[meteorite-list] Hubble Zooms in on Comet 17P/Holmes

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 15 Nov 2007 17:46:58 -0800 (PST)
Message-ID: <200711160146.RAA15646_at_zagami.jpl.nasa.gov>

http://www.spacetelescope.org/news/html/heic0718.html

Photo Release - heic0718: Hubble zooms in on heart of mystery comet

15-Nov-2007: The NASA/ESA Hubble Space Telescope has probed the bright
core of Comet 17P/Holmes which, to the delight of sky watchers,
mysteriously brightened by nearly a million-fold in a 24-hour period
beginning October 23, 2007.

Astronomers have used Hubble's powerful resolution to study Comet
Holmes' core for clues about how the comet brightened. The orbiting
observatory's Wide Field Planetary Camera 2 (WFPC2) monitored the comet
for several days, snapping images on 29 Oct., 31 Oct. and 4 Nov.
Hubble's crisp "eye" can see details as small as 54 kilometres across,
providing the sharpest view yet of the source of the spectacular
brightening.

The Hubble image at right, taken on 4 Nov., shows the heart of the
comet. The central portion of the image has been specially processed to
highlight variations in the dust distribution near the nucleus. About
twice as much dust lies along the east-west direction (the horizontal
direction) as along the north-south direction (the vertical direction),
giving the comet a "bow tie" appearance.

The composite colour image at left, taken Nov. 1 by the amateur
astronomer Alan Dyer, shows the complex structure of the entire coma,
consisting of concentric shells of dust and a faint tail emanating from
the comet's right side.

The nucleus - the small solid body that is the source of the comet's
activity - is still swaddled in bright dust, even 12 days after the
spectacular outburst. "Most of what Hubble sees is sunlight scattered
from microscopic particles," explained Hal Weaver of The Johns Hopkins
University Applied Physics Laboratory of Laurel, Maryland in the USA,
who led the Hubble investigation. "But we may finally be starting to
detect the emergence of the nucleus itself in this final Hubble image."

Hubble first observed Comet 17P/Holmes on June 15, 1999, when there was
virtually no dusty shroud around the nucleus. Although Hubble cannot
resolve the nucleus, astronomers inferred its size by measuring its
brightness. Astronomers deduced that the nucleus's diameter was
approximately 3.4 kilometres, about the distance between the Arc de
Triomphe and the Louvre glass pyramid in Paris. They hope to use the new
Hubble images to determine the size of the comet's nucleus to see how
much of it was blasted away during the outburst.

Hubble's two earlier snapshots of Comet Holmes also showed some
interesting features. On 29 Oct. the telescope spied three "spurs" of
dust emanating from the nucleus while the Hubble images taken on 31 Oct.
revealed an outburst of dust just west of the nucleus.

The Hubble images however do not show any large fragments near the
nucleus of Comet Holmes, unlike the case of Comet
73P/Schwassmann-Wachmann 3 (SW3). In the spring of 2006 Hubble
observations revealed a multitude of "mini-comets" ejected by SW3 after
the comet increased dramatically in brightness. Ground-based images of
Comet Holmes show a large, spherically symmetrical cloud of dust that is
offset from the nucleus, suggesting that a large fragment broke off and
subsequently disintegrated into tiny dust particles after moving away
from the main nucleus. Unfortunately, the huge amount of dust near the
comet's nucleus and the relatively large distance from Earth (240
million kilometres, or 1.6 astronomical units for Holmes versus 15
million kilometres, 0.1 astronomical units for SW3), conspire to make
detecting fragments near Holmes nearly impossible right now, unless the
fragments are nearly as large as the nucleus itself.

Notes for editors:

The Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency.

The Applied Physics Laboratory, a not-for-profit division of The Johns
Hopkins University, meets critical national challenges through the
innovative application of science and technology. For more information,
visit www.jhuapl.edu.

The Hubble Comet Holmes observing team comprises H. Weaver and C. Lisse
(The Johns Hopkins University Applied Physics Laboratory); P. Lamy
(Laboratoire d'Astrophysique de Marseille, France); I. Toth (Konkoly
Observatory, Hungary); M. Mutchler (Space Telescope Science Institute);
W. Reach (California Institute of Technology); and J. Vaubaillon
(California Institute of Technology).

Credit for Hubble image: NASA, ESA, and H. Weaver (The Johns Hopkins
University Applied Physics Laboratory)

Credit for ground-based image: A. Dyer, Alberta, Canada

Links:

NASA photo release <http://hubblesite.org/news/2007/40>
Johns Hopkins University <http://www.jhuapl.edu>

Contacts:

Philippe Lamy
Laboratoire d'Astrophysique de Marseille, France
Tel.: +33-4-91-05-59-32
Cellular: +33-630-14-92-33
E-mail: philippe.lamy at oamp.fr

Lars Lindberg Christensen
Hubble/ESA, Garching, Germany
Tel: +49-(0)89-3200-6306
Cellular: +49-(0)173-3872-621
E-mail: lars at eso.org

Donna Weaver/Ray Villard
Space Telescope Science Institute, Baltimore, USA
Tel: +1-410-338-4493/4514
E-mail: dweaver at stsci.edu/villard at stsci.edu

Mike Buckley
Johns Hopkins University Applied Physics Laboratory, Laurel, USA
Tel: +1-240-228-7536
E-mail: mike.buckley at jhuapl.edu

Dr. Hal Weaver
Johns Hopkins University Applied Physics Laboratory, Laurel, USA
Tel: +1-443-778-8078
E-mail: hal.weaver at jhuapl.edu
Received on Thu 15 Nov 2007 08:46:58 PM PST