Humans have sampled a number of sites on the Moon; American astronauts landed at 6 sites on the moon’s nearside and brought back rocks from those sites, and 3 Soviet Luna missions landed on the lunar nearside and returned small soil samples to the Earth in the 1970s. However, since that time, scientists have recognized there are rocks from the Moon we just don’t have in these collections.
There are rock types that have been identified on the Moon’s surface based on analyses of the spectra of the surface from orbiting spacecraft. There are some rock types that have been identified in lunar meteorites, but with no knowledge of where they came from on the Lunar Surface. All of the rocks picked up by the previous missions were 3.5 billion years old or older, while there are lava flows on the Moon’s surface that appear far younger based on the limited number of craters on them – indicating there is younger volcanism on the Moon. Finally, no one has ever found a sample of the lunar mantle, even though it should be exposed at the bottom of some of the Moon’s craters.
That’s a lot of rocks on the Moon we still haven’t seen, and there’s another issue with our current sample collection – almost all of the Apollo samples were collected pretty close to the Imbrium impact crater, the most recent truly gigantic crater on the Lunar nearside. Therefore, a lot of the samples in our current collection are either fully Imbrium impact debris or are at least contaminated by it.
All that together means…there’s a lot of lunar geology still to be done, and targeted lunar sampling missions would be of extreme scientific interest. Tomorrow, the nation of China is scheduled to launch Chang’e 5, their 5th lunar spacecraft and their first attempt to collect and return samples from the Moon’s surface.
Chang’e 5 is a similar design to previous lunar sampling spacecraft – it has an orbiting spacecraft with a service module, a lander with a descent and ascent stage, and a capsule to bring the samples back through the atmosphere. The lander also includes scientific instruments including a ground penetrating radar and cameras to characterize the landing site.
For scientific purposes, Chang’e 5 is targeted for a site in Oceanus Procellarum, the ocean of storms, which, based on the paucity of craters on the surface, contains some of the youngest lava flows on the Moon, an estimated ~1.5 billion years old. While we can see that these rocks look basaltic in spectral analyses, we can’t tell from orbital spectra whether these rocks might have slightly different mineralogy or chemistry. We can’t analyze trace element abundance or isotope ratios from orbit; is there anything that distinguishes these rocks from the other basaltic rocks on the Moon? Right now, we don’t know because we’ve never sampled anything like these rocks.
Chang’e 5 is solar powered, so it has 14 days of light to land, drill into the surface, collect its samples, and launch back towards Earth. Interestingly, it will also bounce off of Earth’s atmosphere – using the bounce to skip across and slow down prior to landing in Mongolia.
If this mission is successful, China has proposed additional uncrewed sampling missions, including a potential target near the lunar south pole where it is hoped that deeper mantle rocks might be exposed by a gigantic impact crater.
This video from a few years ago shows the proposed spacecraft design, including the lander and various pieces of the orbiters.
-JBB
Video source:
https://www.youtube.com/watch?v=25g0JFJEArI
References:
https://spacenews.com/china-is-quietly-preparing-for-november-launch-of-the-change-5-lunar-sample-return-mission/
https://www.planetary.org/video/change-5-sample-return-video
