NASA missions come packaged two ways. They're either deep explorations of the familiar---STEREO's focus on the sun, the International Space Station's study of what microgravity does to the human body---or a trip to some crazy place no one has ever seen before. But still, any strange, distant object the agency targets will likely hold some clue about the origins of life. Humans are spacefaring narcissists that way.
NASA's newly announced Lucy and Psyche missions fall squarely into the second category. The robotic missions, planned to launch in 2021 and 2023 respectively, are set to target mysterious, unstudied asteroids. Lucy will follow NASA's Juno mission out to Jupiter to study the Trojan asteroids orbiting with the gas giant, and Psyche will visit an odd metal asteroid, 16 Psyche, in the main asteroid belt---the only object of its kind in our solar system. Both missions hope to build on scientists' understanding of the history of the solar system, its planets, and, of course, life. Psyche may solve some space exploration problems, too. Because a metal asteroid? Sure sounds like a good place to mine.
Both Lucy and Psyche are the most recent missions of the long-running NASA Discovery program, which specializes in missions that are quick, focused, and inexpensive---capped at just $450 million each. Lucy and Psyche beat out a number of Venus-related planetary science proposals (we can already smell that beefcooking), and to be honest, it's clear why.
"Small bodies are really the fossils of planetary formation," says Hal Levinson, a planetary scientist at the Southwest Research Institute and Lucy's principal investigator, in a NASA press conference. Small objects like asteroids and comets are the building blocks of the universe, dating back to the solar system's infancy. Lucy and Psyche's targets have been whizzing around since the Sun was just 10 million years old. Venus ain't got nothing on that.
The Trojan asteroids around Jupiter---named after heroes of the Trojan war---are a vast swarm trapped by Jupiter's gravity. But rather than orbit Jupiter, they share Jupiter's orbit, with one half leading and the other trailing the planet on its trip around the sun. "It's the last never-before-explored population of objects this side of Pluto," says Alan Stern, New Horizons' principal investigator. The mission builds on the work Stern and his team did for New Horizons: According to Stern, much of the team and instrument payload are direct carryovers from the Pluto-bound mission. Asteroid mission whizzes from the OSIRIS-REx are helping out too.
Which isn't to say Lucy isn't breaking new ground with the Trojan asteroids. "One of the surprising aspects about the population is its diversity in color and spectra," says Levinson. That diversity points to the bodies forming in different areas of the solar system with distinct characteristics. Which is why Lucy is going to six of them. "In the history of unmanned exploration we have only visited six main belt asteroids, and that has revolutionized our understanding of the solar system," says Levinson. Studying so many new asteroids at the same time could provide a great leap forward.
Out in the main asteroid belt, 16 Psyche is in a class by itself. It is the only large metal object in the entire solar system. And according to the best scientific guesses, that means it's probably the core of a planet so heavily bombarded that the rocky exterior broke away completely. "This is the only time a human being is ever going to see a core," says Lindy Elkins-Tanton, Psyche's principal investigator and planetary scientist at Arizona State University. "The best we’ve ever imaged it is as a point of light. We don't know what a metal world---its cliffs, its mountains, its impact craters---is going to look like."
When you add the potential planetary science discoveries to the possible gains for space exploration and asteroid mining, scientists start to get pretty psyched about Psyche. "I’m hoping we fill in a whole number of steps in how we get from dust and sand grains and to a planet," says Elkins-Tanton. "And find resources needed by humans as we explore further into the solar system." Specifically, 16 Psyche might have hydrated minerals from which astronauts could extract water. And chances are some of those metals will be worth mining.
Plus, both Psyche and Lucy will build on the asteroid orbiting knowledge scientists have gained in planning and executing missions like OSIRIS-REx, Rosetta, and Dawn, making these small bodies even likelier to be the spacefaring leapfrog points of the future. Which doesn't mean that the path forward for these missions will be easy---both are still challenged by navigational and scientific unknowns. "We have to make science in the biggest increments we can," says Elkins-Tanton. "We're aiming toward big questions." Uncovering the origins of planets is a big ask, but in the 2020s, Psyche and Lucy will give it their best try.
