Thursday, February 25, 2010

Now it can be told

Stu Roosa was the Command Module Pilot on Apollo 14, and I was the Mission Scientist. In early 1970, during the discussions of the best landing site for the mission, Stu and I proposed and fought for locations toward the western limb of the Moon. We lost this battle because the consensus was that Apollo 14 should be sent to Fra Mauro (3.6oS, 17.5oW), where Apollo 13 was supposed to have landed. This site was favored because it is on the ejecta blanket from the magnificent Copernicus crater.

My favorite western sites were the crater Grimaldi (at 5.2oS, 68.6oW), and Rima Sirsalis, a rille (i.e., a linear trough) that begins at the crater Sirsalis (5.7oS, 61.7oW) and runs in a direction west of south to the crater Darwin (19.8oS, 69.1oW). I could make a good argument for these sites – but Stu and I also had an ulterior motive that we could not reveal without being ridiculed. The launch in June 2009 of the Lunar Reconnaissance Orbiter (LRO) persuades me that I should now come clean.

Grimaldi was interesting because it is one of the places where observers have reported Transient Lunar Phenomena (flashes of light or brief episodes of haziness in the crater, possibly due to volcanism). Unfortunately, we had no photographic evidence of these events, and the anecdotal reports were not given much credence in the lunar science community.

In retrospect, Grimaldi would have been a good choice for a lunar landing: observations from later Apollo missions and from Lunar Prospector in 1998 have detected emissions of radon in the vicinity, and there appears to be a mascon (mass concentration) under the crater. This suggests that it was formed by the impact of a dense asteroid that is still buried there. The relationship between this and the apparent gaseous emissions is an interesting question.

Rima Sirsalis is more than 350 km long, making it one of the longest rilles on the Moon. It averages 3.7 km wide and 230 meters deep. In 1970, the prevailing theory was that rilles were collapsed lava tubes, but it was hard to force this rille into that model because lava flows down hill and this one runs up and over mountain ranges.

Here again, later observations have made Rima Sirsalis more interesting than we knew. There is an unexplained linear magnetic anomaly associated with the rille, so that the surface field there is the strongest on the Moon (although still weak in comparison with the Earth's field), and there is also a strong gravity anomaly nearby.

This is the question Stu and I had asked ourselves: if alien spacefarers had visited the Moon some time in the past, and wanted to make contact when the primitive life on Earth had evolved into something interesting, where might they have left some indication of their presence for us to find?

Of course we did not believe in the alien monolith in the 1968 Clarke/Kubrick movie 2001: A Space Odyssey, but alien artifacts on the Moon were not (and are not) totally impossible.

The answer to the question seemed obvious: Mare Orientale, which is a vast multi-ringed crater centered at 17.5oS, 81.6oW, stretching across the western limb. The outer ring of mountains, called Montes Cordillera, is 930 km in diameter. The tallest peaks are 30,000 feet above the central basin, higher than Mt Everest is above sealevel.  There is nothing remotely like it anywhere else on the Moon.

The eastern mountains can be seen in profile from the Earth, especially at maximum lunar libration (the small rotation of the line of sight from the Earth because of the eccentricity of the Moon's orbit). Earth-based observations as early as 1871 suggested that these mountains surrounded a large crater, but we didn't have a good picture of it until 1967, when NASA's Lunar Orbiter 4 returned this photo.

The grey splotches on the Moon are called maria (Latin for 'seas") because that's what Galileo thought they were when he first saw them with a telescope. If the Moon were rotated 80o relative to the Earth, Orientale would be the most obvious naked-eye feature, a giant bullseye with a diameter nearly one third of the visible disc. Early observers knew nothing of asteroids and impact craters, so Orientale might well have seemed artificial, leading to the conclusion that there was a civilization on the Moon capable of construction on this astonishing scale. The possible effect of that on the intellectual development of our species is an interesting subject for speculation.

From the aliens' presumed point of view, Orientale would be a good place to leave a marker. It provides an unmistakable focus of attention, but we creatures on Earth would not know about it until we achieved spaceflight.

In order to ensure that surface features had distinct but not too elongated shadows, making them easier to see, the mission rules required that Apollo landings occur in the lunar morning, when the Sun was between 5o and 13o above the eastern horizon. The implication was that Orientale would be in darkness throughout the Apollo 14 mission unless the landing site was farther west than about 50oW. If we had pointed this out, and explained why Stu wanted to take photographs of this particular feature from orbit, we would have been dismissed as science fiction nuts.

As it turned out, the Apollo 12 landing site was the farthest west, at 3.0oS, 23.4oW, so none of the Apollo crews saw Orientale in daylight. The Clementine mission in 1994 obtained some pictures, but the resolution was tens of meters, insufficient to reveal a reasonably sized artifact. However, NASA's Lunar Reconnaissance Orbiter (LRO) is now in polar orbit around the Moon, at an altitude of only 50 km. The two LRO narrow-angle cameras image a swath 5 km wide with a surface resolution of 0.5 meters/pixel! 

LRO was intended to survey landing sites for Project Constellation (the return to the Moon), and to look for ice deposits in shaded valleys at the poles. I thought the mission architecture chosen for Constellation was a serious mistake, so I am not sorry that President Obama has canceled that program. I am however glad that he didn't get around to that decision before LRO was launched. Nobody has told it that its principal justification has gone away, so it is still up there, patiently returning images. 

A truly remarkable feature of this space mission is that NASA has set up a website where anybody can specify locations for high resolution pictures. It may take up to a year before LRO passes over your chosen spot, but you will be notified by email when it does.

In memory of Stu Roosa, who died in 1994, I have selected several promising locations for hi-res images in Orientale. Of course I don't actually expect to see an alien artifact, but it is surely worth a look.

Keep your fingers crossed, folks. 

1 comment:

Bill Haynes said...

Phil, I'm not as bashful (or as sensible?) as you.
I really think my article (ref: "Square Craters" describes a trio of really large ancient artifacts.
I invite you to go there and tell me what you think.
You will also see a very crude attempt by a leading lunar scientist to "photoshop" me into thinking I (andNASA) was "seeing things". Bill