Scientists solve 200-year-old mystery of the Sun’s turning blue

Nearly 200 years ago, the Sun appeared blue in Earth's atmosphere, baffling scientists for generations. Researchers have now identified a massive volcanic eruption in 1831 as the cause.

The eruption released vast amounts of sulfur dioxide into the atmosphere, triggering global cooling and unusual climatic conditions that year. 

A study published in the journal "Proceedings of the National Academy of Sciences (PNAS)" pinpointed the Zavaritskii volcano on Simushir Island—an uninhabited and contested territory between Russia and Japan—as the source of the event. 

Scientists from the University of St Andrews, Scotland, examined ice core records from 1831 to support their findings. The lack of eyewitness accounts or written records of the eruption, due to the island's remoteness and sparse habitation, made the investigation challenging. 

Study co-author Will Hutchison described a breakthrough moment when volcanic ash samples from Simushir matched those extracted from the ice core. "Analysing the two ashes together was a genuine eureka moment," Hutchison said in a statement. 

By closely studying the chemistry of the ice at a high temporal resolution, the team confirmed that the eruption occurred in spring-summer 1831. They verified its explosive nature and recovered microscopic ash particles to further validate their conclusions. 

While the mystery of the 1831 eruption and its atmospheric effects has been unraveled, Hutchison emphasized the difficulty of monitoring such remote events even today. "If an eruption like this happened now, we might not be much better prepared than in 1831," he noted, highlighting the challenges of predicting and responding to massive climate-altering eruptions. 

Volcanic eruptions of this magnitude have had significant global impacts in the past. In 1815, the eruption of Mount Tambora in Indonesia led to "a year without summer," as 24 cubic miles of gases, dust, and rocks were ejected into the atmosphere. This event caused global temperatures to drop by 1°C in the Northern Hemisphere. 

Scientists warn of a one-in-six chance of a similarly large eruption occurring this century, with potential economic damages in the trillions. Any cooling effect from such an event would likely be short-lived, as the planet remains on a warming trajectory due to greenhouse gas emissions.