On 16 December 2020 the Chang’e-5 mission, China’s first sample return
mission to the Moon, successfully delivered to Earth nearly two kilograms of
rocky fragments and dust from our celestial companion.
Chang’e-5 landed on an area of the Moon not sampled by the NASA Apollo or
the Soviet Luna missions nearly 50 years ago, and thus retrieved fragments
of the youngest lunar rocks ever brought back for analysis in laboratories
on Earth. The rocks are also different to those returned decades ago.
Early-stage findings, which use geological mapping to link ‘exotic’
fragments in the collected samples to features near the landing site, have
been presented by Mr Yuqi Qian, a PhD student at the China University of
Geosciences, at the Europlanet Science Congress (EPSC) 2021 virtual meeting.
The Chang’e-5 landing site is located on the western edge of the nearside of
the Moon in the Northern Oceanus Procellarum. This is one of the youngest
geological areas of the Moon with an age of roughly two billion years. The
materials scraped from the surface comprise a loose soil that results from
the fragmentation and powdering of lunar rocks over billions of years due to
impacts of various sizes.
The study presented by Qian suggests that ninety percent of the materials
collected by Chang’e-5 likely derive from the landing site and its immediate
surroundings, which are of a type termed ‘mare basalts’. These volcanic
rocks are visible to us as the darker grey areas that spilled over much of
the nearside of the Moon as ancient eruptions of lava. Yet ten percent of
the fragments have distinctly different, ‘exotic’ chemical compositions, and
may preserve records of other parts of the lunar surface as well as hints of
the types of space rocks that have impacted the Moon’s surface.
Qian and colleagues from Brown University and the University of Münster have
looked at the potential sources of beads of rapidly cooled glassy material.
They have traced these glassy droplets to now extinct volcanic vents known
as ‘Rima Mairan’ and ‘Rima Sharp’ located roughly 230 and 160 kilometres
southeast and northeast of the Chang’e-5 landing site. These fragments could
give insights into past episodes of energetic, fountain-like volcanic
activity on the Moon.
The team has also looked at the potential sources of impact-related
fragments. The young geological age of the rocks at the landing site narrows
the search, as only craters with ages less than 2 billion years can be
responsible, and these are relatively rare on the side of the Moon that
faces Earth. The team has modelled the potential contributions from
specific craters to the south and southeast (Aristarchus, Kepler, and
Copernicus), northwest (Harding), and northeast (Harpalus). Qian’s findings
show that Harpalus is a significant contributor of many exotic fragments
among Chang’e-5’s sample haul, and these pieces of rock could offer a way to
address persisting uncertainty about this crater’s age. Some fragments may
have been thrown into Chang’e-5 landing area from nearly 1,300 kilometres
away.
Modelling and review of work by other teams has linked other exotic pieces
of rock to domes rich in silica or to highland terranes, mountains of pale
rock that surround the landing site.
“All of the local and exotic materials among the returned samples of
Chang’e-5 can be used to answer a number of further scientific questions,”
said Qian. “In addressing these we shall deepen our understanding of the
Moon’s history and help prepare for further lunar exploration.”
Reference:
Qian, Y., Xiao, L., Head, J., van der Bogert, C., and Hiesinger, H.: The
Exotic Materials at the Chang’e-5 Landing Site, Europlanet Science Congress
2021, online, 13–24 Sep 2021, EPSC2021-447,
https://doi.org/10.5194/epsc2021-447
Tags:
Space & Astrophysics