Interstellar Winter: Did Galactic Clouds Cause An Ice Age On Earth?

Earth’s weather changes based on where it is in its annual cycle around the Sun – but is it possible the climate can also be affected by the solar system’s position in its orbit around the center of the Milky Way? A new study suggests an ice age period about two million years ago may have been triggered by a kind of interstellar winter. Much like Earth’s magnetic field protects the surface from dangerous radiation from the Sun, the Sun actually protects Earth and the other planets from interstellar cosmic rays.

The solar wind creates a kind of bubble called the heliosphere, which extends 130 Astronomical Units from the Sun – for reference, Earth is 1 AU away, and even Pluto is less than 40 AU out.

What could overpower the Sun so dramatically? Cold clouds of gas drifting around the galaxy have been calculated to be at least 10,000 times denser than the usual interstellar medium, and if the solar system passed through one that pressure could theoretically shrink the heliosphere.

The scientists simulated this scenario, and found the cloud could have blocked the heliosphere for anywhere from a few centuries to a million years, leaving Earth fully exposed to particles in the cloud during that time.

“It is exciting to discover that our passage through dense clouds a few million years ago could have exposed the Earth to a much larger flux of cosmic rays and hydrogen atoms. Our results open a new window into the relationship between the evolution of life on Earth and our cosmic neighbourhood.”

Other studies have linked Earth cycles with events happening on a galactic scale.