Image: ALHA81001
This image shows the crystal structure in the eucrite meteorite ALHA81001, which has been traced to Vesta. The image from the MIT Paleomagnetism Laboratory and the MIT Experimental Petrology Laboratory represents a 0.5 by 0.35 mm section of the meteorite as seen under backscatter electron microscopy.
updated 10/11/2012 9:30:00 PM ET 2012-10-12T01:30:00

Vesta, the brightest asteroid in the solar system, apparently possessed a magnetic field in its infancy that shielded it from the ravages of energetic particles from the sun, researchers say.

The finding could help solve the mystery of why Vesta's surface appears so bright, they add.

Vesta is the second-most-massive asteroid in the solar system, a behemoth 330 miles wide (530 kilometers) that is sometimes visible to the naked eye on Earth. The only asteroid that's more massive is Ceres, which is also classified as a dwarf planet.

Recent evidence suggests that, like Earth, Vesta is divided into a core, mantle and crust, supporting the theory that the giant asteroid is protoplanetary material known as a planetesimal that never fully developed into a planet. Recent scans from NASA's Dawn spacecraft hint that Vesta's metallic core is about 135 miles (220 kilometers) wide and takes up 5 percent to 25 percent of its total mass. [Latest Photos of Asteroid Vesta]

Vesta occasionally experiences collisions, probably with other members of the solar system's main asteroid belt, which lies between the orbits of Mars and Jupiter. These impacts can knock rocks off Vesta, with some of them plummeting to Earth as meteorites.

For the new study, scientists analyzed samples from a shiny black meteorite recovered in 1981 in hills at the end of the Transantarctic Mountains in Antarctica. The rock's oxygen isotope levels matched those astronomers have seen on Vesta, suggesting it originated on that asteroid long ago.

Magnetized crystals within the meteorite suggest Vesta once had a magnetic field strong enough to leave an imprint on its surface rocks. Argon isotopes within the meteorite help pin down its age, suggesting that the asteroid's crust was still magnetized 3.69 billion years ago. (If Vesta had a magnetic field, it probably died well before that, once Vesta's core cooled and slowed.)

The researchers suggest Vesta had a spinning liquid metallic core early in its history. This apparently generated a dynamo, resulting in a magnetic field at least 2 microteslas in strength and perhaps as strong as 10 to 100 microteslas. In comparison, Earth's surface magnetic field is about 30 to 60 microteslas.

"Up to now, it was uncertain if small bodies like asteroids could harbor a dynamo like that observed on larger planets such as Earth,"  lead study author Roger Fu, a planetary scientist at the Massachusetts Institute of Technology, told "It's good to be able to confirm models that said it was possible."

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The researchers think Vesta's ancient magnetic field may have shielded the asteroid from scouring by winds of electrically charged particles from the sun. This could help explain why its surface is so bright — the solar wind normally would darken the asteroid over time.

These findings could help researchers learn more about how the building blocks of the rocky planets grew and evolved.

"Earth and the other terrestrial planets are made of objects like Vesta," Fu said. "The coolest thing to me is that we're learning more and more about planetesimals, about this critical stage in the early solar system."

Fu and his colleagues plan on looking at ancient meteorites to see if magnetic fields were present before even planetesimals formed in the solar system's protoplanetary disk. They detail their findings in Friday's issue of the journal Science.

Follow for the latest in space science and exploration news on Twitter @Spacedotcomand on Facebook.

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Gallery: The new solar system

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Photos: Month in Space: January 2014

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  1. Southern stargazing

    Stars, galaxies and nebulas dot the skies over the European Southern Observatory's La Silla Paranal Observatory in Chile, in a picture released on Jan. 7. This image also shows three of the four movable units that feed light into the Very Large Telescope Interferometer, the world's most advanced optical instrument. Combining to form one larger telescope, they are greater than the sum of their parts: They reveal details that would otherwise be visible only through a telescope as large as the distance between them. (Y. Beletsky / ESO) Back to slideshow navigation
  2. A balloon's view

    Cameras captured the Grandville High School RoboDawgs' balloon floating through Earth's upper atmosphere during its ascent on Dec. 28, 2013. The Grandville RoboDawgs’ first winter balloon launch reached an estimated altitude of 130,000 feet, or about 25 miles, according to coaches Mike Evele and Doug Hepfer. It skyrocketed past the team’s previous 100,000-feet record set in June. The RoboDawgs started with just one robotics team in 1998, but they've grown to support more than 30 teams at public schools in Grandville, Mich. (Kyle Moroney / AP) Back to slideshow navigation
  3. Spacemen at work

    Russian cosmonauts Oleg Kotov, right, and Sergey Ryazanskiy perform maintenance on the International Space Station on Jan. 27. During the six-hour, eight-minute spacewalk, Kotov and Ryazanskiy completed the installation of a pair of high-fidelity cameras that experienced connectivity issues during a Dec. 27 spacewalk. The cosmonauts also retrieved scientific gear outside the station's Russian segment. (NASA) Back to slideshow navigation
  4. Special delivery

    The International Space Station's Canadian-built robotic arm moves toward Orbital Sciences Corp.'s Cygnus autonomous cargo craft as it approaches the station for a Jan. 12 delivery. The mountains below are the southwestern Alps. (NASA) Back to slideshow navigation
  5. Accidental art

    A piece of art? A time-lapse photo? A flickering light show? At first glance, this image looks nothing like the images we're used to seeing from the Hubble Space Telescope. But it's a genuine Hubble frame that was released on Jan. 27. Hubble's team suspects that the telescope's Fine Guidance System locked onto a bad guide star, potentially a double star or binary. This caused an error in the tracking system, resulting in a remarkable picture of brightly colored stellar streaks. The prominent red streaks are from stars in the globular cluster NGC 288. (NASA / ESA) Back to slideshow navigation
  6. Supersonic test flight

    A camera looking back over Virgin Galactic's SpaceShipTwo's fuselage shows the rocket burn with a Mojave Desert vista in the background during a test flight of the rocket plane on Jan. 10. Cameras were mounted on the exterior of SpaceShipTwo as well as its carrier airplane, WhiteKnightTwo, to monitor the rocket engine's performance. The test was aimed at setting the stage for honest-to-goodness flights into outer space later this year, and eventual commercial space tours.

    More about SpaceShipTwo on PhotoBlog (Virgin Galactic) Back to slideshow navigation
  7. Red lagoon

    The VLT Survey Telescope at the European Southern Observatory's Paranal Observatory in Chile captured this richly detailed new image of the Lagoon Nebula, released on Jan. 22. This giant cloud of gas and dust is creating intensely bright young stars, and is home to young stellar clusters. This image is a tiny part of just one of 11 public surveys of the sky now in progress using ESO telescopes. (ESO/VPHAS team) Back to slideshow navigation
  8. Fire on the mountain

    This image provided by NASA shows a satellite view of smoke from the Colby Fire, taken by the Multi-angle Imaging SpectroRadiometer aboard NASA's Terra spacecraft as it passed over Southern California on Jan. 16. The fire burned more than 1,863 acres and forced the evacuation of 3,700 people. (NASA via AP) Back to slideshow navigation
  9. Where stars are born

    An image captured by NASA's Spitzer Space Telescope shows the Orion Nebula, an immense stellar nursery some 1,500 light-years away. This false-color infrared view, released on Jan. 15, spans about 40 light-years across the region. The brightest portion of the nebula is centered on Orion's young, massive, hot stars, known as the Trapezium Cluster. But Spitzer also can detect stars still in the process of formation, seen here in red hues. (NASA / JPL-Caltech) Back to slideshow navigation
  10. Cygnus takes flight

    Orbital Sciences Corp.'s Antares rocket rises from NASA's Wallops Flight Facility on Wallops Island, Va, on Jan. 9. The rocket sent Orbital's Cygnus cargo capsule on its first official resupply mission to the International Space Station. (Chris Perry / NASA) Back to slideshow navigation
  11. A long, long time ago...

    This long-exposure picture from the Hubble Space Telescope, released Jan. 8, is the deepest image ever made of any cluster of galaxies. The cluster known as Abell 2744 appears in the foreground. It contains several hundred galaxies as they looked 3.5 billion years ago. Abell 2744 acts as a gravitational lens to warp space, brightening and magnifying images of nearly 3,000 distant background galaxies. The more distant galaxies appear as they did more than 12 billion years ago, not long after the Big Bang. (NASA / NASA via AFP - Getty Images) Back to slideshow navigation
  12. Frosty halo

    Sun dogs are bright spots that appear in the sky around the sun when light is refracted through ice crystals in the atmosphere. These sun dogs appeared on Jan. 5 amid brutally cold temperatures along Highway 83, north of Bismarck, N.D. The temperature was about 22 degrees below zero Fahrenheit, with a 50-below-zero wind chill.

    Slideshow: The Year in Space (Brian Peterson / The Bismarck Tribune via AP) Back to slideshow navigation
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