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About this Project

Nearly 150 years ago, the Challenger Expedition laid the foundation for modern understanding of our oceans. Among the contributions that scientists on board HMS Challenger made was the dawning realization of the fundamental link between the ocean and all life on Earth. Today, preparations are underway for another great expedition, one that could help us answer, once and for all, one of the greatest questions in human history: Is life on Earth unique or are conditions to support life potentially common throughout the universe?

The quest for evidence of life on other planets is not new. From the time that humans first understood that Earth itself is not unique, but just one planet among several orbiting a star that is itself one of many throughout the galaxy, people have gazed at the night sky and wondered what other forms of life might exist beyond our home. Since the 1960s, NASA’s astrobiology program has been conducting a careful search for signs of extraterrestrial life. That search has become ever more expansive, venturing well beyond our solar system in an effort to hunt for planets that have astrophysical similarities to Earth in the so-called “Goldilocks Zone” around other stars in the galaxy that could support the presence of liquid water on the surface of a planet.

But then came information from two NASA missions inside our solar system suggesting that extraterrestrial life might be present much closer to our home. The Galileo Mission arrived at Jupiter in 1995 and began circling the planet for eight years. The data it sent back provided strong evidence of liquid oceans on three of its moons: Europa, Titan, and Ganymede. More recently and most significantly, the 1997-2017 Cassini Mission to Saturn discovered water-rich gas plumes venting from the icy surface of Saturn’s moon Enceladus. Analysis of those plumes suggests Enceladus may have seafloor hydrothermal vents similar to those on Earth that could be providing the necessary energy to sustain extant life.

Together, discoveries from these two missions mean that the search for life beyond Earth has reached a critical new phase. Planetary science and ocean science have begun to converge as it has become clear that multiple planetary bodies within our solar system host saltwater oceans in contact with a rocky, mineral-rich seafloor, just as Earth does.

For both planetary and ocean scientists, these discoveries have been a game-changer because they strongly suggest that finding life beyond Earth does not require futuristic technologies enabling interstellar space travel. Instead, our most direct path could be to continue robotic exploration of the ocean worlds within our own solar system–locations that are not only well within our reach, but that also hold a liquid-ocean environment of a type that today’s ocean scientists are already intimately familiar and that engineers are already accustomed to exploring.

Among the current estimate of at least a dozen ocean worlds in our solar system, scientists have identified six as prime candidates for exploration in the quest to find extraterrestrial life: three moons of Jupiter (Europa, Ganymede, and Calisto), two moons of Saturn (Enceladus and Titan), and Neptune’s moon, Triton. With the exception of the ocean on Enceladus, which Cassini sampled indirectly by flying through its icy plumes with instruments that were never designed to analyze such a sample, we know very little, yet, about the composition of the oceans on these worlds, or their capacity to sustain and nurture life. As a result, the same scientific discipline that has strived, since the Challenger expedition, to understand Earth’s oceans now finds itself faced with an opportunity to play a critical role in the exploration of other ocean worlds.