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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).
Right:
The impact site, with current moon phase shown. Updated daily.
Image courtesy: ESA. [More]
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
(ALPO), here
(ESA) and, in many languages, here
(REA Brazil).
"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.
![see caption](images/smart1/threeorbits3.jpg)
Above:
Possible SMART-1 impact times and coordinates. Image courtesy:
ESA. [More]
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 for updates and more information.
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Author: Dr. Tony
Phillips | Production Editor:
Dr. Tony Phillips | Credit: Science@NASA
More
Information |
A
message from ESA SMART-1 project scientist Bernard H.
Foing: "We
welcome the American amateur and professional observers
to join the SMART-1 impact campaign. US colleagues will
perform observations from mainland and NASA IRTF at
Hawaii, and we look for the complete picture from these
worldwide data. SMART-1 impact is also an interesting
dry run, in preparation for NASA LCROSS
impactor that will target polar ice deposits in
early 2009".
Lunar
Impacts, Observing Tips for Amateurs -- from the
Association of Lunar and Planetary Observers.
More
observing tips -- from the Secção Lunar / REA -
BRASIL
SMART-1
-- ESA home page
Right:
SMART-1 approaches the Moon, an artist's concept. Credit:
ESA. [More]
Crash
Landing on the Moon -- (Science@NASA) In 2009, a
NASA spacecraft called LCROSS will crash into the Moon
in search of lunar water.
A
Meteoroid Hits the Moon -- (Science@NASA) NASA astronomers
video-taped a space rock hitting the Moon.
The
Sky is Falling -- (Science@NASA) Every day more
than a metric ton of meteoroids hits the Moon
The
Vision for Space Exploration |
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