Chapter 9:

The Moon On Line at High Resolution

http://www.lpi.usra.edu/research/lunar_orbiter/index.html

The Lunar and Planetary Institute (LPI) has created a digital version of the "Lunar Orbiter Photographic Atlas of the Moon," published in 1971 and considered "the definitive reference manual to the global photographic coverage of the Moon." The site includes all 675 plates contained in the original work, digitally enhanced to increase photo quality. Visitors can view images by feature name, listed alphabetically or by descending latitude and longitude, or they can search by feature name, photo number, or coordinate range. Returns include a large thumbnail image, photo number, feature name, latitude and longitude, size, sun angle, spacecraft altitude, and medium photo center latitude and longitude. Students and general users may wish to consult the even easier to use Consolidated Lunar Atlas, which allows browsing by a long list of plates, thumbnails, or even better, an interactive image map.

LunarSat

The website can be found at: http://www.lunarsat.de

20 July 1999 is Apollo 11's 30th Anniversary

"One small step" anagram

"That's one small step for a man, one giant leap for mankind."
- Neil Armstrong

The Anagram:
"Thin man ran; makes a large stride, left planet, pins flag on moon! On to Mars!"

IceBreaker mission

In the absence of a NASA plan for a future lunar spacecraft, the private company LunaCorp and the Robotics Institute of Carnegie Mellon University are planning to send the "IceBreaker" mission to the moon in 2002. A rover is to land near the crater Peary, looking for ice both with a radar and a drill.

URL's:
LunaCorp: www.lunacorp.com/
Robitics Institute of CMU: www.ri.cmu.edu/

NEW ANALYSES FROM LUNAR PROSPECTOR PUBLISHED

LOS ALAMOS, N.M., Sept. 4, 1998 - Refined calculations of lunar water amounts and unique lunar compositional maps appeared today in the journal Science as part of the first publications of detailed analyses of data returned from NASA's Lunar Prospector mission.

Scientists from the U.S. Department of Energy's Los Alamos National Laboratory are lead authors on four of the papers in Science, with significant contributions from the Observatoire Midi-Pyrenees in Toulouse, France. Los Alamos built three of Lunar Prospector's five onboard instruments.

Refined calculations of lunar water amounts are tenfold higher than the lower limit -- based on preliminary, conservative estimates -- released in March. The additional analysis also shows the water is likely confined to localized areas near the poles, rather than spread out evenly across the polar regions, as was assumed in making the earlier estimates.

Water amounts, inferred from measurements of hydrogen in the lunar soil, are of great interest because of their potential impact on plans for colonization.

Compositional measurements show that the well-known impact basin Mare Imbrium -- one of the large, dark areas visible in the full moon -- is unlike any other spot on the moon, which theories of lunar evolution will have to account for.

"This mission has been an overwhelming success," said Los Alamos' Bill Feldman "We've gotten beautiful science from two of our three instruments. The third, we just haven't had time to analyze the data yet."

"These data will generate ripples that will spread throughout the planetary science community," said Rick Elphic. "We're barely scratching the surface of the analysis; we haven't begun to touch on the many ramifications for the origin and evolution of the moon."

The Los Alamos papers describe:

o the first application of neutron spectroscopy to planetary exploration, used on Lunar Prospector principally to look for the presence of water, but showing unexpected value for studying lunar composition as well;

o the first mapping of the entire lunar surface in gamma rays, which reveals compositional variations across the surface;

o and a comparison between Lunar Prospector neutron measurements and spectroscopic data from the Clementine spacecraft, which orbited the moon in 1994.

Los Alamos scientists built Lunar Prospector's neutron spectrometer, gamma ray spectrometer and alpha particle spectrometer. Spectrometers measure the numbers and energies of particles or photons encountered. Data from the neutron and gamma ray spectrometers figure into the Science papers; the alpha particle data are yet to be analyzed.

Neutrons and gamma rays emanate from the moon's surface as a result of cosmic rays -- high-energy particles traveling through space in all directions -- striking nuclei in the lunar soil. When a cosmic ray hits a nucleus it can eject neutron particles or high-energy gamma ray photons in response. Some of the neutrons and gamma rays travel upward where instruments aboard Lunar Prospector intercept them.

"The gamma ray measurements are ideal for spotting elements incorporated into materials that formed below the moon's crust," said Los Alamos' David Lawrence.

The moon once was hot and molten and as it cooled minerals crystallized and sank to form the core, if they were heavy, or floated upward to form the crust, if they were light. The last material to solidify contained thorium, potassium, gadolinium and samarium, which do not readily incorporate into minerals. These elements are signatures of the moon's subsurface mantle region, and their presence on the surface indicates some process -- volcanic events or impacts strong enough to punch through the crust -- must have dredged them up from the interior.

"Studies of these materials provides us a window into the moon's interior," Elphic said.

Thorium and potassium create standout gamma-ray signals, and their emissions neatly trace out Mare Imbrium's outer rim. Lawrence said this signal "provides a telltale sign of deposition by ejecta. This indicates that around Mare Imbrium the dredge-up process, at least in part, was related to an impact."

A different compositional story appears at the South-Pole Aitkin basin, the largest impact crater in the solar system and, therefore, presumably from an event strong enough to poke through the lunar crust. Although the Aitken basin region shows enhanced gamma ray emissions from thorium, it is not nearly as bright as Mare Imbrium. The impact event apparently dredged up much less potassium- and thorium-rich materials than at Mare Imbrium.

For an independent look at the distribution of dredged-up lunar mantle, the Los Alamos scientists compared their neutron spectrometer data with Clementine data.

"You can see compositional variations with neutrons in ways people had not realized previously," Lawrence said. "We've obtained far more composition information from the neutron data than we expected we would."

The elemental makeup of the lunar soil affects the energies of neutrons emanating from it. Over regions rich in iron and titanium, for example, Lunar Prospector will encounter an abundance of fast-moving neutrons and a deficit of slow ones. Other elements don't produce as many energetic neutrons yet don't absorb slow ones efficiently, leading to enhanced numbers of these. By looking at the relative numbers of neutrons of different energies scientists can determine what elements are in the lunar soil.

Gadolinium and samarium, key indicators of material from the moon's interior, interact very efficiently with slow neutrons. They can appear in small concentrations in the soil yet have a large impact on the low-energy neutron emissions.

By comparing their neutron measurements against Clementine's data for iron and titanium, the Los Alamos scientists found a large residual signal around Mare Imbrium they attribute to the presence of gadolinium and samarium. This signal did not appear in other locations where scientists would expect to see subsurface material dredged up.

"Something special happened around Imbrium; you don't see this sort of chemistry anywhere else on the moon," Elphic said. "It also confirms that the moon is very inhomogeneous -- at least for these elements. These data are going to be fairly restricting to theorists: whatever happened did not happen all over the moon, just in this one spot."

Another element that provides a unique signature in the neutron measurements is hydrogen. Scientists think hydrogen is most likely bound up in water molecules in the lunar soil, trapped frozen in regions of craters near the poles that never see direct sunlight.

"The data show clearly where the hydrogen is," Feldman said. "It's localized in spots near the poles, and it has to be buried, about half a meter or so.

"In making our initial estimates, we assumed the water was spread over the 'footprint' of the instrument," Feldman said, which is how much surface area the instrument can detect at any moment, a square approximately 120 miles on a side at Lunar Prospector's current altitude. "As we've gotten more data we've found that it's not spread out as we first assumed, but concentrated."

When they presented their initial results in March, the scientists said the water was likely in the form of a fine frost spread through the lunar soil. Further data analysis now allows the possibility of deposits of solid ice, Feldman said.

Feldman currently estimates there may be as much as three billion metric tons of water ice at each of the poles, with 15 percent more at the north pole than at the south pole.

Scientists assume comets carry the water ice to the moon. The comets basically vaporize on impact, and the water molecules migrate to the permanently shaded regions at the poles. These regions are so cold that once a water molecule enters them it gets stuck.

http://www.lanl.gov/external/news/releases/

Lunar Prospector results show how meteor impacts have shaped the moon's magnetic field

Berkeley -- The first four months of data from the Lunar Prospector, a satellite that has orbited the moon since January, has yielded a wealth of new information about magnetic fields on the moon and the possible geologic history of the lunar surface.

In particular, magnetic field measurements by an instrument built at the University of California, Berkeley Space Sciences Laboratory give strong support to the theory that giant meteor impacts billions of years ago created areas of strong magnetic field diametrically opposite the impact site on the lunar surface.

"We have analyzed data from most of two impact basins on the lunar surface, Mare Imbrium and the Sea of Serenity, and remarkably the correlation that we first glimpsed on the Apollo missions 25 years ago still holds," said Robert Lin, a professor of physics at UC Berkeley and one of the principal investigators for the magnetic mapping project. "The fact that regions of strong magnetic field cover whole basins antipodal to the point of impact makes the hypothesis that the magnetism has something to do with these large impacts seem much firmer."

These regions of strong magnetic field also create their own miniature magnetospheres several hundred kilometers across, akin to the much larger magnetospheres that surround planets like Earth and block the solar wind. "These mini-magnetospheres are close to the minimum size you can get in the solar system, and are the smallest ever observed," said Lin, who serves as director of the Space Sciences Laboratory.

The findings are reported in a special section of this week's issue of the journal Science devoted to the first scientific findings from Lunar Prospector, launched Jan. 6 of this year and the first NASA moon mission in 25 years. Prospector has been orbiting the moon at about 100 kilometers (63 miles) above the surface since its insertion into a lunar polar orbit in mid-January, telemetering data from five scientific instruments. Research papers discussing data from the other instruments also appear in the Sept. 4 issue of Science.

The moon has no global magnetic field like the Earth because it no l onger has an internal dynamo, so it was a surprise when magnetometers placed by astronauts on the surface in the 1970s detected a faint magnetic field, as large as hundreds of nanoteslas (the Earth's field is on the order of 30,000 nanoteslas). When Lin and now professor emeritus of physics Kinsey Anderson built an electron detector that flew aboard Apollo 15 in 1971 and Apollo 16 in 1972, they quickly realized they could use the instrument to remotely map the magnetic fields on the surface.

Though crude and covering only about 10 percent of the lunar surface, the measurements nevertheless indicated a correlation between meteor impact basins - dark, roughly circular features on the face of the moon - and strong magnetic fields on the diametrically opposite side of the moon. "What was a fairly good hint in the Apollo measurements has turned into a strong correlation in the Lunar Prospector data," said David Mitchell, a research physicist at UC Berkeley's Space Sciences Laboratory.

Lin and Anderson collaborated in building the current electron reflectometer aboard the Lunar Prospector in the first return mission since Apollo 16. Its polar orbit will allow the team to map the entire surface of the moon with ten times the resolution, down to 20-30 kilometers (12-20 miles). A complete map of the surface will be completed within several months, Lin said, at which point the instrument will remap in even greater detail the areas of high magnetic field, down to about four kilometers resolution -- a scale of about two miles.

The first set of data, with resolution down to 50 kilometers (31 miles), included measurements of nearly the entire area opposite the impact basins called Mare Imbrium and Mare Serenitatis, or Sea of Serenity. Magnetic fields were as high as 40 nanoteslas, or about one one-thousandth that of the Earth.

Surprisingly, the magnetic field in these antipodal regions was coherent over an area of a couple hundred kilometers - about 100 miles - rather than being a jumble of randomly oriented regions, which is typical of most of the lunar surface. When this happens, the area can screen out the solar wind that normally impinges on the lunar surface, just as the Earth's magnetic field screens out the high-energy particles in the solar wind. The electron reflectometer observed a bow shock and magnetosheath, both created when the solar wind hits a magnetosphere, and Mitchell predicts that with more detailed measurements they are certain to detect the magnetosphere directly.

Since the solar wind is thought to darken the lunar soil, this may explain lighter areas of the moon, and in particular spiral swirls called Reiner Gamma swirls. These albedo swirls are regions of contrasting light and dark, reminiscent of cream stirred into coffee.

Lin and his colleagues think the lighter areas may be areas screened from the solar wind by magnetic fields strong enough to generate a mini- magnetosphere.

"Our previous look at the magnetic moon was during the Apollo missions and it was very coarse," said Mario Acuna, a member of the team located at NASA's Goddard Space Flight Center in Greenbelt, Md. "The moon was previously interpreted as just a dead body with nothing interesting going on. With the new magnetic field data from Lunar Prospector, we are discovering that there is nothing dead about the moon - the interaction with the solar wind is much more complex than it appeared. Using Lunar Prospector is like using a magnifying glass because it has much higher resolution and can make measurements with greater frequency. This is typical of science - when you look closer, you see a lot more complexity."

Theorists came up with an explanation for magnetic fields antipodal to impact basins not long after the Apollo measurements hinted at a correlation. When a large meteor hits the moon, it and much of the lunar surface is vaporized and thrown into space, forming a cloud of debris and gas larger than the moon itself. Because of the heat released in the collision, much of the gas is ionized plasma in which the atoms are stripped of one or more electrons.

Such plasmas exclude magnetic fields, so as the cloud spread around the moon it pushed the moon's magnetic field in front of it. When the plasma cloud finally converged on the diametrically opposite side of the moon - a mere five minutes after impact - the squeezed magnetic field would be quite large, Lin said.

At the same time debris was falling back on the lunar surface, concentrated at the antipodal site also. If this debris crashed into the surface during the time when the magnetic field was high, it could have undergone shock magnetization. When rock is shocked, as when hit with a hammer, it can suddenly lose its own magnetic field and acquire that of the surrounding region.

If the moon today has no magnetic field, then where did the original magnetic field come from? Dating of Apollo moon rocks hints that during the period 3.6-3.85 billion years ago the moon did have a magnetic field, probably because its core was still liquid and spinning enough to generate a magnetic field comparable to that of the Earth. Mare Imbrium, Mare Serenitatis and two other impact basins that show evidence of strong antipodal magnetic fields, Mare Orientalis and Mare Crisium, all seem to have been created during this time period when the moon had a magnetic field.

"The data are still sparse and the interpretation is still a guess, but very soon I think we'll have proof that this is the story," Lin said.

The electron reflectometer determines the surface magnetic field by measuring the energy and incoming direction of electrons reflected from magnetic fields on the lunar surface. Charged electrons from the solar wind corkscrew around the magnetic fields as they approach the surface, and as the magnetic field increases they spiral tighter and tighter until, if the field is strong enough or the angle of approach shallow enough, they reverse direction and corkscrew back into space. The energy and angle of approach of the reflected electrons thus indicate the strength of the magnetic field at the surface.

Collaborators on the electron reflectometer experiment include project engineer David Curtis, physicist Charles W. Carlson and J. McFadden at UC Berkeley's Space Sciences Laboratory; L.L. Hood of the Lunar and Planetary Laboratory at the University of Arizona, Tucson; and A. Binder at the Lunar Research Institute, Gilroy, Calif.

Lunar Prospector Results

See their results about ice on the moon, gravity maps, and so on.