China’s lunar rover win
AFEW months ago, I wrote about a great result obtained by China: having a spacecraft make the first-ever soft landing on the far side of the Moon.
The craft was Chang’e 4, and it carried with it a little wheeled rover called Yutu-2.
Now, Yutu-2 has been moving across the lunar surface for several months, although it is still quite close to the main lander.
It has returned many images of the landing site area inside von Kármán crater, which is within the large lunar feature known as the South Pole-Aitken Basin.
The crater Von Kármán was named after Theodore von Kármán (1881-1963), a scientist who was active in the field of aerodynamics, as well as many other topics.
In addition to making available the first pictures of the lunar far side taken from the surface, the mission has already generated some scientific results.
The South Pole-Aitken Basin is a huge impact feature, and it was hoped that the landing there would provide an opportunity to sample some material from the Moon’s mantle, which lies below the crust but may have been
brought closer to the surface.
On the far side of the Moon, the crust is believed to be thicker than on the side facing Earth, but such a large impact may have been enough to “churn up” some mantle material.
Results published in May seem to indicate that this may have happened.
Analysis of observations made by a device called a Visible and Near Infrared Spectrometer (VNIS) carried on Yutu-2 has revealed the presence of possible mantle material.
However, the large impact itself may not have been enough to bring the mantle material all the way to the surface.
The results point to the possibility that a later impact within the basin, which produced a nearby crater called Finsen, may have done the final job of spreading this material across the surface, including inside Von Kármán crater.
The crater Finsen was named after Niels Ryberg Finsen, a Nobel prize winner who was active in the field of phototherapy, application of light to relieve certain medical disorders.
Although Yutu-2 has been roving since January, it has covered a total of only about 271m so far.
Several of the pictures it has returned show the landing craft in the distance, and the wheel tracks that the rover has left in the fine lunar surface material.
In looking at such images, I am sure that many of us who were around in 1969 and listening to Neil Armstrong after he stepped onto the Moon will remember his words, “The surface is fine and powdery”.
This material is called the regolith, and has a powdery consistency largely as a result of bombardment by both large and very small objects over billions of years.
The mission has seen good co-operation between China and the USA.
In particular, NASA had access to information about the location of the landing site.
On several occasions NASA’s Lunar Reconnaissance Orbiter (LRO), in orbit around the Moon, has taken pictures of the lander and the little Yutu-2 rover.
The LRO’s camera has enough resolution (sharpness) to do this, even though it orbits at an average altitude of about 50km above the surface.
The two objects occupy only a few pixels, but are clearly visible.
It is only occasionally that LRO is able to image the site.
LRO is in a polar orbit, passing almost exactly above the Moon’s north and south poles, and completes each orbit about every 113 minutes.
However, the Moon is rotating underneath the LRO, so each time the craft goes around the Moon, it passes over a different area.
It is therefore quite some time — about a month — before the craft can image the same part of the lunar surface again.
The Chinese have done spectacularly well with this mission. Martin George is manager of the Launceston Planetarium at the Queen Victoria Museum and Art Gallery.