Shackleton (crater)

lunar crater data


caption=South lunar pole as imaged by Clementine. Shackleton is in the small, dark patch at center. "NASA photo".
latitude=89.9
N_or_S=S
longitude=0.0
E_or_W=E
diameter=19 km
depth=2 km
colong="0"
eponym=Ernest ShackletonThe Shackleton crater, named after Ernest Shackleton, a noted explorer of Antarctic, lies at the south pole of the Moon. The peaks along the crater rim are exposed to almost continual sunlight, while the interior is perpetually in shadow. The low-temperature interior of this crater functions as a cold trap that may capture and freeze volatiles shed during comet impacts on the Moon. Measurements by the Lunar Prospector spacecraft showed higher than normal amounts of hydrogen within the crater, which may indicate the presence of water ice.

Description

The rotational axis of the Moon lies within the rim of the Shackleton crater, and is only a few kilometers from its center. The crater is small (about 19 km in diameter), and from Earth is viewed edge-on in a region of rough, cratered terrain. The rim is slightly raised about the surrounding surface and it has an outer rampart that has been only lightly impacted. No significant craters intersect the rim, which may indicate a relatively young feature. [cite web
date = January 13, 2006
url = http://www.esa.int/esa-mmg/mmg.pl?b=b&type=I&mission=SMART-1&single=y&start=1&size=b
title = SMART-1 view of Shackleton crater at lunar South Pole
publisher = ESA/SMART-1 | accessdate = 2006-10-20 ]

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. [cite conference
author=P.D. Spuddis, K.R. Stockstill, W.J. Ockels, M. Kruikft
title = Physical Environment of the Lunar South Pole from Clementine data: Implications for Future Exploration of the Moon
booktitle = Lunar and Planetary Science Conference, vol. 26
pages = 1339 | date = March, 1995
url = http://adsabs.harvard.edu/abs/1995LPI....26.1339S ] Continuously illuminated mountains have been termed peaks of eternal light and have been predicted to exist since the 1900s.

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. [cite book
author=Ben Bussey and Paul Spudis
title=The Clementine Atlas of the Moon
publisher=Cambridge University Press
location=London | year=2004 | id=ISBN 0-521-81528-2 ]

Exploration

From the perspective of the Earth, this crater lies along the southern of the Moon, making observation difficult. Detailed mapping of the polar regions and farside of the Moon did not occur until the advent of orbiting spacecraft. The Shackleton crater lies entirely within the rim of the immense South Pole-Aitken basin, which is 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. [cite conference
author = C. M. Pieters, M. Duke, J. W. Head III, B. Jolliff
title = Science Options for Sampling South Pole-Aitken Basin
booktitle = 34th Annual Lunar and Planetary Science Conference
date = March 17-21, 2003 | location = League City, Texas
url = http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1366.pdf
accessdate = 2006-12-07 |format=PDF]

A neutron spectrometer on board the Lunar Prospector spacecraft detected enhanced concentrations of hydrogen close to the northern and southern lunar poles, including the crater Shackleton. [cite journal
last = Feldman | first = W. C.
title=Fluxes of Fast and Epithermal Neutrons from Lunar Prospector: Evidence for Water Ice at the Lunar Poles
journal=Science | year=1998 | volume=281 | issue=5382
pages=1496
url=http://adsabs.harvard.edu/abs/1998Sci...281.1496F
doi=10.1126/science.281.5382.1496
pmid=9727973 ] At the end of this mission in July 1999, the spacecraft was crashed into the nearby Shoemaker crater in the hope of detecting from Earth-based telescopes an impact-generated plume containing water vapor. The impact event did not produce any detectable water vapor, and this may be an indication that the hydrogen is not in the form of hydrated minerals, or that the impact site did not contain any ice. [cite web
author=D. Isbell, D. Morse, B. Rische
date = October 13, 1999
url = http://science.nasa.gov/newhome/headlines/ast13oct99_1.htm
title = Moon Water Still a Mystery
publisher = Science@NASA | accessdate = 2006-12-07 ] Alternatively, it is possible that the crash did not excavate deeply enough into the regolith to liberate significant quantities of water vapor.

From images of the crater edge taken from orbit, Shackleton appears to be a relatively young crater. A young crater would indicate that the inner sides are relatively steep, which may make traversing the sides relatively difficult for a robotic vehicle. [cite web
author=J.J. Zakrajsek, D.B. McKissock, J.M. Woytach, J.F. Zakrajsek, F.B. Oswald, K.J. McEntire, G.M. Hill, P. Abel, D.J. Eichenberg, T.W. Goodnight
month = March | year = 2005
url = http://gltrs.grc.nasa.gov/cgi-bin/GLTRS/browse.pl?2005/TM-2005-213555.html
title = Exploration Rover Concepts and Development Challenges
publisher = NASA | accessdate = 2006-12-07 ] In addition, it is possible that the interior floor might not have collected a significant quantity of since its formation. However other craters in the vicinity are considerably older, and may contain significant deposits of hydrogen, possibly in the form of water ice. (See Shoemaker crater, for example.)

Radar studies following the Lunar Prospector mission demonstrate that the inner walls of Shackleton are similar in reflective characteristics to those of some sunlit craters. In particular, the surroundings appear to contain a significant number of blocks in its "ejecta" blanket, suggesting that its radar properties are a result of surface roughness, and not ice deposits, as was previously suggested from a radar experiment involving the Clementine mission. [cite journal
author=B.A. Campbell, D.B. Campbell
title=Regolith properties in the south polar region of the Moon from 70-cm radar polarimetry
journal=Icarus | year=2006 | volume=180
issue=1 | pages=1–7
url=http://adsabs.harvard.edu/abs/1998Sci...281.1496F | doi=10.1016/j.icarus.2005.08.018] This interpretation, however, is not universally agreed upon within the scientific community. [cite web
last=Paul Spudis | title = Ice on the Moon
url = http://www.thespacereview.com/article/740/1
year = 2006]

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. [cite news
last = Buck | first = John
title=New NASA Ames Spacecraft to Look for Ice at Lunar South Pole
publisher=NASA | date=April 10, 2006
url=http://www.nasa.gov/centers/ames/news/releases/2006/06_21AR.html
accessdate=2006-12-07 ] The EDUS will impact at about 2.5 km/s., and 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

Some sites along the crater rim receive almost constant illumination. At these locales sunlight is almost always available for conversion into electricity using solar panels, potentially making them good locations for future moon landings. [cite conference
author = D. B. J. Bussey, M. S. Robinson, P. D. Spudis
title = Ideal Landing Sites near the Lunar Poles
booktitle = 35th Lunar and Planetary Science Conference
date = March 15-19, 2004 | location = League City, Texas
url = http://adsabs.harvard.edu/abs/2004LPI....35.1582F
accessdate = 2006-12-07 ] The temperature at this site is also more favorable than at more equatorial latitudes as it does not experience the daily temperature extremes of 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. [cite journal
author=A.P. Ingersoll, T. Svitek, B.C. Murray
title= Stability of polar frosts in spherical bowl-shaped craters on the moon, Mercury, and Mars
journal=Icarus | year=1992 | volume=100
issue=1 | pages=40–47
url=http://adsabs.harvard.edu/abs/1992Icar..100...40I | id=ISSN 0019-1035 | doi=10.1016/0019-1035(92)90016-Z] Any water vapor that arrives here following a cometary impact on the Moon 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 as to whether or not the hydrogen is in the form of ice, as well as to the concentration of this "ore" with depth below the surface. Resolution of this issue will require future missions to the Moon.

This crater has also been proposed as a future site for a large infrared telescope. [cite conference
author = D. B. J. Bussey, M. S. Robinson, P. D. Spudis
title = Design and Construction of a Lunar South Pole Infrared Telescope (LSPIRT)
booktitle = 34th COSPAR Scientific Assembly, The Second World Space Congress
date = October 10-19, 2002
location = Houston, Texas
url = http://adsabs.harvard.edu/abs/2002cosp.meetE.113V
accessdate = 2006-12-07 ] 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. [cite conference
author=Burton L. Sharpe, David G. Schrunk
title = Malapert Mountain Revisited
booktitle = Proceedings of Space 2002: The Eighth International Conference And Exposition On Engineering, Construction, Operations, And Business In Space
pages = 129-135 ]

NASA has named the rim of Shackleton crater as a potential candidate for its lunar outpost, slated to be up and running by 2020 and continuously staffed by a crew by 2024. The location would promote self-sustainability for lunar residents, as perpetual sunlight on the south pole would provide energy for solar panels. Furthermore, the shadowed polar regions are believed to contain the frozen water necessary for human consumption and could also be harvested for fuel manufacture. [cite news
last=Kluger | first=Jeffry | title=Promising the Moon
publisher=CNN | date=December 5, 2006
url=http://www.time.com/time/nation/article/0,8599,1566272,00.html?cnn=yes
accessdate=2006-12-07 ]

ee also

* Colonization of the Moon
* Lunar ice

References

External links

* cite news
title=Best site for Moonbase revealed
publisher=BBC News | date=March 16, 1999
url=http://news.bbc.co.uk/1/hi/sci/tech/297783.stm
accessdate=2006-12-07
* cite news
author=F. Morring, Jr.
title=NASA Sending Piggyback Impactors With Lunar Reconnaissance Orbiter
publisher=Aviation Week | date=April 11, 2006
url=http://www.aviationnow.com/avnow/news/channel_space_story.jsp?id=news/LRO04116.xml
accessdate=2006-12-07
* cite web
author = B. H. Foing, J.-L. Josset
date = October 20, 2006
url = http://www.esa.int/SPECIALS/SMART-1/SEMP7QOFHTE_0.html
title = Shackleton crater: SMART-1’s search for light, shadow and ice at lunar South Pole
publisher = ESA/SMART-1 | accessdate = 2006-10-20
* cite web
last = Wood | first = Chuck | date = November 14, 2007
url = http://www.lpod.org/?m=20071114
title = A View of Our Future
publisher = Lunar Photo of the Day
accessdate = 2007-11-14