The Lucy mission to Jupiter's Trojan asteroids has been chosen by NASA for flight under the agency's Discovery Program. Lucy will carry an ASU-designed and -developed thermal emission spectrometer, which will measure surface temperatures on each asteroid the spacecraft visits, said Philip Christensen of the university's School of Earth and Space Exploration.

"I'm really excited about this instrument, the third to be built here at SESE," said Christensen, thermal emission spectrometer designer and principal investigator.

The device continues a growing tradition of hands-on engineering for exploration that has become hallmark of the school, said Christensen, Regents' Professor of geological sciences.

The announcement Wednesday came as NASA also selected for development an ASU-led mission to a metallic asteroid.

Both projects were approved through NASA's Discovery Program, a series of cost-capped exploratory missions into the solar system.

The Lucy mission was named for the iconic fossil skeleton, since it will investigate a particular collection of primitive asteroids that scientists hope may uncover fossils of planetary formation.

Its flight plan calls for a 2021 launch. Among the potential targets for an extended mission is asteroid 52246 Donaldjohanson, named for the discoverer of the Lucy fossil and director of ASU's Institute of Human Origins in the School of Human Evolution and Social Change.

Originating at the Southwest Research Institute in Boulder, Colorado, the mission is under the direction of principal investigator Harold Levison of the Southwest Research Institute.

The target objects for the Lucy mission are asteroids that have never before been studied at close range. These minor planets circle the Sun at same distance as Jupiter, roughly five times farther out than Earth, and in the same 12-year orbit as Jupiter. Through a quirk of orbital dynamics, they remain caught in two swarms, one leading and one trailing Jupiter as it orbits the sun.

The first of these asteroids was discovered in 1906 and named for the Greek warrior Achilles from Homer's epic poem "The Iliad."

As more asteroids were discovered in similar orbits, astronomers started naming them after Homeric Greek and Trojan warriors. Those with Greek names orbit ahead of Jupiter, the Trojan-named ones orbit behind. Collectively, however, both groups are called Trojans, and there are now nearly 6,200 known asteroids in Trojan orbits with Jupiter.

The mission should arrive among the Trojans in 2027 and visit six asteroids by 2033.

Because Jupiter's Trojan asteroids orbit far from the Sun, they all have very cold surfaces. The role in the mission for TES, Christensen said, is to measure temperatures with great precision all over each asteroid that the Lucy spacecraft visits.

"By mapping how temperatures vary by the local time of day," Christensen explained, "we can map the surface properties of these previously unknown objects."

That will help planetary scientists decipher their histories and how they have changed since the solar system's early days.

"With each new mission," Christensen said, "we're expanding the types of solar system objects we're studying here are ASU."

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