February 28, 2008

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Sim Pole

image by NASA-JPL

Yesterday NASA released a series of image products derived from new radar studies of the area near the lunar South Pole. Using the Goldstone Radar and two smaller antennas 13 km away, three images with 20 m resolution were obtained at different librations. The librational offsets permitted creation of a high resolution topographic grid, which combined with the images, is the basis for the products. The most dramatic is a simulation of a month at the pole, with shadows tracking around a complete circle. There are also simulations of a south polar fly-over and a landing, as well as maps of topography right at the pole and derived from that a map of slopes. Although NASA was surprised that topography there was much more rugged than previously understood, they shouldn't have been. It has long been known that this is the most rugged area of the Moon. The slope map shows the upper inner rim of Shackleton (S) to be about 30°, as I have previously inferred from comparisons with craters of similar size. The topo map shows something else that has long been suspected - neither Malapert nor Cabaeus are single craters - they probably should not have names. Leibnitz Beta (LB) is the largest high plateau in this area - higher than Malapert Peak (south of the crater) and other M-lettered peaks. For some reason the NASA press release states that the previous highest resolution data was from Clementine, which is said to have 1 km resolution. But Clementine's resolution was better than 100 m, similar to Lunar Orbiter IV's images of the pole, and the Arecibo Radio Telescope also produced a 20 m resolution image in 2006! These new data are not unique for spatial resolution but in having high topographic resolution.

Chuck Wood

Technical Details
Rotation of image with north up and nomenclature by CAW. Names from earlier LPOD and Clementine Atlas.

Related Links
Rükl plates 73, V & VI
Clementine Atlas 137, 138 & 144

Yesterday's LPOD: Umbral Image

Tomorrow's LPOD: A Forgotten Corner

(1) I thought there were 30,000-plus foot peaks in this area that were higher than the Himalayas and Mt. Everest on Earth.(??) The map, however, seems to indicate maximum elevations in the 20,000-foot range. Still high, but not enough to put Earth's highest mountains in second place.

It is interesting to learn about the technology and scientific methods being used to measure the Moon. The information can come in handy at public star parties. I actually had someone scoff when I showed Mare Crisium in my scope and mentioned its size. The disbelieving comment was something like: "How do THEY know how big it is?"


(2) Bill,

This looks to me like the finest topographic map of the Moon's south pole to date, and its ability to recreate shadow patterns that match those actually observed by Lunar Orbiter and Clementine (if true) suggests it must be pretty accurate. I understand from the principal investigator, Scott Hensley, that the same technique could be applied to any part of the Moon visible from their tracking station. I don't know if NASA is interested, but it sounds to me like a very cost-effective way to gather a uniform set of basic topographic data for the Moon's nearside that we currently lack -- far cheaper and simpler, I would think than a space mission.

I don't think the results so far contradict the earlier information you were relying on. Keep in mind that the elevation values you've heard quoted don't refer to the absolute heights you see plotted in the LPOD figure's legend (on a scale with an arbitrary zero point), but rather to differences in elevation between nearby points.

To accurately estimate elevation differences from the LPOD photo you have to open it (or better the higher resolution version on the NASA website referenced) in something like Photoshop that displays pixel value in terms of "Hue, Saturation and Value". You then need to determine the Hue at the point of interest and try to find the matching Hue in the topographic scale they provide.

Using this technique you will find, for example, that the high point to the NE of Scott (hue 280°) is at about 3600 m elevation compared to a point 45 km away on the floor of Scott at about -5300 m. That's an elevation difference of 8900 m or 29,000 ft. The shadows observed in Lunar Orbiter photos of Scott suggest this is not far off. You will find an even larger elevation difference in Cabeus: from the magenta peak (4200 m) to the bottom of the red-brown pit on its floor (-6100 m) is a difference of 10300 m (34,000 ft) in a distance of 65 km.

9000-10000 m is quite compatible with the "30,000 ft plus" value you've heard quoted; and relative to comparably nearby valley floors, the lunar peaks near the South Pole appear to be considerably more rugged than most of those on Earth. A famous terrestrial analog familiar to Americans is the drop-off from the peak of Mt. Whitney to the bottom of Death Valley which (according to the Wikipedia) is a drop of 4500 m in 123 km.

Mount Everest is certainly taller than any of these if its peak is measured relative to something like the bottom of the Marianas Trench, but the ocean bottom is a long ways away (from Everest to the Marianas bottom is about 20000 m, but over a distance of 6000 km). I don't have a firm figure for this, but again relying on the Wikipedia, Mt. Everest is said to rise no more than 5000 m relative to the nearby terrain at its "base". It apparently rises about 7500 m above the Kathmandu Valley, about 150 km away; and the distance from Everest to the coastline at Calcutta (relative to which it rises its "full" 9000 m) looks to me to be about 800 km. To a low point in the ocean (relative to which I'm sure it would rise several 1000 m more), looks much farther.

So the possibility, near the Moon's south pole, of being able to descend (or ascend) 10000 m or so in a distance of about 50 km would seem to exceed anything possible on Earth.

- JimMosher-lg.jpg JimMosher

(3) Jim,

Thanks very much for your explanation! A NY Times Science article posted today (2-29-08) makes the same point--that the distance from the floor of a crater to the top of a nearby peak, for example, can be 37,000 feet in this part of the Moon. It certainly would be a challenge for astronauts to move around in this region.



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