Lucy will visit six of Jupiter’s Trojan asteroids, while Psyche will aim for the exposed, metal-rich core of an ancient protoplanet.
On Wednesday, NASA officially greenlit two new missions for its Discovery Program, an initiative that focuses on low-cost spaceflight endeavors (their development is capped at $450 million each) with high scientific yields.
The winning spacecraft are named Lucy and Psyche; Lucy is set to visit a whopping six Trojan asteroids, a class of space rocks in Jupiter's vicinity, while Psyche will journey to a curious world called 16 Psyche, thought to be the exposed metallic core of a protoplanet.
Both missions aim to expand our knowledge of the early solar system, when the Sun was a wee 10 million-year-old stellar infant. (It's a middle-aged 4.6 billion years old today.)
"These are true missions of discovery that integrate into NASA's larger strategy of investigating how the solar system formed and evolved," said Jim Green, NASA's planetary science director, in a statement.
"We've explored terrestrial planets, gas giants, and a range of other bodies orbiting the Sun," Green continued. "Lucy will observe primitive remnants from farther out in the solar system, while Psyche will directly observe the interior of a planetary body. These additional pieces of the puzzle will help us understand how the Sun and its family of planets formed, changed over time, and became places where life could develop and be sustained—and what the future may hold."
Jim Green announces two new Discovery Program missions. Video: NASA/YouTube
The plan is to launch Lucy in October 2021 for arrival at the main asteroid belt in 2025. From there, it will journey on to the Trojan asteroids, a diverse population of over 6,000 known objects that are thought to be relics from the genesis of the solar system. As Jupiter formed and found its orbit, the Trojans became gravitationally corralled within Lagrangian points both ahead and behind the gas giant's path around the Sun.
Lucy, which is named for the early hominid that has shed light on humanity's origins, will visit six of these unique objects between 2027 to 2033, studying them for clues about the origins of our larger cosmic neighborhood.
Psyche, meanwhile, is set for launch in 2023, an Earth gravity assist in 2024, and a Mars flyby in 2025. From there, it will travel to its target, arriving in 2030. With a diameter of 130 miles (210 kilometers), 16 Psyche is one of the largest asteroids known in the belt, and has long fascinated scientists due to its high iron and nickel content, which resembles the center of terrestrial planets like Earth. Scientists think 16 Psyche might have been a developing planet of its own in the early solar system, until it was bombarded down to its core by massive collisions with other objects.
"This is an opportunity to explore a new type of world—not one of rock or ice, but of metal," said the mission's principal investigator Lindy Elkins-Tanton in a statement. "16 Psyche is the only known object of its kind in the solar system, and this is the only way humans will ever visit a core. We learn about inner space by visiting outer space."
Both missions are headed for fascinating targets, no doubt, but the selection has drawn some criticism in the wider science community. Commentators have pointed out that the choice to fund Psyche, with its vast and valuable metal deposits, may well be a nod to the burgeoning asteroid mining industry. In a NASA telecon held on Wednesday, Elkins-Tanton said that indeed, 16 Psyche would be a good asset for future mining, calling it potentially the "perfect stepping stone to the outer solar system."
Meteorologist Eric Holthaus, science writer Rebecca Boyle, and geophysicist Mika McKinnon all expressed concerns on Twitter that these asteroid-focused Discovery trips are taking precedence over missions to worlds with atmospheres; missions that could help understand and even mitigate climate change on Earth.
This is especially obvious since Lucy and Psyche were selected from a field of five candidate projects outlined in fall 2015, which included two concepts to study Venus—arguably the most useful world for climate change studies outside of Earth.
Lucy and Psyche were also chosen over a proposal for a Near Earth Object Camera (NEOCam) which would vastly accelerate the rate at which potentially hazardous asteroids are discovered and characterized. But though it didn't select NEOCam this year, NASA said it would extend the project's provisional funding for another year, so perhaps it will also get the go-ahead down the line.
Discovery-class missions have developed a great track record so far; the past 12 include the Stardust trip to return a sample of a comet's dust trail, the Kepler space telescope, which has discovered thousands of exoplanets, and the New Horizons probe that visited Pluto in July 2015. Hopefully, Lucy and Psyche live up to the successes of their forebears.
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