Unusual features on North Massif

In January 2013, Moon Zoo user jaroslavp posted some interesting images in the Interesting terrain thread.

The images are from the base of the North Massif feature, close to where the Apollo 17 astronauts landed in the Taurus-Littrow valley. This image gives an overview of the NAC image from which the other images were taken (Note: North is at the bottom!):


The following images are from the marked area.

This image shows two areas with irregular boundaries – I can’t imagine what sort of process formed them.


NAC: M162107606RE Latitude = 20.2 Longitude = 30.7

Close to the previous image is this area showing odd striations and cross-hatching on the surface, possibly caused by entrained debris flow from an impact event. This may also explain the strange features in the previous image. The impact event that created the Serenitatis Basin may have been the event responsible.

Jules recently posted an Image of the Week about the Taurus-Littrow valley which has a great overview image showing the North and South Massifs: Moon landing at Taurus-Littrow

References
Taurus-Littrow (Wikipedia)

Approach to Taurus Littrow Valley (LROC)

Flying over Taurus-Littrow

The LRO took many images of the Apollo 17 landing site at Taurus-Littrow. Here is a glorious oblique “spaceship-eye” view of the Sculptured Hills and massifs surrounding the landing site taken from from M1096343661R and L. The position of the Lunar Module is marked on the second image.


Two NAC images have been stitched together and the aspect ratio tweaked to around 4:1. (click image for larger version.)

Can you find the Moon?

A puzzle for you this week. Can you tell the difference between a moon, a planet and minor planet? Below are images of craters on our Moon, Vesta and Mercury but which is which? Superficially very similar but there are differences. Click on the letters below for links to reveal the answers.

Don’t peek until you have had a guess!

a  b  c

Proclus lava flow

I was exploring Proclus crater recently and spotted a diamond-shaped flow of lava in the south-western region which is shown below.

Proclus crater is about 28km in diameter and is one of the brightest craters on the Moon, second only to Aristarchus. It has a bright ray system which is asymmetric, probably caused by a shallow-angle impact.


NAC strip: M104211600RC Overview of lava flow.


Edge of lava flow showing cracks, melt pools and boulder erosion.

‘Incoming!’ LPOD lunar photo of the day, 31 Jan 2006

Has a good overview of the creation of Proclus crater and its asymmetric ray system.

Two views of Rupes Recta

Sketching the Moon is an ancient and still widely practised art. It requires patience and plenty of time and must be an excellent way to familiarise yourself with the lunar terrain. Cameras are very good at picking up subtle detail and shading missed by the human eye but the advantage of a drawing is that it is a faithful representation of what you can actually see through the eyepiece.  For this week’s Image of the Week I have borrowed the most recent LPOD (Lunar Picture of the Day), a drawing of Rupes Recta (the straight wall) in Mare Nubium at 22.1°S 7.8°W . This 110 km long linear rille is 240-300 m high and 2.5 km wide. Although not very steep the rille casts a dramatic shadow when illuminated by a low Sun.

Rupes recta, and craters Birt, Thebit, Thebit A and Thebit L. Both images have been rotated so that south is up.

Frank McCabe’s drawing using a
13.1” f/6 Dobsonian telescope

LRO view
from ACT-REACT Quick Map

The LROC image was taken at a much higher illumination angle but lunar features clearly match and the amount of detail in the drawing is remarkable. In these images the trio of overlapping craters Thebit, Thebit A and Thebit L are to the left of Rupes Recta and Birt crater is to the right.

December 19: Splashdown

After 13 days in space Eugene Cernan, Ronald Evans, and Harrison (Jack) Schmitt aboard the Apollo 17 command module Challenger parachuted to a safe splashdown at 19:20 GMT on 19 December 1972, 648 km southeast of American Samoa. The last humans to have walked on the Moon.

Challenger makes a perfect splashdown

The crew arrive by helicopter aboard the rescue ship Ticonderoga

images NASA

There is still much to learn from the Apollo 17 mission. Moon Zoo needs your help to explore the Apollo 17 landing site.  Celebrate the anniversary with us. Go to http://www.moonzoo.org/ and start clicking! Follow “live” mission tweets from @moonzoo

December 18: 10 more facts about Apollo 17

1. Jack Schmitt discovered some unusual orange coloured “soil” later found to contain volcanic glass.


http://www.lpi.usra.edu/captem/slide_1.html

2. The Apollo 17 mission patch.

http://airandspace.si.edu/collections/imagery/apollo/PATCHES/Apollo17patch.jpg

3. Apollo 17 was the eleventh and final mission to carry astronauts in the Apollo space program.

4. The command module was named America and the the ascent stage of the lunar module was Challenger.

The descent stage was left on the Moon at coordinates 20.19080°N 30.77168°E.

LROC Video of the site here.

5. Lunar rovers were used on Apollo missions 15, 16. and 17.

Apollo 17’s Lunar rover Apollo Lunar Surface Journal

6. Apollo 17 was the only Apollo mission to carry the Traverse Gravimeter Experiment (TGE.) The TGE made measurements of the lunar gravity and its variation over time. It also investigated tidal distortions of the shape of the Moon.

7. Jack Schmitt turned to from space exploration to politics and in January 1977 he began a six-year term as one of New Mexico’s Senators in Washington. His was on the Commerce, Science and Transportation Committee; the Banking, Housing and Urban Affairs Committee and the Select Committee on Ethics.

8. The name of the Apollo 17 recovery ship was USS Ticonderoga.

9. There were no seats in the Lunar Module.

10. The Apollo programme defined 10 mission types from A (unmanned test flights) to J (extended lunar scientific missions). Apollo 17 was a J-type mission.

December 17: Eugene Cernan’s regret

Hindsight is a wonderful thing. Just when space travel seemed almost normal, Gene Cernan left his Hasselblad camera on the Moon as an experiment in how solar radiation would affect the lens. He assumed that another mission would be able to retrieve and study it firmly believing that the Apollo programme was just the beginning rather than the end of sending humanity to the Moon.

He said: “I left my Hasselblad camera there with the lens pointing up at the zenith, the idea being someday someone would come back and find out how much deterioration solar cosmic radiation had on the glass. So, going up the ladder, I never took a photo of my last footstep. How dumb! Wouldn’t it have been better to take the camera with me, get the shot, take the film pack off and then (for weight restrictions) throw the camera away?”

A Hasselblad camera like the one Gene Cernan left behind

NASA via Daily Mail

December 16: Moon Rover


Lunar rovers
(or Moon buggies) were used on the last 3 Apollo missions. A rover allowed astronauts to explore further and carry more equipment. It had a 90 inch wheelbase and a top speed of 22 kph.


Apollo Lunar Surface Journal


APOD

There is still much to learn from the Apollo 17 mission. Moon Zoo needs your help to explore the Apollo 17 landing site.  Celebrate the anniversary with us. Go to http://www.moonzoo.org/ and start clicking! Follow “live” mission tweets from @moonzoo

December 15: Measuring the regolith thickness at the Apollo 17 site

By  Ian Crawford
(Department of Earth and Planetary Sciences, Birkbeck College)

 Estimating the thickness of the unconsolidated lunar regolith is one of the major scientific objectives of Moon Zoo. This is because understanding the thickness of the regolith in different regions of the Moon will address a number of important scientific questions. For example, as regolith thickness increases with time, measuring the regolith thickness in areas which have not been dated by returned samples will help provide additional surface age estimates. Conversely, measuring the regolith thickness on surfaces with well-determined ages (such as the Apollo landing sites) will help us determine the regolith accumulation rate. Improved global regolith thickness maps will also provide important information for future exploration of the Moon, including the quest to identify future lunar resources.

There are three ways in which studies of small craters can be used to estimate regolith thickness. The first is to determine the minimum size of craters which have excavated blocks of bedrock (i.e. boulders) from below the regolith layer (Fig. 1).  If the crater dimensions are known, then an estimate of a maximum depth of excavation can be estimated as about one-tenth of the diameter.

Figure 1. LROC image of a boulder-covered bench crater. The crater has formed in a basaltic regolith close to the Apollo 12 landing site. The impact has punched through the thin regolith cover and into the harder rock, excavating large blocks that have covered the surrounding surface. This example is 130m in diameter, so the regolith here must be less than about 13m deep. By determining the maximum size of craters in this area which have not excavated boulders the actual depth of the local regolith can be determined. (LROC image M114104917L/ASU/NASA).

The second method relies on identifying flat floors or benches within a crater, which also indicates that a crater has penetrated an overlying regolith layer to a stronger layer beneath. Figure 1 again provides an example. For features like this a simple expression has been derived which estimates the regolith thickness from the ratio of the bench diameter to the overall crater diameter. For the example shown in Figure 1 this indicates a regolith depth of about 6 m, consistent with the upper-limit of 13m estimated from the presence of boulders around the rim.

The third method is more subtle, and exploits the process of impact gardening, whereby rocky surfaces are disaggregated and overturned by meteorite impacts, thus destroying the record of previous impact cratering events. The equilibrium diameter is identified when the cumulative number of craters seen on the surface is less than the number actually produced, and can be recognized as a change in slope in a graph which plots number of craters in a given area as a function of their size. Because the number of craters buried under new regolith depends on the regolith thickness, measuring the equilibrium diameter gives a guide to the latter.

In order to test these different methods it is necessary to apply them to areas where the regolith thickness has been directly measured. However, this can only be done at the small number of Apollo landing sites where seismic measurements of regolith thickness were conducted. By far the best estimates have been provided by the Apollo 17 Lunar Seismic Profiling Experiment (LSPE). For this experiment the astronauts deployed eight small explosive packages during their traverses around the Taurus-Littrow Valley (Fig. 2) which, when detonated, provided seismic signals for detectors setup close to the Lunar Module.

Figure. 2. One of eight explosive packages deployed by the Apollo 17 astronauts to provide data for the lunar seismic profiling experiment which measured the thickness of regolith in the Taurus-Littrow Valley. The Apollo 17 LRV is in the foreground and the lunar module, where a geophone detector array was deployed to collect the signals, in the middle distance about 300 m away (NASA)

By measuring the time taken for the seismic signals to travel from the explosive packages to the detector, geophysicists were able to determine the thickness of both the regolith layer and the underlying lava flows at the Apollo 17 landing site. The results are shown in Fig. 3.

Figure. 3. Subsurface structure under the Taurus-Littrow Valley, as determined by the Apollo 17 seismic profiling experiment. The numbers indicate seismic wave speed in meters per second. Yellow represents the lunar crust, which outcrops locally as the South Massif (“LM impact” schematically indicates where the Apollo 17 Lunar Module ascent stage was crashed into the South Massif to provide an additional seismic data point). The green layers indicate the thickness of basaltic lava that has flooded the valley to a depth of about 1.4 km. The thick black line shows the regolith layers (inset). (Image adapted from a paper by M.R. Cooper et al., published in Reviews of Geophysics and Space Physics, Vol. 12, pp. 291 – 308, 1974).

Five separate layers were identified below the surface of the Taurus-Littrow valley:

(i)  The topmost layer, 4 m deep with the very low seismic wave speed of 100 m/s, is interpreted as being due to the local regolith.

(ii)  Beneath the regolith is a layer with a velocity of 327 m/s, which is still too low for solid rock. It may be due to more consolidated regolith, or possible highly fractured lava.

(iii)  At a depth of 32 m the velocity rises to 495 m/s, and this is interpreted to be the fractured and/or vesicular top of the lava flow filling the valley.

(iv)  At a depth of 390 m the velocity rises to 960 m/s. This is interpreted as being due to a more coherent basalt unit.

(v)  Finally, at a depth of 1.4 km the velocity rises sharply to 4.7 km/s, and this is interpreted as being due to crustal bedrock underlying the lava layers.

The deeper layers are too deep to be probed by craters found in the MoonZoo images, although the presence of a lava layer at a depth of about 30m is consistent with the excavation of basaltic blocks from 300-400 m diameter craters in the valley floor. Where MoonZoo can really help is to confirm that the seismic boundary at a depth of 4m (which will be probed by craters about 40 m across), and to determine whether the underlying layer is more consistent with fractured basalt or compact regolith.

In order to address these issues, we need MoonZoo users to look carefully at craters in the images of the Apollo 17 area, determine their sizes accurately, and note the presence of boulders around the rims and/or interior benches or flat floors. Don’t worry that scales are not provided on the MoonZoo images (this is deliberate to avoid the possibility of biasing the results), but users may be sure that the sizes and morphologies of all thecraters in these images are relevant to the task in hand.

 Ian Crawford is based in the Department of Earth and Planetary Sciences, Birkbeck College, London, and is a member of the MoonZoo science team. This blog article is based on a longer article published in the December 2012 issue of the Royal Astronomical Society journal Astronomy and Geophysics.