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♪♪♪

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NASA’s Lucy mission is going to be the first mission

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to explore the Trojan asteroids.

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These are asteroids that live in two swarms:

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one that’s ahead of Jupiter, and another that’s behind Jupiter,

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and we want to go and look at these building blocks of the planets,

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the ones that didn’t get accumulated into the planets,

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to really learn about the evolution of our solar system.

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Lagrange points are these stable regions of space.

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They’re around pretty much every planet in the solar system.

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Jupiter, by virtue of being the largest planet in the solar system, 

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it also has the biggest Lagrange points.

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And these are little stable reservoirs where asteroids get in,

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but they never come out.

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In reality, what we have is sort of a snapshot

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of what the solar system looked like billions of years ago.

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Early in the solar system, the giant planets were migrating outward,

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away from the Sun, and at one point there was chaos in the solar system.

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Some small bodies were ejected out of the solar system, 

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others could have been trapped in these Lagrange points,

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and that’s one theory for how the Trojan asteroids

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came to be where they are today.

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♪♪♪

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My job as a mission architect here at Lockheed Martin it’s very interesting,

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and it sort of encompasses the biggest picture of the mission.

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What is the trajectory?

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What sort of propulsion do you need to fly that trajectory?

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What does the spacecraft look like?

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So in the case of, for example, Lucy, it’s like:

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“Okay, it’s going out five times further from the Sun than the Earth is,

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and so it’s going to need big, huge solar arrays just because of that.”

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Lucy has three scientific instruments on board the spacecraft,

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and we’ll also be using two of the spacecraft’s subsystems

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to contribute to the science investigation.

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With the LORRI instrument we’ll be able to get panchromatic images,

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which will tell us about the geology and the crater history,

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which gives us the age of the surface.

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With the TES instrument we’ll be able to measure the temperature

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of the surface at different points,

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and with the Ralph instrument we’ll be able to measure

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the composition of the surfaces.

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♪♪♪

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The Jupiter Trojans, they have a variety of surface characteristics.

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They have different colors and different surface compositions,

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and that leads us to believe that maybe they formed somewhere else.

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In choosing the Lucy targets, we wanted to be able to compare

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different objects that have different surface properties, but a very similar orbit.

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Lucy will visit one main-belt asteroid and seven Trojan asteroids.

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I don’t think there’s been a single NASA mission that will have visited

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as many objects on separate orbits in the solar system

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as the Lucy mission will.

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We launch in October of 2021.

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That trajectory just basically does a one-year loop around the Sun

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and comes back to Earth in October of 2022,

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and that will slingshot us out now onto a trajectory that takes

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a little more than two years to come back to the Earth.

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Now we’re moving a whole lot faster than we were.

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We get that trajectory set up, and that second Earth gravity assist

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takes that velocity and redirects it in the direction we want

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that will take us out to the Trojan space.

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On our way out to the L4 swarm of the Trojans,

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we’re going to visit a main-belt asteroid.

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That main-belt asteroid is named Donaldjohanson,

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after the discoverer of the Lucy fossil.

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We named the Lucy mission in honor of the Lucy fossil

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because we learned so much about hominid development and evolution

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from that fossil, just like we’re going to learn about

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the solar system evolution from the Lucy mission.

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From there, we take a couple of years off and we continue to cruise up,

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until we get to August 2027,

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and there we encounter our first Trojan asteroid, it’s called Eurybates.

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It’s the product of a huge collision that happened

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millions and millions of years ago.

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Something big hit it and just blew it apart,

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and so Eurybates is the biggest chunk of that cataclysmic impact.

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And it’s a C-class asteroid, which is kind of interesting because

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there’s a lot of C-class asteroids in the main belt,

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there’s very few of them in Trojan space.

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So that’s one of the mysteries we’re going to get at – is, okay,

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why is Eurybates so different?

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As we’ve studied it and tried to refine its orbit,

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we’ve discovered it’s got a little moon, and so we’re going

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to try to get pictures of that too as we fly by.

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And about a month later, in September of 2027,

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we’re encountering our second Trojan asteroid: Polymele.

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So it’s one of the smaller objects.

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We’re flying by at about six, seven kilometers per second.

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We have to take pictures like crazy as we fly by,

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but we’re not stopping at any of these.

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We come to our next object, Leucus, and it’s “wash, rinse, repeat.”

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And so we snap pictures like crazy at Leucus and then about seven months

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after that, we do the exact same thing at another object called Orus.

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And that’s the last L4 swarm object that we’re going to be visiting,

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and from there we start dropping down back into the inner solar system, now.

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So, we were out past Jupiter’s orbit a little ways,

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now we’re falling back in towards the Earth,

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so the trajectory is sort of set up to sort of return back to Earth for free.

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And we use that to redirect the trajectory now towards our final Trojan asteroid,

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and so this is an object out in the L5 swarm,

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so it’s trailing Jupiter by about sixty degrees.

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It’s a roughly equal-mass binary system called Patroclus and Menoetius.

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You can imagine it’s sort of like this dumbbell in space.

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So imagine a great big dumbbell spinning around, you know,

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but there’s no bar there, it’s just the objects orbiting each other.

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It’s a very rare thing to find in the inner solar system,

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however, if you look out past the orbit of Pluto,

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equal-mass binaries are kind of common out there.

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Another clue, it’s like – okay, are these objects in the Trojan swarm,

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are they maybe related to the Kuiper belt objects out there past Jupiter?

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And if they are, this would be amazing, we can go and visit

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Kuiper belt objects by just going out to Jupiter.

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We really have never seen Trojan asteroids up close before,

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and we want to understand their geology,

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look at the craters on the surface to understand the history of their surfaces,

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understand the composition of their surfaces so that we can maybe

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learn something about where they formed.

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And all of those will be clues to help us understand

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how the solar system evolved.

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♪♪♪