Meteorites smash into the planets in our solar system relatively frequently, releasing more energy, by orders of magnitude, than our planet’s largest earthquakes. Some scientists predict that if enough energy from these impacts reaches the Earth’s core, it could disturb the geodynamo—a self-sustaining process that generates the magnetic field.
Researchers have examined several small craters around the globe but, so far, have found no evidence that the impacts perturbed the magnetic field. Now, scientists have turned their attention to the Manicouagan crater—one of the largest impact craters on Earth—to find out if a greater amount of energy release might be enough to rattle the dynamo. The crater formed in the Late Triassic, roughly 214 million years ago, when a meteor as large as 6 kilometers wide crashed into what is today Québec, Canada.
In the mid-1990s, companies began exploring the crater for mineral deposits, and although the search has so far proved fruitless, the 1.5-kilometer-deep holes drilled beneath the crater have given scientists a unique view into the crater’s deep structure.
Here Eitel et al. carried out a paleomagnetic study of rocks from the crater. When a meteorite hits the Earth, it creates intense heat and pressure that can melt the shocked region. As the melt slowly solidifies, magnetic minerals in the newly created rock record the orientation of the Earth’s magnetic field at that location. To find out how the magnetic field changed over time, the team collected 198 samples from 25 sites throughout the crater, on top of the material obtained from the mining companies, and then measured the samples’ magnetic signals back in the lab.
Their study found that the magnetic direction and intensity recorded in all the Manicouagan crater rocks were remarkably similar—detecting no erratic changes in the magnetic field over a several-thousand-year time span immediately following impact. The authors concluded that the energy released during formation of the massive Manicouagan impact crater was too weak to affect the geodynamo.
Also, the authors note, given the size and well-preserved state of Manicouagan, it is unlikely that researchers will find a more suitable crater on Earth to further test the hypothesis. However, that doesn’t mean it’s impossible for a meteorite strike to disturb a planet’s magnetic field: Although the Manicouagan crater is large by Earth standards—no known craters have rim diameters greater than 200 kilometers across—it is quite small compared to craters throughout the solar system. Impact basins on the Moon and other planets can be thousands of kilometers wide. (Journal of Geophysical Research: Solid Earth, doi: 10.1002/2015JB012577, 2016)
—Kate Wheeling, Freelance Writer
Citation: Strelich, L. (2016), Can meteorite impacts disturb a planet’s magnetic field?, Eos, 97,doi:10.1029/2016EO045105. Published on 8 February 2016.