where the sun was positioned two million years in the past—and, with it, the heliosphere, and the rest of the solar system. They also mapped the path of the Local Ribbon of Cold Clouds system, a string of large, dense, very cold clouds mostly made of hydrogen atoms.
Their simulations showed that one of the clouds close to the end of that ribbon, named the Local Lynx of Cold Cloud, could have collided with the heliosphere.
If that had happened, says Opher, Earth would have been fully exposed to the interstellar medium, where gas and dust mix with the leftover atomic elements of exploded stars, including iron and plutonium.
Normally, the heliosphere filters out most of these radioactive particles. But without protection, they can easily reach Earth. According to the paper, this aligns with geological evidence that shows increased 60Fe (iron 60) and 244Pu (plutonium 244) isotopes in the ocean, on the moon, Antarctic snow, and ice cores from the same time period. The timing also matches with temperature records that indicate a cooling period.
“This paper is the first to quantitatively show there was an encounter between the sun and something outside of the solar system that would have affected Earth’s climate,” says Opher, who is an expert on the heliosphere.
Wow, another twist on the past and ice ages. As I said before, what happens in space matters.
I love the name. The Galactic Death Cloud comes to mind, too.
There is precedence.