October 12, 2012
Meteorite Shows Vesta Once Had Active Dynamo
Lee Rannals for redOrbit.com — Your Universe Online
Scientists have determined that the second-most-massive asteroid in the solar system may have once had an active dynamo.A meteorite found in Antarctica believed to be from Vesta holds clues to the asteroid once harboring a molten, swirling mass of conducting fluid generating a magnetic field, or dynamo.
Scientists suspect that the composition of asteroids offer information about the diversity of planetary bodies within the early solar system.
“We´re filling in the story of basically what happened during those first few million years of the solar system, when an entire solar system was dominated by objects like this,” Roger Fu, a graduate student in MIT´s Department of Earth, Atmospheric and Planetary Sciences (EAPS), and the study´s first author, said in a press release. “These bodies are really like miniature planets.”
Benjamin Weiss, an associate professor of planetary sciences in EAPS, said that with this information, Vesta could become the smallest known planetary object to have generated a dynamo.
The team set out first to determine the magnetization and the age of a meteorite sample, and then to check that its magnetic field was due to an early dynamo.
They obtained a meteorite sample from Vesta that was originally discovered in Antarctica back in 1981. The sample retains magnetic properties that scientists have been studying for years.
The team first looked at the rock's tiny crystals, and measured the alignment of these minerals, or the rock's magnetic "moment." The researchers demagnetized the rock until they found the magnetization they believed was the oldest remnant of a magnetic field. Next, they determined the age of the rock by analyzing the meteorite for evidence of argon, which is produced from the natural decay of potassium.
Scientists can heat the rock, and measure the amount of argon-40 released in order to try and determine its age. The more released, the older the rock is. This technique allowed scientists to determine that the Vesta meteorite is 3.7 billion years old.
The team believes that an early dynamo likely magnetized the surface of Vesta within the first 100 million years of the asteroid's history. When the meteorite formed 3.7 billion years ago, it would have become magnetized due to exposure to fields emanating from the surrounding crust.
Evidence for a dynamo on Vesta gives weight to the theory that other small bodies in the solar system may have also harbored similar dynamos.
“The moon´s ancient dynamo is given added credibility by this measurement,” Christopher Russell, a professor of geophysics and space physics at the University of California at Los Angeles (UCLA), said in a press release. “Another small body, Jupiter´s moon Ganymede, today appears to have an active dynamo in its core. This measurement makes that interpretation more credible as well.”
Fu said Vesta is interesting because it is one of the building blocks that eventually formed the planets. He said this is a remnant that is still preserved because it didn't end up forming a planet.
“It´s only 500 kilometers (310 miles) across, but it actually had many of the same global processes that the Earth has," Fu said in the release.
The researchers published their study in the journal Science.