PLEASE NOTE:


*  

Date sent: Wed, 23 Jul 1997 12:18:06 -0400 (EDT)
From: Benny J Peiser <B.J.PEISER@livjm.ac.uk>
Subject: HAVE A NICE SUMMER
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL

SUMMER TIME ON THE CC-LIST

Two weeks after a very successful meeting of SPACEGUARD UK at the
Royal Greenwich Observatory (10 July) and an even more enlightening
SIS Cambridge Conference at Fitzwilliam College (11-13 July), most
list members, I am certain, will be looking forward to a sunny and
refreshing summer break. My wife and I will be in continental Europe
from 26th July to 20th August. Should you come across interesting and
newsworthy items during that time, please do not hesitate to post
r e l e v a n t information on the list.

After the summer break, list members will be consulted whether or not
to i) terminate, ii) continue or iii) reorganise this network
originally set up in the run-up of the 2nd SIS Cambridge Conference.

Have a nice, refreshing and happy summer break.

Benny J Peiser



*

Date sent: Wed, 23 Jul 1997 09:35:00 -0400 (EDT)
From: Benny J Peiser <B.J.PEISER@livjm.ac.uk>
Subject: Discovery of a Satellite Around Asteroid 3671 Dionysus
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL

DISCOVERY OF A SATELLITE AROUND A NEAR-EARTH ASTEROID

from: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
-----------------------------------------------------------------------------

ESO Education and Public Relations Dept.

Press Release 08/97

For immediate release: 22 July 1997

----------------------------------------------------------------------------
Text and photos with all links are available on the ESO Website at URL:

http://www.eso.org/outreach/press-rel/pr-1997/

----------------------------------------------------------------------------
DISCOVERY OF A SATELLITE AROUND A NEAR-EARTH ASTEROID

In the course of the major observational programme of asteroids by the
Institute of Planetary Exploration of the German Aerospace Research
Establishment (DLR) [1] in Berlin, two of the staff astronomers,
Stefano Mottola and Gerhard Hahn, have discovered a small satellite
(moon) orbiting the asteroid (3671) Dionysus.

The new measurements were obtained with the DLR CCD Camera attached
at the 60-cm Bochum telescope at the ESO La Silla Observatory in Chile.

This is only the second known case of an asteroid with a moon.

Moons and planets

Until recently, natural satellites were only known around the major
planets. The Moon orbits the Earth, there are two tiny moons around
Mars, each of the giant planets Jupiter, Saturn, Uranus and Neptune has
many more, and even the smallest and outermost, Pluto, is accompanied
by one [2].

However, the new discovery now strengthens the belief of many
astronomers that some, perhaps even a substantial number of the many
thousands of minor planets (asteroids) in the solar system may also
possess their own moons. The first discovery of a satellite orbiting an
asteroid was made by the NASA Galileo spacecraft, whose imagery,
obtained during a fly-by of asteroid (253) Ida in August 1993, unveiled
a small moon that has since been given the name Dactyl.

(3671) Dionysus: an Earth-crossing asteroid

In the framework of the DLR asteroid monitoring programme, image
sequences are acquired to measure an asteroid's brightness variations
caused by the changing amount of sunlight reflected from the asteroid's
illuminated surface as it spins, due to its irregular shape. The
brightness variations may be used to derive the asteroid's rotational
properties, such as speed of rotation and spin axis orientation.

Asteroid Dionysus [3] was put on the observing list because it belongs
to a special class of asteroids, the members of which occasionally come
very close to the Earth and have a small, but non-negligible chance of
colliding with our planet. Most of these objects move in highly
elliptical orbits that lie partly inside, partly outside that of the
Earth. They are accordingly referred to as `Earth-crossing asteroids'
or Apollo-type asteroids, after the proto-type of this group, (1862)
Apollo, that was discovered in 1932 by Karl Reinmuth in Heidelberg [4].

The orbital characteristics of Dionysus lead to moderately close
approaches to the Earth every 13 years, with the one in 1997 being the
first since its discovery that is favourable for extensive
observations. On July 6, 1997, it passed within 17 million km of our
planet. At that time it was visible from the southern hemisphere with a
moderately-sized telescope as a relatively fast-moving object.

The strange lightcurve of asteroid (3671) Dionysus

The first observations of the brightness of this asteroid in late May
1997 showed a `normal' two-maxima-two-minima lightcurve (change of
brightness with time), typical of rotating non-spherical bodies. The
period of rotation was 2.7 hours, i.e., this asteroid spins almost nine
times as fast as the Earth.

However lightcurves observed on two subsequent nights were strikingly
different from the previous ones. In both cases a deeper and shifted
dip was seen, indicative of an attenuation -- an additional dimming of
the sunlight reflected by the asteroid, cf. ESO Press Photo 20/97.

The observers hypothesised that these lightcurve features were due to
an eclipse by an unknown object moving in an orbit around (3671)
Dionysus, thereby covering part of the illuminated surface of the
asteroid at regular time intervals [5]. Fortunately, this hypothesis
can be checked, because the phenomenon should then repeat itself
periodically.

Accordingly, the DLR scientists made a prediction for the next
occurences of dips in the lightcurve, based on the time difference
between the two observed events.

Confirmation of the satellite

Contacts were made with observers located at other observatories, in
order to secure lightcurve coverage over a longer period of time than
was possible from La Silla alone. As a result, a series of lightcurve
measurements were performed from June 3 to 9 in close cooperation with
Petr Pravec and Lenka Sarounova working at the Ondrejov Observatory,
near Prague in the Czech Republic.

Luckily, the weather conditions were favourable at both sites and the
dips in the lightcurve were indeed observed at the predicted times.

Based on the four well observed events, it was then possible to
determine a period of 1.155 days for their occurence. Thus, the
hypothesis of a satellite orbiting around Dionysus was confirmed. As a
result, the International Astronomical Union's Minor Planet Center
located in Cambridge (MA, USA) promptly gave a provisional designation
to the new satellite -- S/1997 (3671) 1.

How big is Dionysus?

Meanwhile, in Hawaii, the world's largest infrared telescope was being
trained on Dionysus to obtain information about its size and
composition. Alan Harris, also a scientist from the DLR in Berlin, and
John Davies from the Joint Astronomy Centre in Hilo, Hawaii, observed
the thermal infrared radiation emitted by Dionysus with the 3.8-m
United Kingdom Infrared Telescope (UKIRT) situated on Mauna Kea.
Similar observations over a broader spectral range were also made by
the European Space Agency's orbiting Infrared Space Observatory.

The thermal or "heat" radiation emitted by an asteroid depends on its
size and the amount of sunlight it absorbs (darker bodies being
warmer). In the case of Dionysus the measured radiation was much weaker
than expected, indicating that the asteroid has an intrinsically bright
(reflective) surface and is only about 1 km in diameter. This is much
smaller than (253) Ida, the only other asteroid known to have a moon,
which is about 60 km across.

Further observations

Eventually it should be possible to determine the orbital radius of the
satellite, its size and the inclination of its orbital plane. In order
to obtain the data necessary for these determinations, observations
will be continued during the present period of good visibility that
lasts until September-October 1997. For this reason the discoverers
have initiated an international observation campaign devoted to the
study of this intriguing object and now involving astronomers from many
countries.

How common are such satellites?

Satellites in orbit around small bodies in the solar system --
asteroids and cometary nuclei -- have been predicted on theoretical
grounds for a long time, even though there is no consensus among
planetary scientists about the actual numbers of such systems.

Hints about the existence of asteroid satellites also come from the
presence of double impact craters on the Moon and other planetary
surfaces. This suggests that the projectiles forming these craters were
`double' asteroids. Moreover, measurements obtained when an asteroid
passes in front of a relatively bright star (a so-called `occultation')
have on a few occasions shown features which could be interpreted as
due to the presence of a satellite. However, because of the difficult
nature of such measurements, it has never been possible to draw
unambiguous conclusions.

The existence of double asteroids was invoked earlier by Petr Pravec
and Gerhard Hahn to explain the unusual features observed in the
lightcurves of two other Earth-approaching asteroids 1991 VH and 1994
AW1. In the case of Dionysus, however, it is possible to predict
eclipse events and to confirm them by subsequent measurements.

There is therefore mounting evidence that asteroid binary systems might
be comparatively common. Observational programmes like the present one
by the DLR and Ondrejov groups will help to verify this possibility.

Where to find additional information

Detailed and up-to-date information about (3671) Dionysus can be found
in the Web at the following URL: http://earn.dlr.de/dionysus.

Notes:

[1] This institute and its parent organisation are known in Germany as
Institut fuer Planetenerkundung and Deutsche Forschungsanstalt fuer
Luft- und Raumfahrt e.V. (DLR).

[2] See ESO Press Release 09/94 of 18 May 1994.

[3] Asteroids are small solid planetary bodies revolving around the Sun
in orbits that are mostly located in the so-called Main Asteroid Belt,
confined between the orbits of Mars and Jupiter. Most of them are
thought to be fragments derived from catastrophic, past collisions
between larger asteroids. By mid-1997, the orbits of about 8000
asteroids in the solar system were sufficiently well known to allow
them to be officially numbered by the rules of the International
Astronomical Union. (3671) Dionysus was discovered in 1984 at the
Palomar Observatory (California, USA) and is named after the Greek god
of wine.

[4] The gravitational influence of the giant planet Jupiter can modify
the orbits of asteroids located in particular regions of the Main Belt
(the effect is refered to as `orbital perturbations'). As a result, the
orbit of an asteroid may `cross' that of a major planet, and eventually
it may become a NEO, i.e. a near-Earth object. The orbits of NEO's are
highly unstable over times comparable to the age of the solar system.
This instability can result in a collision with one of the terrestrial
(inner) planets, or with the Sun, or in the ejection of the asteroid
out of the solar system. The present orbit of (3671) Dionysus is such
that this object is not likely to collide with the Earth in the
foreseeable future.

[5] The method of analyzing the lightcurve of Dionysus consists of
`removing' (subtracting) the normal short-period brightness variations
due to rotation of the asteroid and plotting the residuals against
time, cf. Press Photo 20/97. The residual lightcurve shows a clear
resemblance with typical lightcurves of eclipsing binary stellar
systems (in which two stars move around each other, producing mutual
eclipses) and leads to a model of two bodies revolving around a common
gravitational centre, in an orbital plane containing both the Earth and
the Sun.


----------------------------------------------------------------------------
Information from the European Southern Observatory

ESO Press Photo 20/97

For immediate release: 22 July 1997


Lightcurves of Asteroid (3671) Dionysus

This figure shows the lightcurve data from observations of asteroid
(3671) Dionysus, made from ESO on June 8th, 1997. These observations
confirm that this asteroid is accompanied by a small moon (natural
satellite).

In this diagramme, the abscissa indicates the time and the ordinate the
light intensity (brightness), expressed on the logarithmic magnitude
scale. The three curves have been shifted vertically by an arbitrary
amount so as not to overlap.

The upper curve shows the `normal', periodic light variation due to the
2.7 hour rotation of the irregularly shaped asteroid. This curve has
been derived by fourier analysis of photometric observations taken
during the period June 1-16.

The middle curve displays the observations taken on June 8th, revealing
an eclipse event.

The bottom curve represents the difference between the observed curve
(middle) and the average curve (upper). This procedure `removes' the
light variations caused by the rotation of the asteroid. The minimum
caused by an eclipse in the double asteroid system is now clearly seen.
The similarity with the lightcurve of a partial eclipse in a double
stellar system is striking.

This is the caption to ESO PR Photo 20/97 [GIF, 10k] which accompanies
ESO Press Release 08/97 (21 July 1997). It may be reproduced, if credit
is given to the European Southern Observatory.

Copyright ESO Education & Public Relations Department
Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany

-



*

Date sent: Wed, 23 Jul 1997 08:37:35 -0400 (EDT)
From: Benny J Peiser <B.J.PEISER@livjm.ac.uk>
Subject: New Studies of Martian Meteorite Launched
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL

from: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>

National Science Foundation

NSF PR 97-50 July 17, 1997

Media contact:
Lynn Simarski
(703) 306-1070/lsimarsk@nsf.gov

Don Savage
NASA Headquarters
(202) 358-1547

Program Contact:
Scott Borg
(703)306-1033/sborg@nsf.gov

NEW STUDIES OF MARTIAN METEORITE LAUNCHED

The National Science Foundation has awarded grants for seven new
projects to study Martian meteorite ALH84001 in greater depth. The
grants are part of a coordinated program with NASA to further
investigate possible traces of ancient life in the Martian rock.

After the announcement last August that the meteorite may harbor
fossils of ancient Martian life, NSF and NASA called for further
research into the evidence. The agencies set up a coordinated,
interdisciplinary program which included joint review of research
proposals. NASA announced on June 19 that it had awarded 16 individual
grants under the program.

NSF's seven new grants, totaling nearly $800,000 for projects over two
or three years, will use advanced instrumentation to further analyze
the provocative rock. Some projects will study ALH84001 itself. Others
will investigate analogous features in terrestrial rocks from
environments that may resemble those of ancient Mars -- hot springs and
other extreme habitats of earthbound microbes -- to provide a better
context for understanding the tiny structures in the Martian rock.

Meteorite ALH84001 is one of about 8,000 meteorites collected in
Antarctica by U.S. researchers. NSF is the lead agency for managing the
collection and distribution of Antarctic meteorites, done in
collaboration with NASA and the Smithsonian Institution. Samples of
ALH84001 are being sent to the researchers from the Antarctic Meteorite
Laboratory at NASA's Johnson Space Center in Houston. The samples,
typically only a few grams apiece, are handled similarly to the lunar
samples collected during the Apollo program.

The new research will include scanning the meteorite for extremely
fine-scale alteration of the mineral interface by microbes. Other
studies will focus on the meteorite's carbon isotopes to see if they
reflect a ratio typical of microbial life, and develop a chemical
method to fingerprint biological activity in meteorites using different
isotopes of iron, some of which may be taken up preferentially by
living organisms.

Still other projects will look at mineral particles -- oxides and
sulfides of iron -- with potential as "biomarkers" (signs of past life)
both in the Martian meteorite and in bacteria on Earth. Some
researchers will attempt to: fix the temperature and fluid composition
under which the meteorite's minerals formed, presently an area of
controversy; develop thermodynamic models for mineral alteration in
hydrothermal environments; and delineate the rock's temperature history
and its past infiltration by fluids.

Institutions receiving the grants are the University of
Wisconsin-Madison, the University of Wisconsin-Milwaukee, California
Polytechnic State University-San Luis Obispo, Iowa State University,
Arizona State University, University of Minnesota, University of
California-Santa Cruz, University of Hawaii, Washington University in
St. Louis, and the California Institute of Technology.

-NSF-

Editors: For further details on the new grants, contact Scott Borg, NSF
polar earth sciences program manager, at 703-306-1033, or by e-mail at:
sborg@nsf.gov.



*

Date sent: Wed, 23 Jul 1997 08:34:34 -0400 (EDT)
From: Benny J Peiser <B.J.PEISER@livjm.ac.uk>
Subject: FIREBALL RELEASE
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL

USAF SATELLITES RECORD ATMOSPHERIC FIREBALL DISINTEGRATION

from: Rolf Sinclair/NSF Physics Division <rsinclai@nsf.gov>

Regarding the USAF News Release about the event that occurred over the
Indian Ocean near the Cocos Island:

It is interesting to rephrase the energy released: since the radiant
energy (7.2E11 joules) is of order 5-10% of the total energy
dissipated, the event was a few kilotons total (taking 4.184E9 joules =
1 ton TNT-explosive-equivalent). This is rather small as such things
go, since the Tunguska event was about 15 Megatons. It does point out
that rather "small" events can be detected by these means. (Small in
the sense of the damage they'd do to humans en masse.)

It would be useful to obtain an estimate of the efficiency with which
such events would be detected by these means as a function of energy
release. It does appear that it would be easy to monitor the rate of
multi-kiloton events. This event occurred at about 4:30 AM local time.
It must have been just before or at local dawn. It would be interesting
to know if the event was visible to the naked eye.

Rolf Sinclair
-------------------------------------------------------------------------------

From: PETER@danlon.physics.uwo.ca
Date: Mon, 21 Jul 1997 19:09:39 -0400 (EDT)
Subject: FIREBALL RELEASE

USAF NEWS RELEASE

From: Headquarters Air Force Technical Applications Center
Office of Public Affairs
Patrick AFB, Fl.,
32925-3002
(407)-494-7332

Date: July 21, 1997

*********************************************************************
On 27 April, 1997 at 22:34:21 UT, sensors aboard U.S. Department of
Defense satellites recorded the bright flash of an apparent meteoroid
disintegration in the atmosphere. The location of the flash was
approximately 16.6S, 87.5E. Peak flash intensity recorded (assuming a
6000K blackbody radiation (BB) model) was 3.0E11 watts per steradian,
corresponding to a visual magnitude of -22.7. Total radiated energy,
using the same 6000K BB model, was 7.2 E11 joules.

For further information, contact Air Force Technical Applications
Center Public Affairs at (407) 494-4403.
*********************************************************************

PLEASE NOTE: THIS USAF BOLIDE INFORMATION RELEASE AND ALL PREVIOUS
RELEASES CAN BE FOUND ON THE WWW AT
http://phobos.astro.uwo.ca/~pbrown/usaf.html



CCCMENU CCC for 1997

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