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NASA's Lucy asteroid mission will explore mysteries of the early solar system

An artist's depiction of the Lucy spacecraft studying an asteroid.
An artist's depiction of the Lucy spacecraft studying an asteroid. (Image credit: Southwest Research Institute)



"I've been dreaming of sending a spacecraft to the Trojan asteroids for more than a decade," Cathy Olkin, the mission's deputy principal investigator and a planetary scientist at the Southwest Research Institute (SwRI) in Colorado, told "This opportunity is just outstanding."

Related: Meet the 8 asteroids NASA's Lucy spacecraft will visit

NASA's $981 million Lucy mission, which is scheduled to launch on Saturday (Oct. 16) at 5:34 a.m. EDT (0934 GMT), is a daring expedition that will make six carefully orchestrated flybys: one in the main asteroid belt, the rest among Jupiter's Trojans. The mission's agenda relies on the nimble data gathering necessitated by flyby visits and a convenient celestial alignment that offers scientists a veritable treasure trove of eight intriguing space rocks.

"We were amazingly lucky about being able to get such a rich set of targets," Hal Levison, the mission's principal investigator and another planetary scientist at SwRI, told "Some of these objects, they would be interesting objects to send spacecraft to even if that were the only target the spacecraft were going to."

That's a model that recent asteroid missions like Japan's Hayabusa2 and NASA's OSIRIS-REx, followed; each spacecraft spent months studying its near-Earth asteroid before eventually snagging a sample to deliver to scientists.

But Lucy can't stay at any one space rock without breaking the bank, since orbiting an asteroid requires much more fuel than flying past one. Instead, Lucy will become the first mission to make so many flybys in the outer solar system, and it will approach its targets at a hurtling pace of 3 to 6 miles (5 to 9 kilometers) per second. That's a whopping 10,800 to 21,600 mph (18,000 to 32,400 kph).

To grasp the enormity of that challenge, Olkin suggested imagining running a 10K race — but in just a second or two. "I really love the challenge of it, because it makes the science return so much richer," Olkin said. "With a flyby, every moment is precious."



The allure of the Trojans 



"They occupy a very small region of space, and yet, they're very different from one another," Levison said. "They really are a mystery."


He said he hopes that the data Lucy gathers will give scientists a better understanding of how closely this and other theories match the real past of the solar system. When he entered the field in the 1980s, he said, scientists were short on theories, but now that's changed. "We've gotten to the point where I think we have more ideas floating around and don't have the data to be able to figure out which one's right," Levison said.


Comparison among the Trojans and among asteroids in general is at the heart of Lucy's science. "These guys have been sitting in the same place and so they've had the same evolutionary pathway since they got trapped in their swarm," Levison said. "So the differences we see really are going to be fundamental differences on the bodies."

To that end, the flybys are coordinated so that scientists can easily compare the details of observations gathered at different asteroids. Among others, the observations include color photographs of the Trojans' surface, infrared spectrometry to identify different compounds on their surfaces and analysis of Lucy's communication signal from Earth that will tell scientists how dense each asteroid is.

A rich itinerary 

The team built the spacecraft's itinerary around two asteroids that were generally quite similar in size and orbit, but one gray and one red.

"If we found a pair like that, we know that they've had the same collisional history because they're on the same orbits, they're the same size, the same solar radiation — all that's been the same for the last 4 billion years, give or take," Levison said. "So if we saw differences between the two, we would know that was telling us something important about their intrinsic properties."


"That was where we started and the rest was luck, basically," Levison said.


The flyby is a bonus — the asteroid will be near the path that Lucy had to travel anyway on its journey out to the Trojans — but the object is still intriguing. It's one member of a clump of asteroids that are the fragments of a much larger space rock that was smashed to bits, a type of asteroid that scientists haven't seen before. And astronomers even know about when the collision in question occurred.

"This object is very young," Levison said. "It's estimated to have an age between 100 and 200 million years, which makes it one of the youngest things in the solar system."

A set of artist's depictions show the seven primary targets of the Lucy mission.  (Image credit: NASA's Goddard Space Flight Center Conceptual Image Lab)

On to the Trojans 

Lucy's first Trojan target is Eurybates, the gray component of the pair at the heart of the mission's design. It, like Donaldjohanson, is a fragment from an impact. "It's the largest asteroid from a collisional family, and that makes it very interesting," Olkin said.



Levison said he hopes the visit will help scientists understand collisions, which are a crucial step of planet formation. "We see the biggest member of this population, the brightest of the guys in the clump, and then around it is one of the smallest things, so comparing those two objects is going to be interesting too," he said.

Next, Lucy will bang out three quick flybys. First, in September 2027, Polymele, a smallish redder asteroid that may also represent a fragment of a larger lost rock. Seven months later comes Leucus, with a weirdly slow spin that likely affects the asteroid's temperature. Next comes Orus, the red member of the color-comparison pair that Lucy is built around.

That schedule means that the bulk of Lucy's flybys will come during just 15 months in late 2027 and 2028, Olkin noted. "It's going to be a very busy time."

A grand finale 



"This is, I must admit, my favorite — I know you're not supposed to have favorite kids, but this one is my favorite," Levison said of the pair, called a binary.


And out at that distance, the objects are essentially untouched. "These things are far enough away from the planetary system that the violence of planet formation never affected them," Levison said. The theory, then, is that Patroclus and Menoetius is one of just a few formerly plentiful equal-mass binaries in the heart of the solar system to survive the havoc of the solar system's early days.

"It's one of the lone survivors that we can easily get to with a spacecraft," Levison said. "To me, that's very profound."

And, in accordance with Lucy's comparison work, Patroclus and Menoetius will serve as a key contrast to the spacecraft's first Trojan, Eurybates. "We're going by one object that underwent a really massive collision and therefore sort of was beginning to be involved in planet formation, and an object that we think is pristine," Levison said. "Being able to compare those two things are going to be really, really important."


"I don't know what we're going to see, so I can't say that I have an expectation of this or that," Olkin said. "We're going to send a spacecraft there and we're going to learn about it because that's the process of how we do science."



Meghan Bartels
