By Friday morning, we can expect that any aliens on the moon will be really ticked off at us.
But if we're really lucky, the drinks they pour to toast our demise will be, er, on the rocks.
Friday is the day NASA's LCROSS mission (short for Lunar CRater Observation and Sensing Satellite) sends a spent booster rocket crashing into a crater near the lunar south pole, looking to see if there is ice mixed in the soil of the crater's floor. Scientists think there may be billions of gallons of it, but so far they haven't been able to prove it.
So the LCROSS booster will go plowing into the moon's surface at 5,600 miles per hour. It is expected to make a crater about 60 feet across -- and send 350 tons of rock and soil flying in all directions, creating a plume several miles high. If there is ice mixed in, a small satellite, flying on the same path less than 400 miles behind the rocket, should be able to detect it before it crashes too, about four minutes later.
"We can directly measure water ice, and then we can fly right through the plume," said LCROSS project manager Daniel Andrews.
The whole thing is set to happen at 7:31 a.m. ET on Friday, and telescopes on earth (plus the Hubble telescope in orbit and other spacecraft) will be watching.
At best, mission managers say, they will see a small flash at the impact point. But many will be equipped with spectrometers, instruments that measure the chemical composition of the plume. And if they see water...
"If we find water there, it will change the course of exploration," said Rusty Hunt of NASA's Ames Research Center in Mountain View, Calif. "If there's water near the south pole, we'd go there. The people who settled the Old West were able to live off the land, so to speak, and we'd do the same."
Hunt is a flight director for LCROSS, which was launched from Florida in June. The plan is for him to be in charge when the flight comes to its violent end, and the measurements begin.
Was Apollo Wrong?
In 1972 the last Apollo astronauts came home from the moon, and that was that. The consensus was that the rocks they had found were dry as dust -- even more so, in fact.
But the conventional wisdom has changed.
In 1994 a military space probe called Clementine, sent to map the moon as a way of testing sensors for possible Defense Department use, found evidence of ice in the shadowed corners of craters near the moon's south pole.
In 1998 a NASA probe called Lunar Prospector was sent to confirm Clementine's findings, and as it orbited the moon it found evidence of large amounts of ice in the lunar soil.
The working theory is that comets, crashing into the moon over the eons, left tons of ice. In most places it would have vaporized quickly. But some craters near the moon's south pole are so deep -- and the angle of sunlight is always so shallow -- that ice could have remained frozen.
Crashing on the Moon: NASA Probe Looks for Ice
The earlier probes only took indirect measurements to suggest lunar ice. But could they be right? Engineers on Earth almost salivate at the thought.
That is because NASA's current mandate, laid out by President Bush and so far backed by President Obama, is to use the moon as a base for human exploration of Mars and beyond. As part of Project Constellation, they would set up camp in their Altair landing ships.
If there is frozen water there -- H2O -- it could be used for drinking, or broken down into its components of hydrogen and oxygen for fuel, air to breathe, and myriad other uses.
Exploring on a Budget
LCROSS, by NASA standards, is a low-cost mission, with a fixed budget of $79 million -- a good chunk of money, but remember that the movie "Transformers: Revenge of the Fallen" has grossed about $400 million since its release in June.
There has been long debate over the merits of sending astronauts back to the moon, but if LCROSS finds water, it will make the lives of future astronauts much simpler.
"It's a pretty simple mission with profound implications," said Hunt, the flight director. He added that Friday, impact day, is his birthday.