Subsurface water on Jupiter’s moon Europa is one place humans plan to search for life. This artist’s concept shows a massive plume of underground water erupting from the moon’s surface. (Credit: NASA/ESA/K. Retherford/SWRI)

As humans explore the solar system, the tantalizing possibility of discovering extraterrestrial life continues to pop up. But the goal of most scientists is to discover existing life on another world, not to accidentally bring it there from Earth. Whether travelers are ro