The only time that a formally designated NASA “life detection” mission was flown to another planet or moon was when the two Viking landers headed to Mars forty years ago.

The odds of finding some kind of Martian life seemed so promising at the time that there was little dispute about how much energy, money and care should be allocated to making sure the capsule would not be carrying any Earth life to the planet. And so after the two landers had been assembled, they were baked at more than 250 °F for three days to sterilize any parts that would come into contact with Mars.

Although the two landers successfully touched down on the Martian surface and did some impressive science, the life detection portion of the mission was something of a fiasco — with conflict, controversy and ultimately quite a bit of confusion.

Clearly, scientists did not yet know enough about how to search for life beyond Earth and the confounding results pretty much eliminated life-detection from NASA’s missions for decades.

But scientific and technological advances of the last ten years have put life detection squarely back on the agenda — in terms of future searches for fossil biosignatures on Mars and for potential life surviving in the oceans of Europa and Enceladus. What’s more, both NASA and private space companies talk seriously of sending humans to Mars in the not-too-distant future.

With so many missions being planned, developed and proposed for solar system planets and moons, the issue of planetary protection has also gained a higher profile. It seems to have become more contentious and, to some, seems far less straightforward than it used to be.

A broad consensus appears to remain that taking Earth life to another planet or moon, especially if it is potentially habitable, is a real possibility that is both scientifically and ethically fraught. But there are rumblings about just how much time, money and attention needs to be brought to satisfying the requirements of “planetary protection.”

In fact, it has become a sufficiently significant question such that the first plenary session of the recent Astrobiology Science Conference in Mesa, Arizona was dedicated to it. The issue, which was taken up in later technical sessions as well, was how to assess and weigh the risks of bringing Earth life to other bodies versus the benefits of potentially sending out more missions, more often and more cheaply.

It is not a simple problem, explained Andrew Maynard, director of the Risk Innovation Lab at Arizona State University. Indeed, he told the audience of scientists that it was a “wicked problem,” a broadly used term for issues that are especially complex and involve numerous issues and players.

Read more at the Many Worlds blog.