astroengine writes "Australian scientists who modeled conditions on Mars to examine how much of the Red Planet was habitable have said that "large regions" could sustain life. Using decades of global data, the researchers have evaluated the entire planet, and found that 3 percent of the Martian volume could sustain Earth-like microbial life. As a comparison, only one percent of the volume of Earth contains life. However, the only habitable regions are below the Martian surface where the temperature and pressure could sustain liquid water." Link to Original Source
If it happens once, it's a bug. If it happens twice, it's a feature.
If it happens more than twice, it's a design philosophy.