Apollo 17: The View from Lunar Orbit
The Scientific Instrument Module on the Apollo 17 Service Module. The Metric and Panoramic Cameras, along with the Infrared Radiometer and Ultraviolet Spectrometer were located there. The VHF antenna, one of three antennas used by the Lunar Sounder, is visible at the base of the Service Module.
The science return from the Apollo 15, 16, and 17 missions was enhanced by the inclusion of a set of orbital science instruments that were carried in the Scientific Instrument Module (SIM) of the Service Module. On all three missions, this included high resolution photography using the Metric Camera and Panoramic Camera. The Metric Camera obtained photos that were typically 165 km on a side with a horizontal resolution of 20 meters. The Panoramic Camera obtained images in narrow strips, 20 km wide in the direction of orbital motion and 320 km long across the ground track, with a resolution of 1-2 meters directly below the spacecraft. Photos from both cameras were taken with substantial overlap to produce stereo images, which allowed lunar heights to be determined with an accuracy of better than 10 meters vertically. The film for these cameras was retrieved from the Service Module and stored in the Command Module during a spacewalk by the Command Module Pilot while on the return voyage from the Moon back to Earth. During Apollo 17, the Metric Camera was used on 15 orbits and during the early hours of the return to Earth, obtaining 2140 usable photographs. The Panoramic Camera was used on nine orbits and during the early hours of the return to Earth, obtaining 1574 usable photographs. This covered virtually all of the Moon visible in sunlight to the Apollo 17 crew.
The Apollo 17 Landing Site
This Metric photograph shows the Apollo 17 landing site (black diamond), which was located on the floor of the Taurus Littrow Valley in the eastern rim of the Serenitatis impact basin. The South Massif (SM), North Massif (NM), and Sculptured Hills (SH) were important sampling sites during the mission.
Serenitatis Basin Floor
This Metric photograph shows about 160 kilometers of southeastern Mare Serenitatis. The surface in this region is composed of basalt, emplaced between about 3.0 and 3.5 billion years ago. Several ridges, termed wrinkle ridges, are seen in this picture. The weight of several kilometers of mare basalt caused the surface to sag somewhat, and the resulting motion caused the surface to buckle, producing the ridges. These ridges are generally less than 100 meters high. Similar ridges are seen in other lunar mare basins, including Mare Humorum, Mare Imbrium, Mare Nectaris, and Mare Crisium. In the lower right portion of the picture, the surface is a darker gray. This material, near the southern edge of Mare Serenitatis, formed in a different, somewhat older episode of lava emplacement. In this older material, there is a set of narrow valleys, termed graben. When the central part of the mare sags due to emplacement of a basalt load, material on the edge of the mare may be uplifted and stretched, producing the graben.
Imbrium Basin Rim
This oblique Metric photograph was taken looking south across Mare Imbrium, which is the smooth region at lower right. Mare Serenitatis is the smooth region at upper left, and Sinus Medii is the smooth region at upper right. The Apennine Mountains, which form part of the main rim of the Imbrium Basin, are prominent in the center of the photograph. In places, the Apennines are more than 4 kilometers higher than Mare Imbrium.
Euler Crater
The crater Euler in Mare Imbrium has a diameter of 28 kilometers and is about 2.5 kilometers deep. It is typical of craters in this size range on the Moon. These two Metric photographs illustrate the structure of Euler as seen in different illumination conditions. In the first photograph, taken at a very shallow sun angle (very early in the lunar morning), the long shadows obscure the inside of the crater and highlight structures surrounding the crater. Material that was ejected from the crater and deposited in the region around the crater is visible as a clearly defined, rough ejecta blanket. When this ejecta lands on the lunar surface, it sometimes creates additional craters, termed secondary craters, that are much smaller than the original crater. Numerous small secondary craters are visible around Euler, extending out to about one crater diameter from the rim of Euler.
The second photograph of Euler was taken about one Earth day after the first photograph. At that time, the sun was higher in the sky and the shadows were less pronounced. The ejecta blanket and secondary craters are less obvious than in the previous photograph. However, more detail can be seen in the crater's interior. A small peak is present at the center of the crater, and material that has slumped off the crater rim is present in many places on the crater floor. These structures are characteristic of most craters of this size on the Moon.
Copernicus Crater
Copernicus Crater, 93 km in diameter, is viewed obliquely in this photo taken from the Command Module by the crew using a Hasselblad camera. Copernicus is a morphologically fresh, relatively young crater. It is an excellent example of a large lunar impact crater, including a flat floor, slumping terraces on the crater walls, and a group of central peaks.
Other Instruments
On Apollo 17, the Scientific Instrument Module also carried the Infrared Radiometer, Ultraviolet Spectrometer, and Lunar Sounder Experiments. The Infrared Radiometer measured how the temperature of the lunar surface varied by time of day and night, recording temperatures between 85 and 480 Kelvin. Because soil and rock heat up and cool down at different rates, this data was used to determine the size of rocky blocks in impact craters and to measure the distribution of blocks with distance from the crater.
The Ultraviolet Spectrometer measured the composition of the tenuous lunar atmosphere. Molecular hydrogen was measured to have an abundance of 6000 atoms per cubic centimeter. Atomic and molecular oxygen, atomic and molecular nitrogen, carbon monoxide, carbon dioxide, and xenon could not be detected. Previous measurements had suggested that volcanic degassing sometimes occurs over the Aristarchus Plateau, but transient degassing was not detected by the UV Spectrometer. The spectrometer did detect a transient atmosphere from lunar module engine exhaust, but it dissipated within a few hours. The spectrometer was also used to observe astronomical targets during the return to Earth, including the Earth, the Milky Way, and selected stars.
The Lunar Sounder used radar at three wavelengths between 2 and 60 meters to look up to 2 km into the lunar crust. This deep penetration was possible both because of the long wavelength of the radar waves and because the Moon’s interior is quite dry and thus does not absorb radar waves efficiently. In Mare Serenitatis, the Sounder detected layering in the basaltic crust at 0.9 and 1.6 km but did not detect the base of the basalt. In Mare Crisium, a layer in the basalt was measured at 1.4 km depth. This data, in combination with other observations, indicated that the total thickness of the basalt in Mare Crisium was 2.4 to 3.4 km. In southern Mare Serenitatis, the Sounder measured subsurface structure beneath several wrinkle ridges (see photo above), which indicates that the ridges were formed primarily by motion along faults in the lunar crust.
