[meteorite-list] How To Observe SMART-1's Impact on the Moon

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Sep 1 19:26:40 2006
Message-ID: <200609012326.QAA08599_at_zagami.jpl.nasa.gov>

http://www.newscientistspace.com/article/dn9891-how-to-observe-smart1s-impact-on-the-moon.html

How to observe SMART-1's impact on the Moon
David Shiga
New Scientist
01 September 2006

When it collides with the Moon on Saturday night, the SMART-1 spacecraft
might create a bright spot of light that could be visible using a simple
pair of binoculars. The effect could last about a minute - but will only
be visible from some parts of the world.

The European Space Agency's SMART-1 probe has been orbiting and studying
the Moon since late 2005. But it is almost out of fuel, and mission
planners have adjusted its orbit to make it crash on the Moon at a time
and place that will be visible from Earth (see Lunar probe aims to crash
into the Moon
<http://www.newscientistspace.com/article/dn9830-lunar-probe-aims-to-crash-into-the-moon.html>).

The expected impact time is 1041 PDT on Saturday (0541 GMT on Sunday).
It will be visible in an area that extends from the central parts of
North and South America westward as far as Australia. Unfortunately,
observers on the eastern coast of the Americas - except for Florida -
and in Europe and Asia will not be able to view the crash.

The spacecraft will come screaming in at an angle of just 1? relative to
the lunar surface. So there is a small chance that the spacecraft could
crash earlier, at 0036 GMT, if it hits the rim of a crater called
Clausius before it can reach the planned impact site. If it were to hit
the rim, whose height is not known precisely, the impact would be
visible mainly from South America and the North American East coast.

Final burn

However, mission planners are performing one last burn on Friday to
raise the spacecraft's orbit by 600 metres and prevent an early crash.
"We want to be sure we avoid this rim," SMART-1 project scientist
Bernard Foing told New Scientist.

SMART-1 will be travelling at 2 kilometres per second when it hits the
surface and is expected to blast out a crater 3 to 10 metres across.
Heat from the impact should vaporise rock and soil in the area, creating
a flash of light that will last about 0.1 second. The flash itself will
probably be too faint to see except with very large telescopes.

But the impact will also throw up a plume of material that could be much
brighter. The Moon will be a little more than half lit, with the impact
site on the dark side, not far from the Moon's south pole. If the plume
is lofted as much as 20 kilometres above the surface, it will reach
sunlight.

If only 1% of the ejected material rises that high, this would create a
cloud with a brightness of about magnitude 6, "which would be visible
with binoculars or a small telescope", Foing says. The cloud might stay
lit for a few tens of seconds before falling back to the surface, he says.

Foing estimates the cloud might be about 10 kilometres across.
Relatively large telescopes may be able to resolve smaller structures
within the cloud, but small telescopes or binoculars will probably only
show a point of light, he says. Listen to Foing describe the impact on
New Scientist's latest podcast
<http://media.newscientist.com/data/av/podcast/newsci-20060901-another-one-bites-the-moon-dust.mp3>.

Known impactor

Scientists hope to learn more about the physics of impacts by studying
the SMART-1 crash. "Impacts are important in the history of the solar
system," Foing says. "They shape the planets at different scales."

Scientists have managed to glimpse meteorites hitting the Moon before,
and SMART-1 may resemble these impacts. Watch a movie of a meteorite
hitting the Moon
<http://www.spaceweather3.com/swpod2006/14jun06/movie760.gif>.

But Foing says the SMART-1 impact will be more informative than previous
observations of meteorite impacts because the mass and speed of the
impacting object are known precisely ahead of time.

A Japanese space probe called Hiten was also observed from Earth when it
was intentionally crashed into the Moon in 1993. But those previous
impacts have not been as widely observed as the SMART-1 crash will be,
Foing says.

About a dozen professional observatories will watch for the impact,
including NASA's Infrared Telescope Facility in Hawaii, US, and the
Earth-orbiting Odin radio telescope.
Received on Fri 01 Sep 2006 07:26:37 PM PDT