That other scientific instrument the eye

Apollo is very unusual in the history of planetary science, for although it carried the kind of instruments that most probes to the Moon and planets would sport, it had one extra resource - a human. Therefore, while the instruments of the SIM bay were looking down at the Moon, the command module pilot, if he was not too busy, could also peer out of a window and report and photograph what he saw.

Coming as they did from the test pilot fraternity, none of the Apollo CMPs was a career scientist. However, like most of their colleagues exploring the surface, their profession made them very skilled observers, adept at perceiving, remembering and describing details of what they saw. Moreover, compared to the photographic films used throughout the Apollo programme for image capture, the dynamic range of the human eye, and its ability to discern subtle hues, is more able - especially when coupled with a curious mind - to scan intelligently for interesting detail. The increasing scientific focus of the later Apollo missions meant that it was not only the surface crews who were trained intensively in geology. The CMPs were also coached in geology by Farouk El-Baz, an enthusiastic teacher who focused on the interpretation of a landscape from an aerial perspective. In exercises prior to their missions, they were taken up in small aircraft to fly over the types of terrain on Earth that were considered valuable in helping them to interpret the Moon's terrain. This often meant flying above volcanic landscapes in the western deserts of the United States and Hawaii. When in lunar orbit, the CMP could then scan the surface below, looking for features that might be of further interest to geologists on Earth. Since the photography from the cameras in the SIM bay would not be seen until they had been processed after the flight, the CMP could help ground-based scientists to plan further photographic sorties while the mission was still in progress. This actually occurred during Al Worden's solo tenure in Endeavour as he coasted over the western plains of Mare Imbrium. The Sun had just risen across this basaltic expanse and the lighting was very low, bringing out the more subtle undulations in the surface, as he explained to Capcom Karl Henize.

''At this low Sun angle, I can very clearly see some lava flows coming out of what appears to be a ridge, extending in both directions from the ridge. And I wasn't set up this time to take a picture of it, but it might be interesting on the next pass if we could get a PAD to take a picture of that.''

''Very interesting. Which window are you looking out?"

''I'm looking out window 3.'' This was the circular window built into the spacecraft's main hatch.

''Thank you,'' replied Henize. ''Sounds like an interesting observation, and I'm sure the guys down below will be sending you up more work to do as a result. Be careful there, now.''

The ground crew duly passed up instructions for Al to use his Hasselblad and the

Lobate lava flows running across the surface of Mare Imbrium, photographed by Apollo 15.

mapping camera to photograph these flow features. The extremely thin flow and the others Worden could see were compelling evidence that areas like Mare Imbrium had been filled by lava in a sequence of small eruptions over a long period of time. Worden talked about them after the flight.

"I get the impression that there are just hundreds of flows that filled up the basin. They all look like, for example, you'd take a pail of water and sluice it out into a skating rink and let it freeze in place; then, if you do that 15 times around the same area, you would get this overlapping mixed up ice. All the flows were very thin and appeared as if they came out and froze in place.''

Worden's flight path took him directly over Mare Serenitatis, a roughly circular sea of frozen lava that had filled an impact basin. On the west side of this 700-kilometre plain stood an impressive range of rounded mountains, the Apennines, beyond which, his colleagues were exploring a magnificent embayment cut through by the meanders of Hadley Rille. There was another range on the eastern side of Serenitatis that was rather less majestic, known as the Taurus Mountains. Within this highland area, south of the crater Littrow, stood a cluster of fine hills between which were a series of valleys whose floor was as dark as any place on the Moon. Worden regularly observed this area, studying how the hues of the Serenitatis lavas changed towards the mare shore. On his third viewing opportunity, he looked more closely at the dark valley floors.

"Okay. I'm looking right down on Littrow now, and a very interesting thing. I see the whole area around Littrow, particularly in the area of Littrow where we've noticed the darker deposits, there are a whole series of small, almost irregular shaped cones, and they have a very distinct dark mantling just around those cones. It looks like a whole field of small cinder cones down there. And they look - well, I say cinder cones, because they're somewhat irregular in shape. They're not all round. They are positive features, and they have a very dark halo, which is mostly symmetric, but not always, around them individually.''

"Beautiful, Al,'' replied his Capcom Bob Parker.

Worden's observation of cinder cones from orbit, along with his earlier descriptions of distinct coloration in the region, became one of the major reasons that scientists sent Apollo 17 into one of these valleys 17 months later, to look for the much desired evidence of recent lunar volcanism. The pull of volcanics was powerful enough to counter arguments from other quarters that another landing site at the edge of a major mare would be too similar to the Apollo 15 site, and that the ground track of Apollo 17's SIM bay instruments would cover a landscape little different to Apollo 15's - a point that prompted the decision to assign Apollo 17's SIM bay a different set of instruments.

It has been said that because the CMPs on the J-missions had been trained to look for volcanics, that is exactly what they found. Worden's 'cinder cones' observation is a case in point. One of these cones was later named Shorty crater, by the Apollo 17 crew of Eugene Cernan and Jack Schmitt. When they visited it during their exploration of the Taurus-Littrow valley, they were astonished to discover deposits of bright orange soil on the rim of what was obviously an impact crater, not a volcanic cone. As so often happened on Apollo, and with any true exploration,

Apollo 17's landing site at Taurus-Littrow. CSM America is visible above centre and the dark-haloed crater, Shorty, is the arrowed smudge.

theories were found wanting and had to be replaced with new interpretations based on ground truth. The twist in the story of Shorty was that although this crater was of impact origin, as shown by its nature, its orange soil was indeed from volcanic processes. It consists of tiny orange glass beads that have been dated at 3.64 billion years old when, as molten rock, they were sprayed from a 'fire fountain' to rise perhaps hundreds of kilometres into the lunar sky before falling into the valley, soon to be buried by a lava flow. The impact that created Shorty had simply excavated these ancient volcanic deposits, depositing them as an ejecta blanket of dark material around the crater.

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