By examining the properties of a primitive relic from our early solar system-- a meteorite that hit Earth more than 60 years ago-- scientists have gathered the first physical evidence that an intense magnetic field played a significant role in sculpting the spinning disk of dust and gas that gave rise to our solar system.
Some 4.6 billion years ago, our solar system began to take shape as the material from a collapsing cloud was drawn together by gravity, forming the beginnings of our sun. At the same time, motions within this cloud caused it to rotate, and it eventually flattened out into a swirling disk, called a protoplanetary disk, which served as the birthplace of our planets.
More than 99% of the mass within this primordial disk comprised ionized gas; the remainder consisted of particles of dust that began to coalesce as they crashed into each other, forming the initial seeds of terrestrial planets, moons and asteroids. Meanwhile, the cloud’s gas rapidly spiraled into the growing sun, leaving our star with 99% of the solar system’s mass.
Observations of young stars within our galaxy have led scientists to believe that this process of protoplanetary disk evolution occurred at a rapid rate, perhaps taking just a few million years for the disk to disappear. But what drove this incredible amount of gas into the sun within such a short time frame has remained a well-educated guess, although many theoretical models involved magnetic fields as a potential mechanism.
“Magnetic fields can introduce viscosity into the disk, essentially making the gas in it more sticky,” said study author Roger Fu. “This means gas of differing orbits interacts more strongly with each other, and more gas falls toward the star.”
Now, for the first time, MIT scientists have gathered experimental evidence that a powerful magnetic field did indeed play a significant role in molding the early protoplanetary disk and also helped drive immense amounts of gas into the newborn Sun.
For the study, which has been published in Science, the team analyzed a primitive meteorite that hit India in 1940. The rock formed around 4.5 billion years ago and, remarkably, it has preserved its properties from when it first formed, acting like a time capsule of our early solar system. Other meteorite samples studied previously have been of little use as they had been altered in some way, for example by heating or moisture, which erases the magnetic information.
They focused on tiny metallic grains within microscopic pellets called chondrules which, like a compass, aligned with the emerging solar system’s magnetic field. Using an extremely sensitive kind of magnetic field sensor, the scientists were able to measure both the magnetic orientations and strength of each grain.
Using these calculations, the researchers were able to determine that the chondrules were magnetized in a field of between 5 to 54 microteslas in strength. This means that the nascent solar system possessed a magnetic field that was approximately as strong as the Earth’s magnetic field, and up to 100,000 times stronger than what exists in interstellar space today. This, they concluded, was strong enough to propel gas from the protoplanetary disk towards the Sun at an extremely fast rate.
If the researchers can get their mitts on more well-preserved meteorites from different times and areas during solar system formation, then they may be able to extend this work and scrutinize the nature of the magnetic fields in protoplanetary disks.