The Solar System passed through a cool interstellar cloud about 2 million years ago, the study suggests

The cool, dense interstellar clouds of our Milky Way Galaxy are four to five orders of magnitude denser than their diffuse counterparts. A team of astronomers from Boston University, Harvard University and Johns Hopkins University has found evidence that two to three million years ago, our Solar System encountered one of these dense clouds, dense enough to interfere with the solar wind. .

Ofer and many others. They show that the interstellar medium through which the Sun has passed for the past two million years contains cold, compact clouds that can severely affect the heliosphere. Image credit: NASA / JPL-Caltech.

Most stars form winds and move through the interstellar medium around them.

This motion creates a sheath that protects the planets from the interstellar medium. The Sun’s shell is the heliosphere.

It’s made up of a steady stream of charged particles called the solar wind, which extends past Pluto and surrounds the planets in what astronomers call the local bubble.

It protects us from radiation and interstellar rays that can alter DNA, and scientists believe it’s one of the reasons life evolved on Earth.

According to the new study, the cold interstellar cloud compressed the solar system in a way that briefly placed Earth and other planets in the solar system outside the solar system’s influence.

„Our paper is the first to benchmark that there was an encounter between the Sun and something outside the solar system that could have affected Earth’s climate,” said Professor Merav Ober of Boston University.

„Stars are moving, and now this paper shows not only that they are moving, but that they are undergoing drastic changes.”

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To study this phenomenon, Professor Ofer and colleagues looked back in time, using sophisticated computer models to visualize where the Sun was two million years ago – as well as the heliosphere and other parts of the Solar System.

They also mapped the path of a local ribbon system of cold clouds, a string of large, dense, very cold clouds composed mostly of hydrogen atoms.

Their simulations show that one of the clouds near the tip of that ribbon, dubbed the Local Links of Cold Cloud, may have collided with the heliosphere.

If that had happened, Earth would have been fully exposed to the interstellar medium, where gas and dust mix with the remaining nuclear components of exploded stars, including iron and plutonium.

Normally, the heliosphere filters out most of these radioactive particles. But without protection, they can easily reach the earth.

According to the paper, this is consistent with geological evidence showing simultaneous increases in iron-60 and plutonium-244 isotopes in the oceans, the Moon, Antarctic ice and ice sheets.

The timing also matches the temperature records indicating the cooling period.

„Our region of space beyond the solar system rarely affects life on Earth,” said Harvard University professor Avi Loeb.

„It’s exciting to discover that our passage through dense clouds a few million years ago may have exposed Earth to a very large 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 surroundings.”

„The external pressure of the cold cloud’s local lynx can continue to block the heliosphere for a couple of hundred years to a million years, depending on the size of the cloud.”

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„But once Earth moved away from the cold cloud, the heliosphere engulfed all the planets, including Earth.”

„The exact effect the cold clouds had on Earth is unknown—if it triggered an ice age.”

„But there are some other cold clouds in the interstellar medium that may have met in the billions of years since the birth of the Sun.”

„And it will stumble in a million years.”

The authors are now working to determine where the sun was seven million years ago.

Pinpointing the location of the Sun and its cool cloud structure over the last several million years is made possible by data collected by ESA’s Gaia mission, which creates the largest 3D map of the galaxy and provides an unprecedented look at the speed of stars. move.

„This cloud actually existed in our past, and if we pass through a massive one, we will be exposed to the interstellar medium,” Professor Ober said.

“This is just the beginning. We hope this paper opens the door to further study of how the Solar System was affected by external forces in the deep past and how these forces shaped life on our planet.

The Paper Published today in the newspaper Natural Astronomy.


M. Uber and many others. Earth’s direct exposure to the cold dense interstellar medium 2–3 Myr ago. Nat Astron, published online June 10, 2024; doi: 10.1038/s41550-024-02279-8

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