncorrelated, We have compared the results=20
of an Opik code (H. J. Melosh and W. B, Tonks, Meteoritics 28, 398=20
(1993)) and a fast integrator (H, F. Levison and M, J, Duncan, Icarus=20
108, 18 (1994)) to investigate the regimes of validity of the=20
Opik-Arnold approach, We investigate the transfer of ecliptic comets=20
from Neptune-crossing orbits to observable Jupiter-family comets, the=20
dynamics of Halley-type comets, and the transport of meteorites among=20
the terrestrial planets, In all cases, the Opik code overestimates=20
the median lifetime of the small bodies, although both codes show a=20
rapid initial loss of objects followed by a slow decay, For martian=20
impact ejecta, some of which find their way to Earth as the SNC=20
meteorites, the Opik code substantially overestimates lifetimes=20
because of its neglect of secular resonances, which rapidly pump=20
eccentricities (B, J, Gladman ed at, Science 271, 1387 (1996)). (C)=20
1999 Academic Press.

====================================================

(12) TIDAL SPLITTING & ROTATIONAL BREAKUP OF COMETS

B.J.R. Davidsson: Tidal splitting and rotational breakup of solid=20
spheres. ICARUS, 1999, Vol.142, No.2, pp.525-535
     =20
*) UPPSALA ASTRONOMICAL OBSERVATORY,BOX 515,S-75120 UPPSALA,SWEDEN

A number of new expressions for the Roche limit are derived in order=20
to investigate the splitting behavior of cometary nuclei when passing=20
close to massive bodies. These expressions handle both tensile and=20
shear failure, taking the radius, density, material strength,=20
rotation period, and spin axis orientation of the body into account.=20
The critical period for which bodies in free space disrupt due to the=20
centrifugal force is also investigated, resulting in functions=20
depending on radius, density, and material strength. (C) 1999=20
Academic Press.

----------------------------------------
THE CAMBRIDGE-CONFERENCE NETWORK (CCNet)
----------------------------------------
The CCNet is a scholarly electronic network. To subscribe/unsubscribe,=20
please contact the moderator Benny J Peiser <b.j.peiser@livjm.acdot uk>.=20
Information circulated on this network is for scholarly and=20
educational use only. The attached information may not be copied or=20
reproduced for any other purposes without prior permission of the=20
copyright holders. The fully indexed archive of the CCNet, from=20
February 1997 on, can be found at:
http://abob.libs.ugadot edu/bobk/cccmenu.html

------- End of Forwarded Message


To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at:
http://www.tiacdot net/users/lewkaren/meteorobs/subscribe.html