[meteorite-list] SMART-1 to Crash the Moon

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Aug 30 12:10:14 2006
Message-ID: <200608301607.JAA14323_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/headlines/y2006/30aug_smart1.htm

SMART-1 to Crash the Moon
NASA Science News
August 30, 2006

August 30, 2006: Amateur astronomers, grab your telescopes. A spaceship
is about to crash into the Moon, and you may be able to see the impact.

The spacecraft: SMART-1, a lunar orbiter belonging to the European Space
Agency (ESA).

The impact site: Lacus Excellentiae (The Lake of Excellence), an ancient,
100-mile wide crater in the Moon's southern hemisphere.

The time to watch: Saturday, September 2nd at 10:41 p.m. PDT (Sept. 3rd,
0541 UT).

Why is SMART-1 crashing? There's nothing wrong with the spacecraft,
which is wrapping up a successful 3-year mission to the Moon. SMART-1's
main job was to test a European-built ion engine. It worked beautifully,
propelling the craft in 2003 on a unique spiral path from Earth to the
Moon. From lunar orbit, SMART-1 took thousands of high-resolution
pictures and made mineral maps of the Moon's terrain. One of its most
important discoveries was a "Peak of Eternal Light," a mountaintop near
the Moon's north pole in constant, year-round sunlight. Peaks of Eternal
Light are prime real estate for solar-powered Moon bases.

But now SMART-1 is running low on fuel. It has to come down sometime???and
soon - so ESA mission scientists decided to crash it in a place where the
crash can be seen from Earth and studied.

When SMART-1 hits the ground, it will explode in a flash of light. This
won't be the sort of explosion we'd see on Earth. The Moon has no oxygen
to support fire or combustion. Instead, the flash will be caused by
rocks and soil made so hot by the impact that they suddenly glow.

The area will be in complete darkness at the moment of impact, so much
the better to see the flash. How bright will it be? No one knows.
Estimates range from 7th to 15th magnitude. In other words, it might be
bright enough for backyard telescopes--or so dim that even big
professional observatories won't see a thing. The only way to find out
is to look. Observing tips may be found here
<http://www.lpl.arizona.edu/%7Erhill/alpo/lunarstuff/lunimpacts.html>
(ALPO) and here
<http://sci.esa.int/science-e/www/area/index.cfm?fareaid=98> (ESA).

"We'll be watching," says Bill Cooke, the head of NASA's Meteoroid
Environment Office at the Marshall Space Flight Center in Huntsville,
Alabama. "Measuring the brightness of SMART-1's impact is important to
our research."

His group at the Marshall Space Flight Center has spent the last year
watching things hit the Moon - not spacecraft, but meteoroids. "The Moon
is under constant bombardment from meteoroids," says Cooke. "They hit
the ground and explode just like SMART-1 will do." The Moon actually
sparkles, slowly and faintly, as one space rock after another hits the
ground.

[chart]
Above: Possible SMART-1 impact times and coordinates. Image courtesy:
ESA. [More <http://sci.esa.int/science-e/www/area/index.cfm?fareaid=98>]

Cooke's group has a knack for this kind of work: Using only two small
telescopes, they've spotted eight meteoroid impacts this year, almost
doubling the number of confirmed sightings in all of the history of
astronomy before 2006. Cooke attributes their success to improvements in
digital video cameras, which they use to record the brief flashes.

Lunar impacts interest NASA greatly. Astronauts are going back to the
Moon and "we need to know what kind of danger meteoroids pose to both
people and moon bases," explains Cooke. How often do they hit? And what
kind of damage do they do?

Think of SMART-1 as a controlled, man-made meteoroid impact, he says.
"We know exactly how much kinetic energy SMART-1 packs. And, if all goes
well, we're going to see how bright a flash it makes. This will help us
interpret our meteoroid data."

When SMART-1 hits, it won't plunge straight into the ground. "The
spacecraft will enter Lacus Excellentiae at a shallow angle, only a few
degrees from horizontal," notes Cooke. For this reason, it will gouge a
long, narrow crater, about a meter wide and many meters long. The
grazing impact should kick up a plume of debris - no one knows how high.
If it rises high enough, the plume might catch some sunlight and become
visible to telescopes on Earth. The chances of this, however, are slim.
The main event is the flash of heat and light at the "point" of impact.

Another side-effect of the shallow approach is uncertainty about when,
exactly, SMART-1 will strike. The spacecraft is due to glide low over
the floor of Lacus Excellentiae several times on Sept. 3rd. Mission
controllers believe it will hit on orbit number 2890 at 0541 UT. But it
could equally well hit one orbit earlier or one orbit later.
Possibilities are summarized in the table, above. The nominal impact
time favors observers in western parts of North America and across the
Pacific Ocean. Depending on when SMART-1 hits, however, almost anyone
could catch the flash.

Visit the SMART-1 home page
<http://sci.esa.int/science-e/www/area/index.cfm?fareaid=98> for updates
and more information.
Received on Wed 30 Aug 2006 12:07:25 PM PDT