If a massive solar storm hit the Earth today, it would destroy technology and take us back to dark times. Fortunately for us, such events are extremely rare. But four billion years ago, eerie space weather might well have been the order of the day. Only instead of the apocalypse she would create life. This is the startling conclusion of a study published recently in Nature Geosciences. It builds on previous discoveries about young sun-like stars made by the Kepler space telescope. It turned out that young luminaries are extremely unstable and release an incredible amount of energy during "solar superflares." Our wildest space weather will look like drizzle by comparison.
NASA's Vladimir Hayrapetyan showed that if our sun were as active for 4 billion years, it could make the Earth more habitable. According to Hayrapetyan's models, when solar superflares unwound our atmosphere, they initiated chemical reactions that contributed to the accumulation of greenhouse gases and other essential ingredients for life.
“For four billion years, the Earth should have been deeply frozen,” Hayrapetyan says, referring to the “weak young sun paradox,” first formulated by Carl Sagan and George Mullen in 1972. The paradox came when Sagan and Mullen realized that the Earth had signs of liquid water 4 billion years ago, but the Sun was 30% dimmer. “The only way to explain this is to somehow turn on the greenhouse effect,” Hayrapetyan said.
Another mystery about the young Earth is how the first biological molecules - DNA, RNA, and proteins - collected enough nitrogen to form. As it is today, the atmosphere of ancient Earth consisted mostly of inert nitrogen (N2). Although special bacteria, "nitrogen fixers", figured out how to break down N2 and convert it into ammonia (NH4), early biology lacked this ability.
The new study offers an elegant solution to both problems in the form of space weather. The research began several years ago when Hayrapetyan was studying the magnetic activity of stars in the Kepler database. He found that G-type stars (like our Sun) were like dynamite in their youth, often releasing pulses of energy equivalent to 100 trillion atomic bombs. The most powerful geomagnetic storm that humans have experienced that caused blackouts around the world, the Carrington event of 1859, pales in comparison.
“This is a huge amount of energy. I can hardly imagine it,”says Ramses Ramirez, an astrobiologist at Cornell University who was not involved in the study but works with Hayrapetyan.
Very soon it dawned on Hayrapetyan that he could use this discovery to look into the early history of the solar system. He calculated that 4 billion years ago, our Sun could fire dozens of superflares every few hours, and one or even several of them could hit the magnetic field every day. “You could say the Earth has been constantly being attacked by the giant Carrington events,” he says.
Using numerical models, Hayrapetyan showed that solar superflares must be powerful enough to drastically compress Earth's magnetosphere, the magnetic shield that surrounds our planet. In addition, charged solar particles had to punch a hole in the magnetosphere near the poles of our planet, entering the atmosphere and colliding with nitrogen, carbon dioxide and methane. “So, all these particles interact with molecules in the atmosphere and create new molecules - a chain reaction,” says Hayrapetyan.
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These solar-atmospheric interactions produce nitrous oxide, a greenhouse gas with a global warming potential of 300 times that of CO2. Hayrapetyan's models suggest that enough nitrous oxide could have been produced at that time for the planet to start heating up strongly. Another product of the endless solar storm, hydrogen cyanide (HCN), could fertilize the surface with the nitrogen necessary to form the first building blocks of life.
“People looked at lightning and falling meteorites as ways to initiate nitrogen chemistry,” says Ramirez. "I think the coolest thing about this work is that no one has thought of looking at solar storms before."
Now biologists will have to determine whether the exact mixture of the desired molecules could have been born after a superflare, and then give rise to life. This research is already under way. Scientists at the Institute of Terrestrial Life Sciences in Tokyo are already using Hayrapetyan's models to plan new experiments to simulate conditions on ancient Earth. If these experiments can produce amino acids and RNA, perhaps space weather will be added to the list of possible sparks of life.
In addition to everything else, Hayrapetyan's models could shed light on the habitability of Mars in the past. The Red Planet is believed to have been full of water four billion years ago. Such research will also come in handy in the search for life outside our solar system.
After all, we are just beginning to figure out what constitutes a “potentially habitable zone” of a star, where planets can have oceans with liquid water. But now the habitable zone is determined only by the brightness of the star.
“Eventually, we will find out if the energy of a star can help create biomolecules. Perhaps without her life would be a true miracle."
ILYA KHEL