The heliosphere is formed by solar winds
The solar system may have passed through a dense cloud about two million years ago, possibly plunging the Earth into a "deep freeze", with multiple Ice ages coming and going until about 12,000 years ago, according to new research.
The solar system, comprising the Sun and eight planets, along with several dwarf planets such as Pluto, is wrapped in a "giant bubble", called the heliosphere, according to the US space agency, NASA.
The heliosphere is formed by solar winds, which are a constant flow of charged particles coming from the Sun, travelling up to three times the distance to Pluto. The "giant bubble" protects us from rays from the galaxy that can potentially alter our genes, according to NASA.
Ice ages, when glaciers cover a major part of the Earth's surface, are said to occur for a number of reasons, including the planet's tilt and rotation, shifting plate tectonics, volcanic eruptions, and carbon dioxide levels in the atmosphere.
"But what if drastic changes like these are not only a result of Earth's environment, but also the Sun's location in the galaxy?" asked the researchers, including those at Boston University, US.
The latest study, published in the journal Nature Astronomy, found that the cold instellar cloud interfered with the heliosphere in a manner such that the Earth, along with other planets, were no longer under its protection. The interstellar medium refers to the space in between stars and beyond the heliosphere in our galaxy.
The researchers believe the findings show that the Sun's location in space might shape Earth's history more than previously considered.
"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," said lead author Merav Opher, an astronomy professor at Boston University.
"Stars move, and now this paper is showing not only that they move, but they encounter drastic changes," said Opher.
For the study, the researchers used computer models to visualise the positions of the Sun, the heliosphere and the planets two million years in the past.
They found that one of the clouds, forming the Local Ribbon of Cold Clouds system -- a string of large, dense, very cold clouds in our galaxy -- could have collided with the heliosphere. The cloud is called Local Lynx of Cold Cloud.
The researchers said that if this had actually happened, the Earth would have been fully exposed to the interstellar medium, where gas and dust mix with the leftover atomic elements of exploded stars, including iron and plutonium -- most of which is filtered out by the heliosphere.
However, in the absence of the protection, the particles could easily reach the Earth, they said.
The researchers also said that the event aligned with evidence on Earth showing increased levels of iron and plutonium in the ocean, on the moon, Antarctic snow, and ice cores from the same time period.
The timing also matches with temperature records indicating a cooling period, they said.
"Only rarely does our cosmic neighbourhood beyond the solar system affect life on Earth," said co-author Avi Loeb from Harvard University.
"It is exciting to discover that our passage through dense clouds a few million years ago could have exposed the Earth to a much larger flux of cosmic rays and hydrogen atoms. Our results open a new window into the relationship between the evolution of life on Earth and our cosmic neighbourhood," said Loeb.
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