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NASA’s Lucy mission is going to be the first mission
to explore the Trojan asteroids.
These are asteroids that live in two swarms:
one that’s ahead of Jupiter, and another that’s behind Jupiter,
and we want to go and look at these building blocks of the planets,
the ones that didn’t get accumulated into the planets,
to really learn about the evolution of our solar system.
Lagrange points are these stable regions of space.
They’re around pretty much every planet in the solar system.
Jupiter, by virtue of being the largest planet in the solar system,
it also has the biggest Lagrange points.
And these are little stable reservoirs where asteroids get in,
but they never come out.
In reality, what we have is sort of a snapshot
of what the solar system looked like billions of years ago.
Early in the solar system, the giant planets were migrating outward,
away from the Sun, and at one point there was chaos in the solar system.
Some small bodies were ejected out of the solar system,
others could have been trapped in these Lagrange points,
and that’s one theory for how the Trojan asteroids
came to be where they are today.
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My job as a mission architect here at Lockheed Martin it’s very interesting,
and it sort of encompasses the biggest picture of the mission.
What is the trajectory?
What sort of propulsion do you need to fly that trajectory?
What does the spacecraft look like?
So in the case of, for example, Lucy, it’s like:
“Okay, it’s going out five times further from the Sun than the Earth is,
and so it’s going to need big, huge solar arrays just because of that.”
Lucy has three scientific instruments on board the spacecraft,
and we’ll also be using two of the spacecraft’s subsystems
to contribute to the science investigation.
With the LORRI instrument we’ll be able to get panchromatic images,
which will tell us about the geology and the crater history,
which gives us the age of the surface.
With the TES instrument we’ll be able to measure the temperature
of the surface at different points,
and with the Ralph instrument we’ll be able to measure
the composition of the surfaces.
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The Jupiter Trojans, they have a variety of surface characteristics.
They have different colors and different surface compositions,
and that leads us to believe that maybe they formed somewhere else.
In choosing the Lucy targets, we wanted to be able to compare
different objects that have different surface properties, but a very similar orbit.
Lucy will visit one main-belt asteroid and seven Trojan asteroids.
I don’t think there’s been a single NASA mission that will have visited
as many objects on separate orbits in the solar system
as the Lucy mission will.
We launch in October of 2021.
That trajectory just basically does a one-year loop around the Sun
and comes back to Earth in October of 2022,
and that will slingshot us out now onto a trajectory that takes
a little more than two years to come back to the Earth.
Now we’re moving a whole lot faster than we were.
We get that trajectory set up, and that second Earth gravity assist
takes that velocity and redirects it in the direction we want
that will take us out to the Trojan space.
On our way out to the L4 swarm of the Trojans,
we’re going to visit a main-belt asteroid.
That main-belt asteroid is named Donaldjohanson,
after the discoverer of the Lucy fossil.
We named the Lucy mission in honor of the Lucy fossil
because we learned so much about hominid development and evolution
from that fossil, just like we’re going to learn about
the solar system evolution from the Lucy mission.
From there, we take a couple of years off and we continue to cruise up,
until we get to August 2027,
and there we encounter our first Trojan asteroid, it’s called Eurybates.
It’s the product of a huge collision that happened
millions and millions of years ago.
Something big hit it and just blew it apart,
and so Eurybates is the biggest chunk of that cataclysmic impact.
And it’s a C-class asteroid, which is kind of interesting because
there’s a lot of C-class asteroids in the main belt,
there’s very few of them in Trojan space.
So that’s one of the mysteries we’re going to get at – is, okay,
why is Eurybates so different?
As we’ve studied it and tried to refine its orbit,
we’ve discovered it’s got a little moon, and so we’re going
to try to get pictures of that too as we fly by.
And about a month later, in September of 2027,
we’re encountering our second Trojan asteroid: Polymele.
So it’s one of the smaller objects.
We’re flying by at about six, seven kilometers per second.
We have to take pictures like crazy as we fly by,
but we’re not stopping at any of these.
We come to our next object, Leucus, and it’s “wash, rinse, repeat.”
And so we snap pictures like crazy at Leucus and then about seven months
after that, we do the exact same thing at another object called Orus.
And that’s the last L4 swarm object that we’re going to be visiting,
and from there we start dropping down back into the inner solar system, now.
So, we were out past Jupiter’s orbit a little ways,
now we’re falling back in towards the Earth,
so the trajectory is sort of set up to sort of return back to Earth for free.
And we use that to redirect the trajectory now towards our final Trojan asteroid,
and so this is an object out in the L5 swarm,
so it’s trailing Jupiter by about sixty degrees.
It’s a roughly equal-mass binary system called Patroclus and Menoetius.
You can imagine it’s sort of like this dumbbell in space.
So imagine a great big dumbbell spinning around, you know,
but there’s no bar there, it’s just the objects orbiting each other.
It’s a very rare thing to find in the inner solar system,
however, if you look out past the orbit of Pluto,
equal-mass binaries are kind of common out there.
Another clue, it’s like – okay, are these objects in the Trojan swarm,
are they maybe related to the Kuiper belt objects out there past Jupiter?
And if they are, this would be amazing, we can go and visit
Kuiper belt objects by just going out to Jupiter.
We really have never seen Trojan asteroids up close before,
and we want to understand their geology,
look at the craters on the surface to understand the history of their surfaces,
understand the composition of their surfaces so that we can maybe
learn something about where they formed.
And all of those will be clues to help us understand
how the solar system evolved.
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