Origin of enormous troughs on giant asteroid Vesta revealed

Scientists have been trying to determine the origin of unusual troughs on asteroid Vesta since their discovery just last year.

Last Updated: Sep 27, 2012, 16:50 PM IST

Washington: Scientists have been trying to determine the origin of unusual troughs on asteroid Vesta since their discovery just last year.

Now, a new analysis supports the notion that the troughs are faults that formed when a fellow asteroid smacked into Vesta’s south pole.

The research reinforces the claim that Vesta has a layered interior, a quality normally reserved for larger bodies, such as planets and large moons.

Asteroid surface deformities are typically straightforward cracks formed by crashes with other asteroids. Instead, an extensive system of troughs encircles Vesta, the second most massive asteroid in the solar system, about one-seventh as wide as the Moon.

The biggest of those troughs, named Divalia Fossa, surpasses the size of the Grand Canyon by spanning 465 kilometers (289 miles) long, 22 km (13.6 mi) wide and 5 km (3 mi) deep.

The origin of these troughs on Vesta has puzzled scientists. The complexity of their formation can’t be explained by simple collisions.

New measurements of Vesta’s topography, derived from images of Vesta taken by NASA’s Dawn spacecraft last year, indicate that a large collision could have created the asteroid’s troughs.

But, this would only have been possible if the asteroid is differentiated -- meaning that it has a core, mantle and crust -- said Debra Buczkowski of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.

Because Vesta is differentiated, its layers have different densities, which react differently to the force from the impact and make it possible for the faulted surface to slide, she added.

“By saying it’s differentiated, we’re basically saying Vesta was a little planet trying to happen,” she said.

Most asteroids are pretty simple. “They’re just like giant rocks in space,” said Buczkowski. But previous research has found signs of igneous rock on Vesta, indicating that rock on Vesta’s surface was once molten, a sign of differentiation. If the troughs are made possible by differentiation, then the cracks aren’t just troughs, they’re graben.

A graben is a dip in the surface that forms when two faults move apart from each other and the ground sinks into the widening gap, such as in Death Valley in California. Scientists have also observed graben on the Moon and planets such as Mars.

The images from the Dawn mission show that Vesta’s troughs have many of the qualities of graben, said Buczkowski.

For example, the walls of troughs on simpler asteroids such as Eros and Lutetia are shaped like the letter V. But Vesta’s troughs have floors that are flat or curved and have distinct walls on either side, like the letter U -- a signature of a fault moving apart, instead of simple cracking on the surface.

The scientists’measurements also showed that the bottoms of the troughs on Vesta are relatively flat and slanted toward what’s probably a dominant fault, much as they are in Earth-bound graben.

These observations indicate that Vesta is also unusually planet-like for an asteroid in that its mantle is ductile and can stretch under a lot of pressure.

There are other qualities of Vesta that could be clues to how the troughs formed. For example, unlike the larger asteroid Ceres, Vesta is not classified as a dwarf planet because the large collision at its south pole knocked it out of its spherical shape, said Buczkowski.

It’s now more squat, like a walnut. But if Vesta has a mantle and core, that would mean it has qualities often reserved for planets, dwarf planets and moons -- regardless of its shape.

Buczkowski said scientists will continue to sort that data out and improve on computer simulations of Vesta’s interior.

Her team’s research will be published online in Geophysical Research Letters, a journal of the American Geophysical Union.