What should be the roles of humans and robots in space exploration, including the search for life beyond Earth? This question will be important for the newly announced NASA goal of human landings on the Moon by 2024, followed by a lunar outpost and future human flights to Mars.
Sometimes this issue is posed as a binary choice: humans or robots. But this oversimplifies the issues. First, the answer is almost certainly context dependent. It should be discussed separately depending on the mission being considered. For example, humans might be very useful in exploring the Moon or Mars, but they certainly are not appropriate for the moons of Jupiter. Humans are important on the International Space Station, but they would be worse than useless for an astrophysics mission. Second, this really is a false dichotomy. Humans are deeply involved in all space missions, but in an age of telepresence and artificial intelligence, they do not necessarily need to be physically present. As one example, consider a human on Mars’s moon Phobos teleoperating a vehicle on the martian surface; she would not be on Mars, yet certainly she would be part of a space mission. Or compare that with the same human on Earth teleoperating a vehicle on the martian surface. Where do we draw the line? How important is it for a human to be physically on another world?
One of the most challenging situations involves the search for life beyond Earth. This is probably the most important question in space science, and as far as we know Mars is the most likely place for life that is within reach for detailed exploration. Mars is also the one place where humans might realistically live off-Earth. The problem is that we really don’t know how to search for life remotely, especially if we consider the possibility of truly alien biochemistry. The Viking mission nearly fifty years ago was the only attempt that has been made to land a robotic life-detection instrument on Mars, and it failed to answer the questions despite near-perfect instrumental performance. Almost surely a team of humans on Mars could do a much better job, and that might be the only way to approach such a challenging task. However, the presence of humans, who carry with them a complex microbial ecosystem (their microbiome) from Earth, could mask or even destroy any indigenous life. By sending humans, we might end forever our one chance of finding exolife (to say nothing of the ethical issue of possibly destroying the native life of another planet).
One then begins to consider other ways to approach this issue, such as defining “safe” or quarantined areas on Mars where humans could land without the risk of contaminating the entire planet. The aforementioned teleoperations by a human on Phobos offer another possibility. But would any astronaut be willing to devote a major part of their professional life to a trip to Mars but not be permitted to actually land there? These issues about the role of humans in space are about to become important to scientists and (potentially) to the public, and they need skeptical analysis.