On the night of July 4, 2005, all ESO telescopes continued their extensive
observing campaign of Comet Tempel 1. But this time, they were able to see the
effect of the impact on the comet. The astronomers were clearly not
disappointed.

The impact occurred at 07:52 CEST but because the comet has already set in Chile
at that time, observers at the La Silla Paranal Observatory could only start
observing several hours later. The first observations were done in the infrared
by TMMI2 at the 3.6m telescope at La Silla, at 21:20 CEST (still daylight in
Chile).

These first observations showed the comet to be 2 to 3 times brighter in the
infrared than the day before the impact. The coma is also much more extended
than it was until before the impact.

At sunset in Chile, all 7 telescopes of the La Silla Paranal Observatory went
into operations. The FORS2 multi-mode instrument on Antu, one of the 8.2m Unit
Telescope of the VLT array, took stunning images, showing that the morphology of
the comet had dramatically changed: a new bright fan-like structure was now
visible.

The fan lies in the southern part of the image and is rather bright and well
defined. This feature is an addition to those that were already visible during
the previous days, that seems to still be underlying the new one. Behind this
fan, the old coma from yesterday is still present. The new structure is about
15,000 km large, indicating that the matter has been ejected with a speed of
about 700 to 1,000 km/h.

Further observations during the week will study the evolution of this fan,
revealing if the probe has activated a new region of the surface and how long
that region remains active.

The fan is visible through the reflection of sunlight on dust grains. The fact
that the big plume is not uniform in colour probably indicates that different
dust size are traveling at different speeds.

Other telescopes have provided observations of the comet as well. NACO took some
images of the central part of the coma, while UVES performed high-dispersion
spectroscopy of the comet, in order to compare with the previous nights. First
estimates indicate the emission lines to be more pronounced by 10 to 20 %.

At La Silla, the SOFI instrument at the NTT telescope, imaged the comet in the
near-infared. An image in the J-band also shows the dust shell from the impact
in the south-western quadrant of the coma. The very inner coma (indicated by the
white box) shows on-going enhanced activity compared to the pre-impact level.

The astronomers at the La Silla Paranal Observatory will continue to observe
Comet Tempel 1 for another four days in order to monitor precisely its long-term
behaviour.

All the images and links are available at http://deepimpact.eso.org/obseso8.html

With kind regards,

The ESO Public Affairs Dept.