Climate on Earth is obviously influenced by the Sun, our nearest star, but it appears that exploding distant stars might play a role too. Supernovae have been linked to the formation of clouds, so they might be affecting the climate from a significant distance.
Supernovae eject a lot of cosmic rays, high-energy electrically charged particles, and when they reach the atmosphere they are capable of knocking electrons off atoms and turning them into ions. As reported in Nature Communications, these ions can help with the formation of aerosols that produce the seeds that start clouds.
The study has several implications. Since cloud coverage affects global weather patterns and temperatures, the number of cosmic rays will play a role in climate variations. Variations in the Sun's magnetic field change the flux of cosmic rays that reach Earth and over a much longer period of time, as the Solar System moves around the Milky Way, the Earth might pass through a richer (or poorer) cosmic ray region.
“Finally we have the last piece of the puzzle explaining how particles from space affect climate on Earth. It gives an understanding of how changes caused by Solar activity or by supernova activity can change the climate,” lead author Henrik Svensmark, from the Technical University of Denmark, said in a statement.
The motivation for the study was to propose and test an aerosol-growth mechanism. Large aerosols were already identified as culprits for water condensation in the atmosphere, but it wasn’t exactly clear how they could grow to be big enough to do that. Estimates suggest that small aerosols need to get about a million times heavier before they can start making clouds.
The team suspected a space phenomenon was involved. Historically, slightly more extreme temperatures (before we started messing up the climate) have been recorded with solar activity and the team looked for what might be causing the growth of the aerosols. In laboratory experiments, the researchers were able to recreate the growth produced by the ions.
It will be interesting to now see if observations can be conducted in the atmosphere and to find out how much of a role the cosmic rays play in a real system. This data could help us better understand our own climate and maybe even the weather on exoplanets too.