The culmination of the great push to the Moon, announced in 1962 by President John F. Kennedy as a major goal for all humankind, were the six manned landings between July 1969 and December 1972 onto the lunar surface. Each site had been imaged at various times by the Lunar Orbiters, as seen in this next set of panels:

Apollo 11 and 12 sites were both in mare terrain. Apollo 14 was located in Fra Mauro ejecta emanating from the huge cratering event that produced the Mare Imbrium Basin. Apollo 15 landed near the Apennine Mountains, made up of rim rocks composed of lunar crust pushed up when the Imbrium Basin was formed. Apollo 16 visited Highlands units, consisting of the Cayley Formation (supposedly volcanic deposits, as interpreted pre-launch, but shown by the mission to be consolidated impact ejecta). Apollo 17 also sought volcanic pyroclasic units, predicted to occur around the Taurow-Littrow Mountains but, except for the notable orange layers (glass droplets splashed out of mare lavas before they hardened) within the regolith (debris "soil"), the rocks exposed in the massifs (high hills) were again made up of ejecta.

Some of the astronaut photography concentrated on black and white high resolution scenes of specific targets on the surface, such as this picture of the Apollo 17 landing site in the Taurus-Littrow region, where the last visit to the Moon took place in December, 1972:

Familiarize yourself with the geography of this scene; note especially the patterns of the massifs (hills in the highlands) that stand out as bright against the darker central lava-covered plains around the touchdown site. Now, look at this ground scene:

The photo was taken by Astronaut Jack Schmitt (a geologist), partly to show the Lunar Module (LM) sitting safely on the plains against a background of a massif (mountain block); Astronaut Eugene Cernan is at the controls of the mobile Lunar Rover used for excursions up to several miles from the LM. Comparing the two views of the Apollo 17 site, see if you can decide whether you are looking at South Massif (bottom of first image) or North Massif?

The Apollo program remains the paramount achievement of Man himself in Space. The greatest reward from the journeys to the Moon lies in the nearly 368 kilograms (810 pounds) of rock samples collected by the astronauts. Almost three decades later, scientists continue to subject these materials to - without doubt - the most intense analysis and scrutiny of any natural substances taken from a planetary body. Starting in 1970. every year in March hundreds of geoscientists meet at the Johnson Space Center near Houston for the annual Lunar and Planetary Science Conference to report on new findings and exchange hypotheses on the interpretation and implications of recent data. From examination of the lunar rocks several fundamental ideas have emerged: differentiation of a primitive planetary body; the nature of its early surface; the pre-eminence in non-mare rocks of shock effects from impact cratering; the age and history of the Moon; and its origin (prevailing opinion: derived from accretion of terrestrial debris hurled into space after being ejected from a huge impact on the early Earth that resulted in crustal/mantle materials attaining orbital velocities; a variant of this model, held by some, is that much of the material came from the incoming body, probably an asteroid whose size approached that of Mars).

The appearance of typical lunar rock specimens is shown in the display here:

The large central rock is a breccia, that is, a rock composed of fragments of other rocks that accumulate from various (usually distant) sources which are then welded together by heat and pressure. These fragments represent impact debris from more than one area of the Moon that make up the principal deposits of the outer layers of the Moon - part of the 1-3 km (~ 0.6-1.85 miles) thick lunar ejecta blanket first proposed and described in 1971 by the writer of this Tutorial. The dark material in this specimen is basalt - the solidified end produce of iron-rich lava that fills lunar marias. The lighter rock fragments probably originated from the lunar highlands, which has been shown by Surveyor and Apollo sampling to consist of rocks with a high percentage of grayish feldspars (Ca-Na aluminosilicates) that cause the highlands to appear lighter in tone (higher albedo or reflectivity). The smaller rock samples surrounding the large specimen are vesicular basalt pieces (dark) and individual highlands rocks (light) collected nearby on the same mission.

The views presented so far highlight the two dominant characteristics of the lunar surface: 1) the mare/highlands dichotomy, and 2) the abundance of circular features, nearly all being impact craters and basins but some of probable volcanic (caldera) origin. This next scene emphasizes both characteristics by showing an exaggerated false color image of the front side of the Moon taken by the multispectral vidicon onboard the Galileo spacecraft (described later in this Section). The highlands, with their higher reflectances, are presented in shades of red and orange and the lower reflectance maria in blues and greens.

After Apollo, the Moon was not specifically revisited for 22 years until an unmanned spacecraft, Clementine (funded by the Dept. of Defense), orbited it to conduct mapping studies between February 19 and April 21, 1994 using UV/Visible, Near IR, and High Resolution Cameras, Lidar (a radar altimeter), and a radar-like unit that transmits in the S-Band radio frequency (2.293 GHz; 13.19 cm wavelength). Look first at a topographic map of both front and far sides of the Moon in which elevation differences have been calculated from stereo data obtained from high resolution photographs and radar altimetry data acquired by the Clementine spacecraft as it orbited the lunar surface.

Among specialized products were more detailed maps of lunar topography (elevations) and global maps of the distribution of several chemical elements, such as iron (Fe) and titanium (Ti), determined by analyziing reflectance variations at 0.75 µm and 0.95 µm, where these elements absorb irradiation. The Fe map, reproduced below, indicates that, while iron is widespread, its maximum concentrations are in a broad region on the nearside roughly coincident with the vast lava outpourings into Oceanus Procellarum and several other mare basins.

Clementine made a controversial "discovery" which, if proved correct, has major implications for humans returning to the Moon. Its S-Band radio unit detected abnormal reflections from the rim of a huge crater at the lunar South Pole, in areas permanently sheltered from the Sun's rays. These reflections could be due either to water ice or to some abnormal surface roughness condition. If indeed ice (in amount estimated to be enough to fill four large swimming pools), then this precious material (which supplies water needed for life and also oxygen when broken down by electrolysis) might allow establishment of a manned base on the Moon. Transport of sufficient water and oxygen for long stays is presently beyond our technical capability. The source of this ice, if it truly is there, is postulated to be infall of cometary material (comet heads contain ice).

This observation, and the intriguing results of Clementine's compositional mapping, has led to a follow-on mission. For the first time in 25 years, NASA has returned to the Moon with a small, but versatile orbiting satellite called Lunar Prospector. The entire mission including data analysis is another effort by NASA to achieve high scientific returns at relatively low cost (for LP, $65 million). Launched on January 6, 1998 by an Agena rocket, Prospector now is operating in a 100-km high circumlunar polar orbit from which the entire Moon will be mapped over a 3-year lifetime in more detail than from Clementine. Here is an artist's sketch of the spacecraft:

The spacecraft, just 4.5 ft high and 4 ft in diameter, weighing 660 pounds, receives its power from solar cells that surround its exterior. A conical communications antenna (top) is capped by a S-Band radio sensor designed to measure lunar gravity employing a Doppler effect procedure. From the 8 ft boom or mast extending to the front left, a Magnetometer/Electron Reflectometer at its end will conduct improved measurements of the Moon's magnetic and particle fields. Terminating the left rear mast is the Gamma Ray Spectrometer which can detect these elements: U, Th, K, Fe, Ti, O, Si, Al, Mg, and Ca. On the right boom are the Alpha Particle Spectrometer, that will seek radon gas measurements to assess lunar radioactivity as a clue to volcanic and other current events, and the Neutron Spectrometer, that will determine the presence of Hydrogen and can detect water ice (its confirmation from Clementine results is a major goal).

The first results on ice detection were released during an exciting press conference held on March 5, 1998. Around both Poles, the neutron spectrometer has indeed detected neutrons released from hydrogen by natural cosmic ray bombardment of water ice in craters with sheltered shadow zones. The initial estimates of amount, to be fixed more accurately with later observations, amount to 10 to 300 million tons. If melted, this larger number would fill a "lake" 10 square kilometers in area (3.1 x 3.1 km) to a depth of 10 meters. Surprisingly, the North Pole region contains about 50% more ice than its southern counterpart. The source of the water ice is probably residues from cometary bodies that impacted the polar regions, forming craters but allowing much of the comet mass to survive embedded in the target. The implications are encouraging for future exploration of the Moon to the extent that a manned base facility can be established and occupied over extended time owing to availability of vital water (usable both for consumption and as a source of hydrogen suitable as a fuel). However, landing in polar regions is technically more difficult but doable. The dream of a permanent observation post on our satellite is now much more feasible.

More details on Lunar Prospector are given at the Web site at the National Space Science Data Center and the Mission Management Home Page at NASA Ames Research Center. As data and maps are accrued and released by NASA, they will be placed in the Web version of this Tutorial and will appear in later CD-ROM versions.

There are literally thousands of informative and often exotic images of the Moon taken by various remote sensors. Reluctantly, we must take leave of our satellite to begin an impressive journey through the Solar System. We start with the two innermost planets - Mercury and Venus.

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