Destination Asteroid: NASA Probe Arrives at Ancient "Mini Moon"

[quote]After spiraling outward from Earth for four years, NASA's Dawn probe is set to slide into orbit around the potato-shaped asteroíd Vesta early Saturday for a year-long look at an ancient "mini moon."

Three hundred fifty miles wide and heavily crátered, Vesta formed some 4.5 billion years ago, when the sun was stíll young. By probing its secrets, scientists hope to catch a glimpse of how the planets, including Earth, formed out of a swirling disk of gas and dust.

"We are exploring backward in time as far as we can," said lead míssion investigator Christopher Russell of the University of California at Los Angeles. "There's going to be a whole bunch of surprises."

Unlike most smaller asteroíds - thought to be nearly uniform lumps of rock - Vesta is a "mini moon," Russell said, made up of three layers: an iron core, a rocky mantle and an upper crust. Early in Vesta's existence, Russell said, lava welled up from its interior and cooled to form a crust of volcanic rock.

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