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Shields up! How Earth's magnetic field saved early life from the sun

A new study found that protective magnetic fields were vital for the development of life on Earth, as the activity of a young star can strip an unprotected planet of its atmosphere.

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    Artist's illustration of the young Sun-like star Kappa Ceti. The star features large starspots and high magnetic activity. Scientists believe studying the star could unlock secrets about our own Sun's past.
    M. Weiss/CfA
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There’s a new addition to the checklist of requirements for life: magnetic shields.

On Wednesday, a new study revealed a magnetic field is vital to protect life on a planet from the ravages of a star. A young Earth harboring the first fledgling forms of life would likely have been buffeted by its active young sun.

"To be habitable, a planet needs warmth, water, and it needs to be sheltered from a young, violent sun," lead author José-Dias do Nascimento of the Harvard-Smithsonian Center for Astrophysics (CfA) and University of Rio G. do Norte (UFRN), Brazil says in the press release.

Data from meteorites suggests that the is about 4.6 billion years old. Life on Earth is believed to have existed as early as 4.1 billion years ago. So, to determine what the sun was like when life was getting started, scientists looked outside of our solar system.

Kappa Ceti is a star located roughly 30 light-years away – a  relatively short journey on the cosmic scale. Despite being in the same neighborhood, the star is still too far away to be observed via normal telescopes, but scientists are able to observe its magnetic field with precision and compare it with that of our own star.

The differences are stark. Compared to our sun, Kappa Ceti is young, energetic, and dangerous. But it’s the right age – 400 million to 600 million years old – and scientists believe in the past our sun would have had similar characteristics to this star. Stellar winds would have been 50 times stronger, and flares would have been more explosive.

The team of scientists used the data collected from Kappa Ceti and modeled what its impact would have been on a young Earth. In the model, a young Earth managed to scrape by. Our planet’s early magnetic field would have been about as strong as today or a little weaker, but its magnetosphere, the area protected by the field, would have been one-third to one-half as large as it is now, according to the press release.

"The early Earth didn't have as much protection as it does now, but it had enough," Dr. do Nascimento says.

The Earth’s natural protection would have allowed early life to continue growing. On another planet with less protection, strong stellar winds at the levels put off by Kappa Ceti would have heavily damaged the atmosphere.

Researchers in the study referenced Mars as an example of a planet that lost most of its atmosphere due to a weak magnetic field. Mars was once warm enough for oceans, but atmospheric loss has turned it to into a cold desert planet.

The Christian Science Monitor's Pete Spotts reported on a NASA estimate that placed the number of "habitable," Earthlike planets down to potentially one around every four sunlike stars discovered, which buoyed hopes for discovering a host of life on other planets in 2010.

But as the number of conditions surrounding what it took to achieve life on Earth builds, some scientists have suggested the chances of find life could be far smaller.

Kappa Ceti has revealed additional dangers Earth may have faced. The foreign star explodes in “superflares,” which could be up to 100 times more powerful than any flare observed from the sun and completely strip a planet's atmosphere, according to the press release.

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