A study of records dating back to the 13th century, which dealt with the phenomenon of the "strange red sky," led Japanese scientists to discover a severe cosmic storm that occurred about 800 years ago.
Solar activity often only reaches Earth's inhabitants in the form of beautiful auroras. However, solar flares, outside our planet's magnetic shield, can become a deadly threat; solar proton waves hurl particles traveling at speeds of up to 90% of the speed of light.
Had the Artemis 2 missions coincided with a series of such flares, the astronauts would have received a lethal dose of radiation.
In a new study published in the Proceedings of the Japan Academy, scientists from the Okinawa Institute of Science and Technology in Japan have proposed a unique way to "read" the history of solar activity, through an unexpected combination of modern physics and medieval poetry.
Highly accurate measurements of the carbon-14 isotope are a laborious and time-consuming process. To determine which historical periods to study, researchers turned to the Meijitsuki Chronicle, written by the Japanese poet Fujiwara no Teika. In February 1204, this poet described "red lights in the northern sky above Kyoto." Although proton waves themselves do not cause the aurora borealis, they are often associated with geomagnetic storms.
The poet's diaries helped scientists guide their research; they studied the wood of 'Asunaru' (Japanese juniper) trees buried underground, which were discovered during excavations in Aomori Prefecture. They were able to detect a carbon-14 mutation dating back to the period between the winter of 1200 and the spring of 1201.
This event belongs to the "near-catastrophic" category, which is three times weaker than super-catastrophic storms, but occurs more frequently and poses a serious threat to satellites and future lunar bases.
The analysis not only confirmed the occurrence of a specific solar flare, but also allowed for the reconstruction of solar cycles during that era. It revealed that around 800 years ago, our star behaved differently than it does today; the solar activity cycle currently lasts about 11 years, whereas at the beginning of the 13th century it was only between 7 and 8 years.
Professor Hiroko Miyahara said: "Short cycles indicate extremely high solar activity," adding that the detected flare occurred at the peak of one of these cycles.
This discovery filled gaps in the understanding of cosmic weather history, as combining data from tree-ring science and ancient historical texts allowed for a more complete picture to be formed.
However, scientists faced a new puzzle; it turned out that some historical records of auroras at low latitudes coincide with periods of minimal solar activity, which contradicts modern scientific models.
