Before the sun fully formed, tiny bits of rock were already recording the magnetic forces present in the very early solar system. More than 4.5 billion years later, scientists have learned how to read that record.
The ancient rocks suggest that the turbulent cloud of gas and dust that gave rise to our solar system was shot through a powerful magnetic field. That field may have helped feed the growing sun, researchers report August 24 in the Proceedings of the National Academy of Sciences. The findings suggest gravity may not have acted alone to build our solar system or the countless other planetary systems in the Milky Way and beyond.
That ancient record is preserved in meteorites — time capsules of material that formed long ago. In particular, rocks that contain specific speckly mineral inclusions really turn back the clock. These inclusions solidified more than 4.5 billion years ago, before the sun and planets, says Cauê Borlina, a planetary scientist at Purdue University in West Lafayette, Ind. “They’re forming before everything else.”
Scientists have long debated whether the gas that makes up the sun was shepherded into place mainly by gravity or by a magnetic field. Previous studies suggest the presence of a solar system –wide magnetic field after the sun formed. What’s been much harder to determine is whether that field was already present during the sun’s earliest stages of formation, Borlina says.
He and his colleagues analyzed a meteorite that fell to Earth in 2008. The team focused on five inclusions containing iron, an element whose electrons readily rearrange to record magnetic fields. Using sensitive magnetometers, the researchers measured magnetic fields of a few gauss, a common unit of magnetism. That’s several times stronger than Earth’s current magnetic field.
Simulations of planetary system formation predict that stronger magnetic fields will transport more gas toward the nascent star, Borlina says. During the sun’s earliest, or Class 0, phase some models suggest it could have gobbled up more than 300 Earth masses of gas each year. The newly measured field is strong enough that magnetism could have contributed substantially to that feeding frenzy. “You can’t ignore the contribution of magnetism,” Borlina says.
These results provide an important look at the solar system’s very beginnings, says Indrani Das, a theoretical astrophysicist at the Academia Sinica Institute of Astronomy and Astrophysics in Taipei, Taiwan. “This is one of the first measurements that has been done of the Class 0 phase.”
Still, these findings need to be bolstered with measurements from other meteorites, Das says. “We need a bigger sample size.”
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