The exploration of the outer Solar System has revealed a plethora of amazing worlds, the likes of which were little known or even unheard of just a decade ago. Among the most remarkable and tantalizing discoveries are the “ocean moons” such as Europa and Enceladus, which have oceans or seas of liquid water beneath their icy surfaces. Other moons like Titan, Ganymede, and Callisto may also have them, and even some asteroids. Titan also has seas and lakes of liquid methane/ethane on its surface. With all that water, these small worlds have become a primary focus in the search for possible life elsewhere in the Solar System. Now, a new NASA budget proposal wants to take that a step further and fund new missions to these watery moons.
The 2016 budget proposal from the U.S. House Appropriations Committee calls for the creation of an “Ocean Worlds Exploration Program” which would fund new missions to Europa, Enceladus, and Titan. From the proposal:
“Many of NASA’s most exciting discoveries in recent years have been made during the robotic exploration of the outer planets. The Cassini mission has discovered vast oceans of liquid hydrocarbons on Saturn’s moon Titan and a submerged salt water sea on Saturn’s moon Enceladus. The Committee directs NASA to create an Ocean World Exploration Program whose primary goal is to discover extant life on another world using a mix of Discovery, New Frontiers and flagship class missions consistent with the recommendations of current and future Planetary Decadal surveys.”
This is exciting news for those who have been advocating such missions. The bill provides $140 million to continue development of a new Europa mission, including a lander—$110 million more than requested. An additional $86 million goes toward developing new missions to Enceladus and Titan.
As Kevin Hand, a senior scientist at NASA’s Jet Propulsion Laboratory, noted: “The next few decades, if our exploration proceeds in a visionary manner, there are three key missions from the standpoint of searching for extant life. We should go to Europa and explore its subsurface ocean. We should land in the methane, and ethane lakes of Titan. And We should fly through and dive into the plumes of Enceladus.”
The bill also calls on NASA to launch the Europa mission by 2022; previously, NASA had only committed to a vague “mid-late 2020s.” The mission would utilize the Space Launch System (SLS) and may be a version of the previously proposed Europa Clipper, which would make repeated flybys of the moon. A lander, of course, would be a fantastic addition.
NASA’s Planetary Science Division receives $1.557 billion in funding overall, a very welcome announcement.
Jupiter’s moon Europa has long been of astrobiological interest to planetary scientists; a global water ocean lies beneath the outer icy crust, which is now thought to be quite similar to Earth’s oceans or soda lakes in salinity. New evidence suggests there is even sea salt on Europa’s surface. The rocky ocean floor could also provide nutrients and minerals for any putative life forms. With water, heat, and nutrients available, the Europan ocean is now considered to be one of the best places in the Solar System to search for life, even if only microbes. Even the darkest, deepest oceans on Earth are teeming with life.
More recently, Saturn’s moon Enceladus has been added to the water worlds list. The Cassini spacecraft found geysers of water vapor/ice crystals erupting from deep fissures in the moon’s icy surface at the south pole. They are now thought to originate from a subsurface ocean or sea of water, much like on Europa. There is also now evidence for hydrothermal activity on the ocean floor, much like on Earth. Cassini has already flown through and sampled the plumes directly, finding water vapor, ice crystals, salts, and organics. Cassini can’t identify living microbes in the plumes, but the data it has returned now makes Enceladus another place that scientists are keen to explore further.
Titan, Saturn’s largest moon, is very unique, with seas, lakes, rivers, and rain of liquid methane/ethane. It is much too cold for liquid water on the surface, but Cassini has also provided evidence for a subsurface ocean on this moon as well, although little else is known about it at this point. According to some scientists, it is also conceivable that some kind of primitive life could exist in the hydrocarbon seas and lakes, although it would be quite different than anything on Earth. Titan’s surface and atmosphere are both rich in organic material; even if there is no life, Titan is still considered to be a deep-freeze version of early Earth, with possible pre-biotic chemistry occurring which could provide clues to how life started on Earth.
All three of these moons provide a unique opportunity for exploration in the outer Solar System and could help to answer the question of how life arose on Earth and whether it exists anywhere else in the Solar System.
Another positive note is that the bill provides funding for both the Opportunity rover on Mars and the Lunar Reconnaissance Orbiter to continue after being faced with possible cancellation. As noted by Eric Berger, “This is a marvelous day for planetary science and the search for life.”