The solar system passes through very cold clouds that changed the climate – DW – 06/10/2024

An interstellar cloud crossed the solar system two million years ago that was so dense and cold that it changed the climate on Earth, a discovery that shows the Sun’s position in space can influence Earth’s history to a much greater extent than previously thought.

This was confirmed by an international team of researchers, led by astrophysicist Merav Ofer, professor of astronomy at Boston University and a member of the Radcliffe Institute at Harvard University, and the results of their work. It is published in Nature astronomy.

Two million years ago, Earth was a very different place, where human ancestors coexisted with saber-toothed tigers, mastodons, and huge rodents, and the planet had fallen into a deep freeze, with multiple ice ages following one another until about 12,000 years ago.

The Earth and the Sun in the heliosphere "In the form of a croissant": The solar system was outside the heliosphere for a brief period two million years ago.
Earth and Sun in the “croissant-shaped” heliosphere: The solar system briefly fell out of the heliosphere two million years ago.Image: Illustration from the Harvard Radcliffe Institute

Scientists have theorized about the causes of ice ages, such as the planet’s tilt and rotation, changes in plate tectonics, volcanic eruptions, or levels of carbon dioxide in the atmosphere, but the new work suggests that these radical changes are only caused by the Earth’s environment, as well as The position of the sun in the galaxy.

Scientists have found evidence that about two million years ago, the solar system encountered an interstellar cloud so dense that it could have interfered with the solar wind.

Protective shield

The solar system is surrounded by a protective shield of plasma emanating from the sun, known as the heliosphere, and consists of a continuous flow of charged particles, called the solar wind, which extends beyond Pluto and envelops the planets in what is called a “giant bubble.”

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That bubble protects Earth from radiation, galactic rays that can alter DNA. Scientists believe this is partly why life on Earth evolved as it did. According to work published Monday, the cold cloud compressed the heliosphere in a way that put Earth and other planets in the system. Solar briefly outside the influence of the heliosphere.

“This work is the first of its kind to show that there was a collision between the Sun and something outside the solar system that would have affected the Earth’s climate,” says Ofer, an expert in the heliosphere, in the same scientific publication.

Merav Ofer led the team that studied the sun's interaction with the dense cloud.
Merav Ofer led the team that studied the sun’s interaction with the dense cloud.Photo: Tony Rinaldo/Courtesy of the Harvard Radcliffe Institute

To study this phenomenon, Ofer and his collaborators “looked back” in time, using sophisticated computer models to visualize the position of the sun two million years ago, and with it the position of the heliosphere and the rest of the solar system.

They also tracked the path of the “local cold cloud belt” system, a string of large, dense, very cold clouds made up mostly of hydrogen atoms, and their simulations showed that one of the clouds near the end of that band could collide with the cloud. Heliosphere.

The solar system will cross the clouds like this again

If it had happened this way, Over asserts, Earth would have been completely exposed to the interstellar medium, where gas and dust mix with the atomic elements left over from exploding 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 researchers, this is consistent with geological evidence that shows an increase in some isotopes in the ocean, on the moon, and in the snow of Antarctica. And in ice cores from the same time period.

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It is impossible to know the exact impact of cold clouds on Earth, or whether they sparked an ice age, but scientists know that there are at least a few other cold clouds in the interstellar medium that the Sun may have encountered in the universe. Billions of years since its birth, it is likely to falter further in a million years or so.

Determining the position of the Sun millions of years ago, as well as the cold cloud system, is made possible thanks to data collected by the European Space Agency’s Gaia mission, which is building the largest 3D map of the galaxy and providing a view of the unprecedented speed at which stars move.

little (if, Nature astronomy)

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