The sun protects humans from cosmic rays and dust from beyond the solar system by enveloping in the heliosphere - a bubble of solar wind that extends past Pluto. These rays would damage the ozone layer and interstellar dust can dim sunlight and trigger an ice age.
The astronomers found Earth is exposed to between one and 10 interstellar assaults every billion years. Habitable planets around a red dwarf, which account for three of every four stars, are never exposed. That's because they need to be close to these dim stars to be warm enough to be habitable, they said.