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Two asteroid missions get nod from NASA

Artist’s concepts of the Lucy and Psyche missions. Credit: SWRI and SSL/Peter Rubin

NASA has selected two robotic missions to visit asteroids in the early 2020s from a field of proposed interplanetary probes, approving projects to explore a metallic relic from the early solar system and a half-dozen so-called Trojan objects left over from the formation of the outer planets.

The Lucy and Psyche spacecraft will join NASA’s line of cost-capped Discovery missions, a program under which the agency’s Mars Pathfinder rover, the Messenger mission to orbit Mercury, and the Dawn probe currently orbiting the dwarf planet Ceres were developed, built and launched.

Picked from a slate of 28 proposals submitted to NASA in 2014, Lucy and Psyche will visit worlds never before seen close-up as scientists seek to sort out the violent early history of the solar system, in which proto-planets coalesced from mergers and collisions between rocks and boulders in a disk around the sun.

Lucy will launch in October 2021 on a preliminary trajectory to escape the bonds of Earth’s gravity, then return for flybys to use the planet’s gravity to slingshot toward the mission’s targets in the asteroid belt and beyond.

The probe’s first destination in April 2025 will be the asteroid DonaldJohanson, named for the paleoanthropologist who discovered the fossil of Lucy, a human ancestor whose partial skeleton was discovered in Ethiopia in 1974. The Lucy spacecraft will then head as far as 5 billion miles (8 billion kilometers) from the sun on a series of high-speed passes through groups of Trojan asteroids, primitive worlds trapped by Jupiter’s gravity in swarms ahead of and behind the giant planet’s path.

Lucy will fly by at least six Trojan asteroids at close range from August 2027 through March 2033, the first time a spacecraft has visited a member of the Trojan population, which some scientists estimate may number in the hundreds of thousands of objects.

“Lucy is a flyby mission,” said Harold Levison, the mission’s principal investigator from the Southwest Research Institute in Boulder, Colorado. “Lucy fits in with NASA’s history of exploration — first you do flybys, then you do rendezvous and then you do landings. In our case, in order to cover the diversity that we need to cover, we need to move quickly through the Trojan swarms to cover a lot of real estate, and that means that we’re doing flybys only.”

The Jupiter Trojans may hold clues about the evolution of the solar system, especially the outer planets and the formation of Jupiter and its moons, scientists said. The frozen mini-worlds could be time capsules, keeping the characteristics they had more than 4 billion years ago, before scientists believe the immense pull of Jupiter’s gravity trapped them in their current locations.

Because of their distance from Earth, fragments from the Jupiter Trojans have never fallen to the ground as meteorites, robbing scientists of any insight into their history and make-up.

“These objects are totally unknown,” Levison said. “Not only are they unknown because we’ve never really visited them with a spacecraft, unlike almost every other small body population in the solar system, these objects do not contribute to the meteorite record on Earth. Comets, main belt asteroids, near-Earth asteroids, all are contributing, but not Trojans because of their proximity to Jupiter’s orbit.”

The Psyche mission, named for its destination, will depart Earth in October 2023. Its trajectory will take the spacecraft on gravity assist flybys around Earth and Mars in 2024 and 2025, then to the asteroid Psyche in 2030, where the probe will enter orbit for at least 12 months of detailed measurements and observations.

“Psyche is a small world that’s made entirely of iron-nickel metal,” said Linda Elkins-Tanton, the Psyche mission’s principal investigator from Arizona State University. “Humankind has visited rocky worlds, and icy worlds, and worlds made of gas, but we have never seen a metal world. Psyche has never been visited or had a picture taken that was more than a point of light, so it’s apperance remains a mystery. This mission will be true exploration and discovery.”

Asteroid Psyche resides in the outer part of the main asteroid belt between the orbits of Mars and Jupiter, with an average distance of around 2.7 billion miles (4.3 billion kilometers) from the sun, three times farther than the Earth. Telescopic observations indicate Psyche is about 186 miles (300 kilometers) in diameter, but its topography and shape remain a mystery.

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Follow Stephen Clark on Twitter: @StephenClark1.

Source: Space Flight

Two asteroid missions get nod from NASA

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