Hidden Magnetic Patterns Inside Meteorites Reveal Secrets of The Early Solar System
The solar system is downright miserable with magnetic fields. They envelop (most of) the planets and their moons, which interact with the system-wide magnetic field emanating from the sun.
Although invisible to the naked eye, these magnetic fields leave their mark. For example, the earth’s crust is interspersed with magnetic materials that store a paleomagnetic record of the planet’s changing magnetic field. And meteorites, if we’re lucky enough to find them, can tell us about the magnetic field in the environment where they formed billions of years ago.
Most of the meteorites that we study in this way come from the asteroid belt that lies between Mars and Jupiter. But Japanese astronomers have just developed a new means of studying the magnetic material in meteorites from far, far away – providing a new tool for understanding the outer reaches of the early solar system.
“Primitive meteorites are time capsules made of primordial material that were formed at the beginning of our solar system,” said astronomer Yuki Kimura from the Institute of Low Temperature Science at Hokkaido University in Japan.
“To understand the physical and chemical history of the solar system, it is crucial to analyze different types of meteorites from different origins.”
The technique is known as paleomagnetic electron holography in the nanometer range. It uses the powerful technique of electron holography, which examines the interference patterns created by electron waves in a material to understand the structure of that material. On the nanoscale, this creates very high-resolution data.
They then applied this technique to a very special meteorite called the Tagish Lake meteorite. This meteorite fell to Earth in 2000 and was recovered very quickly thereafter, which means that it is unlikely to be significantly altered by the environment in which it fell.
Previous analysis suggested that the meteorite was unusually pristine and formed about 4.5 billion years ago – just a few million years after the sun was formed. Its trajectory suggests it traveled to Earth from the region of the asteroid belt, and the reconstruction suggests that it was about 4 meters (13 feet) tall before it entered the atmosphere.
It also contains magnetite. If this meteorite was hot and melted, all external magnetic fields would have changed and aligned the magnetite along its field lines. As the rock cooled and hardened, these alignments would have set and left a fossil record of this magnetic field.
Based on their electron holographic imaging and numerical simulations, Kimura’s team was able to deduce the story of the Tagish Lake meteorite.
They found that the mother body of the meteorite formed in the Kuiper Belt, the icy region beyond Neptune, about 3 million years after minerals formed in the solar system. There it grew to a size of about 160 kilometers (100 miles) in diameter.
From that point on, it migrated inward toward the asteroid belt, possibly due to disruption from Jupiter’s migration, a process that wreaked some gravitational devastation in the solar system.
During this process – about 4-5 million years after the formation of minerals – the Tagish meteorite was hit by a body about 10 kilometers in diameter that was moving at a speed of about 5 kilometers per second.
According to the team, the magnetite inside the meteorite formed when the mother body heated up to around 250 degrees Celsius due to the radiogenic internal heating combined with the heat of the impact. Then it just hung around, being its original self, until it finally crashed to earth.
This gives rise to new clues as to how the solar system came into being as it is today – a largely mysterious process. The team is now applying its technique to samples from the asteroid Ryugu recovered by the Hayabusa2 probe in hopes of revealing more.
“Our results help us infer the early dynamics of the solar system bodies, which occurred several million years after the solar system was formed, and imply highly efficient formation of the solar system’s outer bodies, including Jupiter,” said Kimura.
“Our nanometer-scale paleomagnetic method will reveal a detailed history of the early solar system.”
The research was published in the Astrophysical Journal.