In Depth

NASA missions aim at asteroid oddballs

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Science  13 Jan 2017:
Vol. 355, Issue 6321, pp. 117
DOI: 10.1126/science.355.6321.117-a

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On 4 January, the agency picked two $450 million missions for Discovery, its low-cost planetary program, and, like several recent probes, both target small bodies. Set for a 2021 launch, Lucy will fly past Jupiter's Trojan asteroids, which share the gas giant's orbit but precede and follow it. Two years later, Psyche will set out for a rare iron and nickel asteroid of the same name. Little is known about Lucy's targets, but the Trojans appear to be too diverse to be simply leftovers from Jupiter's formation. Psyche will orbit the stripped-bare, metallic core of an embryonic planet. The selection of two missions helps the Discovery program get back on track after delays to its most recent selection, the InSight probe to Mars.