If you went swimming at the beach over the long weekend, perhaps you felt invigorated by chilly spring water temps. Cold-water bathers report pain relief from musculoskeletal injuries, and decreased symptoms of depression, as well as mood improvement. A recent survey of 1,114 female cold-­water swimmers found that plunging into icy waters eased symptoms of menstruation and menopause.

The caveats: Only a modest amount of research has been done to investigate the scientific benefits of cold-water swimming. Plus, the practice carries the risk of hypothermia, drowning and cardiac arrhythmia.

What the experts say: The benefits of the practice are “quite difficult” to assess, says James B. Mercer, an emeritus physiologist at UiT the Arctic University of Norway. Most studies on the subject have been small, with generally healthy participants and widely varying water temperatures and salinity levels, so it’s tough to tease out what is behind the perceived benefits.

Every few million years, a supernova goes off close enough to Earth to shower the planet with radioactive debris. Researchers found elevated amounts of the isotope iron 60 in sediments on the deep sea floor and in deep-sea bacteria. This isotope has only one source: the nuclear fire of an exploding star. By measuring its rate of decay, the scientists estimate that it was deposited by multiple supernovas around 2.5 million years ago, perhaps originating in the Scorpius-Centaurus association, a clump of stars about 390 to 470 light-years from Earth.

Why this is cool: “The amount of iron 60 in the sediments is actually quite small, very roughly 100,000 atoms per gram of material,” writes astronomer and Scientific American columnist Phil Plait. “But the astonishing thing is that debris from exploding stars quadrillions of kilometers from us is there at all.”

What the experts say: Researchers determined that a supernova would have to be less than about 160 light-years from Earth to inflict any significant damage, like high energy gamma rays destroying our ozone layer, or a blast of radiation that knocks out our power grid. For now, no such close explosion is likely to happen, Plait writes.