Shackleton (crater)
2007 Schools Wikipedia Selection. Related subjects: Space (Astronomy)
| Crater characteristics | |
|---|---|
 South lunar pole as imaged by Clementine. Shackleton is in the small, dark patch at centre. NASA photo. |
|
| Coordinates | 89.9° S, 0.0° E |
| Diameter | 19 km |
| Depth | 2 km |
| Colongitude | 0° at sunrise |
| Eponym | Ernest Shackleton |
The Shackleton crater lies at the south pole of the Moon. The pole lies within the rim of the crater, and is only a few kilometers from the mid-point. From the perspective of the Earth, this crater lies along the limb of the Moon, making observation difficult. The crater is small and is viewed edge-on in a region of rough, cratered terrain. Detailed mapping of the terrain in the vicinity did not occur until the advent of orbiting spacecraft.
The Shackleton crater lies entirely within the rim of the immense South Pole-Aitken basin, the largest known impact formation in the Solar system. This basin is over 12 kilometers deep, and an exploration of its properties could provide useful information about the lunar interior.
Nearby craters of note include the Shoemaker, Sverdrup, De Gerlache, and Faustini craters. Somewhat further away, on the eastern hemisphere of the lunar near side, are the larger Amundsen and Scott craters, named for two other early explorers of the Antarctic continent.
Exploration
During the Lunar Prospector, the Neutron Spectrometer instrument on board the spacecraft appeared to detect excess hydrogen about the northern and southern lunar poles, including the crater Shackleton. In July, 1999, however, the impact of the Lunar Prospector in the nearby Shoemaker crater did not produce any detectable plume that might reveal resulting water vapor. This may be an indication that the hydrogen is not in the form of hydrated minerals, or else the point of site did not contain any ice.
From the images of the crater edge taken from orbit, Shackleton appears to be a relatively young crater. The edges are clean and not significantly worn. A young crater would indicate that the inner sides are relatively steep, which may make traversing the sides relatively difficult for a robotic vehicle. In addition, the interior floor is not likely to have collected many volatiles since the crater creation. However other craters in the vicinity are considerably older, and may have collected significant deposits of hydrogen. (See Shoemaker crater, for example.)
Radar studies following the Lunar Prospector mission demonstrate that the inner walls of Shackleton is similar in reflective characteristics to the surrounding regolith and similar, but sunlit craters with comparable features. The surroundings appear to contain a number of blocks that landed in the area as ejecta from impacts such as created the Mare Orientale basin.
In 2006, NASA announced that a secondary payload would accompany the Lunar Reconnaissance Orbiter. This device, known as the Lunar Crater Observation and Sensing Satellite ( LCROSS) will observe the impact of the EDUS (Earth Departure Upper Stage) within a crater at a lunar pole. Shackleton crater has been suggested as a potential target for this mission, but the final target has not yet been selected.
After flying through the plume of debris, the LCROSS will subsequently impact in the same crater. The impacts will be monitored from Earth and satellites, with the goal of detecting water ice in the crater. The EDUS will impact at about 2.5 km/s., is expected to create an impact crater about 100 m in diameter and 5 m deep. The resulting debris should reach an altitude of approximately 50 km. The impact of the LCROSS should produce similar results.
Potential uses
Because the orbit of the Moon is only tilted 1.5° from the ecliptic, the interior of this crater lies in perpetual darkness. Peaks along the rim of the crater are almost continually illuminated by sunlight, spending about 80-90% of each lunar orbit exposed to the Sun. (Such a mount has been termed a Peak of Eternal Light, and such a formation has been predicted since the 1900s.)
Due to this almost constant illumination, the crater rim is considered a preferable location for a future lunar outpost. The light could be converted into electricity using solar panels. The temperature at the location is also more favorable than on most of the surface, and does not experience the extremes along the lunar equator where it rises to 100 ° C when the Sun is overhead, to as low as −150 °C during the lunar night.
The continuous shadows in the south polar craters cause the floors of these formations to maintain a temperature that never exceeds about −173 °C, or 100 K. Any water vapor that arrives here due to a cometary impact would lie permanently frozen on or below the surface. This suggests that the crater floors could potentially be "mined" for deposits of hydrogen in water form, a commodity that is expensive to deliver directly from the Earth.
While scientific experiments performed by the Clementine and the Lunar Prospector could indicate the presence of water in the polar craters, the current evidence is far from definitive. There are doubts among scientists whether significant quantities of water are located in these craters. Resolution of this issue will require a future mission to the Moon.
This crater has also been proposed as a future site for a large infrared telescope. The low temperature of the crater floor make it ideal for infrared observations, and solar cells placed along the rim could provide near-continuous power to the observatory. About 120 kilometers from the crater lies the 5-km-tall Malapert Mountain, a peak that is perpetually visible from the Earth, and which could serve as a radio relay station when suitably equipped.