NASA's Lucy mission has launched to explore never-before-seen asteroids

"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."

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 spacecraft is set to fly by an asteroid in the main asteroid belt between Mars and Jupiter, and then it will explore seven of the Trojans. Over the course of its mission, Lucy will end up swinging back to Earth's orbit three separate times for gravity assists that can slingshot it on the right path. That will make Lucy the first spacecraft to travel to Jupiter and return to Earth.

The mission borrows its name from the Lucy fossil, the remains of an ancient human ancestor discovered in Ethiopia in 1974. The skeleton has helped researchers piece together aspects of human evolution, and the NASA Lucy team members hope their mission will achieve a similar feat regarding the history of our solar system.

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).

Lucy will specifically visit these asteroids, all named for heroes you might recognize from Homer's "The Iliad": Eurybates, Queta, Polymele, Leucus, Orus, Patroclus and Menoetius.

Eurybates was chosen because it's the largest remnant of an ancient massive collision, meaning that it could reveal a look at what's inside an asteroid. Observations made using the Hubble Space Telescope found that the small asteroid named Queta is a satellite of Eurybates.

Each of the asteroids Lucy will fly by differ in size and color.

"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."

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.

Lucy will also be about 600 miles (965 kilometers) away from each asteroid during its flyby, as opposed to around 2,000 miles (3,218 kilometers) away from the Arrokoth flyby, which means the Trojan images will have four times better resolution.

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.