Asteroids, many of which are locked in orbits between Mars and Jupiter, are the rocky leftovers of planet formation. The outer planets continually stirred them up, preventing them from combining to form larger bodies. But where did they originally form? And what clues might they offer about the history of planetary migration in the early solar system? In one observation program, NASA’s upcoming James Webb Space Telescope will probe five bodies, three in the main asteroid belt and two Trojan asteroids, to shed new light on the drama that occurred billions of years ago.

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