This week’s image comes from the Moon, and was captured by
the Lunar Reconnaissance Orbiter. It shows the landing site of Apollo 14, the
dark trails in this image are the tracks taken by the astronauts while they
were exploring the Moon’s surface.
This annotated image from NASA shows a
slightly larger area than the one I posted on Monday. The positions of both the
descent stage, and the Apollo Lunar Surface Experiments Package (ALSEP) can be
seen. ALSEP was a suit of instruments left behind on the moon to study its
environment, and includes seismic sensors and magnetometers, as well as instruments
to monitor heat flow and the solar wind.
Being able to see the tracks the astronauts took gives you a
real sense of how they went about exploring this small area of the lunar
surface, it’s not often that we see the impact of human activity on a world
other than Earth. Since the moon has no appreciable atmosphere the environment
around the lunar landing sites is essentially unchanged since the 1960s. We can
see precisely what route the astronauts took. This can be very useful for lunar
science. as it shows us which areas they looked at, and we can work out where photographs
were taken and where samples were collected. It gives us an overview image and allows
us to see how the astronaut’s observations fit into the larger context of the
site.
The lunar landings provide us with rare “ground truth”
information for this handful of places on the Moon. The observations and
samples which the astronauts brought back essentially allow us to calibrate our
remote sensing observations, seeing what is there at the small scale, which
would be invisible from a satellite image. We can examine samples to find out
about the geology of the site, and this has various implications. We are able
to confirm that the rocks collected from the Moon match the composition of some
of the meteorites in our collections, proving that they originated on the Moon.
We can also get precise dates for the age of lunar material using radioisotope
dating, of lunar samples and meteorites. This allows us to constrain the
history of the moon, and provides a baseline for estimating dates from crater
counting.
On the down side our sample size for these ground truth
observations is quite limited. You can see from these images and the others at
the links below that the astronauts only covered relatively small areas in
their exploration of the moon. The later Apollo missions had Lunar Roving
Vehicles (LRVs) which allowed them to cover more ground than the early
astronauts who ventured away from their landers on foot. These vehicles gave
the astronauts substantially more mobility and meant that samples were
collected over a wider area. However, they were only on the moon for a short
period of time, so couldn’t go very far. The Apollo 17 astronauts travelled the
furthest covered a total distance of 35.74 km. The Apollo 17 landing site and
the final position of their rover can be seen in the image below.
This article shows the furthest distances that vehicles have
travelled on other planet (and moons), as of 2013 http://www.space.com/79-distances-driven-on-other-worlds.html.
Both the Oppourtunity and Curiosity rovers on Mars have advanced substantially
in that time, however another rover, manned or otherwise, has not been sent
back to the moon. Although the majority of the moon’s surface remains
unexplored by humans, we can use the observations made by the Apollo astronauts
to shape how we interpret remote sensing data, and send robotic probes to cover
more ground. these landmark missions remain some of the most important steps in
the history of human space exploration, and it will be a long time before we go
further.
It remains to be seen when humans will next visit our
nearest neighbour, but in the meantime robotic observations such as those from
the LRO continue to provide useful data about the surface of our moon, pushing
our knowledge of planetary science forwards as well as showing us the places we
visited in the 20th century.
Image Credits:
Apollo 14 Landing Site NASA LRO team
Apollo 17 Landing site, NASA LRO team.
Further Reading:
Descriptions and images from the Apollo 15 landing site:
http://lroc.sese.asu.edu/posts/491
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