Ryugu asteroid sample analysis

The newest chapter in tracing back the Earth's origins...
14 June 2022


The asteroid Ryugu, out between the orbit of Earth and Mars, as photographed by the JAXA Hayabusa2 spacecraft.


Trying to unpick how our planet began to form, and from what, over 5 billion years ago sounds like an impossible undertaking. But, by studying the “leftovers” from the process of planet formation in the early solar system, we can decipher what the conditions were like and what materials were there at the time. The problem remains where you get that material! But, this week, this cosmic detective story took a step forward with the publication of analysis of samples collected from an ancient asteroid called Ryugu by the Japanese Space agency, JAXA. Samples brought back aboard their Hyabusa 2 probe are now being studied. Chris Smith asked Open University space scientist John Zarnecki to bring him up to speed with what the results are revealing…

John - This mission - Hayabusa 2 - is from JAXA [the Japanese space agency] and it was their second asteroid return mission. These are very demanding and challenging, but both of them have worked and have returned samples to the earth. Now, in the case of Hayabusa 2, it was launched in 2014 and returned with its samples in 2020. And the total amount that was collected was about five and a half grams! You might laugh at that, but, actually, five and a half grams is a lot more than they expected. And, these days, with the incredible analytical equipment that we have in, in laboratories on the earth, you can do an enormous amount with small quantities of material.

Chris - The paper's got hundreds of scientists on it. They,

John - Yeah, I, I tried to count Chris, and I made it 149. <laugh> right. And from 65 different laboratories on four continents. And I mean, that in itself is interesting. That shows you the nature of much of science these days; a lot of science is done by large teams, collaborating internationally, bringing different types of expertise to bear.

Chris - And what has this pretty substantial team demonstrated with this paper? I mean, what are the key findings?

John - There's a couple of things that stand out to me. First of all, it's ironic that it's actually saying in some ways more about material here on the earth than on this particular asteroid. We have thousands of meteorites in various collections on the earth and they fall into different categories and there's one particular category - And there are only a few of this type - they're called CI meteorites - and they are thought to be the most primitive with material representing that, that existed very, very early in the life of the solar system, four and a half billion years ago. One of the reasons this asteroid was chosen as a target is that it's thought to be a primitive asteroid. And the first analysis, published a few months ago, sort of confirms that, that seems to be the case. Now in this paper, this large group analysed the material and compared it with the samples that we have in the meteorite collection. And they found that, broadly speaking, the material was the same, but there were some significant differences. Now we always worry with meteorites to what extent are they contaminated by, in many cases, sitting on the earth for tens or even hundreds of years. This paper is really showing, this is what this material should look like. And anything more that we see in these, uh, samples on the earth are due to contamination.

Chris - What really struck me when I read this paper and I'll quote from part of the introduction, they say the samples consist predominantly of minerals formed in aqueous fluid - in other words, water - on an apparent planetesimal - a planet that was trying to form - the primary minerals were altered by fluids at a temperature of 37 degrees C give or take and have not subsequently been heated to more than a hundred degrees. I mean, that's amazing detail to be able to say about what this asteroid was going through about 5 billion years ago!

John - That is the power of what, what is often called cosmo-chemistry. They can look at the details of the mineralogy, the crystal structure from that. You can decipher the formation conditions because you know certain compounds will only form under certain conditions of temperature and pressure. And that's the way in which you can do this detective work. You can essentially map out the conditions that existed in at least one part of the early solar system. It's staggering, yes.


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