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Listen: Behind the scenes of Japan’s daring asteroid mission

Nature visits the pioneering spacecraft's creators to learn how Hayabusa2 will explore the Ryugu asteroid.

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As Japan lands a third probe on Ryugu asteroid, Nature looks at the Hayabusa2 mission in more detail.

Reporter Noah Baker talks to Makoto Yoshikawa, a mission manager of Hayabusa2 at the Japan Aerospace Exploration Agency.

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TRANSCRIPT

Interviewer: Noah Baker

Back in December 2014, JAXA (the Japan Aerospace Exploration Agency) launched Hayabusa2, the second of JAXA’s missions to collect and return samples from nearby asteroids. Three years later, in June this year, Hayabusa2 arrived at Ryugu, a kilometre-wide asteroid orbiting the Sun between the Earth and Mars.

And less than two weeks ago, one of the trickiest parts of the mission began. The Hayabusa2 mothership dropped the first two of its four payloads — rovers designed to roam or rather hop around the asteroid’s surface, taking pictures. It was a nail-biting time, but the rovers landed safely and have started sending back some incredible images.

It was a big step, but there’s still a lot to come from Hayabusa2 — explosive impactors, sample collections and the landing of the European-designed MASCOT probe. At the time of recording, it’s not yet been released but by the time you listen to this podcast we may be getting the first signals from a successful landing. But more on that later. Right now, I’m headed to Mission Control in JAXA’s Sagamihara Campus, just outside Tokyo, to hear more about those crucial rover landings and what we can expect from the Hayabusa2 mission in the coming weeks and months.

Interviewee: Makoto Yoshikawa

My name is Makoto Yoshikawa and I am a mission manager of Hayabusa2.

Interviewer: Noah Baker

That must mean that this is quite an exciting time for you.

Interviewee: Makoto Yoshikawa

Yes, very exciting because now Hayabusa2 tries to put small lander on the surface. Also, we will try to touchdown so now it is a very exciting period.

Interviewer: Noah Baker

So, it was just last week where the first two rovers landed.

Interviewee: Makoto Yoshikawa

Yes.

Interviewer: Noah Baker

Tell me what was that day like?

Interviewee: Makoto Yoshikawa

Yes, so Thursday our spacecraft started to descent. One day later, it approached about 60 metres above the surface of Ryugu and then the spacecraft released two small rovers. So, at the time project members were very excited and also very happy to see that the separation was successful. And we get first image from small rover and we could see the surface.

Interviewer: Noah Baker

And those images, I’ve seen some of them, they’ve been all over the media. They’re kind of action images which you don’t normally get from space missions. What was your reaction when you first saw them?

Interviewee: Makoto Yoshikawa

So, at first, we saw the image, we think that we could feel the dynamic motion of rover and also, we saw the sunlight. So, we are very surprised to see such a beautiful image.

Interviewer: Noah Baker

And one of the things that the rovers are going to be doing is to continue taking images from Ryugu.

Interviewee: Makoto Yoshikawa

Right. So, we can see many parts of the surface of Ryugu, close up image and so many small rocks and no sun. In that sense, we were also surprised to see the real surface of Ryugu.

Interviewer: Noah Baker

These rovers are not like the rovers people might imagine if they think of the Mars rover or something. They’re somewhat smaller and they move in a very unique way. Tell me about that.

Interviewee: Makoto Yoshikawa

It can hop. It can jump. Inside the rover there is one motor and the motor rotates a weight. Then because the gravity is very small, the reaction of weight motion, the entire rover can move.

Interviewer: Noah Baker

So that’s the first two rovers, but there’s more to come. Tell me what’s next.

Interviewee: Makoto Yoshikawa So, Hayabusa2 has four rovers and lander, so now we released two of them and the next one is a little big one called MASCOT. MASCOT lander was made by the DLR and CNES - Germany and France - and we will release MASCOT lander October 2nd. And after that, MASCOT has a battery and it lasts only 16 hours or so.

Interviewer: Noah Baker

And so that’s three landers now, but that’s still not done. There’s still more to come. What’s next?

Interviewee: Makoto Yoshikawa

Yes. So, last one is also very small rover. Maybe we will release it at the end of the mission, before summer of next year.

Interviewer: Noah Baker

And the very final bit of the mission is one of the biggest challenges you have yet, and that is to collect a sample from the asteroid to bring back. And you’re not just getting a sample from the surface of the asteroid, it’s actually from inside the asteroid and you have to get inside the asteroid first. Tell me what’s going to happen there.

Interviewee: Makoto Yoshikawa

Ah, yes. So, after releasing lander, next big challenge is to get the sample from the surface. So, spacecraft will make a touchdown to the surface late October. So, at first we get the surface material, but next year we will try to make a small crater on the surface of Ryugu. Hayabusa2 has an impactor.

Interviewer: Noah Baker

And this impactor is essentially an explosive device.

Interviewee: Makoto Yoshikawa

Right. It has a two-kilogram copper and this will be accelerated to about 2 kilometres per second. The impactor mission is very risky and so when impactor explodes, Hayabusa2 spacecraft hides behind the asteroid and if a spacecraft hides behind the asteroid, we cannot see the impact event. So, before Hayabusa2 hides, it will release a small camera so the small camera can watch the impact. So, this is a very complicated and risky mission but a very exciting mission.

Interviewer: Noah Baker

So, from what you’ve told me, this is a very elaborate and complicated mission with many, many stages. What are you trying to find out?

Interviewee: Makoto Yoshikawa

Our main purpose is to study the organic matter because Ryugu is a C-type asteroid and normally C-type asteroids have organic matter and also water. The organic matter we will get from Ryugu is before Earth’s life born. I mean, maybe we can study the original material that create the life on the Earth.

doi: 10.1038/d41586-018-06908-x

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