Archive | December 2012

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 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.

2. The Apollo 17 mission patch.

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


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 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.


December 14: The final EVA

The final excursion on the lunar surface took place on the 14th December [GMT] and lasted over 7 hours. In all, 66 kgs of basalts, rock and soil samples were collected, many gravimeter measurements were taken and results from several experiments were recovered for return to Earth. As part of the Lunar Seismic Profiling Experiment explosive packages were left on the surface and were detonated remotely after liftoff of the ascent stage. This experiment consisted of an array of four geophones, three of which formed a triangular array about 100 metres on a side with the fourth geophone in the centre of the triangle. Eight explosive packages were placed around the geophone array at distances ranging from 0.1 to 2.7 km and these were detonated remotely once the astronauts were clear of the lunar surface. The signals from these explosive events plus the impact of the Apollo 17 LM at a range of 8.7 km from the array were used to create a model of the near surface lunar structure.

One of the Lunar Seismic Profiling explosive charges with radio antenna deployed [NASA]

Lunar Seismic Profiling Experiment

A plaque located on the landing gear of the lunar module was unveiled before the crew entered the module for the last time.

Apollo 17 plaque


December 13: It’s Orange!

Coloured soil on the Moon is unusual. Apollo 15 found green glass deposits but mostly the Moon is a variety of greys and browns. Jack Schmitt, a geologist, was, therefore, understandably elated to discover something very different – and orange. This is how Schmitt told Cernan what he had found:

SCHMITT There is orange soil!
CERNAN Well, don’t move it ’till I see it.
SCHMITT It’s all over, orange!
CERNAN Don’t move it ’till I see it.
SCHMITT I stirred it up with my feet.
CERNAN Hey it is, I can see it from here.
SCHMITT It’ s orange!
CERNAN Wait a minute, let me put my visor up, it’s
still orange!
SCHMITT Sure is. Crazy! Orange!
(from the Apollo Mission Transcripts)

Listen to and watch the discovery here.

Apollo Lunar Surface Journal

The patch of soil was the result of fire fountains of volcanic lava which cool before falling back to the surface as tiny orange glass beads.

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 and start clicking! Follow “live” mission tweets from @moonzoo

December 12: I was strolling on the Moon one day…

The song “The Fountain in the Park” as featured in Tom and Jerry, Bugs Bunny and Mickey Mouse cartoons and sung by Judy Garland in “Strike up the Band” was given the Schmitt and Cernan treatment while setting up experiments during an EVA. Watch the astronauts enjoying themselves in this video. (placed on You Tube by Jordaxe12.)

Transcript from the mission transcripts:

SCHMITT (Singing) I was strolling on the Moon one day, in the merry merry month of December-
CERNAN May – May’s the month.
SCHMITT – May – that’ s right.
CERNAN May is the (garble) month.
SCHMITT – when much to my surprise, a pair of funny eyes (singing)
CAPCOM (Capsule Communicator back in mission control) Sorry about that, guys, but today may be December.

December 11: Moon landing at Taurus-Littrow

Challenger landed on the lunar surface at 19:48 GMT on 11 December 1972.

Taurus-Littrow valley

Apollo Lunar Surface Journal

The view from Challenger’s window (click to enlarge)

Apollo Lunar Surface Journal

The Taurus–Littrow valley was chosen because of its geologically varied terrain. The crew were hoping to collect different soils, relatively young lavas which filled the valley floor and older crustal material from the North and South Massifs. Several large boulders had rolled down the massifs providing additional sampling opportunities.

December 10: 10 facts about Apollo 17

1. 40 years after they left prints in the lunar dust the astronauts’ boots left more bootprints on Earth. Gene Cernan went to the Adler Planetarium in his home town of Chicago along with fellow Apollo 17 astronaut Harrison Schmitt. They made casts of their Apollo boots for the “Shoot for the Moon” exhibit at the Planetarium.

Image The Adler Planetarium FaceBook page

2. Apollo 17’s Harrison Schmitt was the only scientist (a geologist) to visit the Moon.

3. Fe, Fi, Fo, Fum and Phooey were the five astro-mice that accompanied the crew of Apollo 17.

4. The astronauts spent 75 hours on the Moon.

5. They spent 22 hours outside the vehicle on the lunar surface.

6. They travelled 36 kilometres in the lunar rover.

7. Lunar samples were collected at 22 locations in the Taurus-Littrow Valley region.

8. The astronauts collected 741 individual rock and soil samples with a total mass of 111 kilograms.

9. The flag is still standing. See the Apollo 17 flag shadow!

J Fincannon Apollo Lunar Surface Journal

10. Apollo 17 broke several records including the longest lunar landing flight carrying astronauts; the longest total lunar surface extravehicular activities; the largest lunar sample return, and the longest time in lunar orbit.

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 and start clicking! Follow “live” mission tweets from @moonzoo