That other scientific instrument: the eye

Apollo is very unusual in the history of planetary science, lor 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, w’hile 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 w7as 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 saw7. 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, made it 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 also received instruction in the subject from 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 u’ere considered likely to assist them in interpreting the lunar terrain. This often meant flying above volcanic landscapes in the western deserts of the United States and Hawaii. In lunar orbit, the CMP could then seek features that might be of further interest to El-Baz and his colleagues. Since the photography from the cameras in the SIM bay w7ould not be seen until they had been processed after the flight, the CMP could help scientists to plan further photographic sorties while the mission was still in progress. An example of this occurred during A1 Worden’s solo tenure in Endeavour as he coasted over western Mare Imbrium. The Sun had just risen across this basaltic expanse and the lighting was so shallow that it brought out the more subtle undulations in the surface, as he explained to Capcom Karl Ilenize.

“.At this low7 Sun angle, I can very clearly see some lava flow’s 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 window7 are you looking out?”

“I’m looking out window 3." This was the circular window on the 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 scientists duly passed up instructions for Worden to use his Hasselblad and the mapping camera to photograph these features. The extremely thin flows he saw 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. He 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, another 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 Serenilatis that was rather less majestic, known as the Taurus Mountains. Within this highland area, south of the crater Liu row. stood a cluster of fine hills between which were a series of valleys whose floors were as dark as any place on the Moon. Worden regularly observed this area and closely studied 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, fm 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 Capeom Bob Parker.

This report of cinder cones, along with Worden’s earlier descriptions of distinct colourations in the region, became one of the major reasons for sending Apollo 17 into one of these valleys 17 months later to seek evidence of recent lunar volcanism and determine whether the dark mantling was pyroclastic in origin. The pull of volcanics was sufficient to counter arguments from other quarters that to land at the edge of another major mare would essentially be a repeat of Apollo 15. even to the extent that the ground track would cover much the same landscape. In turn, this latter point prompted the decision to assign Apollo 17‘s SIM bay a different set of instruments in order to further study that track.

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. When they visited it, 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, theories proved lacking 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 did turn out to be related to volcanic processes. The soil consists of Liny 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 dark mantling across the whole valley was a mixture of ancient orange and black pyroclastic glass. At one end. light-toned avalanche deposits had been laid on Lop and the impact that created Shorty had simply punched through to excavate the ancient volcanic deposits as an ejecta blanket of dark material around the crater.