In just 50 years, the reach of humankind in our solar system has expanded enormously. We have sent probes to orbit every planet, and landed on (or dived into, in the case of gas giants) most. Probes have seen the sunrise on Mercury and felt a cool breeze on Mars. Some missions have even succeeded in acquiring rock and dust samples, and returning them to earth. Apollo 11 in 1969 was the first to do this; later the process was automated in the Soviet Luna probes of the 1970s. In the 1990s samples of the solar wind were captured, and in 2006 particles from the tail of a comet were brought to earth for further study. Sample return mission to Mars have been proposed for the future, and given enough time, mission to and from the Jovian moons may be possible.
When planning an exploratory mission to another celestial body that could (in theory) support life, scientists make every effort to sterilise the probe of all earthly lifeforms. Microbes from earth might colonise the foreign world, and might even displace the native wildlife (in other words alien microbes). Proof of life on another planet those that would be of immeasurable interest to scientists and the public alike, but earthly organisms in the equipment would most likely pollute the result of the off-earth experiments.