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Lunar Prospector searching for water smashes moon

1998's $63 million 354-pound Lunar Prospector spacecraft's 18-month lunar orbit was first of NASA's Discovery series of faster, better, cheaper space explorations, first to explore the moon's surface on a purely scientific mission since Apollo 17 in 1972. The mission was envisioned 11 years ago by space colonization advocate Alan Binder, its primary purpose to survey lunar resources: the elements of its rocks, its magnetic and gravity fields and the possibility of polar water ice. Prospector completed over 6,800 orbits, dipping to within 6.2 miles as its 5 instruments analyzed the moon's chemistry, gravity and magnetic fields. Prospector did everything expected - mapped the moon's surface and resources and discovered the lunar core. Reading the moon's poles, an instrument detected hydrogen's chemical signature, suggesting water's presence.

Lunar ice can provide drinking water for lunar bases near the poles so water wouldn't have to be brought from Earth. The water could also irrigate crops in underground lunar farms or be chemically broken down into its basic elements: oxygen for breathing and hydrogen for rocket fuel or electrical generators. The lunar base could become a launch point for interplanetary probes no longer having to lift the weight of fuel from Earth's much stronger gravity. Prospector detected large quantities of hydrogen at the moon's poles, indicating presence of water ice. Prospector discovered hydrogen when it detected neutrons emanating from the moon's surface. Their interaction with lunar soil indicated hydrogen. Most lunar hydrogen came from solar winds. Shadowed depths of the moon's polar craters are never exposed to solar winds. Hydrogen there would be from water-bearing meteors and comets. Water ice may have existed for billions of years in these shadow reservoirs of temperatures below -280 degrees F. With frozen water in the crater the collision would vaporize the ice and create a vapor of water molecules. Sunlight would quickly break the water down into hydrogen and hydroxyl, a chemical formed when ultraviolet radiation frees a hydrogen atom from water. If the vapor cloud is dense enough, sunlight will cause the hydroxyl molecules to be visible to powerful telescopes using ultraviolet radiation detectors. 6.6 billion tons of water ice may be buried in the top foot and a half of lunar soil at shadowed bottoms of craters in the polar regions.

Prospector mapped hydrogen distribution on the moon's surface, inferring presence of water. What's the form of the hydrogen? Water ice, or implanted by solar winds? If it's water ice, it's brought by comets and meteors. Its primary mission complete, Lunar Prospector was maneuvered into a 16-mile elliptical orbit at times 6.2 miles above the moon's surface. For 6 months it took a high-resolution look at the moon to confirm previous findings. Prospector's current orbit was too low to provide a sufficiently steep shot necessary to plunge into the crater. Likelihood of hitting the crater is 99%. The experiment has only a 10% chance of success because water ice could be anywhere in the crater rather than evenly distributed. Not finding anything doesn't mean anything. Too many things can go wrong. We might not hit enough water to make a signal. It's marginal. If we don't succeed, if we don't hit water - and there's no guarantee we'll hit it - another mission will have to fly. Crashing Prospector in a controlled way can do one more bit for science, prove it's water and save $100 million. Crashing Prospector hopes to squeeze more data from the spacecraft and determine once and for all if water ice exists in lunar soil. Estimates show as much as 200 million metric tons of water mixed in the top 18 inches of lunar soil near the poles. Only a fraction - 100 pounds (12 1/2 gallons) lasting 13 hours and taking 3 months to analyze - may be vaporized by the spacecraft's crash, enough to prove presence of water. Low on fuel, Prospector would crash anyway.

Not all researchers accept the premise the crash produced proof of water. A Stanford electrical engineering professor and geology professor theorize that lunar ice, if it ever existed, reacts chemically with dust to form a substance similar to water-containing minerals in a concrete paste. They contended the crash could produce a water vapor plume even with water not previously present. Binder's not impressed with their theory because the shadowed bottom of the crater is so cold it would slow such chemical reactions. Not that they're wrong, but their analysis won't hold water. It will take several months to analyze data. Prospector's impact produced sufficient heat to vaporize water ice but not enough to break down mineral crystals. If we see water vapor, it's because it hit water ice. Icy comets may have delivered water to the moon, their impact locking water ice at bottoms of craters where the sun never shines. Prospector found indirect evidence for water ice.

Guiding the spacecraft to a precise impact in the crater was a tricky maneuver but everything went on schedule. The plan was for the spacecraft to fire rockets to slow down and start a speedy dive toward a crater. After coming in at a very low angle, it was to clear a half-mile-high rim by 1/2 mile, then crash into the 2 1/2-mile-deep crater, releasing energy equal to that of crashing a 2-ton car at over 1,100 MPH, generating enough heat to melt lunar ice and create a cloud of water vapor detected by Earth and space telescopes. 24 hours before the dive, Ames radioed orders to fire the spacecraft's thrusters, putting it into an elliptical orbit ranging from 6.2 to 142 miles altitude, giving controllers the angle they need to crash into the 2 1/2-mile-deep crater without hitting the rim, with barely enough fuel, just before the spacecraft slipped behind the moon and lost contact with Earth. It was a time-delayed command telling the spacecraft precisely when to fire its thrusters for the final blast into the crater. They ignited the final fuel reservoir and sent Lunar Prospector on a death march. 1 hour later it hit a targeted crater The 3,780-mph impact of the spacecraft expected to with the force of a 2-ton truck traveling 1,100 MPH. The ejected plume, up to hundreds of kilometers above the surface, was watched by observatories around the world. Hubble, the Submillimeter Wave Astronomy Satellite in Earth orbit, earthbound McDonald Observatory in west Texas and Hawaii's Keck Telescope observed the crash.

Since Prospector's radio signals weren't picked up again the spacecraft must have hit the moon, its precise impact point unclear. Everything went normally, indicating it got to the impact site. Had the automatic rocket firing behind the moon not gone as planned the spacecraft would reappear still in orbit and sending radio signals. No dust cloud or other visible indication of impact was detected by telescopes. Prospector was to complete its voyage by smashing near the lunar south pole into a shadowed crater maybe containing frozen water. The spacecraft could explode on the moon with enough force to spiral a plume of dust and vapor into its sky. Earth and space telescopes searching the plume for water hoped for a visible plume or dust cloud from the impact. No immediate sightings were reported from observatory telescopes focused on the moon. Prospector skimmed at a near-horizontal angle over the rim of a 26-mile crater near the moon's south pole, slamming it into the permanently shadowed base of the far wall. MacDonald telescopes continue taking data, recording measurements in ultraviolet light, analyzed for the chemical signature of water. Powerful Earth telescopes disappointingly detected no dust cloud. Lack of dust doesn't mean a search for lunar water failed. Telescopes using UV filters will continue looking for clues of water vapor splashed into the lunar sky by the impact. The crash site is the final resting place for USGS astronomer Eugene Shoemaker, one of the world's leading lunar impact authorities. After a car crash killed him a lipstick-size metal container of his ashes was glued to Prospector's brace before launch.

Patient, dedicated work of skywatchers

Mt Hamilton scientists scan moon for activity, seek distant planets

Eerily silent mountaintop, surrounded by rolling coastal range thick with green trees and wheat-colored grass giving the terrain a permanently autumnal look, haunted by foxes, badgers, tarantulas, bobcats, skunks, deer, wild pigs and cougars. A few inches of early June snow fell. After dark, toward the west and south, sodium-yellow glow of San Jose and smaller towns filters through valley hazes. On really dark nights they resemble minor galaxies.

On the misty eastern horizon rose the pumpkin-orange moon, the central actor in a predawn celestial drama. The sky thronged with twinkling stars and ghostly galaxies, oceans of them shimmering across a cosmos too vast and complex to grasp. Astronomers struggle to observe a far closer, lesser light, a pinprick of luminosity they hope would briefly flare on the moon's shadowy underside, a pinprick heralding the end of the historic Lunar Prospector space mission and perhaps final proof of a science-fictionish hypothesis. Flashlight beams bobbed through Lick's dark corridors as other astronomers pursued an equally glamorous task: seeking planets orbiting distant stars. This century-old observatory atop Mt Hamilton is the Bay Area's No. 1 eye on the cosmos - a veritable village of telescope domes big and small, where astronomers and students map the universe while most Northern Californians sleep.

Gazing at a spectacular reddish-orange Pacific sunset, energetic, bright-eyed resident astronomer Elinor Gates exclaimed: "I keep thinking: They let me work here! Astronomy's so romantic, so gee-whiz. Who isn't interested?" she demanded. It's the world's most obvious question. Gates has a nearby apartment on the mountain. Native to Woodbridge CT where her mother was a chemist, her father a mathematician and her stepfather a physicist, she speaks of space with the bubbly enthusiasm, clarity and erudition of a budding Carl Sagan.

2:51 a m Saturday Gates and colleague Debra Fischer huddled in different observatories on the mountain and watched the moon. 240,000 miles away the Bay Area's emissary to the moon - the $63 million Lunar Prospector robot, built and operated by local scientists and engineers - plunged to its doom on the lunar surface. Would the robot's crash-landing be visible from Earth? Although the odds were against it Fischer, Gates and professional and amateur astronomers worldwide hoped to see something - anything - of its demise. The robot was expected to hit the moon at faster than a mile a second with a slight chance of spewing clouds tall enough to be seen from Earth, providing smoking-gun confirmation of Prospector's most celebrated discovery, the existence of frozen water in permanently shadowed, hence permanently frigid, craters at the lunar poles. The spaceship indirectly detected the ice, a relic of countless fallen comets plunking onto the lunar surface for billions of years like so many dropped ice cream cones, using a sensor detecting neutron particles reflected by water molecules.

In Saturday's wee hours Gates and Fischer saw no immediate evidence of Lunar Prospector's kamikaze crash into an unnamed crater in the lunar outback. No spark of light, no vapor plume, no dust cloud. Minutes ticked by in Gates' office, where she huddled not over a telescope like astronomers of yore but over a colorful computer work station. Its screen showed an image of the moon, transmitted electronically from an adjacent building housing the 40-inch reflecting telescope. The moon's limb - where visible terrain ends and the black void of space begins - showed no telltales glows or smudges indicating Lunar Prospector's demise, as if the space probe had vanished without a trace. Anxiously she kept glancing at her computer, which displayed among other things a window linked to her e-mail service. By e-mail she could remain in near-instant contact with astronomers observing elsewhere, for example at McDonald Observatory in Fort Davis, Texas, or at Keck Observatory atop Mauna Kea in Hawaii. If something obvious happened on the moon she expects it would have hit the e-mail by now. Yet no new e-mail flooded in. At 3:03 a m her office phone rang. Fischer called from another observatory at the Lick complex attached to the dome housing the giant 120-inch telescope, once a titan of the astronomical world, now the 8th-largest telescope of its kind anywhere.

Fischer and a colleague used a spectrograph to look for evidence of sodium rising from the moon's surface. Using computers in a different office, Fischer saw no immediate evidence of sodium. They have the same problem we are, Gates said afterward with a sigh. Their inability to see a vapor or dust cloud, or a sodium signal from dust, didn't mean these didn't exist. They might be so dim they were washed out by the brilliance of the almost-full moon, and might be detected in closer analysis of the data. No results doesn't mean there's no ice in that crater. Similar disappointment greeted other observers. It's too early to draw conclusions.

Fischer and colleagues worldwide made news discovering the first known multiple-planet system beyond our own - a system of at least 3 planets orbiting the star Upsilon Andromedae 44 light-years away. A light-year is 6 trillion miles, the distance light travels in a year. The search for extrasolar planets, pioneered in the mid-1990s, is now big business at Lick. A favorite extrasolar planet-spotting technique is to look for subtle Doppler shifts in dark lines in the rainbow-like spectra of light from stars. Shifts are caused by variations in stars' positions caused by back-and-forth gravitational tugs of unseen planets orbiting them. Although the stars are tens of trillions of miles away, spectrographs can sense a Doppler shift as slight as 10 feet a second, as fast as you can ride a bike.

Astronomers Laurance Doyle and Lee Rottlers detected extrasolar planets by training a Lick telescope on a star in the constellation Draco, measuring extremely faint drops in its brightness caused by a planet orbiting that star and passing briefly between it and Earth, using an 1800s telescope to achieve a 2000s goal. By this technique Doyle hopes to make the first discovery of an extrasolar planet roughly as big as Earth. Previous astronomers discovered Jupiter-sized planets. Serious extrasolar planet searching has its light-hearted moments. Scurrying with her flashlight through the observatory, kept dark so stray light won't interfere with observations, Fischer teased a colleague alone in an office by imitating a ghost spookily calling out his name: "Lee-e-e-e-e Rott-t-t-t-l-l-l-ers!" Moscow, Idaho, students named planets Twopiter for a planet twice as big as Jupiter, Fourpiter for one 4 times as big, and Dinky for the smallest planet.