The observational data that demonstrates the availability of organic molecules and water throughout the cosmos raises the possibility that living systems can exist beyond Earth. Other data allow us to argue that life could be transported between planetary bodies and could, possibly, become established on another world.
Current models indicate that there are natural means to propel organisms into interplanetary space.
In addition, experimental evidence from the orbiting Long Duration Exposure Facility and from at least one Surveyor lunar lander indicates that some common terrestrial microorganisms can survive in excess of five years. Finding life in extreme environments on Earth suggests that life might survive in liquid water niches on other planetary surfaces, and that certain life forms may be common throughout our Solar System. For several reasons pertinent to astrobiology, we must determine if life from one world can establish an evolutionary trajectory on another. Establish models to determine probabilities for life's transport to, and survival on another planet. Search for evidence of an external origin for terrestrial life, or of exchanges between the biosphere of Earth and of that Mars or other planets.