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The early sun produced powerful x-ray emissions that may have helped to ensure the survival of our planet, scientists say. Data from NASA's Chandra X-ray Observatory suggest that violent x-ray flares, which reached temperatures of 100 million kelvins, may have rocked the surrounding disk from which planets formed and prevented Earth from rapidly spiraling into the sun and being destroyed.
An international team of astronomers focused Chandra on the Orion Nebula for 13 days, resulting in one of the instrument's deepest observations yet. Located 1,500 light-years from Earth, the Orion Nebula provides a way for scientists to study how our sun behaved in its early years: of this stellar nursery's more than 1,000 stars imaged by Chandra, 27 of them are prototypes of the young sun. Over the study period, which was equivalent to looking at the young sun for nine months, the team detected 41 large x-ray flares thousands of times larger than any modern-day solar flares detected. The findings indicate that around 4.5 billion years ago, our sun experienced a flare each week, on average. The activity has since died down, with solar flares now occurring on the order of once a year.
The researchers hypothesize that the early mighty flares could have aided in the formation of our solar system. Theoretical calculations reveal that turbulence caused by forceful x-ray eruptions can disrupt planet-forming disks. "Although these flares may be creating havoc in the disks, they ultimately could do more good than harm," explains team member Eric Feigelson of Penn State University. "These flares may be acting like a planetary protection program." That's because without the disruption, the core of a burgeoning planet could lose angular momentum through its interaction with gas in the disk and fall into the star. When turbulence jostles the core, however, the protoplanet is more likely to survive. The results will appear in a supplement of the Astrophysical Journal dedicated to the Chandra Orion Ultradeep Project in October 2005.