Our sun seems fairly quiet these days, with a largely stable regular solar cycle visible through sunspots and flare activity, but billions of years ago it was simply a threat. Scientists have just found evidence of what the sun and early solar system may have looked like, and it’s more violent than we imagined.
The sun regularly ejects huge clumps of plasma into space. These coronal mass ejections (CMEs) sometimes reach Earth and create beautiful auroras. Occasionally they are powerful enough to disrupt energy systems. But when our solar system was young, these outbursts were far more extreme, and they may have had a fundamental impact on whether life could even emerge on Earth.
A coronal mass ejection (CME) imaged by NASA and ESA’s Solar and Heliospheric Observatory (Credit: NASA/GSFC/SOHO/ESA)
The problem is that we can’t go back in time to observe the little sun’s behavior, and aside from the little geological information we have, we have no evidence to analyze. Instead, a team of researchers led by Kosuke Namekata of Kyoto University did the next best thing: They observed a young star that resembles what our sun looked like billions of years ago.
By coordinating observations from the Hubble Space Telescope and Earth observatories in Japan and Korea, they observed a star called EK Draconis that required a split-second time measurement. Hubble searched for scorching hot plasma in the ultraviolet wavelengths, while ground-based telescopes simultaneously tracked cooler gases through visible light.
*EK Draconis light curve recorded from TESS data*
What they saw was remarkable. First came a plasma wave with a temperature of 100,000 Kelvin, racing at speeds of up to 550 kilometers per second. Ten minutes later, cooler gas followed at 10,000 degrees at a more modest 70 kilometers per second. This was the first time anyone had captured both temperature components of a CME of a young star like the Sun in real time.
The hot plasma carried far more energy than the cool material, which would have had a significant impact on an early Earth. Frequent, powerful CMEs like these would have bombarded the early atmospheres of Earth, Mars, and Venus with intense shocks and energetic particles. These forces could erode or chemically transform planetary atmospheres.
This is where the story of life gets interesting. While this sounds destructive and quite brutal, some theories suggest that these violent conditions were actually necessary. The energetic particles and strong CMEs may have helped create biomolecules and greenhouse gases that are essential for the emergence and survival of life on a young planet. The same violent radiation that could destroy an atmosphere could also create the chemical building blocks that make life possible. The strength and timing made the difference.
“What inspired us most was the long-standing mystery of how the vigorous activity of the young sun influenced the nascent Earth.” – Kosuke Namekata from Kyoto University
This work not only tells us about Earth’s past, but also helps us understand the habitability of exoplanets across the universe. To assess the habitability of a rocky planet around other stars, they must consider what kind of stellar activity these worlds experienced in their youth. A planet’s potential for life may depend not only on its distance from its star, but also on whether it survives crucial early bombardments that could either help or destroy the chances for biology to emerge.
Source: Coronal mass ejections at the beginning of the solar system
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