Scientists believe Earth may have briefly lost its protection from the sun about two million years ago, as the solar system passed through a dense cloud of gas and dust between stars, leaving it to endure the extreme conditions of interstellar space.

At that time, early human ancestors shared our planet with prehistoric animals such as mastodons and saber-toothed tigers. This is also the period when Earth was in the midst of an ice age that ended only 12,000 years ago. Ice ages are caused by a number of factors, including our planet’s tilt and rotation, the level of carbon dioxide in its atmosphere, as well as changes in plate tectonics and volcanic eruptions on its surface. However, given the time when scientists believe Earth fell into interstellar space, this research suggests that radical changes in our planet’s climate, such as the beginning and end of ice ages, may also depend on our solar system’s location in our own galaxy.

More specifically, the team behind the new findings suggests that the Solar System may have encountered a dense mass of interstellar gas and dust as it crossed the Milky Way two million years ago. And this patch could be thick enough to block the flow of charged particles called the “solar wind” coming from the Sun and hitting the Earth, potentially causing the temperature to drop dramatically.

“This paper is the first to show quantitatively that there is a collision between the Sun and something outside the Solar System that could affect Earth’s climate,” said lead study author Merav Ofer, a space physicist and heliosphere expert at Boston University. in practice.

solar system, time travel

Our entire Solar System is surrounded by a “giant protective bubble of plasma” from the Sun known as the “heliosphere”. This protective shield is created when the solar wind pushes through the interstellar medium, dragging material between stars in the Milky Way. The heliosphere is constantly replenished by the constant stream of charged particles from the Sun flowing past Pluto.

The heliosphere protects the Earth’s surface from radiation and galactic rays that could potentially affect the DNA of living things. This protection is so important that many scientists believe it is integral to the origin and evolution of life on Earth.

This team believes that a cold cloud of interstellar matter may have once interfered with the solar wind in a way that caused the heliosphere to contract. This could for a short time (in the cosmic sense) take the Earth and other planets of the solar system out of the protection of the heliosphere.

“Stars are moving, and this paper shows that they are not only moving, but also undergoing drastic changes,” Ofer said. he added.

To determine the impact on Earth of bombardment of the heliosphere with dense interstellar dust, Ofer turned back time using advanced computer models. This allowed him and his team to visualize the position of the Sun two million years ago and determine where the heliosphere and the rest of the Solar System were at that time.

They also tracked the progression of a string of dense, cold gas called a “local cold cloud system” as it moved across the Milky Way. This showed that a single dense cloud at the edge of a local cold cloud band system, called a “local cold cloud ridge”, could collide with the heliosphere.

This would result in Earth being exposed to the interstellar medium, including the heavy and radioactive elements living within it and the remnants of massive stars that died in supernova explosions. The heliosphere normally blocks these particles; Without this protection, these radioactive elements could fall to Earth. This could explain the increase in iron 60 and plutonium 244 isotopes in snow and ice cores of Antarctica and the Moon corresponding to the period two million years ago. The time of collision of the heliosphere with the Cold Cloud Local Line coincides with the cooling period of the Earth two million years ago.

Ofer suggests that pressure from a local cold cloud feature may have confined the heliosphere for a period of several hundred years or up to a million years. Ofer said it all depends on how big the cloud is. He added that after the effects of this dense cloud pass, the heliosphere will surround the planets again.

However, it is currently difficult to determine precisely the impact of this cold interstellar cloud on Earth and whether it actually triggered an ice age. The team will now delve further into the past to find other times when the Solar System was intersected by dense interstellar clouds and determine whether these are consistent with ice ages.

He and his team are also currently investigating the effects of so much hydrogen and radioactive material passing through Earth’s atmosphere.

“This cloud was indeed in our past, and if we passed over something this large, we would be exposed to the interstellar medium,” Ofer said. “This is just the beginning.” The team’s research was published Monday, June 10, in Nature Astronomy.