Sunday, February 12, 2017

Surveyor 3 - the only multi-occupation site on the Moon

I've been looking at the amazing pictures of astronaut Alan Bean visiting the Surveyor 3 robotic lunar landing craft to remove a camera for return to Earth, in 1969. Something so obvious suddenly struck me and I wondered why I had not seen it before.

Surveyor 3 was part of a series of landing missions that left seven craft on the surface of the Moon. In November 1969, Apollo 12 landed on the edge of a crater, just 180 m from Surveyor 3, launched two years before. The two astronauts, Pete Conrad and Alan Bean, walked over the Surveyor 3 and removed a camera and a couple of other pieces for analysis. (This analysis showed evidence of 'scouring' on the Surveyor surfaces, a result of dust stirred up by the Apollo 12 landing).

Image courtesy of NASA
All of the Apollo sites are of a particular type: there's a landing module, numerous places where samples were taken, cameras and flags set up, the "toss zone" of discarded objects, the odd rover, and countless astronaut bootprints. 

Surveyor 3 is the only lunar site with astronaut footprints that was not a human landing mission. So you have an interesting mismatch of archaeological traces - a spacecraft which is not capable of containing human bodies, nor of moving, yet surrounded with the evidence of human movement.

You could argue that Surveyor 3 and Apollo are now part of the same site as they preserve evidence of interaction between the two locations. They're close in both time and space.

It's like a rockshelter with archaeological deposit, with only sparse evidence of occupation - some stone tools and a hearth -  at 18 000 years before present (bp), followed 10 000 years later by a denser layer of stone tools, bones, and hearths. Imagine this time frame telescoped with the acceleration of modern technology and spread flat across the landscape instead of stratified.

In archaeology, it's not unusual to find evidence of people incorporating artefact and places from the past into their lives. Stone tools from older campsites are re-used and sharpened, sometimes thousands of years later; masonry is scavenged from old buildings to be incorporated into newer ones. This is a practice known as spolia

This isn't exactly re-use; it's more in the nature of a scientific sample. Still, it illustrates something about how artefacts often move between space and Earth and end up out of context.

So, unlike all other lunar landing sites at the present time, the Surveyor 3 site is the only one which is the result of multiple visits. It's a rare human-robot encounter on a far world, receding further into the past with each passing year.

And incidentally, 2017 is Surveyor 3's 50th anniversary.