* Astronomy

These images, taken by the Optical Monitor on board ESA's XMM-Newton observatory on 3 and 4 July 2005, show a comparison between the states of the comet before and just after impact.


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The images were taken in the blue (top) and ultraviolet channels (bottom) of the instrument. The ultraviolet images show the emissions of hydroxyl ions, the direct decay product of water.
About 1.5 hours after the impact, the brightness of hydroxyl groups is increased by a factor of about five. Later, about 4.5 hours after the impact the ultraviolet emission is decreased again which indicates that the peak has passed.

The presence of water in Tempel 1 is consistent with preliminary measurements of the composition of the comet made last week by the ALICE instrument on ESA's Rosetta spacecraft.

Time line

All times are approximate, Earth-received time, Central European Summer Time (CEST)

4 July
07:52 - IMPACT
08:10 - NASA expected to confirm impact
12:00 - First NAVCAM image of impact from Rosetta space probe expected
17:00 - First science results from Rosetta expected after 17:00
17:30 - Debris cloud expected to reach maximum brightness
20:00 - First images expected from Hubble Space Telescope
22:00 - First image expected from ESO Chile
22:30 - ESA's OGS Tenerife begins observations
5 July
00:30 - First images expected from OGS Tenerife
02:00 - More images expected from ESO Chile

Comet Tempel 1 produced a blast that has scientists puzzling over at NASA's Jet Propulsion Laboratory in California.

"Geez, and we thought it was going to be subtle. That was considerably brighter, and had considerably more material coming out, than I had expected" -Don Yeomans, JPL scientist of the Deep Impact science team.

The aim of the cosmic collision was to punch a hole in the comet's crusty surface and reveal details about the primordial material in the interior of the comet.
One reason for the spectacular burst could be that puncturing the comet's crust released subsurface pressure, allowing a much bigger plume of ejecta to spurt out.

A few amateur astronomers noted a that the comet has brightened by 2 magnitudes.

NASA's Hubble Space Telescope captured the dramatic effects of the collision.


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This sequence of images shows the comet before and after the impact.
The image at left shows the comet about a minute before the impact. The encounter occurred at 05:52 GMT.
In the middle image, captured 15 minutes after the collision, Tempel 1 appears four times brighter than in the pre-impact photo. Astronomers noticed that the inner cloud of dust and gas surrounding the comet's nucleus increased by about 200 kilometers in size. The impact caused a brilliant flash of light and a constant increase in the brightness of the inner cloud of dust and gas.
The Hubble telescope continued to monitor the comet, snapping another image (at right) 62 minutes after the encounter. The gas and dust ejected during the impact are expanding outward in the shape of a fan. The fan-shaped debris is traveling at about 1,800 kilometres an hour, or twice as fast as the speed of a commercial jet. The debris extends about 1,800 kilometres from the nucleus.

"How a washing-machine sized impactor could produce such a large disturbance is going to take some explanation" -Don Yeomans.

Even before the impact itself, the twin spacecraft - the impactor itself, and the flyby craft which moved aside to observe it - were both returning images far more detailed than any previous images of a comet's nucleus. At about 28 centimetres, the maximum image resolution is almost 100 times better than the previous best comet images, taken in 2004 by the Stardust mission.

The pictures show numerous perfectly circular features, which could either be impact craters or sinkholes. They also display long linear features and a varied topography of rough areas and one smooth region.
Dozens of observatories on Earth, as well as four in orbit, were also watching the comet at the time of impact, during which the comet brightened to six times its pre-impact level.
It will take days to collect and analyse all the measurements.
But it is already clear that there are some unidentified spectral features in the light reflected from the ejected material, meaning the mission's goal of learning new things about the internal composition of the comet will clearly be fulfilled.



And the amazing images returned by the probe immediately after the impact represent just 10% of the total taken.

"There are many more spectacular images." - Michael A'Hearn
The Deep Impact team were not only delighted by the success of the impact, but also by the survival of the flyby spacecraft after it was spattered by debris from the comet`s tail, or coma.

"It is completely intact" - Keyur Patel, the Deep Impact deputy project manager. And pictures returned since show that the craft's optics survived as well, escaping a feared sandblasting of its lenses.
But there is one possible downside to the spectacular plume produced by the impact; The fan of dust was so large, bright and long lasting that it may have blocked the flyby craft's attempts to take pictures of the resulting crater.
The craft only had a 13-minute window to take such pictures.

"The dust we kicked up made things a little more difficult - it's fairly opaque" - Don Yeomans .

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After 172 days and 268 million miles of deep space stalking, Deep
Impact successfully reached out and touched comet Tempel 1. The collision between the coffee table-sized impactor and city-sized comet occurred at 05:52 GMT.

"The challenges of this mission and teamwork that went into making it a success, should make all of us very proud." - Rick Grammier, Deep Impact project manager, NASA's Jet Propulsion Laboratory

"This mission is truly a smashing success. Tomorrow and in the days ahead we will know a lot more about the origins of our solar system" - Andy Dantzler, director of NASA's Solar System Division.

Official word of the impact came 5 minutes after impact when, at 05:57 GMT, an image from the spacecraft's medium resolution camera was downlinked to the computer screens of the mission's science team showed the tell-tale signs of a high-speed impact.

"The image clearly shows a spectacular impact. With this much data we have a long night ahead of us, but that is what we were hoping for. There is so much here it is difficult to know where to begin." - Dr. Michael A'Hearn, University of Maryland, Deep Impact principal investigator.

The celestial collision and ensuing data collection by the nearby Deep Impact mothership was the climax of a very active 24 hour period for the mission which began with impactor release at 06:07 GMT on July 3.
Deep space manoeuvres by the flyby, final checkout of both spacecraft
and comet imaging took up most of the next 22 hours. Then, the impactor got down to its last two hours of life.

"The impactor kicked into its autonomous navigation mode right on
Time. Our preliminary analysis indicates the three impactor targeting manoeuvres occurred on time at 90, 35 and 12.5 minutes before impact." - Shyam Bhaskaran, Deep Impact navigator.

At the moment the impactor was vaporizing itself in its 6.3 miles a
second collision with comet Tempel 1, the Deep Impact flyby spacecraft
was monitoring events from nearby and will continue to do so for the
next several days.

"The flyby surviving closest approach and shield mode has put the cap on an outstanding day. Soon, we will begin the process of down linking all the encounter information in one batch and hand it to the science team" - Rick Grammier.

Deep Impact will provide a glimpse beneath the surface of a comet,
where material from the solar system's formation remains relatively
unchanged.
Mission scientists expect the project will answer basic questions about the formation of the solar system, by offering a better look at the nature and composition of the frozen celestial travellers known as comets.

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The flyby spacecraft continued to send back images, some of which still showed a bright cone of debris coming from the comet's new crater some 45 minutes after impact.
The flyby craft passed by the nucleus through the heaviest dust of the coma.

"It came out the other side without a single system damaged" Keyur Patel, deputy project manager at the Jet Propulsion Laboratory.


"Unbelievable. How did we make such a big splash?" -Don Yeomans, JPL.

Ground-based and space-based telescopes, such as Hubble, got images of the brightening of the comet, too.
Many more pictures will follow.
Come back here for other updates...

-- Edited by Blobrana at 10:08, 2005-07-04