THE sun provides ideal conditions for life to thrive, right? In fact, it periodically leaves Earth open to assaults from interstellar nasties in a way that most stars do not.
The sun protects us from cosmic rays and dust from beyond the solar system by enveloping us in the heliosphere 鈥� a bubble of solar wind that extends past Pluto. These cosmic rays would damage the ozone layer, and interstellar dust could dim sunlight and trigger an ice age. However, when the solar system passes through very dense gas and dust clouds, the heliosphere can shrink until its edge is inside Earth鈥檚 orbit.
In a , David Smith at the University of Arizona in Tucson and John Scalo at the University of Texas, Austin, calculated the squeezing of various stars鈥� protective 鈥渁strospheres鈥�. They 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鈥檚 because they need to be close to these dim stars to be warm enough to be habitable. 鈥淭he bottom line is that habitable planets around red dwarfs are better protected from climate catastrophes than Earth is,鈥� says Smith.
Advertisement
