Lucy will embark on a 12-year mission to explore Jupiter's Trojan asteroid swarms, which have never been observed. The Trojan asteroids, which borrow their name from Greek mythology, orbit the sun in two swarms -- one that's ahead of Jupiter, the largest planet in our solar system, and a second one that lags behind it.
Lucy the first spacecraft with potentially vital information
Lucy is the first spacecraft designed to visit and observe these asteroids, which are remnants from the early days of our solar system. The mission will help researchers effectively peer back in time to learn how the solar system formed 4.5 billion years ago. Lucy's 12-year mission could also help scientists learn how our planets ended up in their current spots.
"At the heart of Lucy is the science and how it's going to talk to us about the Trojans," said Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate. "It's so important to go observe them because these asteroids tell us about a chapter of our own story -- in this case, the history when the outer planets were forming in the solar system," Zurbuchen said. "I'm still amazed by the fact that if you pick up a rock or you look at one of those planetary bodies and you add science to it, it turns into a history book."
Visiting mysterious asteroids
There are about 7,000 Trojan asteroids, and the largest is 160 miles (250 kilometers) across. The asteroids represent the leftover material still hanging around after the giant planets in our solar system, including Jupiter, Saturn, Uranus and Neptune, formed. Even though they share an orbit with Jupiter, the asteroids are still very distant from the planet itself -- almost as far away as Jupiter is from the sun, according to NASA.
The Trojans "are held there by the gravitational effect of Jupiter and the sun, so if you put an object there early in the solar system's history, it's been stable forever," said Hal Levison, the principal investigator of the Lucy mission, based at the Southwest Research Institute in Boulder, Colorado. "These things really are the fossils of what planets formed from."
Both the fossil and the mission are a nod to the Beatles tune "Lucy in the Sky With Diamonds," which is why the logo for the Lucy mission includes a diamond.
Over 12 years, Lucy will travel nearly 4 billion miles (6.4 billion kilometers) moving at about 400,000 miles per hour (17,881.6 meters per second).
"One of the really surprising things about the Trojans, when we started to study them from the ground, is just how different they are from one another," Levison said. " So if you want to understand what this population is telling us about how the planets formed, you need to understand that diversity and that's what Lucy is intended to do."
A feat of engineering
The Lucy spacecraft is more than 46 feet (14 meters) from tip to tip, largely due to its giant solar panels -- each about the width of a school bus -- designed to keep up a power supply to the spacecraft's instruments. But Lucy also has fuel to help it execute some skilled maneuvers on the way to the asteroids.
It took a team of more than 500 engineers and scientists to conceptualize and build the spacecraft, said Donya Douglas-Bradshaw, Lucy project manager at NASA's Goddard Space Flight Center.
"Lucy will be NASA's first mission to travel this far away from the sun without nuclear power," said Joan Salute, associate director for flight programs at NASA's Planetary Science Division."In order to generate enough energy, Lucy has two very large circular solar arrays that open up like Chinese fans. These open up autonomously and simultaneously, and it happens about one hour after launch."
Lucy will use three science instruments to study the asteroids, including color and black-and-white cameras, a thermometer, and an infrared imaging spectrometer to determine the composition of the asteroids' surface materials. The spacecraft will communicate with Earth using its antenna, which also can be used to help determine the masses of the asteroids.
The instruments will enable the science team to search for satellites around these asteroids as well as craters on their surfaces, which can help determine their ages as well as the origin and evolution of the asteroids.
Lucy will fly by the asteroids at about 15,000 miles per hour (6,705 meters per second), about four times slower than when NASA's New Horizons spacecraft zipped by Pluto and the distant object Arrokoth, said Hal Weaver, principal investigator for Lucy's L'LORRI instrument at the Johns Hopkins Applied Physics Laboratory.
Once the Lucy mission has finished, the team plans to propose an extended mission to explore more Trojans. The spacecraft will remain in a stable orbit that retraces the path of its exploration between Earth and Jupiter, and it won't have a chance of colliding with either for over 100,000 years. Eventually, if the orbit does grow unstable, it will likely head on a doomed mission to the sun or get kicked out of our solar system.