Leave no trace

After hoovering up as much data on Jupiter as it can, the Juno probe will ultimately destroy itself, plunging into the giant planet's atmosphere in February 2018. Why not just leave it alone and let it do its thing until it breaks down, like the Opportunity rover, which is still trucking around the surface of Mars 12 years after it landed? To preserve Europa. 

No one is claiming that there's life on Europa, but the chance is significant enough that NASA wants to avoid contaminating it with terran microbes. As a result, Juno's mission includes a self-destruct sequence that will prevent fragments from raining down on the Jovian moon. The fact that microbes from Earth are potentially hardy enough to survive being frozen across space for five years, then baked in Jupiter's radiation, is a testament to the fact that something could be alive under the crust of Europa's frozen sea. 

NASA has an Office of Planetary Protection ("all of the planets, all of the time") that presumably guides US policy on the preservation of other bodies in our solar system. This isn't intended as an insult, but their website looks like I might have designed in 1999.

I can only imagine what will happen when global capitalism drives the tendrils of exploration/exploitation beyond the moon, spearheaded by institutions with little interest in keeping Europa microbe-free if it requires paying for one more ounce of rocket fuel.