Asteroids, comets and where to find them

Summary

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Science In Action – "Asteroids, Comets and Where to Find Them"

BBC World Service – September 11, 2025
Broadcast from the European Planetary Science Congress, Helsinki

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Overview

This episode of Science in Action explores groundbreaking missions and discoveries related to the smallest members of our Solar System: asteroids and comets. Recorded on location at the European Planetary Science Congress, host Roland Pease brings listeners the latest updates from leading scientists involved in NASA and global missions. The episode spotlights the Lucy mission's asteroid encounters, the rare opportunity to observe interstellar comet 3I Atlas, and the international excitement over the upcoming near-Earth flyby of asteroid Apophis in 2029.

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Key Discussion Points and Insights

1. The Focal Point: Small Bodies of the Solar System

• Roland Pease sets the theme:
  • Rather than focusing on planets, this episode zeroes in on asteroids and comets—“small, but important, nonetheless, for what they tell us about how the solar system came to be.” (01:59)

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2. NASA's Lucy Mission: Surprises in the Asteroid Belt

Speaker: Hal Levison, Principal Investigator, NASA Lucy Mission

• Asteroids as Fossils

  • "They're fossils of the solar system." (02:19)
  • The mission is named "Lucy" after the famous fossil, emphasizing their historical importance.

• Encounter with Donald Johansen

  • Purpose: Test instruments before approaching Jupiter’s Trojans.
  • “All the important science is being taken in 24 hours. We can't go back if we screw up.” (04:04)
  • Unique features: Bilobed, likened to a “rubber duck” or “bowling pin.” (04:06)
  • "The neck of the bowling pin turns out to be just weird. It's overly smooth... the craters are all there, but they're all deformed and warped." (04:17)
  • Geologically active: The material between the lobes is moving, thought to be caused by the YORP effect—a change in the asteroid’s spin due to sunlight. (05:08)

• First Flyby Learnings

  • Contrast in asteroid appearances: Dinkinesh was unexpected, Donald Johansen resembled predictions. (05:52)
  • “It’s like a crime scene that you’re going through.” (05:41) – Pease on interpreting rapid flyby data.

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3. The Quest to Observe Interstellar Comet 3I Atlas

A rare observation window with multiple missions involved:

Speakers:

• Je Kot, Deputy Project Scientist, Europa Clipper Mission
• Tom Statler, Lead Scientist for Small Bodies, NASA HQ

Europa Clipper’s Opportunity

• “The Europa Clipper will... pass by the comet within one astronomical unit.” (08:15)
• Using navigation (star) cameras to observe, as main science cameras are unavailable. (08:50)
• The spacecraft will fly through the comet’s tail—allowing plasma and dust analysis: “We can determine the species and charge state.” (09:30)
• Urgency and improvisation: Mission team quickly mobilized after the opportunity was recognized. (10:06)

Coordinated NASA Observation Effort

• Tom Statler outlines multi-mission approach:
  • Other involved missions: Psyche (also near the comet), Mars orbiters and rovers, Heliophysics and Sun-observing missions, and James Webb Space Telescope. (12:10-13:47)
  • The challenge and value of observing from different viewpoints: “One of the most interesting things you can do to observe a comet is to look at the scattered sunlight off of the dust from different angles and at different colors, different wavelengths." (13:47)
• Statler on the significance:
  • “It’s a sample probably from the early stages of the formation of a completely different planetary system.” (15:02)
  • Opportunity to compare with Solar System comets: “How is it similar to and different from our own homegrown comets.” (15:18)
  • “It’s an exciting time to be a planetary scientist… especially to be interested in our solar system’s small bodies.” (15:39)

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4. Apophis 2029: Seismic Science, International Collaboration, and Ambition

European Seismic Mission on Apophis

Speaker: Naomi Murdoch, French Space Agency, CENS

• Mission Plans and Science Goals

  • RAMSES: Deploying two cubesats; one will land a seismometer on Apophis, an asteroid about 340m across. (19:05)
  • Unprecedented science: “First ever seismic measurements on the surface of an asteroid.” (19:30)
  • Why seismic? Earth’s close approach will “pull on Apophis... probably going to be the spin rate. So how fast it's moving. And as it changes its spin rate, the body is going to reorganize internally.” (20:07)
  • Excitement: “It’s a once in a lifetime opportunity.” (19:35)
  • Seismometer prepared for tiny signals – hoping to “detect these very small amplitude signals... and then we're just going to hope for the best.” (20:47)

• Assurances

  • Landing won’t disturb the asteroid: “Low velocity landing... is not going to change anything for Apophis.” (21:18)
  • Timeline: Deployed “several hours before the close encounter… expect[ing] to see the majority of these seismic signals” a few hours after closest approach. (21:59)
  • Personal enthusiasm: “This is really, really special. It's a really special mission for lots of reasons.” (22:07)

China’s Apophis Flyby Mission

Speaker: Jiang Yang Li, Sun Yat Sen University

• China planning a quick flyby and observation; will park in a stable halo orbit at L1, “wait for the asteroid to come by.” (24:15-24:49)
• Tiny 44 kg spacecraft; will observe and measure Apophis’ surface and estimate its mass using a secondary satellite: “Maybe micrometers change [in the distance between satellites] over tens of kilometers.” (27:00)
• Goal: Detect surface changes post-encounter with Earth’s tidal forces, and weigh Apophis using relative satellite movement. (26:22, 27:07)

International Collaboration and Historic Parallels

• Li draws parallel between Apophis 2029 and the 1986 Halley’s Comet flybys, a global festival of planetary science. (22:46)
• Pease and Li agree this event is “a unique science opportunity the whole world can take part in.” (23:24)

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Notable Quotes and Memorable Moments

• Hal Levison: “I look at these small bodies and I say, they're fossils of the solar system.” (02:19)
• Roland Pease: “It’s like a crime scene that you’re going through.” (05:41)
• Je Kot: “The Europa Clipper mission will luckily be on the right side of the sun and will pass by the comet within one astronomical unit.” (08:15)
• Tom Statler: “Who doesn't love an interstellar comet? Everybody is excited by this, everybody wants to do it.” (13:22)
• Naomi Murdoch: “Earth is going to pull on it and it's going to change a lot of things about Apophis, but one of them is probably going to be the spin rate... And as it does that, the blocks are going to move against each other and they're going to create seismic signals inside the body.” (20:07)
• Jiang Yang Li: “...this festival for this tiny object. That’s exciting.” (23:24)
• Tom Statler: “It’s an exciting time to be a planetary scientist... a wonderful time to be doing such groundbreaking science that really enlightens the history of our solar system and benefits all of humanity.” (15:39)
• Naomi Murdoch: “We've done seismology on the moon, we've done seismology on Venus, we've done seismology on Mars. We've never done seismology on an asteroid, so it's a first.” (22:07)

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Key Timestamps

| Timestamp | Segment | |-----------|--------------------------------------------------------------------| | 01:16 | Conference virtual opening; planetary science context | | 02:19 | Hal Levison on asteroids as “fossils”; Lucy mission overview | | 03:04 | First results from Lucy flyby of asteroid Donald Johansen | | 05:08 | YORP effect and asteroid surface activity explained | | 07:17 | Je Kot on Europa Clipper’s trajectory and new science opportunity | | 08:15 | Je Kot details plan to observe comet 3I Atlas with Europa Clipper | | 10:46 | Tom Statler on NASA’s coordination for 3I Atlas observations | | 12:10 | Psyche, Mars orbiters/rovers, James Webb, and multiple missions collaborating | | 13:47 | Statler explains the value of multi-angle, multi-wavelength observations | | 15:02 | The significance of 3I Atlas as an interstellar “sample” | | 17:58 | Naomi Murdoch on Europe's Apophis mission and its seismometer | | 19:05 | Design and challenge of seismometry on Apophis | | 20:07 | Apophis expected to "creak" under Earth's gravity | | 22:46 | Jiang Yang Li contextualizes international collaboration – Halley parallel | | 24:15 | Details of China’s L1 orbit Apophis flyby mission | | 27:07 | Using twin satellites to measure Apophis’ mass |

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Conclusion

In this packed episode, Roland Pease provides an immersive journey into humanity’s innovative efforts to study asteroids and comets—small bodies with outsized importance for understanding the solar system. From NASA’s Lucy revealing “crime scenes” in the asteroid belt, to the rush of multiple spacecraft preparing to catch fleeting glimpses of an interstellar comet, and the unprecedented international focus on Apophis’ close approach, planetary scientists are harnessing rare opportunities for fundamental discoveries. The prevailing tone is one of excitement, collaboration, and ambition—a testament to a scientific community captivated by the mysteries of the smallest objects in space.

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Transcript

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[Je Kot]

Esteemed guests dear participants, welcome to the.

[Roland Pease]

20Th Europe Planet Science Congress.

[Je Kot]

This year, again jointly with our friends from the dps, we're overjoyed to be hosted at Finlandia hall in beautiful Helsinki.

[Roland Pease]

Which indeed is lovely. And this joint meeting of US European in fact, they hear from all over the world. Planetary scientists is where Science in Action from the BBC World Service is coming from. And the scientists here are talking about all the planets we're familiar with Mercury, Venus, Mars, Jupiter, all the way out to poor old minor planet Pluto and beyond. Exoplanets in other solar systems are also on the agenda.

[Je Kot]

Ahead of you lies a week of exciting science awards and keynote lectures, panel discussions, workshops.

[Roland Pease]

But in fact, for this edition of Science in Action, I'm ignoring all the big things we call planets, and I'm focusing instead on the small rocks and snowballs they call asteroids and comets. Small, but important nonetheless for what they tell us about how the solar system came to be.

[Hal Levison]

I look at these small bodies and I say, they're fossils of the solar system. So when we put the mission together, we named it after a fossil because it's going to tell us about our history, just like the Lucy fossil is telling us about our history.

[Roland Pease]

Lucy is NASA's mission, with some of the freshest results at this meeting. Heading out to Jupiter's orbit, it's taken the chance of some valuable sightseeing while passing through the asteroid belt.

[Hal Levison]

My name's Hal Levison. I'm from the Southwest Research Institute in Boulder, Colorado, and I am the Lucy principal investigator.

[Roland Pease]

And when I was talking to people in the foyer here, they said, the talks you have to Go to are Lucy because they're the ones who've got something new to say.

[Hal Levison]

We have something new to say. So we have recently flown by a small main belt asteroid called Donald Johansen. The purpose was to test out our instruments to make sure everything was working. The interesting thing about Lucy in general is that it's a 12 year mission and all the important science is being taken in 24 hours. We can't go back if we screw up. So the whole purpose of doing these main belt asteroids was to make sure that all the processes were in place, that we made sure we knew what we were doing when we got to the Trojan. And Donald Johansson was the perfect example. Just comes up and goes. It being so small actually was a challenge.

[Roland Pease]

So how long was this encounter that you had then with Don Johansson?

[Hal Levison]

An hour of science, important science. It turns out that it's an interesting object. So it's bilobed, so it has two pieces.

[Roland Pease]

So it's a bit like a rubber duck, I think.

[Hal Levison]

Yeah, I think of it more as a bowling pin. But the neck of the bowling pin turns out to be just weird. It's overly smooth, the craters are all there, but they're all deformed and warped and we don't really understand where that came from.

[Roland Pease]

But it looked like two different asteroids that got stuck together and then there's some grits or some dust in between them, but it's not.

[Hal Levison]

That's true. But that grid and dust between them is geologically active.

[Roland Pease]

It's moving.

[Hal Levison]

It's moving and that's what makes it weird. Let's take a step back. This object is part of what we call the Aragoni family, which is a breakup of an asteroid really recently, about 130 million years ago. Okay. So these things form as two asteroids hit one another and they can come together and form these bilo doppler.

[Roland Pease]

I mean the gravity on this must be incredibly weak. There's no gravity. So what's moving stuff around? Why is it moving?

[Hal Levison]

Well, the spin rate of it has been changing over time because of something called yorp, which is sort of a thermal effect that the object absorbs light from the sun and reradiates it and it doesn't do it axisymmetrically. And as a result that the asteroid can actually spin up or spin down based on if you shape sort of.

[Roland Pease]

Self propelled in a funny way.

[Hal Levison]

Yeah, it's sort of like a little propeller.

[Roland Pease]

Yeah, right. It's been tumbling and that's then moving stuff around inside.

[Hal Levison]

We don't know yet. But that's sort of the thinking that we've got.

[Roland Pease]

I mean, you said that this is based off about an hour's observation. You fly by, you get these pictures. I think what's so extraordinary is the interpretation, like a crime scene that you're going through.

[Hal Levison]

There's no doubt. And, you know, we've done two of these so far. Right. And they're very different. Right. The first one of these was an object that we named Dinkinesh. And we had a conception in our mind of what Dinkinesh would look like. And it looked nothing like what we thought. But within, I would say, half an hour of seeing it, we were like, oh, yeah, I know how you can do that. Donald Johansson, on the other hand, looked exactly like we expected it to look like. So just goes to show how the experience can be different. And we're going to observe Comet ATLAS too. You are? Yeah.

[Roland Pease]

Tell us about that. Because that's something else we're really interested.

[Hal Levison]

In, so some history. ATLAS is an interstellar comet. It's going to go through perihelion when it's on the other side of the sun from the Earth.

[Roland Pease]

That's its closest approach to the sun. But it's the wrong side from us to see.

[Hal Levison]

It's the wrong side. So we're not going to be able to observe it from the Earth.

[Roland Pease]

Earth.

[Hal Levison]

So a large fraction of NASA's flying spacecraft that happen to be on the right side of the solar system will be observing it. And Lucy's one of them. We're probably the least interesting of the ones, just because for us, it's too close to the sun and we can't point our instruments towards the sun.

[Roland Pease]

But there are others, and I reckon every active interplanetary mission is represented here. So let's see who else is joining in the 3i Atlas feeding frenzy.

[Je Kot]

My name is Je Kot. I'm the deputy project scientist for the Europa Clipper mission, working at the Johns Hopkins Supply Physics Lab. The Europa Clipper mission will go to Jupiter's moon, Europa. It will actually orbit Jupiter while flying by Europa 49 times. And our goal is to determine the habitability of the Moon. The Moon has an icy shell that's several 10 kilometers thick. And underneath there is a global ocean. And the ocean actually has two times as much water as we find on Earth.

[Roland Pease]

And it's already launched.

[Je Kot]

It's already launched. It launched on October 14th of last year. We just passed Mars orbit. We're now returning back to Earth for another trajectory correction. And we'll then Go out to Jupiter, where we arrive in 2030.

[Roland Pease]

But as I understand it, that's why suddenly you've given yourself some extra work in the next month or two, because you're going to get a good view when the Earth can't of this interstellar comet. 3i Atlas.

[Je Kot]

Correct. The Europa Clipper mission will luckily be on the right side of the sun and will pass by the comet within one astronomical unit. So that's about 150 million kilometers.

[Roland Pease]

So how are your orbits working at this point? You're going around the sun, it's going past the sun, and you're going to get a be able to turn the cameras, is that right?

[Je Kot]

We are flying in the ecliptic plane and the object that's coming in is somewhat oblique to that. We are able to use our star camera to observe the comet flying by.

[Roland Pease]

So this is a navigation camera.

[Je Kot]

This is a navigation camera that tells us which way we are oriented.

[Roland Pease]

But you can get science with it.

[Je Kot]

You do what you can. Yes.

[Roland Pease]

Okay, so that's going to be a tantalizing glimmer, as it were, on the horizon.

[Je Kot]

Yes.

[Roland Pease]

I've heard that the comet has a tail. There's one mission that's going to fly through.

[Je Kot]

We will be flying through that tail. So the tail is driven by the sun. It will propagate radially away from the sun and we are right going through that region. We don't know how large that area will be. We don't know how the plasma will look like, but we'll certainly have the opportunity to observe it.

[Roland Pease]

What sort of things can you measure then inside the tail, you measure the.

[Je Kot]

Composition of the comet. The material comes off the comet and then gets turned into plasma in the solar wind. And as soon as plasma is an ionized gas, and as soon as it's in that state, it can be registered by the plasma instrument and we can determine the species and charge state. Unfortunately, our main camera still has the COVID on and will not be able to observe it.

[Roland Pease]

Oh, well, that's really interesting because you have a serious mission to do, but this is not core to your mission at all and you don't want to jeopardize presumably any of the key features of your spacecraft.

[Je Kot]

Correct. This object was identified, if I recall correctly, on July 1. It was about a week later when some of our science team said, there is this opportunity and everyone was scrambling. And within a few hours we were able to get the project excited to implement the observations as we can. This turned into a much bigger thing organized by my NASA Headquarters. There's actually many spacecraft that will be able to observe this comet at various stages this morning. Tom Statler is here, who's organizing this from NASA headquarters. And you may be able to ask him more questions about the other assets that we'll be able to observe.

[Roland Pease]

Tom Statler, I wonder where he is.

[Tom Statler]

Hi, I'm Tom Statler. I'm lead scientist for Solar System Small Bodies at NASA headquarters in Washington, D.C.

[Roland Pease]

And everyone I've been talking to about 3i Atlas said if you want to know what NASA's doing about seeing it when we can't see it from Earth, ask Tom.

[Tom Statler]

Well, it's nice of them to say that. 3I Atlas is a wonderful object. It's the third discovered interstellar object. We know that it's interstellar because it's coming through our solar system so quickly. It can't be gravitationally bound to the sun. And right at the time when a comet is likely to do its most interesting things, that is when it's passing closest to the sun, Earth is around the wrong side. But we do have these deep space assets, most of which are on the correct side of the sun to be observing three I atlas. And so we're coordinating with all the mission teams to figure out who is in good position to observe, what they might be able to observe, when they might be able to observe. It fell to me to gather all of that information and understand what they're doing.

[Roland Pease]

So two of those missions are the Europa Clipper, which is heading towards Jupiter and its moons. And then there's the Lucy mission, which is going through the asteroid belt. What else have you got that's over in the right direction?

[Tom Statler]

Oh, my. Well, we have Psyche, which is on its way to a rendezvous with asteroid Psyche in the main belt. And they actually get the next opportunity to observe. Actually, this week, Psyche is passing pretty close to 3i Atlas. Only a couple of tenths of an astronomical unit, so they'll be able to do some interesting imaging. Then, of course, the comet is passing quite close to Mars. So all of our assets at Mars have been looking into whether it's possible for them to observe.

[Roland Pease]

So this is what Mars Orbiter is it?

[Tom Statler]

The Mars Orbiter is also the Mars rovers. So, for example, Mars Reconnaissance Orbiter has the High Rise Camera that has done high resolution mapping of the Mars surface. They will be observing both rovers, Opportunity and Perseverance, they're going to try to observe. But of course, it's good to remember for all of these planetary missions, the cameras are generally designed to look at sunlit surfaces. Right. So the rover teams, they're not quite sure whether they'll quite be able to get it, but they're going to try anyway. It's a challenging observation for them.

[Roland Pease]

When you were talking to these people, were they saying, oh look, we've got better stuff to do, or were they all saying, oh, we want to be part of the party?

[Tom Statler]

Who doesn't love an interstellar comet? Everybody is excited by this, everybody wants to do it. And those few missions that, you know, they did the calculation to see can we actually do this or not? And sometimes the answer turned out to be no, we're not going to be able to get it. And they're very disappointed.

[Roland Pease]

And is there a danger they're going to sort of duplicate their efforts if they're all just taking pictures of the same thing from a slightly different angle, or do they have different capabilities?

[Tom Statler]

Both. So the different spacecraft have different instruments, different capabilities, but it's not from almost the same direction, it's from very, very different directions. And so one of the most interesting things you can do to observe a comet is to look at the scattered sunlight off of the dust from different angles and at different colors, different wavelengths. And that kind of information can tell you about the makeup of the dust, the size distribution of the dust, things that comet people really, really want to know about. I shouldn't leave out though. In addition to our interplanetary spacecraft, we also have, of course, the Near Earth based observatories and James Webb Space Telescope has been observing and will observe in the future. But also the solar physics, the heliophysics missions are also going to be able to observe at some level because of course they're designed, even though they're close to the Earth, they're designed to look at the, the sun. Right. So if they're looking at the sun, in principle, they can see the comet passing behind the Sun. They're making a best effort. They're not 100% sure that they'll be able to get good data. Then again, comets are sometimes unpredictable. And 3i Atlas has not been warmed up by a star in several billion years. So who knows what it's going to do when it reaches its closest point.

[Roland Pease]

I guess that is the most exciting thing is in sense it's a sample probably from the early stages of the formation of a completely different planetary system. So it sort of expands our view of the way that planetary systems work.

[Tom Statler]

Exactly. And really what we want to be able to see is how is it similar to and different from our own homegrown comets. So it's, in so many ways it is an exciting time to be alive. It is. It's an exciting time to be a planetary scientist. And especially it's an exciting time to be interested in our solar system's small bodies because we have all of these missions to asteroids and that have been studying comets and we have this newly discovered population of interstellar objects. It's a wonderful time to be doing such groundbreaking science that really enlightens the history of our solar system and benefits all of humanity.

[Roland Pease]

I get the feeling that Tom Statler is one of those people who makes the wheels turn at NASA. In fact, I came across him a year ago when I joined scientists planning for the highly unusual flyby of asteroid Apophis close over our heads, closer indeed than some satellites in 2029. And that, like this was for a special out and about edition of Science in Action from the BBC World Service.

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[Roland Pease]

There are moments when these international conferences are absolutely insane. There's so many people packed into the hall just at the moment, but I can see just over there, Naomi Murdoch, who's from the French space agency cens. And the last time I spoke to her, it was about their plans to send a mission to the asteroid Apophis, which is going to be coming past Earth in 2029. I want to know what's going on.

[Naomi Murdoch]

So it could be a nice collaboration. It would be a line with both projects and you can take away the data.

[Jiang Yang Li]

Yeah.

[Roland Pease]

Hi, Naomi.

[Naomi Murdoch]

Hi.

[Roland Pease]

We haven't spoken since that meeting about going to Apophis.

[Naomi Murdoch]

That was a great meeting.

[Roland Pease]

Well, is it going to happen?

[Naomi Murdoch]

Is it going to happen? Well, we really, really, really hope so. Everything's been moving forward so you've got.

[Roland Pease]

To launch it in 2028, is that right?

[Naomi Murdoch]

Start of 2028 and then it will.

[Roland Pease]

Catch up over the year before the encounter with Earth and all that in 2029.

[Naomi Murdoch]

2029, a couple months before the encounter, which of course is going to happen on Friday 13 April. Because nature loves to do that type of thing. Exactly.

[Roland Pease]

So I mean, you're building all the bits for it now.

[Naomi Murdoch]

So we're building the bits. ESA has got some bridging funding because we need to have a little bit of money in order to continue with the platform until we have a big decision coming up in November. But in the meantime, all the instruments are being built. We are working very hard on our seismometer.

[Roland Pease]

Well, that's what I want to know about. You told us that you're going to be landing a seismometer on this thing that's not much bigger than an aircraft carrier.

[Naomi Murdoch]

Yeah, 340 meters. And the idea is that the Ramsey space mission, which is the European space mission, is going to deploy two cubesats. These are little satellites the size of shoeboxes. And one of those cubesats is going to go down and land on the surface of this body with hardly any gravity, land bounce, stay on the surface and carry with it our seismometer in order to make, make the first ever seismic measurements on the surface of an asteroid.

[Roland Pease]

I mean, that was just a dream. When I talked to you, is that, I mean, have you beaten the competition?

[Naomi Murdoch]

Well, I think we managed to convince the science community and ESA that it's a very important instrument to have. It's a once in a lifetime opportunity. You know, Apophis is coming by. That type of event happens once every 7,500 years. Okay. It's really rare, but this nature is giving this opportunity to us. It's the perfect situation for a seismometer because Earth is going to pull on Apophis as it comes past and it's going to generate these seismic quakes.

[Roland Pease]

The asteroid is going to creak, as it were, because of the gravitational pull.

[Naomi Murdoch]

Yeah, yeah. Earth is going to pull on it and it's going to change a lot of things about Apophis, but one of them is probably going to be the spin rate. So how fast it's moving. And as it changes its spin rate, the body is going to reorganize internally. Because we think that Apophis is not just a lumber rock. It's lots and lots and lots of rocks together in a rubble pile, as we call it. And so if you change how it spins very abruptly, it's going to have to reorganize in a different way. And as it does that, the blocks are going to move against each other and they're going to create seismic signals inside the body.

[Roland Pease]

Does the machine have to be incredibly sensitive? Do you know how strong these earthquakes is? Apophis quakes are going to be.

[Naomi Murdoch]

We're trying our best to understand, been trying to work really hard with models to predict what are the seismic signals that we're going to see as Apophis comes past the Earth. So what we're doing is we're making sure that we've got an instrument that's as sensitive as we can be in order to detect these very small amplitude signals. And then we're just going to hope for the best.

[Roland Pease]

I mean, I just find it's mind boggling the idea of doing this. Would they allow you to put the seismometer on Apophis before it goes past yet? Because you might mess things up.

[Naomi Murdoch]

Well, there's been lots of studies that have been done and all of the space agencies are in agreement that the low velocity landing of the cubesat is not going to change anything for Apophis. We're going to arrive, you know, at centimeters, tens of centimeters per second, maximum. It's really, really, really slow. So we're going to be deployed, we're going to land at least several hours before the close encounter so that we can be on the surface, measure what's happening as Apophis comes by. And we expect that just after the passage, really close to the Earth, so by maybe three to six hours after. That's when we're expecting to see the majority of these seismic signals. The shaking, the dancing of Apophis going on. We're going to be seeing those effects.

[Roland Pease]

How exciting is, I mean, what I love is you're so enthusiastic about it, but amongst all the missions you've done, I mean, is this number one?

[Naomi Murdoch]

Oh, I can't answer that question. But this is really, really special. It's a really special mission for lots of reasons. It's a first, okay, we've done seismology on the moon, we've done seismology on Venus, we've done seismology on Mars. We've never done seismology on an asteroid, so it's a first. We're building the equipment ourselves at Isaya Supero. So that's really exciting as well, to be providing our own payload. We have huge support from the French Space Agency and from the international community for this first in a once in a lifetime and first seismic experiment. So it's really exciting.

[Roland Pease]

Well, I know what I'll be doing. April 13, 2029.

[Naomi Murdoch]

I'll see you there.

[Jiang Yang Li]

I like to think about the Apophis flyby as like comet highly flyby in 1986, right? There were six spacecraft fly by Comet Halley at that time. That includes the spacecraft from the Soviet Union, from esa, from Japan. So that was a very good example for such a collaboration and for such a rare event, you know, in planetary science. So this I think will be similar. Imagine this has been like 40 years, more than 40 years. And then there's another opportunity for people to come together to have this festival for this tiny object. That's exciting.

[Roland Pease]

That's actually exactly how I feel about this Apophis encounter. A unique science opportunity the whole world can take part in. And now China's taking part.

[Jiang Yang Li]

I'm Jiang Yang Li from Sun Yesen University. I'm a professor there. We're coming up with a mission concept, basically to use a spacecraft to fly by quickly fly by Apophis and take images. And also in this mission we're trying to use this Minecraft together with a small sat to measure the tiny distance change and velocity change between the two objects in order to measure the mass, the tiny mass of the asteroid.

[Roland Pease]

I mean, you say flyby, some of the other people we've spoken to, they're going to be chasing Apophis. But as far as I can tell, what you're going to do is you're going to sort of sit there not far from the Earth and then wait for Apophis to come to you. Is that a fair disclosure?

[Jiang Yang Li]

Yes, that's right. Flyby, in terms of the reference, right, if you're sitting on a spacecraft, it's like the asteroid is zipping by. And if you are sitting on the asteroid, you are looking at a spacecraft coming by very quickly. But for us, technically, we're waiting for the asteroid to come by. And the good thing about this mission is that we're going to wait in the. We call that Lagrange point L1 halo orbit, which is a quasi stable orbit.

[Roland Pease]

This is sort of on the same path as the Earth goes around, but a bit ahead of us, I think.

[Jiang Yang Li]

Is that right, actually a bit of towards the sun, in between the sun.

[Roland Pease]

In between us and the sun.

[Jiang Yang Li]

That's the point. And then in that location, we don't need to use much fuel to maintain the orbit. We can just drift in the orbit and wait for A purpose. So that means we have some flexibility in terms of the launch date. If we launch earlier, we can wait there for a little longer. So that's fine with us.

[Roland Pease]

So, so you're going to sit there on this little orbit and wait for Apophis to fly by. You said you well, how big are these spacecraft you're sending up?

[Jiang Yang Li]

It's a pretty small one. The mass is 44 kg, so I would imagine maybe a few tens of centimeters across.

[Roland Pease]

A few tens of centimeters. So yeah, I could hold it in my hands.

[Jiang Yang Li]

I think so.

[Roland Pease]

And then when Apophis comes by, for how long will it be in view? Because I presume it's going to pretty fast when it goes past.

[Hal Levison]

Right?

[Jiang Yang Li]

You know, that depends on how sensitive our camera is. I did some quick estimate. Looks like we can, we will be able to see the asteroid for like a month before the flyby. For most of the time that it's in the view and we can detect it, it's going to be a dot and slowly increasing its brightness. Right. And then only maybe 15 minutes before the flyby we can, we started to resolve it into multiple pixels and it will grow into a full blown object and then quickly zip by.

[Roland Pease]

And what are you going to learn from your mission that the other missions aren't going to learn?

[Jiang Yang Li]

Well, first of all, we have the camera, so we're going to be able to see how the surface looks like. And also we have spectrometer, so we'll be able to get spectrum and try to figure out the composition of surface composition of this, of Apophis, the kind.

[Roland Pease]

Of materials it's made of.

[Jiang Yang Li]

That's right, yeah, yeah. And also with some modeling efforts, we might be able to see which part of the surface has moved because of the interaction of the Earth's tidal force.

[Roland Pease]

Because they're expecting it to sort of creak as the Earth's gravity pulls on it.

[Jiang Yang Li]

Yeah, yeah. For this mission we're going to have a flyby after the Earth encounter. Right. We don't have the images before the encounter to compare, but we can still use the images and combined with some modeling effort to figure out where on the surface it's more likely to move.

[Roland Pease]

If something's moved, you'll see the track as it moves.

[Jiang Yang Li]

Exactly. We can look for the signs of movement in our images.

[Roland Pease]

The other thing you said is you think you can weigh Apophis. And this is where I think you mentioned there's going to be another smaller satellite.

[Jiang Yang Li]

Yeah. The purpose of the small satellite is to measure the mass of Apophis during the flyby, the gravity field of Apophis will slightly change the distance and the relative velocity of these two satellites. It's going to be a very tiny change.

[Roland Pease]

I mean, how far apart are they? You're not really close. You're going to be what, hundreds of kilometers away?

[Jiang Yang Li]

It's going to be a tiny change over like, you know, kilometers, tens of kilometers distance, maybe micrometers change in over tens of kilometers or 20 kilometers.

[Roland Pease]

I mean, because I'm just trying to think this. I mean, Apophis is tiny. It's tiny. You're a long way from it. What kind of gravity you think you can actually feel its gravitational pull as it.

[Jiang Yang Li]

Well, theoretically the gravitational pull is there.

[Je Kot]

Right.

[Jiang Yang Li]

It's a matter of whether we can see it above the noise.

[Roland Pease]

But I mean, what a. What an adventure to try it.

[Jiang Yang Li]

Yeah, it is exciting thing and we really hope we can do something with this object.

[Roland Pease]

I so hope so. Many thanks to Jan Young Lee of Sun Yat Sen University and also to all the others who've taken time out from this thronging meeting to talk to science and action from the BBC World Service. I just learned there are 1800 participants at this festival of planetary science, each with their own little piece in the puzzle of what makes the solar system tick. I'm Roland Pease. Ella Hub has been frantically bashing my interviews into shape and I hope we'll have some more of them next week. Talking of which, I'm actually in danger of missing the next session, which is on the James Webb Space Telescope. I'll catch you later, Ella.

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