This mission was launched back in June and is part of an ongoing program that NASA has to try and find any water ice that might be trapped in crater shadows. The Moon is primarily an airless, dusty/rocky desert and about the only place where water could be trapped is in areas that do not receive any sunlight. Water is a critical component in making any manned moonbase project a success. Transporting water and other goods from Earth to the moon's surface is expensive. Finding natural resources, such as water ice, on the moon could help expedite lunar exploration.
The missile impact is expected to be so powerful that a huge plume of debris will be ejected. Just as the impact of the Shoemaker-Levy comet fragments into Jupiter revealed a lot of information on the compostion of Jupiter's atmosphere, scientists hope hope that water ice or water vapour will be ejected in the cloud that is thrown up from the impact. As the ejecta rises above the target crater’s rim and is exposed to sunlight, any water-ice, hydrocarbons or organics will vaporize and break down into their basic components.
Following the missile, another part of the spacecraft will be taking pictures and analyzing the ejecta for evidence of water. The instruments include two near-infrared spectrometers, a visible light spectrometer, two mid-infrared cameras, two near-infrared cameras, a visible camera and a visible radiometer. The spectrometers analyze the breakdown of the ejecta materials into their basic components. The infrared cameras will help determine the amount and distribution of the water vapor and the visible camera will tract the location of the impact and the debris plume.
All this will take place in just four minutes and then this craft itself will crash into the Moon itself, producing an even more spectacular explosion. What is interesting about this is that this second explosion should be visible in the 10-12 inch and larger telescopes of amateur astronomers! The projected impact at the lunar South Pole is currently: Oct 9, 2009 at 4:30 a.m. Pacific Daylight Savings Time, which is 9 hours behind Central European Daylight Savings Time of 1:30 PM. So we in Europe won't get much chance to have a peak, but if you get up early enough in the US, depending on where you are, you might be able to see it.
Otherwise, NASA will be providing a live broadcast of this event starting at 3:15 AM PDT which can be seen online: www.nasa.gov/ntv. Additional information on the LCROSS mission can be found here: www.nasa.gov/mission_pages/LCROSS/main/index.html.
No, this is not an attack on an alien base on the moon. Nor is it a misguided attempt of Obama's administration to root out a new Al-Qaeda hiding place. It is not vandalism or scientist's frustration with the lack of funding for space science. It is a valid and useful experiment and a good way to find information without the expense and hazards of a moon landing to bring back samples to Earth.
And while there is some controversy about such an experiment, it should be noted that this is not the first impact by spacecraft on the moon. This past June, the Japan space agency, JAXA, sent its robotic probe, the Kaguya spacecraft, on a controlled impact into the moon after the completion of its mission and the exhaustion of its fuel supply. As this happened on the dark side of the moon, there was not a reach chance to view the ejecta from the impact, but there was a brilliant explosion that was caused purely by the energy of the impact and it was viewed by a number of astronomers with some spectacular images captured by the Anglo-Australian Telescope in New South Wales.
And in 2006, ESA's SMART-1 concluded its scientific observations of the Moon through a small impact on the lunar surface. This kind of conclusion to a lunar mission has actually been common through the years and scientists have watched them closely, gleaning what additional data they could from the debris of such impacts. Observatories around the world have conducted fast imaging of impacts and of the associated ejected material, and spectroscopic analysis, to try and find hints about the mineralogy of the impact areas.
However, this "accepted practice" has not caused the controversy in the past that this week's mission has raised, with some folks exaggerating the impact crater size as being up to 5 miles, others stating that it "...is contrary to space law prohibiting environmental modification of celestial bodies." And even some folks worried about it triggering potential "...conflict with known extraterrestrial civilizations on the moon as reported on the moon in witnessed statements by U.S. astronauts." *sigh*
In truth, there is no actual explosives on board, and the impact vehicle is just the upper stage of the rocket that launched the mission in the first place. It is estimated that it will excavate a crater approximately 20 meters wide and almost 3 meters deep and more than 250 metric tons of lunar dust will be lofted above the surface of the moon. It is not expected to be a spectacular explosion. Though at this time it is unknown about the kind of response we can expect to get from the lunar aliens... (this last sentence is just a joke!!!)