A recent study, published on the pre-print server arXiv, delves into the impact of supernova explosions that occurred 3 million years ago (SN Plio) and 7 million years ago (SN Mio) on Earth. The primary objective was to pinpoint the distances from which these explosive events originated.
Scientists at the University of Illinois employed the use of live radioactive isotope 60Fe, a byproduct of supernovae, to estimate the astronomical distances to these ancient supernovae, SN Plio and SN Mio.
Dr. Brian Fields, a Professor of Astronomy at the University of Illinois and co-author of the study, emphasized the significance of supernovae in the life cycles of stars and their crucial role in astrophysics and cosmology.
To achieve their goals, the researchers conducted meticulous laboratory analyses of 60Fe samples extracted from Earth’s crust, deep-sea sediments, and lunar regolith, dating back to the time of the supernovae. The focus was on determining the distances to these celestial explosions.
The study’s results reveal that SN Plio likely occurred between 20 to 140 parsecs (approximately 65 to 457 light-years) from Earth, with the most probable range being 50 to 65 parsecs (163 to 212 light-years). As for SN Mio, its approximate distance from Earth is estimated to be 110 parsecs (about 359 light-years). For reference, 1 parsec equals approximately 3.26 light-years.
While these distances may seem relatively distant, it’s worth considering how such supernova events could impact the evolution of our solar system. Dr. Fields warns that if a supernova were to explode too close to Earth or a similar planet, the consequences could be catastrophic for life.
Supernova outbursts release high-energy gamma rays, which would irradiate Earth’s atmosphere for months. Although our atmosphere provides some protection, the cost would be substantial: the ozone layer in the upper atmosphere would significantly diminish. This vulnerability would expose Earth to harsh ultraviolet (UV) rays from the sun, which could prove harmful to many forms of life. It would take several years for Earth to regenerate its ozone layer, making such nearby supernova explosions a significant concern.
Supernovae are among the most mesmerizing events in the universe, and they’ve been captivating observers for centuries. The oldest recorded supernova, now called RCW 86 or SN 185, dates back to December 7, 185 A.D., as documented by Chinese astronomers. In their records, they referred to this celestial spectacle as a “guest star” that remained visible in the sky until June 186 A.D. Today, astronomers classify such events as transient astronomical phenomena, and they believe RCW 86, situated roughly 2,800 parsecs (approximately 9,100 light-years) from Earth with a diameter estimated at 85 light-years, was likely a Type Ia supernova.
Dr. Fields emphasizes the rarity of supernova explosions, with just one to three occurring in the entire Milky Way galaxy each century. Fortunately, most of them explode far from Earth and pose no threat to us. However, over vast timescales, it becomes statistically likely that one could occur uncomfortably close to our planet.
While Dr. Fields acknowledges the possibility that a mass extinction event around 360 million years ago might have been caused by one or more supernovae, he reassures us that there are currently “no threatening supernova candidates” nearby—none so close that they would endanger us.
Among the most prominent candidates for a future supernova is Betelgeuse, a red supergiant located approximately 550 light-years from Earth and the second-brightest star in the Orion constellation. Betelgeuse made headlines in late 2019 when it dimmed significantly, leading some to speculate that it was on the brink of going supernova.
However, subsequent observations in August 2020 revealed that the dimming was due to a dust cloud formed by superhot material ejected by the star, a conclusion confirmed in an August 2022 study. When asked about when Betelgeuse might actually explode, Dr. Fields explains that it remains unknown because late phases in the life of massive stars don’t typically cause noticeable changes in their surface regions. As a result, Betelgeuse could be the next supernova in our galaxy, or it might not explode for another 100,000 years. What’s certain is that its eventual demise is inevitable, so we should savor its presence in the Orion constellation while it lasts.
Source: Universe Today