Did a mysterious interstellar cloud cause Earth's ice age?
Roughly two million years ago, Earth may have lost its protection from the Sun, as the solar system traversed a dense cloud of dust and gas between stars. This is the theory proposed by a team of scientists, led by Merav Opher, a space physicist from Boston University. Their research suggests that this interstellar encounter could have significantly impacted Earth's climate, potentially influencing the onset and conclusion of ice ages.
Solar system's encounter with interstellar cloud
The team's findings propose that the dense region could have obstructed the flow of charged particles, known as the solar wind, from the Sun to Earth, potentially causing a drop in temperatures. "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," Opher said.
Impact on Earth's climate and heliosphere
The research team theorizes that a cold cloud of interstellar material, known as the "Local Lynx of Cold Cloud," might have impeded the solar wind, compressing the heliosphere. This could have temporarily removed Earth and other planets from the protection provided by the heliosphere, potentially influencing ice ages and other climatic events.
Evidence from isotopes and cooling period
This collision would have exposed Earth to the interstellar medium, which included heavy and radioactive elements. The timing of this collision corresponds with a cooling period on Earth two million years ago, and an increase in isotopes iron 60 and plutonium 244, found in Antarctic snow and ice cores.
Future research and potential impact
The team is now investigating the impact of hydrogen and radioactive material on Earth's atmosphere. "This cloud was indeed in our past, and if we crossed something that massive, we were exposed to the interstellar medium," Opher said. The researchers are also planning to study other instances when the solar system encountered dense interstellar clouds, to see if these also coincide with ice ages. The study was published in Nature Astronomy.
