This story was updated at 6:52 p.m. EDT.
The moon is due for a double whammy from two NASA probes Friday, with scientists assuring some skeptics that smacking the lunar surface with spacecraft is really okay.
NASA?s LCROSS mission will slam a spacecraft and an empty rocket stage into the moon?s south pole Friday morning at 7:31 a.m. EDT (1131 GMT) in a search for water ice buried in the perpetual shadows of lunar craters.
Scientists are eagerly awaiting the LCROSS crashes and hope they?ll provide a definitive answer on whether lunar water ice could be used to support future astronauts on the moon. But at least one person ? novelist and screenwriter Amy Ephron ? has spoken out against the $79 million mission on her Huffington Post blog and launched a Twitter campaign ("helpsavethemoon") to save the moon from future onslaught.
?I'm not a big fan of explosions, anyway. In Iraq or Afghanistan or the South Pole of the Moon. But who does have a territorial prerogative there?? Ephron wrote. ?Who has jurisdiction? Who has the right to say that it's okay to blow up a crater on the moon??
Apparently, Mother Nature does. The moon is covered in craters, with new ones like those to be created by the LCROSS probes popping up all the time by meteorites that pummel the lunar surface.
?The image of this impact, what we?re doing with the moon, is something that occurs naturally four times a month on the moon, whether we?re there or not,? LCROSS principal investigator Tony Colaprete told reporters Thursday.
The difference with LCROSS is that it is specifically targeted at a certain spot, a crater called Cabeus known to have vast stores of hydrogen-rich material ? a potential sign of water ice ? hidden in shadowed regions that never see the light of day. [Click here to find out how to watch the LCROSS moon crashes in your area.]
It?s that lure of ice that drew the interest of LCROSS scientists. Such a resource could be a boon for NASA?s plan to return astronauts to the moon since it could be used to support a lunar base.
Some SPACE.com readers have expressed concerns over the possibility of the moon crash destroying evidence of the very water ice LCROSS is hoping to uncover.
But mission scientists say that shouldn?t happen. The amount of hydrogen-bearing material is vast within the Cabeus crater, which is 60 miles (98 km) wide and 2.4 miles (4 km) deep. The impressions left by LCROSS and its Centaur rocket are expected to be about 66 feet (20 meters) wide and 13 feet (4 meters) deep. The plume should rise up about 6.2 miles (10 km) and be illuminated by the sun, researchers said.
That?s not to say the LCROSS probes won?t have any effect on the moon. The laws of physics, Colaprete said, mean there will be a miniscule perturbation.
?The impact has about 1 million times less influence on the moon than a passenger?s eyelash falling to the floor of a 747 [jet] during flight,? Colaprete said.
That means the impacts will be little more than a pinprick, if even that, to the moon. But they will still be substantial blows on a human scale.
When LCROSS and its Centaur stage hit, they are expected to kick up about 350 tons of moon dirt. The Centaur stage, which weighs more than 2 tons ? about as much as a sport utility vehicle ? will be first, followed by the smaller LCROSS shepherd craft four minutes later.
The shepherd craft will beam images and data of the impact plume to NASA?s mission operations center at the Ames Research Center in Moffett Field, Calif. A host of Earth-based observatories and amateur astronomers, as well as satellites and space-based assets like the Hubble Space Telescope, Sweden?s Odin satellite and NASA?s powerful Lunar Reconnaissance Orbiter circling the moon, will also scan the resulting plume for evidence of water.
Scientists now know for sure that there are some traces of water on the moon. They announced as much last month citing data from recent spacecraft that revealed the signal for water across wide swaths of the lunar surface.
Rather than steal the LCROSS team?s thunder, the finding only bolstered the team?s spirits and excitement, Colaprete said.
?The one thing we?ve learned about the moon is how much we really don?t know about the moon,? he added. ?And we are still learning and LCROSS is going to provide us additional data to further understand it.?
- Video - Why Bomb the Moon?
- The Greatest Lunar Crashes Ever
- How to Watch NASA's LCROSS Smack the Moon
SPACE.com is providing full coverage of the LCROSS moon crash. Click here for a look at the mission and return to SPACE.com at 6:30 a.m. ET (1030 GMT) for live crash coverage.