[meteorite-list] Aussie Astronomers Prepare for Deep Impact

[Ron Baalke]

http://www.csiro.au/index.asp?type=mediaRelease&id=105Impact

Aussie astronomers prepare for smash hit
CSIRO Media Release
June 28, 2005

Astronomers at Australia's national radio and optical observatories will
watch as a probe released from a spacecraft slams into a comet about 133
million km away at a speed of nearly 37,000 km/h (10.2 km per second).

The cosmic demolition derby takes place about 4pm AEST on 4 July when
the comet, Tempel 1, will be most easily seen from the mid-Pacific.

The 370 kg probe, carried by NASA's Deep Impact spacecraft, has been
travelling toward the comet for 173 days and has travelled over 431
million km.

At the time of the collision the comet will be travelling at 108,000
km/h. The probe will be travelling in almost the same orbit at 80,000
km/h, and will hit the comet at an angle.

The impact may gouge out a crater up to 200 m across and 50 m deep, and
could lead to a flow of gas and dust from the comet's interior lasting
for months. This outflow is what ground-astronomers will be looking for.

The comet will appear to be near the star Spica, the brightest star in
the constellation Virgo, and also near the planet Jupiter. By the time
the sun sets for eastern Australia it will be high in the sky, almost
due north.

Before the impact the comet will not be bright enough to see with the
unaided eye. The impact may brighten it, but by how much is unknown.

When the copper-fortified probe hits the flying iceberg the crash will
be observed by the Deep Impact spacecraft, the Hubble Space Telescope,
and ground-based observatories around the world.

In Australia CSIRO's radio telescopes and the optical telescopes of the
Anglo-Australian Observatory will be watching.

CSIRO's radio telescopes can work in daylight and so scientists will be
able to watch the comet at the time of the impact, and for the following
seven hours.

The Anglo-Australian Observatory's telescopes will be able to see the
comet about two hours after the impact, after the sun has set in eastern
Australia.

Australian telescopes are better placed than telescopes in Europe and
North or South America to see any changes in the comet a few hours after
the impact.

"Australia has excellent radio telescopes," says Dr Paul Jones, a
Visiting Fellow at the Australia Telescope National Facility, who leads
the team using CSIRO's telescopes.

"We'll be looking for specific molecules erupting from the
comet-molecules you can most easily detect in the radio."

"It's not every day you get take part in an experiment like this," says
CSIRO's John Sarkissian, who will be observing with the Parkes
telescope. "We probably won't get another chance for some time."

Because the comet is moving across the sky faster than the background
stars, astronomers will have to use special observing techniques.

"We're going to have to drive the telescope manually at a predetermined
rate," says the Anglo-Australian Observatory's Dr Rob Sharp, who is
observing with the AAO's UK Schmidt telescope at Siding Spring Observatory.

"The Schmidt hasn't been used in this way for quite some time, so we'll
be relying on the expertise of the telescope operators."

Smashing into the comet will give astronomers access to the pristine
material of the comet's interior. Comets preserve material from the
early solar system but their surfaces have been chemically and
physically altered by the Sun's radiation.

The impact of the probe into the comet has been likened to a mosquito
running into a 767 airliner.

The impact will not appreciably modify the comet's orbital path and the
comet poses no threat to Earth now or in the foreseeable future.

CSIRO's Parkes telescope (near Parkes NSW) will be used to look for OH
molecules, which are a sign of water in the comet. CSIRO's Mopra
telescope (near Coonabarabran NSW) and Australia Telescope Compact Array
(near Narrabri NSW) will be used to look for HCN molecules, which are a
general marker for a range of carbon-based molecules.

The Anglo-Australian Observatory's UK Schmidt Telescope (near
Coonabarabran NSW) will be used to measure chemical abundances at many
spots on the comet simultaneously. The Anglo-Australian Telescope (near
Coonabarabran NSW) will study several compounds containing carbon and
nitrogen, to calculate isotope ratios for those elements.