Europa Jupiter System Mission Backgrounder
Background/Significance: Possibility for life. Europa is believed to have an ocean of liquid water, which may support life. The goal of the proposed Europa Jupiter System Mission (EJSM) is to discover if Europa and/or its sister moon Ganymede are habitable.
About Europa: Europa is one of the four large moons of Jupiter that were discovered in 1610 by Galileo Galilei with the newly invented telescope. (The other moons discovered were Callisto, Ganymede, and Io.)
Slightly smaller than Earth's moon, Europa has an icy crust. Like Earth, Europa is thought to have an iron core surrounded by a rocky mantle, and a water ocean covering the surface. Being five times farther from the Sun than Earth, the ocean surface of Europa is frozen over, and covered with cracks caused by shifting ice and tidal forces.
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Europa orbits Jupiter every three and a half days and experiences strong tidal forces that cause the moon to flex and stretch. The flexing happens because Europa's orbit is eccentric (it is oval-shaped rather than a perfect circle), and the tide is much higher when the moon is close to Jupiter than when it is farther away. This continuous flexing creates heat, which makes Europa's interior warmer than from the Sun's heat alone, and it could produce volcanic activity where the ocean meets the rocky interior. The tidal forces also raise and lower the sea beneath the ice, likely causing the cracks we see in images of Europa's surface from visiting robotic probes. Europa's liquid ocean could potentially provide an environment suitable for simple organisms.
History of Exploration of Europa: Over the years, Europa has been visited by eight spacecraft; Pioneer 10, Pioneer 11, Voyager 2, Voyager 1, Galileo, Ulysses, Cassini-Huygens, and most recently (in February 2007) by the New Horizons spacecraft on its way to Pluto. (Europa and Jupiter Comparison Chart)
Future exploration of Europa -- Europa Jupiter System mission (EJSM): With an estimated cost to NASA of $2.7 Billion (FY07), the proposed Europa Jupiter System Mission (EJSM) would consist of two separate vehicles, one provided by NASA and the other by ESA, which would each launch (separately) in 2020 and arrive at the Jupiter system in late 2025 and early 2026.
Both the NASA-built Jupiter Europa Orbiter (JEO), and the ESA-built Jupiter Ganymede Orbiter (JGO) would be powered by chemical propulsion. Venus and Earth gravity assists would speed each spacecraft onward for arrival at Jupiter only 6 years later.
JEO would carry 11 instruments and JGO would carry 10 instruments to study dynamic phenomena such as Io's volcanoes and Jupiter's atmosphere. In addition, the orbiters would map Jupiter's massive magnetosphere and study how it interacts with its moons. The orbiters would also map any liquid water oceans, which are believed to exist beneath the ice shells of Europa and Ganymede.
Also planned is NASA's Jupiter Polar Orbiter (Juno), which will arrive at the Jupiter system in 2016.
EJSM has two major goals with supporting science objectives:
Goal: Determine Whether the Jupiter System Harbors Habitable Worlds. The fundamental theme for EJSM can be further focused into science objectives relating to habitability (focusing on Europa and Ganymede). The main science objectives supporting this goal are:
- Characterize sub-surface oceans
- Characterize the ice shells and any subsurface water
- Characterize the deep internal structure for Ganymede and the intrinsic magnetic field
- Compare the exospheres, plasma environments, and magnetospheric interactions.
- Determine global surface compositions and chemistry
- Understand the formation of surface features, including sites of recent or current activity, and identify and characterize candidate sites for future in situ exploration.
Goal: Characterize the Processes Within the Jupiter System. The Jupiter system includes a broad diversity of objects, including Jupiter itself, 55 currently known outer irregular satellites, the Jovian ring system, four small inner satellites, and the four large Galilean Satellites: Io, Europa, Ganymede, and Callisto. The main science objectives supporting this goal are:
- Understand the Jovian satellite system, especially as context for Europa and Ganymede.
- Evaluate the structure and dynamics of the Jovian atmosphere.
- Characterize processes the Jovian magnetodisk/magnetosphere.
- Determine the interactions occurring in the Jovian system.
- Constrain the origin of the Jupiter system.
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Biochemistry on Europa: Scientists think it very likely that oceans exist beneath Europa's icy crust. If so, life could exist within the liquid water. On Earth, extremophiles (life forms that can survive in extreme variations in temperature and other conditions) have been found living near volcanic vents at the bottom of the ocean. These Earth extremophiles have shown scientists that sunlight is not a requirement for biochemistry, just water warm enough to be liquid, combined with other minerals and food sources.
The Europa Jupiter System Mission (EJSM) would help to answer key questions about the moon: how thick is the ice? As the ice shifts, does liquid water come to the surface where it may be studied by future probes? If biochemistry (life) exists on Europa, EJSM would help to map out sites for future probes and landers to sample frozen microscopic Europa life.
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