Moreover, the huge asteroid isn't just some chunk of uniform rock. Rather, it's now known to be a differentiated object with an iron core about 137 miles (220 km) wide. That's big enough, perhaps, to have once sustained a dynamo like the one that generates Earth's magnetic field, researchers said.
The team figured out the dimensions of Vesta's core in part by carefully tracking Dawn's movements through space, then using this information to calculate Vesta's mass, density and gravitational pull with unprecedented precision. [Video: Vesta Flyover in 3D]
Other Dawn data also back Vesta's protoplanet status. For instance, its surface composition implies a complex geological history that's more similar to that of terrestrial planets than other asteroids, researchers said. And Vesta boasts color variations unlike anything seen on an asteroid before, further suggesting that the massive object is something special.
"We now know that Vesta is large enough to have had its own internal geologic evolution and is not just a battered lump of rock," said Paul Schenk of the Lunar and Planetary Institute in Houston, lead author of another of the new studies.
Two gigantic (and recent) impacts
Vesta's surface is pocked with craters from countless collisions over the eons. Dawn's observations have allowed scientists to reconstruct the protoplanet's impact history by counting these craters, and noting how many impact features overlie others.
Researchers found a huge difference between Vesta's northern and southern halves. The northern part retains a record of some of the asteroid's earliest impacts, while the south was "reset" by two enormous collisions far more recently.
One of these smashups occurred about 2 billion years ago, creating a 249-mile-wide (400-km) basin called Veneneia. But Veneneia was mostly obliterated about 1 billion years ago by another impact, which created the 314-mile (505-km) Rheasilvia crater.
"This basin erased at least half the surface and messed up a lot of the rest of it," Schenk told SPACE.com via email.
The Rheasilvia impact also created strange circular troughs around Vesta's equator and raised a central peak more than twice as high as Mount Everest, Russell said. And it excavated approximately 250,000 cubic miles (1.04 million cubic km) of material, much of which was blasted into space.
"Two hundred and fifty thousand cubic miles is enough to fill the Grand Canyon about a thousand times over," said David O'Brien, a Dawn scientist based at the Planetary Science Institute in Tucson, Ariz. "So this is a very large volume of material."
Both giant craters were likely caused by asteroids between 25 and 36 miles (40 to 60 km) wide, Schenk said. And both impacts seem to have occurred surprisingly late, several billion years after the presumed end of the so-called Late Heavy Bombardment that blasted many craters into Earth's moon and other solar system bodies.
More discoveries to come
The new results are based on data that Dawn gathered during the early stages of its stay at Vesta. The spacecraft will continue studying the protoplanet until Aug. 26, so we should expect more discoveries from the mission, researchers said.
"We have not yet reported on the high-resolution measurements made at low altitudes," Russell said. "We will be searching for water, just like there have been water searches on the moon."
Further, Vesta's far northern reaches have been in shadow thus far, so Dawn has been unable to study large chunks of the protoplanet. But that will change before too long.
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8 Comments
Add CommentIt would be interesting to see an article about proto-panets like Vesta and the moons of Saturn and Jupiter which are also identified as proto-planets - Like Dione. Where were they formed in the solar system, what are the relative sizes of their cores, their surface composition. Some of this must be possible now that both Jovian and Saturian systems have been surveyed extensively, especially Saturn with numerous moon flybys to date.
Reply | Report Abuse | Link to thisI agree with Algie ; these are some of the most fascinating objects in the Solar System ! But in that case, please make it a longer, more detailed article....
Reply | Report Abuse | Link to thisHenri
"please make it a longer, more detailed article...."
Reply | Report Abuse | Link to thisTry reading page 2 or 3, accessed by the links with the appropriate number below the text, or by clicking the 'Next' link in the same area of the page.
Now that that is settled, perhaps we can start strip mining the thing now? Drill, baby, drill.
Reply | Report Abuse | Link to thisWith the huge distance between mars and jupiter, and the aseroid belt contained there it seems possible that two planets may have collided and produced this belt. With some asteroids being "rocky" and others varying as partially or completly metalic suggests these formed in a process of planatary specific gravity/density like the Earth or Mars.
Reply | Report Abuse | Link to thisI have no data to support this theory, but maybe there is.
Dear «village geek», whatever made you think that I hadn't read all three pages of the above article regarding Vespa ? Whatever it was, you were sadly deluded. However, not being a member of the Tweeter generation, I do hope that any coming article on proto-planets will be alloted more than these three brief pages ; the subject certainly deserves that much....
Reply | Report Abuse | Link to thisHenri
Very cool discoveries...and more to come...
Reply | Report Abuse | Link to thisI hope for an asteroid with commercial value, for example, solid gold, that would spur the private sector into developing the means to capture it and drag it into earth orbit for exploitation. A real viable space race would be the result. Government doesn't have the incentive to get us to where many of us wish to be.
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