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October
5, 2009: Just imagine. A spaceship plunges out of
the night sky, hits the ground and explodes. A plume of debris
billows back into the heavens, leading your eye to a second
ship in hot pursuit. Four minutes later, that one hits the
ground, too. It's raining spaceships!
 Put
on your hard hat and get ready for action, because on Friday,
Oct. 9th, what you just imagined is really going to happen--and
you can have a front row seat.
Right:
A computer visualization of LCROSS hitting the Moon on Oct.
9th. Credit: NASA/Ames
The
impact site is crater Cabeus near the Moon's south pole. NASA
is guiding the Lunar Crater Observation and Sensing Satellite
("LCROSS" for short) and its Centaur booster rocket
into the crater's floor for a spectacular double-impact designed
to "unearth" signs of lunar water.
There
are two ways to watch the show.
First,
turn on NASA TV.
The space agency will broadcast the action live from the Moon,
with coverage beginning Friday morning at 3:15 am PDT (10:15
UT). The first hour or so, pre-impact, will offer expert commentary,
status reports from mission control, camera views from the spacecraft,
and telemetry-based animations.
The
actual impacts commence at 4:30 am PDT (11:30 UT). The Centaur
rocket will strike first, transforming 2200 kg of mass and
10 billion joules of kinetic energy into a blinding flash
of heat and light. Researchers expect the impact to throw
up a plume of debris as high as 10 km.
Close
behind, the LCROSS mothership will photograph the collision
for NASA TV and then fly right through the debris plume. Onboard
spectrometers will analyze the sunlit plume for signs of water
(H2O), water fragments (OH), salts, clays, hydrated
minerals and assorted organic molecules.
"If
there's water there, or anything else interesting, we'll find
it," says Tony Colaprete of NASA Ames, the mission's
principal investigator.
Above:
The lunar south pole as it will appear on the night of impact.
Photo Credit - NMSU / MSFC Tortugas Observatory. [larger
image]
Next
comes the mothership's own plunge. Four minutes after the
Centaur "lands," the 700 kg LCROSS satellite will
strike nearby, sending another, smaller debris plume over
the rim of Cabeus.
The
Hubble Space Telescope, the Lunar Reconnaissance Orbiter (LRO),
and hundreds of telescopes great and small on Earth will scrutinize
the two plumes, looking for signs of water and the unexpected.
And
that brings us to the second way to see the show: Grab
your telescope.
"We
expect the debris plumes to be visible through mid-sized backyard
telescopes—10 inches and larger," says Brian Day of NASA/Ames.
Day is an amateur astronomer and the Education and Public
Outreach Lead for LCROSS. "The
initial explosions will probably be hidden behind crater walls,
but the plumes will rise high enough above the crater's rim
to be seen from Earth."
 The
Pacific Ocean and western parts of North America are favored
with darkness and a good view of the Moon at the time of impact.
Hawaii is the best place to be, with Pacific coast states
of the USA a close second. Any place west of the Mississippi
River, however, is a potential observing site.
Right:
The side of Earth facing the Moon at the time of impact. [larger
image] [observing
tips]
When
the plumes emerge from Cabeus, they will be illuminated by
sunshine streaming over the polar terrain. The crater itself
will be in the dark, however, permanently shadowed by its
own walls. "That's good," says Day. "The crater's
shadows will provide a dark backdrop for viewing the sunlit
plumes."
In
an earlier stage of mission planning, scientists hoped to
strike a crater closer to the Moon's limb so that the plumes
would billow out against the dark night sky, providing maximum
contrast for observers on Earth. However, recent data from
NASA's Lunar Reconnaissance Orbiter, Japan's Kaguya spacecraft
and India's Chandrayaan-1 probe altered those plans.
"We've
just learned that Cabeus may contain relatively-rich deposits
of hydrogen and/or frozen water," says Colaprete. "Cabeus
is not as close to the lunar limb as we would have liked,
but it seems to offer us the best chance of hitting H2O."
 The
LCROSS team hopes many people—amateurs and professionals alike—will
observe and photograph the plumes. "The more eyes the
better," says Day. "Remember, we've never done this
before. We're not 100% sure what will happen, and big surprises
are possible."
Right:
Click on the image to find a public viewing event near your
hometown. [more]
Veteran
amateur astronomer Kurt Fisher has prepared a 13 MB slideshow
to help fellow amateurs locate and witness the plumes: download
it . There is also an online LCROSS
observer's group where novices can read introductory articles
and chat with other observers.
"This
is a wonderful opportunity for citizen scientists to join
NASA in the process of discovery," says Day, who urges
observers to submit their images to the LCROSS Citizen
Science Site. "It's a great adventure, and anyone
can participate."
Imagine
that.
Author: Dr.
Tony Phillips | Credit: Science@NASA
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