Astronomers at Boston University have shown that about 2 million years ago, the Sun passed along the edge of a cold cloud of interstellar gas that deformed the heliosphere and exposed Earth to harsh radiation.
2 million years ago, a cold cloud of interstellar gas covered the solar system
The Sun makes one revolution around the center of the Milky Way in about 225 million years. In its orbit, the Sun (and our entire planetary system) is subjected to different conditions because the interstellar medium in the galaxy is not uniform. In the interstellar medium there are so-called "localized cold clouds". These are fairly dense clusters of gas and dust, consisting mainly of hydrogen.
Merav Ofer - professor of astronomy at Boston University and her colleagues suggested that the Sun's path through such clouds could strongly influence both the Earth's climate and the forms of terrestrial life.
The findings are published in the journal
Nature Astronomy.
Astronomers have calculated that the last collision between the Solar System and a cold cloud happened 2 million years ago, when our ancestors were already walking on Earth.
Scientists traced the path of the Sun in the Milky Way and the path of the local cold cloud Lynx (it got its name because it is visible from Earth in the constellation Lynx) 2 million years ago. Such calculations were possible, thanks to the work of ESA Gaia space telescope, which tracks the orbits of one and a half billion stars in our galaxy.
According to astronomers' calculations, when the Sun passed through the Lynx cloud, the dense interstellar medium deformed the heliosphere - streams of charged particles that the Sun constantly ejects. The heliosphere encompasses the entire solar system and shields it from galactic hard radiation. When a cold cloud collided with the heliosphere, the heliosphere was "blown away" and the Earth was exposed to cosmic rays. This led to the bombardment of our planet with radioactive particles, in particular isotopes of iron and plutonium.
Scientists have tested this hypothesis and found traces of isotopes in the ocean, lunar soil, and Antarctic ice cores estimated to be 2 million years old.
According to the model, the deformation of the heliosphere lasted for about 200-300 years, but had severe consequences for the climate - the Earth became sharply colder, and for living organisms, as the bombardment of DNA by cosmic rays leads to mutations, most of which are harmful or even destructive to living organisms. This may have been responsible for the death of many species of megafauna.
Merav Ofer says that the study is just the beginning. Now the scientists will try to trace the path of the Sun and the path of cold clouds in the past much further back than 2 million years and analyze when else the Earth encountered a cold cloud. Merav Ofer notes that, probably, such collisions were not so rare and in the future the Earth will have new encounters with cold clouds, we can not prevent them, but we need to be ready for them.
https://www.newsru.co.il/science_hitech/12jun2024/solar_system.html#
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