By Dr. Cynthia B. Phillips
Planetary geologist at the Carl Sagan Center for the Study of Life in the Universe, SETI Institute
Jupiter's moon Europa could be the best place beyond the Earth to search for life. This small moon, about the size of Earth's Moon, is one of the Galilean moons first discovered 400 years ago by Galileo. The Galilean moons were the first objects observed to orbit another planet, and they revolutionized the way our solar system was understood.
Today, the moons of Jupiter are known to be a scientifically rich part of our solar system, and they are yielding a new revolution in our view of the possibilities for extraterrestrial life. Europa, in particular, may hold the key to understanding the potential for life in our solar system and beyond. Scientists believe that habitability, or the ability of life to survive on a particular world, requires liquid water, the correct chemical elements, and a sufficient source of energy. Beyond the Earth, Mars and Europa are the best places to search for life in our solar system, and Europa is unique because it is believed to have a large ocean of liquid water fairly close to the surface today, underneath its icy crust.
The Galileo spacecraft, which orbited Jupiter from 1995 to 2003, made observations of Europa and the other Galilean moons, and then it was intentionally crashed into Jupiter to avoid any potential contamination of Europa. Galileo observations revealed a smooth, bright icy surface, criss-crossed by an intricate web of fractures and ridges. Scientific analyses of data from its instruments confirmed the probable existence of a layer of water about 50 miles thick beneath the ice. This means that Europa could have more water than in all of the Earth's oceans combined!
Image credit: Mike Carroll, NASA/JPL/Caltech
NASA is currently planning the Europa Jupiter System Mission (EJSM) to follow up on these discoveries. EJSM is an international project, and includes a NASA-built Europa orbiter and a Ganymede orbiter to be built by the European Space Agency. Both spacecraft would study the entire Jupiter system, as well as their targeted moons. Development of such a mission requires a very long lead time, however - even if design and construction of the spacecraft started now, the first Europa data wouldn't be received until 2024!
Exploration of the outer solar system helps us understand not only the habitability of our own solar system, but also the potential for life in other solar systems. Many of the "exoplanets" that have been recently discovered orbiting other stars are giant planets, much more similar in size to Jupiter than to the Earth. While it is unlikely that such giant planets would be habitable, it is quite possible that these other Jupiters have moons orbiting them just like the Galilean moons. If Europa is an inhabited world in our own solar system, this increases the chance that similar moons could be abodes for life in distant solar systems throughout the universe.
The Europa Jupiter System Mission concept is a mature one, and much work has been done over the past decade to mitigate the radiation challenges that come with operating a Europa spacecraft deep inside the radiation belts of Jupiter's strong magnetic field. A mission to Europa has consistently emerged as the top outer solar system flagship-class mission in studies by NASA and the US planetary science community. It is time to commit funding and resources to making this vision a reality.
To learn more about Galileo's 400 years of discovery, the relevance of outer solar system exploration, and the plans for EJSM, visit a special exhibit in Washington DC at the Rayburn House Office Building on Thursday, July 15th. This exhibit is open to the public.