The Pleistocene epoch—with its glaciers, woolly mammoths, and Neanderthals—is still looming in Earth’s rearview mirror, having ended just 12,000 years ago. Now a team of researchers suggests that those hundreds of thousands of years of our planet’s history may have been cold because of a cloud in space that briefly removed Earth from the safety of the sun’s warm glow.
Researchers suggest that about two million years ago, an interstellar cloud intruded into the solar system in such a way that Earth and other planets were briefly outside the solar system. heliosphere, the bubble of charged particles from our host star that today forms an amorphous shell around the system. Their research was published today in Nature Astronomy.
“This paper is the first to quantitatively show that there was an encounter between the sun and something outside the solar system that would have affected Earth’s climate,” said Merav Ofer, an astrophysicist at Boston University and lead author of the study, in an email to Gizmodo. Offer added that the team is “still trying to quantify it with modern climate models,” but with the increase in hydrogen and dust, “Earth would have entered an ice age.”
The Opher team modeled data from HI4PI survey and found that our solar system may have passed through the local band of cold clouds in the constellation Rhys between 2 million and 3 million years ago. The Pleistocene began about 2.6 million years ago. It’s not possible to say for sure whether such cold clouds could catalyze an ice age, the release notes, but more evidence of clouds interfering with the heliosphere could clarify the kind of effects they would have on Earth.
The team’s model reveals that in such a passage, the heliosphere, which encompasses Earth and its neighboring planets, would shrink to about 0.22 AU, or less than a quarter of Earth’s distance from the Sun. To put this into perspective, ESA ratings that the closest boundary of the heliosphere today is about 100 AU from the Sun, about twice as far as the Kuiper Belt.
Outside the heliosphere, Earth would be exposed to iron and plutonium in the interstellar medium, the team argued. Their timeline is consistent with increases in plutonium-244 and iron-60, two isotopes of the respective elements known to arise from events in space, in Antarctic snow, deep-sea sediments and lunar samples. And as Opher added, samples from Mars, if tested in the same way as lunar and Earth samples, could reveal a similar spike in the iron isotope about 2 to 3 million years ago.
The heliosphere may have been blocked for anywhere from a few hundred years to a million years, said Offer at Boston University exemption. The moment Earth and the other planets moved away from the cloud, the heliosphere returned.
To verify their results, the team is now trying to understand the position of the Sun about seven million years ago, where there is evidence of another peak in the ratios of plutonium-244 to iron-60 in Earth’s ice and sediments. They’re trying to create a digital twin — basically a high-tech model — of the heliosphere to better model the kinds of conditions our solar system might have been subjected to. Finally, additional data from ESA’s Gaia mission could further help the team determine the exact position of the Sun at this time in the ancient past.
At least according to the Utah Geological Survey five major ice ages have occurred on Earth. The former occurred more than 2 billion years ago, and the latter began about 3 million years ago. According to NASA, ice ages can start due to a combination of factors, including changes in Earth’s orbit, low amounts of energy from the Sun, composition of the atmosphere, changes in ocean currents, and even volcanoes that are responsible for a year without summer. In other words, we don’t need theories explaining Earth’s various cold snaps, and the jury is out on exactly how the Earth’s being outside the heliosphere might have catalyzed such a cold period.
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