Searching for Life on Other Worlds: Overview of Missions

Astrobiology is a cherished topic in the science news. Many people love considering questions of what extraterrestrial life might be like, what it might have in common with Earth life, and how it might be different. Since the 1960s, NASA and other space agencies have been studying the environments of Mars and other Solar System worlds, looking for clues of potential habitability to, and evidence for, native microscopic organisms.  In recent years years, there’s been an expansion of robotic spacecraft missions carrying experiments relevant to the search for life forms. A disproportionately high number of the missions focus on Mars, while the rest look at asteroids and moons of the outer Solar System and scan across interstellar space to detect and collect initial information on planets of other stars.

NASA has included astrobiology with a varying degree of publicity over the years, sometimes to the point that the astrobiological value of a particular mission is not recognized widely. Some of the Apollo missions bringing astronauts to the Moon, for instance, contributed to astrobiology. Apollo 16 and 17 carried joint American-European experiments called Biostack I and Biostack II, which examined the effects of deep space radiation on a range of organisms, including bacteria, plant seeds, and animal eggs.  Also, following the first three piloted lunar landings (Apollo 11, 12, and 14), returning crews and lunar samples were put into isolation and lunar dust was tested for presence of native lunar microorganisms, based on the rationale that the moon could be a home to its own biosphere.

Roughly ten NASA missions that are now completed have provided data that were of major significance to our understanding of the capability of environments of various Solar System planets and moons to support either native microbial life that might exist, or life forms that we might choose to deposit there. Currently, NASA has two space telescopes –Hubble and Spitzer– contributing directly to the search for planets of other stars and another one gearing up for launch late this year (James Webb telescope). The Cassini probe is still active, examining moons of Saturn, including Titan and Enceladus, both of which are potential targets for future probes carrying instruments designed to look for microbial life forms and complex organic molecules that must precede life. Finally, there are four missions in active status operating on and in orbit of Mars, plus a new rover will be departing for the Martian surface in 2020. Prior to the 2020 probe, another craft will set out to collect a sample from asteroid Bennu and return return that sample for analysis in Earth-bound labs.

In an earlier post, we discussed the value of missions to Jupiter’s moon Europa and Saturn’s moon Enceladus. We’ll be examining more missions in upcoming posts, beginning with the missions relevant to Mars, also known as the Red Planet. We began this discussion six months ago after a discovery confirming the presence of perchlorate (ClO₄-) salts precisely where streaking suggests that water has run recently on the Martian surface. This means that Mars harbors very briny water, which makes its way to the surface from time to time and remains in a liquid state, despite the very low pressure of the Martian atmosphere. That could be good or bad for the prospect of life forms –water being liquid is good, while extremely high salt content is bad– but it also has interesting implications for how we interpret data that were obtained 40 years ago, during the first mission to carry experiments to any planet designed to look directly for life. This was NASA’s Viking mission, which we’ll examine in an upcoming post, just after we look still further back in the history of astrobiology to the time when humanity first applied modern instruments to the search for evidence of life on Mars.

Written by David Warmflash

David is an astrobiologist and science writer. He received his M.D. from Tel Aviv University Sackler School of Medicine, and has done post doctoral work at Brandeis University, the University of Pennsylvania, and the Johnson Space Center, where he was part of the NASA's first cohort of astrobiology training fellows. He has been involved in science outreach for more than a decade and since 2002 has collaborated with The Planetary Society on studying the effects of the space environment on small organisms.