Shackleton (crater)

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Crater characteristics
South lunar pole.
South lunar pole as imaged by Clementine. Shackleton is in the small, dark patch at center. NASA photo.
Coordinates 89.9° S, 0.0° E
Diameter 19 km
Depth 2 km
Colongitude 0° at sunrise
Eponym Ernest Shackleton

Shackleton, named after Ernest Shackleton, a noted explorer of the Antarctic, is an impact crater that lies at the south pole of the Moon. The peaks along the crater's 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.

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[edit] Description

The rotational axis of the Moon lies within Shackleton, 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 that it is relatively young.[1]

Because the orbit of the Moon is tilted only 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.[2] Continuously illuminated mountains have been termed peaks of eternal light and have been predicted to exist since the 1900s.

Nearby craters of note include Shoemaker, Sverdrup, de Gerlache, and Faustini. Somewhat farther away, on the eastern hemisphere of the lunar near side, are the larger craters Amundsen and Scott, named after two other early explorers of the Antarctic continent.[3]

[edit] Exploration

From the perspective of the Earth, this crater lies along the southern limb 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. Shackleton 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.[4]

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.[5] At the end of this mission in July 1999, the spacecraft was crashed into the nearby crater Shoemaker 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.[6] 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 relatively young. A young crater would indicate that the inner sides are relatively steep, which may make traversing the sides relatively difficult for a robotic vehicle.[7] In addition, it is possible that the interior floor might not have collected a significant quantity of volatiles 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 (lunar crater), for example.)

Artist's impression of the Lunar Crater Observation and Sensing Satellite (LCROSS) probe. The crater Shackleton has been suggested as a potential target for this mission, but the final target has not yet been selected.

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.[8] This interpretation, however, is not universally agreed upon within the scientific community.[9]

Optical imaging inside the crater was done for the first time by the Japanese lunar orbiter spacecraft Kaguya in 2007. It did not have any evidence of significant amount of water ice, down to the image resolution of 10 m per pixel.[10][11]

On November 15, 2008, a 34-kg probe made a hard landing inside the crater. The moon impact probe (MIP) was launched from the Indian Chandrayaan-I spacecraft and reached the surface 25 minutes later. The probe carried a radar altimeter, video imaging system, and a mass spectrometer, which will be used to search for water.[12]

Lunar Reconnaissance Orbiter, to be launched in 2009, has a secondary payload known as the Lunar Crater Observation and Sensing Satellite (LCROSS). It will observe the impact of the EDUS (Earth Departure Upper Stage) within a crater at a lunar pole. Shackleton 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.[13]

[edit] Potential uses

Some sites along Shackleton's 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.[14] 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 100 K.[15] 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 Clementine and 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.[16] The low temperature of the crater floor makes 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.[17]

NASA has named the rim of Shackleton 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.[18]

[edit] See also

[edit] References

  1. ^ "SMART-1 view of Shackleton at lunar South Pole". ESA/SMART-1. January 13, 2006. http://www.esa.int/esa-mmg/mmg.pl?b=b&type=I&mission=SMART-1&single=y&start=1&size=b. Retrieved on May 13, 2009. 
  2. ^ P.D. Spudis, K.R. Stockstill, W.J. Ockels, M. Kruikft (March, 1995). "Physical Environment of the Lunar South Pole from Clementine data: Implications for Future Exploration of the Moon". Lunar and Planetary Science Conference, vol. 26: 1339 
  3. ^ Ben Bussey and Paul Spudis (2004). The Clementine Atlas of the Moon. London: Cambridge University Press. ISBN 0-521-81528-2. 
  4. ^ C. M. Pieters, M. Duke, J. W. Head III, B. Jolliff (March 17-21, 2003). "Science Options for Sampling South Pole-Aitken Basin" (PDF). 34th Annual Lunar and Planetary Science Conference. Retrieved on 2009-05-13. 
  5. ^ Feldman, W. C. (1998). "Fluxes of Fast and Epithermal Neutrons from Lunar Prospector: Evidence for Water Ice at the Lunar Poles". Science 281 (5382): 1496. doi:10.1126/science.281.5382.1496. PMID 9727973. http://adsabs.harvard.edu/abs/1998Sci...281.1496F. 
  6. ^ D. Isbell, D. Morse, B. Rische (October 13, 1999). "Moon Water Still a Mystery". Science@NASA. http://science.nasa.gov/newhome/headlines/ast13oct99_1.htm. Retrieved on May 13, 2009. 
  7. ^ 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 (March 2005). "Exploration Rover Concepts and Development Challenges". NASA. http://gltrs.grc.nasa.gov/cgi-bin/GLTRS/browse.pl?2005/TM-2005-213555.html. Retrieved on May 13, 2009. 
  8. ^ B.A. Campbell, D.B. Campbell (2006). "Regolith properties in the south polar region of the Moon from 70-cm radar polarimetry". Icarus 180 (1): 1–7. doi:10.1016/j.icarus.2005.08.018. http://adsabs.harvard.edu/abs/1998Sci...281.1496F. 
  9. ^ Paul Spudis (2006). "Ice on the Moon". http://www.thespacereview.com/article/740/1. 
  10. ^ Junichi Haruyama et al. (2008-10-23). "Lack of Exposed Ice Inside Lunar South Pole Shackleton Crater". Science 322: 938. doi:10.1126/science.1164020. PMID 18948501. http://www.sciencemag.org/cgi/content/abstract/1164020. 
  11. ^ JAXA (October 24, 2008) (in Japanese). 月周回衛星「かぐや（SELENE）」搭載の地形カメラによる南極シャックルトンクレータ内の永久影領域の水氷存在に関する論文のサイエンスへの掲載について. Press release. http://www.jaxa.jp/press/2008/10/20081024_kaguya_j.html. Retrieved on May 13, 2009. 
  12. ^ "India on the moon, Chandrayaan MIP lands". Chitramala. November 15, 2008. http://www.chitramala.com/news/india-on-the-moon-109400.html. Retrieved on May 13, 2009. 
  13. ^ Buck, John (April 10, 2006). "New NASA Ames Spacecraft to Look for Ice at Lunar South Pole". NASA. http://www.nasa.gov/centers/ames/news/releases/2006/06_21AR.html. Retrieved on May 13, 2009. 
  14. ^ D. B. J. Bussey, M. S. Robinson, P. D. Spudis (March 15-19, 2004). "Ideal Landing Sites near the Lunar Poles". 35th Lunar and Planetary Science Conference. Retrieved on 2009-05-13. 
  15. ^ A.P. Ingersoll, T. Svitek, B.C. Murray (1992). "Stability of polar frosts in spherical bowl-shaped craters on the moon, Mercury, and Mars". Icarus 100 (1): 40–47. doi:10.1016/0019-1035(92)90016-Z. ISSN 0019-1035. http://adsabs.harvard.edu/abs/1992Icar..100...40I. 
  16. ^ D. B. J. Bussey, M. S. Robinson, P. D. Spudis (October 10-19, 2002). "Design and Construction of a Lunar South Pole Infrared Telescope (LSPIRT)". 34th COSPAR Scientific Assembly, The Second World Space Congress. Retrieved on 2009-05-13. 
  17. ^ Burton L. Sharpe, David G. Schrunk. "Malapert Mountain Revisited". Proceedings of Space 2002: The Eighth International Conference And Exposition On Engineering, Construction, Operations, And Business In Space: 129-135 
  18. ^ Kluger, Jeffry (December 5, 2006). "Promising the Moon". CNN. http://www.time.com/time/nation/article/0,8599,1566272,00.html?cnn=yes. Retrieved on May 13, 2009. 

[edit] External links

Retrieved from "http://en.wikipedia.org/wiki/Shackleton_(crater)"
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