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