The volcanic rocks collected from the Moon last year are about two billion years old – a billion years younger than the samples returned by previous missions. This new discovery means that the Moon was volcanically active more recently than experts previously thought.
Distant images taken over the years already suggested that the Moon is home to rocks much smaller than those previously brought back to Earth for direct study. Our research, published today in Science, confirms this fact for the first time.
Rock samples were collected by the Chinese National Space Agency during its Chang’e-5 mission in December 2020 – the first time anyone had collected rocks from the Moon since 1976.
During a remote session with colleagues in China, our team at Curtin University helped determine the age of lunar rock samples. The results, although long overdue, were exciting.
Prior to this, the youngest Moon rocks studied on Earth were samples collected by the Apollo and Luna missions in the 1960s and 70s, as well as lunar meteorites. All were at least three billion years old, leading geologists to infer the moon has not been volcanically active since.
But after estimating the age of the new moon rocks based on the rate of decay of radioactive elements in these samples, we determined these latest samples to be about two billion years old. This makes them the youngest volcanic rocks ever identified on the Moon.
Not only is this the first direct confirmation of rock from this age that exists on the Moon, it also confirms that our remote observation techniques are in the works. This is good news for experts studying other planets, especially Mars.
China is planning another Moon landing in 2024 as part of its Chang’e-6 mission, a research that puts Australia at the center of international collaboration to analyze the resulting samples.
Read more: Five reasons India, China and other countries plan to visit the Moon
The fact that the Moon has smaller volcanic rocks than we thought, also means that it must have had relatively recent internal warming that spurred this volcanic activity. Now the challenge is to explain how this happened.
In general, volcanic rocks (or “basalts”) are similar on different rocky planets and moons. But there are some key differences that make them unique. Lunar basalts probably formed under warm conditions, as water is more scarce on the Moon than on Earth. The presence of water can change the temperature at which rocks melt or freeze, and hot formation on the Moon can cause subtle but significant changes in the chemical composition of rocks relative to similar types of rocks on Earth.
Many moon rocks are very high in titanium, for example, which are never seen on Earth, although the rocks collected by Chang’e-5 contain intermediate titanium levels.
Our focus will now be on analyzing more fragments to establish how different they are in chemical composition. Hopefully this will teach us more about the specific conditions under which these rocks initially formed as volcanic magma.
We still need to explain which heat source is responsible for the recent melting internally on the Moon, which formed an internal “lake” of magma associated with volcanic activity, and why it is cold and dormant today. has gone.
Ultimately, this will help us improve the age dating of the entire Solar System, uncovering more mysteries from our cosmic neighborhood.
Read more: Why is the Moon such a crater place?