Astronomical observations of young protostars indicate that early planetary systems evolved from the dust in a protoplanetary disk very quickly - in under five million years. Such short timescales require very efficient mechanism(s) to transport material inward towards the central star, but the mechanism(s) that do this are uncertain. Several have been invoked, however, in which magnetic fields play a key role, either in the stellar wind or in the disk itself.
Astronomers cannot currently directly measure magnetic field strengths in planet-forming regions, but experiments on meteoritic materials in our own Solar system can potentially constrain the strength of early Solar nebular magnetic fields. Chondrules are millimeter-sized constituents of primitive meteorites that formed in brief heating events in the young solar nebula. They probably constitute a significant fraction of the mass of asteroids and even of terrestrial planet precursors. The formation of chondrules, therefore, very likely occurred during a key stage in the evolution of the early solar system. If a stable field was present during their cooling off phase, they should themselves have become slightly magnetized. Determining their magnetic fields should therefore not only constrain models of their formation, but of the disk's evolution as well.
Among the most pristine known meteorites is one called Semarkona. It
contains chondrules of crystalline olivine which, due to their unique
compositional and magnetic properties, can retain their primitive
magnetization even over the eons since they formed and despite their
subsequent histories in the solar system. CfA astrophysicists Xue-Ning
Bai and Ron Walsworth, and their collaborators, isolated eight olivine
chondrules from the Semarkona meteorite; they are tiny, less than a
millimeter in size. Using newly perfected techniques that take advantage
of cryogenic quantum measurements developed in Walsworth's laboratory,
the team was able to detect magnetic fields in these minuscule crystal
samples, and to conclude that the primitive nebula in which these
chondrules formed had a field strength corresponding to about double the
Earth’s current magnetic field (at its surface). The scientists
conclude that the evidence supports the model of chondrules forming in
shocks or collisions between larger bodies, rather than any of the
stellar wind formation theories. They also conclude that the nebular
magnetic fields were large enough to account for the measured rates of
mass transport in the early evolutionary stages. Not least, the result
is an impressive application of newly perfected quantum measuring
techniques.
Reference(s):
"Solar
Nebula Magnetic Fields Recorded in the Semarkona Meteorite," Roger R.
Fu, Benjamin P. Weiss, Eduardo A. Lima, Richard J. Harrison, Xue-Ning
Bai, Steven J. Desch, Denton S. Ebel, Clement Suavet, Huapei Wang, David
Glenn, David Le Sage, Takeshi Kasama, Ronald L. Walsworth, Aaron T.
Kuan, Science, in press, 2014
