Early in the morning on Saturday, October 16, NASA’s Lucy mission, a 12-year journey to uncover answers about the solar system’s early history in Jupiter’s Trojan asteroids, launched on a United Launch Alliance (ULA) Atlas V rocket from Space Launch Complex 41 at Cape Canaveral Space Force Station in Florida.
Named after the fossils of one of the oldest known human ancestors, the Lucy mission will explore two swarms of Trojan asteroids, which scientific evidence indicates are remnants of the material that formed giant planets. Just as the discovery of the Lucy fossils in 1974 in Ethiopia revolutionized our understanding of human evolution, scientists hope the Lucy spacecraft will revolutionize our understanding of the solar system’s formation and evolution.
Over the next 12 years, Lucy will fly by one main-belt asteroid and seven Trojan asteroids, making it NASA’s first single spacecraft mission in history to explore so many different asteroids.
“Today’s launch marks a genuine full-circle moment for me as Lucy was the first mission I approved in 2017, just a few months after joining NASA,” said Thomas Zurbuchen, associate administrator for the Science Mission Directorate at the agency’s Headquarters in Washington. “A true mission of discovery, Lucy is rich with opportunity to learn more about these mysterious Trojan asteroids and better understand the formation and evolution of the early solar system.”
About an hour after liftoff, Lucy separated from the second stage of the ULA Atlas V 401 rocket. It sent the first signal to Earth from its own antenna to NASA’s Deep Space Network, then embarked for the long haul on its journey across the solar system. The spacecraft is now traveling at roughly 67,000 mph on a trajectory that will orbit the Sun and bring it back toward Earth in October 2022 for a gravity assist.
Solar Array Problem?
While both of Lucy’s large solar arrays, each nearly 7.3 meters wide, successfully unfurled and began charging the spacecraft’s batteries to power its subsystems, one of the arrays may not be fully latched, NASA announced Sunday.
“In the current spacecraft attitude, Lucy can continue to operate with no threat to its health and safety,” the agency said. “The team is analyzing spacecraft data to understand the situation and determine next steps to achieve full deployment of the solar array.”
The First Asteroid
Lucy will use its first Earth gravity assist in 2022 to accelerate and direct its trajectory beyond the orbit of Mars. It will then swing back toward Earth for another gravity assist in 2024, which will propel Lucy toward the Donaldjohanson asteroid, located within the solar system’s main asteroid belt in 2025 before heading toward the Trojan asteroids.
Caught in Jupiter’s orbit around the Sun, the Trojan asteroids are like time capsules from the solar system’s birth more than four billion years ago. They split into two swarms, each found near one of Jupiter’s Lagrange points, stable locations in space where smaller masses can be trapped. Equidistant from Jupiter and the Sun, the asteroid swarms are effectively trapped in a gravitational balancing act between the two bodies.
“What we are doing in the big picture is trying to understand how planetary systems form,” said Keith Noll, project scientist for the Lucy Mission. “We have the broadest outlines of that. We know they form from these clouds of gas and dust that collapse and form stars, and then the discs around those are where the planets form. But we don’t have the next level of detail. What we have learned in the last 30 years is that the old view of the solar system as being fairly static — the planets formed the way we see them now, they’ve always been there and been kind of stable — is not what we see when we look at other exoplanetary systems, and we even see evidence in our own solar system that things have moved around and changed. That’s the next level of detail we are trying to understand.”
Using a variety of instruments strapped to the spacecraft, Lucy will measure the asteroids’ mass, shape, density, color, composition and other properties. This data can help scientists on Earth make inferences about the solar system’s history. For example, the Trojans are expected to be covered with craters that not only provide information about smaller, unobservable elements in the system but contain pieces of other broken-up asteroids.
Although cartoon depictions of the solar system make objects appear close to one another, Noll said they are in fact extremely far apart. For that reason, finding “two-for-the-price-of-one” binary asteroid systems is valuable, and Lucy will visit four such systems. The pair of Trojans closest to each other is still roughly 9.3 million miles apart.
In 2033, Lucy will visit the Patroclus-Menoetius binary, which Noll called “one of the most interesting objects in the Trojans.”
“The fact that they are still a binary tells us they probably have not had really major collisions,” he said. “But we also see lots and lots of these equal-mass binaries in the Kuiper Belt, which is out beyond Neptune. And we don’t see many of them out in the Trojans, but this one may be a lucky survivor. It’s one of the most interesting objects in the Trojans, and the fact that we can get it in our mission makes this a spectacular combination of targets.”
Lucy will encounter the first Trojan asteroid in 2027. After completing its first four targeted flybys, the spacecraft will travel back to Earth for a third gravity boost in 2031, which will catapult it to the second Trojan swarm for a 2033 encounter.
“We started working on the Lucy mission concept early in 2014, so this launch has been long in the making,” said Hal Levison, Lucy principal investigator, based out of the Boulder, Colorado, branch of Southwest Research Institute (SwRI), which is headquartered in San Antonio. “It will still be several years before we get to the first Trojan asteroid, but these objects are worth the wait and all the effort because of their immense scientific value. They are like diamonds in the sky.”
“Lucy embodies NASA’s enduring quest to push out into the cosmos for the sake of exploration and science, to better understand the universe and our place within it,” said NASA Administrator Bill Nelson. “I can’t wait to see what mysteries the mission uncovers!”