Lunar explorer: Thomas Smith on studying the Chang’e-5 Moon samples

Taken from the June 2022 issue of Physics World. Members of the Institute of Physics can enjoy the full issue via the Physics World app.

Thomas Smith from the Institute of Geology and Geophysics, Chinese Academy of Sciences, talks to Ling Xin about living in China and being the first foreign national to study Chang’e-5 Moon samples

Thomas SmithDelicate work Thomas Smith from the Institute of Geology and Geophysics, Chinese Academy of Sciences, is studying samples from the Moon returned by the Chang’e-5 mission. (Courtesy: Ling Xin)”>
Delicate work Thomas Smith from the Institute of Geology and Geophysics, Chinese Academy of Sciences, is studying samples from the Moon returned by the Chang’e-5 mission. (Courtesy: Ling Xin)

How did you get into space science?

I’m a geochemist by training and after I did my PhD at the University of Bordeaux, France, in 2010, my supervisor inspired me to study materials from space. I went to Paris for my first postdoc position where I analysed the composition of particles returned from a comet by NASA’s Stardust mission. Then I moved to the University of Bern in Switzerland where I measured and analysed a variety of meteorites for five years until 2017.

Why did you move to China?

I really wanted to continue my research with meteorites, so I reached out to colleagues including a geochemist from China with whom I had worked in Bern. He put me in touch with He Huaiyu, who was studying meteorites at the Institute of Geology and Geophysics (IGG) while waiting for Moon rocks to be brought back by the planned Chang’e-5 mission. I thought studying new lunar samples would be exciting and He invited me to visit Beijing for a week where I was even invited to a wedding. He asked if I wanted to move to China and I joined the IGG in May 2018.

Why are meteorites interesting?

Most meteorites are from the asteroid belt between Mars and Jupiter, a region full of rock fragments that have existed since the beginning of the solar system but failed to form any planet. Bombarded by cosmic radiation, they usually contain noble gases such as helium and neon. Therefore, records of noble gases can be used as a tool to reconstruct the history of a meteorite in space before it landed on Earth. An important part of my work is to measure the concentration of these gases in meteorites to estimate their “exposure age”, which is how long meteorites have been travelling in space before landing on Earth, as well as their size before they entered the Earth’s atmosphere.

What else can we discover about meteorites?

We can also estimate a meteorite’s terrestrial age, or how long it has been here on Earth, by measuring the decay of other radioactive elements in the meteorite. I’ve done such measurements with meteorites found in farmland in Switzerland, and more recently with a meteorite that fell in Xishuangbanna and is believed to have come from a near-Earth object instead of the asteroid belt due to its remarkably shorter exposure age.

How will you use your expertise in meteorites to study lunar samples?

Samples returned from the Moon by the Apollo, Luna and now Chang’e missions are different from lunar meteorites because they don’t go through atmospheric entry and can maintain all the original information. On the Chang’e-5 samples, I proposed a comprehensive analysis of the noble gas “budget” on the Moon, which is understood to involve a mixture of processes including cosmic radiation, comet impacts, solar wind and Earth wind – ionized particles that travelled from the Earth’s atmosphere to the Moon. The results will hopefully tell us which mechanisms dominated and add to what we’ve learned from the Apollo and Luna samples.

What types of samples have you received? What was the application process like?

I received 400 mg of soils as well as two particles – 1 mg and 4.5 mg – as part of the third batch of Chang’e-5 samples distributed to labs in China. I’m very happy with this, as particle samples are rare and hard to get. The proposal for the sample was submitted in Chinese, so I wrote an English draft and asked my Chinese colleagues to translate it. Then I carried out the oral defence in English with slides in Chinese.

How do you go about studying the Moon samples?

The Chang’e-5 lunar samples are stored in a dedicated clean room in one of the IGG buildings. In that clean room, we can do basic, non-destructive characterization of the materials. The soil powder will first be sieved into different grain size bins, handpicked, before non-destructive analyses such as microscopic observations and computed tomography (CT) are performed. CT is important to determine mineral abundances and chemical composition. The handpicked grain particles will then be treated separately and taken to our own lab where we will measure the noble gas compositions of handpicked grain particles. This will be done by firing a laser beam to melt them and in the process release the noble gases.

Have you done this yet?

We are currently testing the lab facilities with standard materials and making sure it’s all ready. Noble gas measurements are challenging because they are in trace amounts, about 10–8 cm3/gram. Our lab is the only lab in China that has all the facilities required to do this kind of measurement. We plan to finish all the experiments by next year.

For Chang’e-7 we are looking at possible in situ measurements of volatiles such as water and nitrogen in the lunar regolith, using a French–Chinese instrument 

So that will keep you busy over the next year?

Yes. My priority will be the Chang’e-5 samples, including making measurements, interpreting data and publishing papers. Our team is also involved in the upcoming Chang’e-7 mission that will go to the Moon’s south pole. For that mission we are looking at possible in situ measurements of volatiles such as water and nitrogen in the lunar regolith, using a French–Chinese instrument that has already been approved.

What’s it like to work and live in Beijing?

Beijing is a huge city compared to my hometown or even Bern. I live in a community a few metro stops from IGG but the trains usually become too packed to get on after 7 a.m. so I get to the office around 6:30 a.m. I’ve got used to a few other things. For example, my Chinese colleagues like to take a short nap after lunch and now I’m used to having post-lunch naps. Otherwise, I’m impressed by the work ethic – there are always experiments going on in the labs.

How have you dealt with the pandemic?

I was in Beijing in January 2020 after spending Christmas with my family in France. My colleagues and I soon heard about the situation in Wuhan. He told me I could go back to France – and keep my job – as most foreigners at IGG chose to leave China. I was among the few who decided to stay and I worked from home, focusing on writing papers with previous data. By mid-March we were allowed to return to the institute, but it was almost empty. Those were a few stressful months.

And what has life in China been like more generally?

The Chinese government got the situation under control pretty quickly. I remember going to parks without a mask in May 2020, while France was experiencing the peak of the first wave. China has been sticking to its zero-COVID policy for over two years now. I feel quite safe here, although code-scanning for tracking (Jiankang Bao) can be tedious sometimes. You have to scan in when you enter a mall, and scan again if you eat at a restaurant inside the mall.

Do you plan to stay in China?

My current contract with IGG ends in May 2024 so I need to think about what happens after that but I will apply for a tenure position at IGG so I hope to stay in China.

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