Could Europa Host Life?

The crisscrossed surface of Europa in 

true color (left) and false color (right). 

Courtesy of NASA/JPL. 

“Follow the water” is a common phrase used when searching for life in the Universe.  Scientists use the presence or absence of water to help evaluate the potential for life on planetary bodies.  If a target is thought to have water then NASA takes steps to protect it from Earth contamination (Planetary Protection).   The main evaluation for if a planet has the potential to host life is based on if it has water.  If there is no evidence for water, then the sterilization procedures for a mission are relaxed.

Europan ridge that may be formed by freezing water.  

Could provide conduit for water to the surface of Europa. 

Courtesy of NASA/JPL.

Europa is one of the planetary bodies that is protected under Planetary Protection procedures.  Europa is a moon with a surface predominantly covered with ice orbiting planet Jupiter.  The first mission to send back images of Europa’s surface was Voyager.  Voyager was launched in the 1970s to study the outer solar system and eventually interstellar space.  Higher resolution images were obtained by the 1989 Galileo mission, which was designed to study the Jovian system.  These images revealed in ice-covered surface resembling a ball of twine, covered with linear ridges.  Data from these missions also revealed that Europa generates its own magnetic field, which provides evidence that there is a briny ocean beneath the surface.

As the water intrusion freezes it exerts pressure in all 

directions and can cause upward flexure (red) and

 sideways compression and flexure (blue) to form a ridge.  

Pressure could crack the ice, allowing water-radiation reactions

 that could be favorable for life on Europa.

Europan ridges are of specific scientific interest because they not only reveal information about geologic processes but also the potential for the existence of shallow water. The interaction of water on Europa with the surface could have implications for the astrobiological potential of the icy satellite.  Jupiter’s magnetosphere  bombards the surface of orbiting moons with radiation.  If water on Europa reacts with the radiation it could produce chemicals that have the potential to nourish life in the water, similarly to how hydrothermal vents sustain life on the ocean floor. 

One hypothesis for Europan ridge formation is that shallow water intrusions within the ice shell could freeze and expand to create the surface features of the ridges.  As the water freezes and expands it exerts a significant amount of pressure on the surrounding ice and may create cracks within the ice in the same way that freezing water in pipes may cause them to burst in winter. These cracks could serve as a conduit for water to reach the surface and react with radiation.

In order to explore the hypothesis that freezing water in the ice could form ridges several questions must be answered.  How much pressure can the freezing water exert on the surrounding ice?   Is this pressure enough to crack the ice?  How deep can the water intrusion be and still be able to create these ridge features.  These questions are being evaluated currently through the use of computer-based models and may allow scientists to follow the water to life.

 References:

Cassidy, T., Coll, P., Raulin, F., Carlson, R. W., Johnson, R. E., Loeffler, M. J., Hand, K. P., et al. (2010). Radiolysis and Photolysis of Icy Satellite Surfaces: Experiments and Theory. Space Science Reviews, 153(1-4), 299-315. doi:10.1007/s11214-009-9625-3

Christopher F. Chyba and Cynthia B. Phillips. (2002). Europa as an Abode of Life. Origins of Life and Evolution of Biospheres (Vol. 32, pp. 46-47). doi:10.1111/j.1744-618X.2010.01158.x

Han, L., & Showman, A. P. (2008). Implications of shear heating and fracture zones for ridge formation on Europa. Geophysical Research Letters, 35(3), 6-10. doi:10.1029/2007GL031957