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GEOPHYSICS

Geophysicists try to learn such things as the densities, temperatures, and depths of boundries of a planet's crust, mantle, and core from instrumental measurements. Other Geophysicists study the physical properties of near-surface rocks such as magnetism and thermal conductivity.

Lunar Prospector

Lunar Crustal Magnetism

Using data obtained both from its Magnetometer and Electron Reflectometer instruments, Lunar Prospector will correlate magnetic anomalies with lunar surface geology

By mapping global locations, strengths and orientations of lunar crustal magnetic fields, scientists can learn more about the relationship between such magnetic fields and the surface selenology. For example, scientists believe that certain lunar surface features, such as the albedo swirls, may have magnetic origins. The swirls resemble unstirred cream in a coffee cup -- researchers suspect that the contrasting light and dark regions might indicate the juxtaposition of irregular magnetic fields.

Compared to that of the Earth, the Moon has a very small magnetic field. While some of the Moon's magnetism is thought to be intrinsic (such as a strip of the lunar crust called the Rima Sirsalis), collision with other celestial bodies might have imparted some of the Moon's magnetic properties. Indeed, a long-standing question in planetary science is whether an airless solar system body, such as the Moon, can obtain magnetism from impact processes such as comets and asteroids.

Magnetic measurements can also supply information about the size and electrical conductivity of the lunar core -- evidence that will help scientists better understand the Moon's origins. For instance, if the core contains more magnetic elements (such as iron) than the Earth, then the impact theory loses some credibility (although there are alternate explanations for why the lunar core might contain less iron).

Crustal Structure

Lunar Prospector's Doppler Gravity Experiment will improve the resolution of existing crustal asymmetry data.

Blanketed atop the Moon's crust is a dusty outer rock layer called regolith. Both the crust and regolith are unevenly distributed over the entire Moon. The crust ranges from 38 miles (60 km) on the near side to 63 miles (100 km) on the far side. The regolith varies from 10 to16 feet (3 to 5 meters) in the maria to 33 to 66 feet (10 to 20 meters) in the highlands. Scientists think that such asymmetry of the lunar crust most likely accounts for the Moon's off-set center of mass. Crustal asymmetry may also explain differences in lunar terrain, such as the dominance of smooth rock (maria) on the near side of the Moon.

High resolution gravity data permits a more accurate calculation of the so-called homogeneity constant, a number which enables scientists to determine the density of the lunar core. This is important information for designing fuel-efficient future lunar missions and landing operations.

Outgassing Sources of the Lunar Atmosphere

With its Alpha Particle Spectrometer, Lunar Prospector will determine whether the outgassing of nitrogen, carbon monoxide and carbon dioxide is related to tectonic activity. In addition, it will determine the resource potential of each particular gas.

The Moon has a relatively insignificant and tenuous atmosphere. One source of this atmosphere is outgassing - the release of gases, for instance radon, which originate deep within the Moon's interior. Compared to the Earth, the Moon is tectonically inactive, however moonquakes do occur. By measuring outgassing events, researchers may also be able to infer information about the character and frequency of that tectonic activity.

When and where gases are emitted tells scientists how the lunar atmosphere is likely formed. Certain elements, such as uranium and thorium, are radioactive -- over time, these elements lose energy and decay into new elements, such as radon and polonium. The energy lost, in the form of gamma rays, alpha particles and beta particles, can be measured by special detectors called spectrometers. Each is a different kind of "time machine" that scientists can use to determine what happened on the Moon days, months, even decades in the past. More abundant gases, such as nitrogen and carbon dioxide and carbon monoxide, are also outgassed along with radon. Knowing when and where lunar outgassing of these gases takes place is important for potential resource utilization.

Current theories about evolution of our Earth/Moon system, namely the impact theory, suggest that the Moon most probably formed 4-5 billion years ago, when the Earth collided with a very large object, ejecting raw materials that eventually became the Moon. However, other theories are perhaps less likely, but still plausible. The Moon's global elemental composition, once it is determined, should provide the best evidence yet to begin to settle this issue.

Impact processes play a major role in shaping the lunar crust. Since the Moon has no substantial atmosphere, the four billion-year-old crust has retained a good record of this impact history. For that reason, the Moon can also provide clues about the history of the Earth. Studying the Moon's crust and its atmosphere unveils secrets about its beginnings, but also of potential lunar resources. Scientists need this information to plan future lunar missions as well as to consider the feasibility of inhabitating our nearest neighbor in the Solar System, the Moon.