What To Know
- The solar system encountered a dense cloud of interstellar gas and dust as it passed through the Milky Way, which had a direct impact on Earth‘s climate.
- The researchers also tracked the progression of a dense cold gas chain called a local ribbon system of cold clouds at the time as it swept across the Milky Way.
- The researchers theorize that the pressure from this cloud of cold gas could have constricted the heliosphere for as little as a few hundred years, or as long as a million years.
About two million years ago, when our human ancestors shared Earth with mastodons and saber-toothed tigers, our planet may have been going through a tumultuous cosmic period, according to a new study led by researchers at Boston University. The hypothesis? The solar system encountered a dense cloud of interstellar gas and dust as it passed through the Milky Way, which had a direct impact on Earth’s climate. If true, this theory would challenge our current understanding of the glacial cycles that have marked Earth’s history.
A protective bubble
At the heart of our Solar System, an invisible sentinel silently watches over our blue planet: theheliosphere. This giant bubble of plasma emanating from the Sun is much more than a simple bulwark against the rigors of interstellar space: it is the ultimate guardian of life on Earth. Created by the incessant ballet of solar winds which propel charged particles through space, the heliosphere protects us from cosmic radiation and galactic rays that roam unhindered in the depths of space. Without this barrier, they could penetrate the Earth’s atmosphere and seriously damage the DNA of living beings, compromising the very survival of life on our planet. Scientists, however, believe that our planet may have briefly lost its protection about two million yearsforced to endure the extreme environment of interstellar space as the Solar System passed through a dense cloud of gas and dust.
A diagram showing the heliosphere protecting the Solar System from the dense and cold conditions of the interstellar medium. Credits: Institut de recherche du Sud-Ouest
A possible meeting
To determine what effect such a bombardment of dense interstellar dust would have had on Earth, the researchers went back in time with sophisticated computer models. This work allowed them to determine the position of the Sun (and therefore the heliosphere) two million years ago. The researchers also tracked the progression of a dense cold gas chain called a local ribbon system of cold clouds at the time as it swept across the Milky Way. According to their analyses, a dense cloud at the tip of this enormous structure could indeed have come into conflict with the heliosphere. This would have left the Earth exposed to the interstellar medium, including the heavy and radioactive elements that populate it. Such an encounter could notably explain an increase in iron-60 and plutonium-244 isotopes found in snow and ice cores from Antarctica and on the Moon, dated to about two million years ago. The timing of this possible encounter also matches a cooling period on Earth at that time. The researchers theorize that the pressure from this cloud of cold gas could have constricted the heliosphere for as little as a few hundred years, or as long as a million years. It all depended on its actual size. The heliosphere would then have reassembled to surround the planets again after the influence of this dense cloud had faded. For now, however, it is difficult to determine precisely what impact this cold interstellar cloud would have had on Earth, including whether it could have actually triggered an ice age. The team will now investigate even further back in time to discover other times when the solar system encountered dense interstellar clouds and determine whether they also corresponded to ice ages. Details of the study are in .
