To Galileo Mission Science Contents PageIn 1973, Mariner 10 photographed the north polar region of the Moon (see photo). Almost 20 years later, Galileo revisited this area, imaging the region for the first time in infrared color and providing new information about the distribution of minerals on the lunar surface. Traveling at over 48,000 kilometers per hour on its way to receiving its last gravity assist at Earth, the spacecraft flew within 110,000 kilometers of the Moon (see photo). The Project's goals for the December 7, 1992, flyby included obtaining multispectral lunar images, calibrating GalileoÕs instruments by comparing their data to those of previous lunar missions, and getting additional baselines for comparing our Moon with the Jovian satellites Galileo will be exploring beginning in 1995.
Galileo imaged the Moon's north pole at several different wavelengths (including infrared wavelengths beyond the range of human vision), a feat never before accomplished. The best of Galileo's images had a resolution of 1.1 kilometers/pixel and were three times the resolution the spacecraft had obtained at its previous lunar flyby. Scientists found evidence that the Moon has been more volcanically active than researchers thought.
The Near-Infrared Mapping Spectrometer (NIMS) imaged the polar region in 204 wavelengths, another first in lunar mapping. These images indicate there is more pyroxene (containing magnesium, iron, and calcium) and olivine (containing magnesium and iron) in the maria than in the highlands. (Maria, or lunar seas, are the large, flat, dark areas on the Moon.) While scientists knew of this compositional difference between the maria and the highlands, "we did not know how to characterize the region near the north pole," pointed out NIMS Principal Investigator Dr. Robert Carlson. "We now know that some of the smooth areas in the polar regions are like the maria." The spacecraft also collected spectral data for dark mantle deposits (areas of local explosive volcanic eruptions). These maria deposits are more spectrally, and therefore more compositionally, diverse toward the near side of the Moon. Specifically, scientists discovered that titanium is present in low to intermediate amounts toward the far side, suggesting that the far side has a thicker crust. This type of spectral data also allows scientists to determine the sequence of meteoric impacts and the thickness of ancient lava flows.
In observing the features of the Imbrium impact basin on the near side of the Moon, the imaging team was surprised to find some hidden maria. These "cryptomaria" are overlain by other features, and can only be seen in special spectral bands. "Nearly 4 billion years ago, the impact in the Imbrium basin threw out a tremendous amount of rock and debris that blanketed the Moon and caused erosion of the highland terrain. The blanketing and sculpture are seen in these images of the north pole," noted Dr. Ron Greeley, Arizona State University, a member of the imaging team. The presence of these cryptomaria extends the previously accepted age and extent of lunar volcanism.
In part, the measurements of the Moon were made to confirm that Galileo's instruments are working properly. Scientists examined information from earlier American and Soviet lunar missions, including actual soil and rock samples brought back from the Apollo 16 and 17 missions. These missions, based mainly in Mare Tranquillitatis and Mare Crisium, discovered a large amount of titanium in the soil. Scientists also compared the data Galileo had gathered at its previous flyby of the Moon in December 1990. All the instruments are indeed working properly.
Galileo's images of the Moon are similar in resolution to the pictures the Voyager spacecraft took of Jupiter's moons. However, when Galileo reaches Jupiter, it will be ten, a hundred, even a thousand times closer to Jupiter's moons than Voyager was. This means that Galileo's images of the Jovian moons will have a resolution up to a thousand times better than that seen in these pictures of our Moon.
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