Earth's atmosphere is our best defense against nearby supernovae, study suggests
Earth's protective atmosphere has sheltered life for billions of years, creating a haven where evolution produced complex lifeforms like us. The ozone layer plays a critical role in shielding the biosphere from deadly UV ...
But the sun is relatively tame. How effective are the ozone and the magnetosphere at protecting us from powerful supernova explosions?
Every million years—a small fraction of Earth's 4.5 billion-year lifetime—a massive star explodes within 100 parsecs (326 light-years) of Earth. We know this because our solar system sits inside a massive bubble in space called the Local Bubble.
It's a cavernous region of space where hydrogen density is much lower than outside the bubble. A series of supernovae explosions in the previous 10 to 20 million years carved out the bubble.
Supernovae are dangerous, and the closer a planet is to one, the more deadly its effects. Scientists have speculated on the effects that supernova explosions have had on Earth, wondering if they have triggered mass extinctions or at least partial extinctions.
A supernova's gamma-ray burst and cosmic rays can deplete Earth's ozone and allow ionizing UV radiation to reach the planet's surface. The effects can also create more aerosol particles in the atmosphere, increasing cloud coverage and causing global cooling.
Artist's impression of a Type II supernova explosion. These supernova produce gamma rays and powerful ionizing radiation that's hazardous to life. Credit: ESO
This graphic from the research article shows the potential atmospheric and climate impacts of a nearby supernova. Gamma rays can deplete the ozone, allowing more UV radiation to reach Earth’s surface. Some UV radiation is ionizing, meaning it can damage DNA. Cosmic rays can also create more condensation nuclei, meaning more clouds and potential global cooling. Credit: Communications Earth & Environment (2024). DOI: 10.1038/s43247-024-01490-9
These panels from the research letter show the ozone column percentage decrease from a 100-fold increase in GCR intensity over nominal. The left vertical axis represents Earth’s latitude, and the x-axis shows the time of year. Ozone loss is more pronounced over the poles due to the effect of Earth’s magnetosphere, where it’s weaker. a is present-day Earth, while b represents an ancient Earth with only 2% oxygen during the pre-Cambrian. Credit: Communications Earth & Environment (2024). DOI: 10.1038/s43247-024-01490-9
These two panels from the research help illustrate the global cooling effect from a nearby SN exposing Earth to 100 times more ionizing radiation. b shows the fractional change in CCN relative to the present day. d shows the fractional change in outgoing solar radiation relative to the present day due to increased cloud albedo. Credit: Communications Earth & Environment (2024). DOI: 10.1038/s43247-024-01490-9