Seeking the origins of life
Queenie Chan speaks about her work on tiny specks of asteroid samples collected by the Hayabusa mission
Why do we have to look at asteroids in space rather than breaking open a meteorite on Earth?
We have already learned so much from meteorite analysis. Meteorites bombard us every day, and we’ve collected thousands of meteorites on Earth. People spend time studying meteorites in every single detail in laboratories, and they’re available in a much larger amount – not just tiny specks, but large rocks of meteorites – so you’ve got a lot more material to study. If you want to look at things like water and organics, it’s better to have a lot more organic material to study, because they don’t really come in large amounts, so you usually need to concentrate on them to be able to study them.
We have learnt so much about organics and water from meteorite studies in the past, but there is one problem, because all meteorites are recovered on Earth. Some are recovered as what we call a
‘find meteorite’, so we have found them on an exploration to Antarctica, for example, and you don’t know how long they’ve been residing in the ice. Most of our samples are recovered from expeditions from Antarctica, but as they’ve been sitting in the ice water for a long time, you don’t know how much terrestrial contamination they have been exposed to. It’s essential that we know what is contamination and what is not, and it’s a challenge to do that.
Some meteorites are recovered as ‘fall meteorites’, so people see when and where they fell and go and collect them as soon as they can. But even in these scenarios the meteorites are still contaminated.
This sample that we studied from Itokawa was collected by the first Hayabusa mission. It was a mission dedicated to go to an asteroid and bring the sample back for analysis. In terms of contamination, this is a much cleaner sample. This is especially important because we were going to look at water and organics, which are abundant on Earth, and we don’t want contamination, which is key. We also know where the sample has come from; we know that it’s an asteroid that has been sitting in its orbit around the Sun and what the orbit looks like. We have got a lot more context about the origin of the sample, rather than just a rock that we know is from outer space and has fallen to Earth.
What makes Itokawa so interesting?
It’s one of what they call the near-Earth asteroids, so it comes really close to Earth during its orbit. To conduct the sampling, people calculate the shortest distance to go to the asteroid and the easiest way to then bring the samples back to Earth by the calculated orbits of both Earth and Itokawa. Another reason why we went to Itokawa is because it is an
S-type asteroid. It is stony and silica rich, and it’s the material of one of the most common types of meteorite found on Earth. It’s called an ordinary chondrite because there are a lot of them, but we know that they’re not ordinary in many other senses, as they tell us a lot about the history of the Solar System. As they are a common type of meteorite found on Earth, you would expect that they contributed a lot of material to Earth, so this is why it’s interesting.
During the orbit of the Hayabusa spacecraft, it took a few images and some measurements and found something very interesting. This asteroid is supposed to be an S-type asteroid, so a stony type – it is not supposed to be rich in carbon. But on the surface of the asteroid, Hayabusa observed a large boulder about six metres [20 feet] across which was really dark in colour and looked like carbon-rich material. It’s very interesting to think that the stony meteorite has got some carbon-rich material that should really be coming from C-type asteroids.
Do you think it’s possible that Itokawa could have collided with a C-type asteroid?
Yes, it’s possible. One thing that we know is that Itokawa is now very small. It’s an elongated asteroid
Everything was very risky, and you have to be doing things really slowly with 100 per cent focus
about 300 by 500 metres [984 by 1,640 feet]. When we study the samples returned from Itokawa, we know that it’s been heated in the past, and the reason for the heating is that the asteroid was a much larger body, at least 40 kilometres [131 miles] in diameter. Itokawa must have been impacted and shattered into pieces in the past. People have been speculating the different possible reasons for that impact, and one of them is that Itokawa collided with a carbon-rich body which caused Itokawa to fracture into pieces. But we still don’t know for sure.
What difficulties did you face with analysing the sample from Itokawa?
It’s extremely stressful, as the sample is so small. Before we analyse the sample we have to find it. The sample was shipped to us on a glass slide. That tiny grain of Itokawa was sitting inside a little dimple on a glass slide with a glass cover on top. When it came to transferring the sample for analysis, you had to be very careful. During the opening of the glass slide, you have some friction, and that little bit of friction could cause a bit of static electricity. The little particle could either stick on the glass slide or it could jump anywhere, so it’s really challenging to even just open the main section slide. Once we opened it, we used a glass needle to pick up the sample, the same way JAXA transported the samples into the slide in the first place. If you put the needle close enough to the grain, just using static electricity it will either bounce away in the wrong direction or it will stick to the needle.
Everything was very risky, and you have to be doing things really slowly with 100 per cent focus – no heavy breathing and really hoping you won’t sneeze when moving the sample! We then mounted the sample on indium – a soft metal – so we can gently press the sample in so it’s fixed on the surface. Once it’s fixed, then we’re like: ‘Okay, it’s okay!’ Also, this sample is from the first round of distribution to scientists around the world and is unique. My colleague Monica Grady was the one who received the particle, as she had written a proposal to get the particle from JAXA allocated to her. She then asked me to help analyse the grain. At that time we had just one grain to study… if we’d have lost it, it would have been horrible.
We used Raman spectroscopy to analyse the sample, and also another instrument called NanoSIMS (Nanoscale secondary ion mass spectrometry) for nanoscale analysis. We used very sensitive analysis techniques to study the sample in detail. Also, because we were doing water and organic analysis you would have to constantly think of ways to prevent contamination caused by yourself in the lab.
How did JAXA decide who would get a piece?
We had to write a full proposal to tell them what we are going to do with a sample. We had to say whether it would be a destructive or nondestructive analysis, what the purpose was, who was in the team and why you think you are capable of handling the particle. Then it was up to JAXA to decide whether or not it was a good proposal and whether they could send the sample to you.
Why did you call your sample ‘Amazon’?
When we got the sample we thought it looked like South America because of the really elongated shape and that the different fragments within the particle looked like different countries within South America. We also found a really interesting carbonrich grain located where the Amazon rainforest would be on the grain, so it’s why we chose to call the sample Amazon.
What made your particle special?
We didn’t really know whether there would be much organic material to study in the grain. It was really after we studied it in detail we thought, ‘hey, we’ve found something really interesting’. Previously researchers have found organic molecules on samples, but they haven’t been able to say whether it’s terrestrial contamination or extraterrestrial organic molecules. Our analysis using isotopic analysis, with the NanoSIMS technique, was the first one which clearly showed extraterrestrial isotopic compositions that are definitely coming from asteroid Itokawa.
Did the ingredients for life come from asteroids?
This isn’t the first identification of organic material on an asteroid. Through analysis of meteorites, researchers have found extraterrestrial organic material. The meteorites must have mainly been coming from asteroids, so this concept has been developed for decades. The first meteorite analysis that found amino acids was in the 1970s, so from that moment onwards people have been aware that we’ve got organic material coming from space.
Our analysis of a sample taken directly from Itokawa also showing organic material is just further evidence towards this idea that organic material could have been delivered to the early Earth by meteorites from near-Earth asteroids. We
now want to know what the material looked like and what those materials are, and now people are working hard in building a linkage between raw ingredients to life. It’s a huge mystery of how that material became life.
What’s the underlying reason for researching asteroids in such detail?
We want to know what things were like on early Earth. But Earth is a very active planet. You’ve got plate tectonics melting rocks, you’ve got weathering processes constantly eroding material. We don’t really know what it was like at the birth of the Solar System and how Earth really formed. We target asteroids because they’re the ‘building blocks’ of planets. Asteroids haven’t been melted in the past – they’re in the same state as when they were formed. It tells us a lot about the origin and formation of our Solar System.
Is there an issue with collecting tiny samples?
You cannot use this to generalise the entire asteroid. For example, we found organic matter, but it doesn’t mean that organic matter is everywhere in the sample. Particles from Itokawa have been distributed to different researchers around the world, and each researcher contributes a different idea to the entire picture. It’s collective knowledge seeking. You cannot use one study to represent the entire Itokawa. Our study is just a small part of the far bigger picture.
Your team is now studying the samples from the Ryugu asteroid taken during the Hayabusa2 mission. Do you expect these to differ a lot from the samples studied from Itokawa?
From Hayabusa2 we know a lot from remotesensing observations of Ryugu. We know that it is a carbon-rich asteroid, so we will probably see more organics in a sample from Ryugu compared to Itokawa, which is very exciting. From other analyses we speculate Ryugu has been heated in the past and that it contains absorbed water in the mineral structure, so it must be organic rich and also have been processed by water in the past, so that is also very interesting. We already know quite a lot about Ryugu from remote-sensing studies, but to really see the details, the messages that it is going to tell us about its history, we really need to study samples in our labs with our most sensitive instruments.
I would also like to say that the research we carry out would not be possible without the collaboration of the entire team. I don’t take credit for the entire piece of work, as it wouldn’t be possible without my collaborators’ involvement. I am part of an excellent team, and it’s really a collective effort that makes all this research possible.