[meteorite-list] Rosetta Observes Comet Impact

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Jul 4 21:04:47 2005
Message-ID: <200507050019.j650J2J18367_at_zagami.jpl.nasa.gov>

http://www.esa.int/SPECIALS/Rosetta/SEMQR06DIAE_0.html

Dust and gas from Comet 9P/Tempel 1 seen by ESA OGS
European Space Agency
Rosetta
5 July 2005

[Image]
Dust from Comet 9P/Tempel 1 seen with the ESA OGS (red filter)
 
Dust and gas are seen in these images of Comet 9P/Tempel 1, as observed
with the 1-metre ESA Optical Ground Station (OGS) telescope, located at
the Observatorio del Teide on Tenerife, Canary Islands.
 
Two different filters have been used in different visible light
observations to study different aspects of the comet's nature. Red
'broadband' filters allowed the detection of dust, while blue
'narrowband' filters, filtering only carbon gaseous compounds, allow the
observations to concentrate mainly on the gas emissions of the comet.

The first set of images (above) here were taken with a broadband red
filter, four days before and about 15 hours after the impact
respectively. The images were exposed for 10 minutes and show the dust
coma of the comet. The dust brightness has increased by 50 percent.

 
 
A strong jet has recently appeared as a direct result of the impact,
pointing north-north-east. The overall coma is very asymmetric in
appearance. All structures must have been created by the outburst
triggered by the impact.
 
 
[Image]
Coma gas from Comet 9P/Tempel 1 seen with the ESA OGS telescope
(narrowband filter)
 
 
The second set of images of Tempel 1 from the OGS telescope use a
narrowband filter (C2 emission band). They show the coma gas mixed with
smaller-sized dust particles than observed in the broadband red filtered
image.

The observations were taken two days before and about 16 hours after the
impact respectively. Also here the coma brightness has increased by 50
percent. Again the same strong jet is visible.

 
 
[Image]
Dust from Comet 9P/Tempel 1 seen with ESA OGS (blue/red filters)
 
In the third set of images, Tempel 1 is seen about 16 hours after the
impact. The two images show the refection of blue (BC filter) and red
(RC filter) light from the dust cloud surrounding the comet nucleus.

These reflections show different dust particle sizes, with blue
particles being smaller than red particles. It is clear that the jet
structure of the smaller dust particles points towards the north (BC
image), whereas the jet composed of larger dust particles (RC image) is
rotated by about 45 degrees towards the north-east.

This means that the direction in which the dust particles were ejected
from the comet nucleus after impact seems to depend on the particle size.

These images introduce ESA?s OGS telescope to the network of Earth-based
observatories already taking part in the one of world?s largest
astronomical observation campaigns - looking at results of the 4 July
comet impact event.
 
For more information:
 
Rita Schulz, Principal Investigator for OGS observations, ESA-ESTEC (The
Netherlands)
E-mail: rita.schulz _at_ esa.int

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http://www.esa.int/SPECIALS/Rosetta/SEMSJ06DIAE_0.html

Rosetta camera view of Tempel 1 brightness
Eropean Space Agency
4 July 2005

These animations, composed of images taken by the OSIRIS Narrow Angle
Camera on board ESA's Rosetta spacecraft, shows how the brightness of
Comet 9P/Tempel 1 developed after impact.
 
 
[Image]
False-colour representation of comet brightness (still)

The separate false-colour images in this sequence from OSIRIS were taken
at five-minute intervals around the impact time of 07:52 CEST (05:52
GMT/UT).

Although in the false-colour images (a still seen here at right) the
increase in visual brightness is not so obvious, it becomes very clear
in the animated surface plot below.

 
 
[Image]
Increase in visual brightness plotted in 3D

In this second animation, at left, the brightness of image pixels seen
by OSIRIS is plotted 'three-dimensionally', i.e. the brighter they are,
the higher they are in the plot.
 
 
[Image]
Still from animated surface plot

Here a still image shows the first and last image from the animated
sequence above.
 
 
[Image]
A 'light curve' of Comet 9P/Tempel 1

Using its clear filter, the OSIRIS Narrow Angle also produced a 'light
curve' of Comet 9P/Tempel 1. This shows how the comet's intensity varies
in time, starting from impact.

The light curve shows that about 30 minutes after impact the brightness
of the comet had increased by five times.

After this phase, scientists also noticed that the brightness level
fluctuated for about one hour with no overall increase, then seemed to
decrease, but much more slowly than the initial increase.

As more data come in from Rosetta, ESA scientists will be able to refine
images and results.

 
 
For more information:
 
Gerhard Schwehm, ESA Rosetta Project Scientist
E-mail: gerhard.schwehm _at_ esa.int
 
Received on Mon 04 Jul 2005 08:19:00 PM PDT