The Search for Life in the Solar System
|
by Tim Porter The Little Space Probe that Could Fire and Ice  There are several reasons why scientists theorize that Europa is covered with a subsurface ocean below an icy crust. Pictures taken by the Galileo spacecraft show that Europa has an extremely smooth surface with very few craters. Such geologic evidence suggests young, changing surface features. In contrast, the Moon, whose surface has remained unchanged for billions of years, is pockmarked with thousands of craters, while only three craters larger than 5 kilometers wide have been discovered on Europa. Scientists use crater counts to help estimate the age of celestial surfaces —more craters lends to a older surface— since the chances for impact are approximately equal throughout the solar system. Large portions of Europa's surface appear very similar to ice floes near the North Pole of Earth. Thousands of dark lines criss-cross the entire surface of Europa, separating the crust into plates, and resemble fault lines on Earth. Scientists believe these lines result as water from below fills the fractures when the surface crust separates and then freezes into place. Europa's sister moon Io demonstrates much different surface activity. Closer to Jupiter than Europa, Io is incessantly heated by Jupiter's massive gravitational pull. As a result, volcanoes cover the surface of Io in stark contrast to Europa's icy features. This gravitational heating could also take place on Europa, although to a much smaller degree. Such internal heating could cause high enough temperatures to allow for liquid water inside of Europa's icy crust. If there is water and heat there is a chance, however small, for life to exist.  Next: Life on Europa? |
The Search for Life in the Solar System 