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New images of protoplanet Vesta reveal mountain bigger than Everest

Planetary scientists are getting an initial look at the protoplanet Vesta via NASA's Dawn mission, revealing a surprising range of features – including long parallel troughs around the equator.

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Perhaps Vesta's most striking feature is an enormous impact basin at its south pole, notes Paul Schenk, a researcher at the Lunar and Planetary Institute in Houston and a member of Dawn's science team.

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Hints of something unusual there appear in Hubble images taken in the late 1990s.

Now it appears the feature might qualify as one of the Seven Wonders of the Solar System. The basin is nearly 300 miles across and between 12 and 15 miles deep. In its center sits the asteroid belt's version of Mt. Everest – a mountain whose base spans just over 100 miles and whose summit soars an average of about 13 miles above the surrounding terrain.

"It's one of the deepest impact craters we've seen in the solar system," he says, adding that it hosts one of the biggest mountains yet found in the solar system.

As if that wasn't enough to suggest Vesta had a rough childhood, the impact basin, dubbed Rhea Silvia, sits atop an older basin of somewhat smaller diameter. "We didn't expect this," Dr. Schenk says, noting that the team has also identified several other, older impact basis north of Rhea Silvia.

One reason the basins are of interest: Researchers hold that meteorites exhibiting a wide range of ages known as HED meteorites come from Vesta. Scientists hope to be able to associate these with some of the impact features they see on Vesta.

Vesta has adorned its surface with another puzzle: long, parallel troughs that look as though some giant held the protoplanet in one hand, turned it slowly, then repeatedly allowed its fingertips to trace the pattern along Vesta's equator.

The troughs have steep, scarp-like walls, flat floors up to 15 miles wide, and stretch up to two-thirds of the way around the sphere.

Vesta's northern hemisphere boasts troughs as well, although they appear more time-worn, says Debra Buczkowski, a planetary geologist at the Johns Hopkins University's Applied Physics Laboratory in Laurel, Md. One of these is roughly 24 miles wide.

As if to underscore Vesta's in-between status, she notes that in some ways the fractures "are behaving like the fractures we would expect on an asteroid. But the sheer scale of them is more similar to what we would see on a planet."

In many ways, these observations are warm-ups. Dawn's instruments carried out these and other measurements during a 21-day survey phase, orbiting some 1,700 miles above Vesta. The craft has now dropped to a 420-mile-high orbit and will begin its lowest-altitude passes – less than 110 miles up – in December.

With each step down the orbital ladder toward Vesta, researches say they expect more remarkable surprises as they map its topography and the minerals it holds.

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