One aspect of planetary formation has remained enigmatic. Observations of young star systems indicate that it usually takes less than five million years for the star’s planets to form—perhaps much less. For that to happen, there must be a really efficient mechanism to bring mass into the protoplanetary disk in which the planets form. Gravity alone doesn’t account for it happening so quickly.

Theoretical explanations abound for the fast accretion of material, some of which involve its interactions with a solar system's magnetic field. Until now, there’s been no way to test these models or determine the role of a magnetic field. By examining a meteorite, however, researchers found indications that the magnetic field in the early Solar System was sufficient to account for the short accretion time.

The researchers studied a meteorite called Semarkona, which was filled with olivine-bearing chondrules. Chondrules are round grains that form as molten droplets but later accrete into the meteoroid they’re found in.

The chondrules in Semarkona likely formed during a brief heating event in the early proto-Solar System nebula, and it would have preserved indications of any magnetic field that was present. The olivine chondrules are very resistant to remagnetization, so it’s unlikely that they’ve been exposed to anything strong enough to significantly alter their magnetic field since then. “No known post-accretional process is likely to have compromised pre-accretional remanent magnetization in Semarkona dusty olivines,” the authors write in the paper.

This makes the chondrules extremely useful for learning about the magnetic conditions in the proto-Solar System. And, based on this study, the Semarkona meteorite's olivine chondrules provide strong evidence that a significant magnetic field was present in the early Solar System.

In addition to distinguishing among possible models of planetary formation, this also provides clues as to how the chondrules themselves formed. We know they’re formed in a short-lived heating event, but the new study suggests that the chondrules were likely formed either in planetesimal collisions or as shock waves passed through the nebula. Planetesimals were small planetary bodies that followed strange, irregular orbits in the early Solar System, colliding with each other and the growing planets. The alternative, heating by the rapidly evolving Sun of this period, would have left traces of a far stronger magnetic field.

New observations and studies like this continue to fill in our knowledge about the Solar system’s formation—and provide useful models that can help us understand exosolar systems.

Science, 2014. DOI: doi:10.1126/science.1258022 (About DOIs).