Europa

Galileo Images of Europa

Image Credit:

NASA/JPL/DLR

 

Europa is the fourth largest satellite of Jupiter, the smallest of the fours Galilean moons, and the second closest to Jupiter of the Galilean moons. It orbits 671,100 km from Jupiter and takes only 3.55 Earth days to go around Jupiter (twice that of Io). It has a density of 3.013 g/cm³, making it about 3 times that of water. It does have a lower density than Io, which will be explained in the next paragraph. It's radius is about 1561 km, making it smaller than the Moon, which is about 1738 km in radius.

Europa has a surface covered with ice and is believed to have subsurface liquid water under the ice. The water is kept liquid by two processes, the insulation from the ice and from tidal forces heating the interior, much like tidal forces keep the interior of Io molten. If life exists anywhere else in our Solar System, this may be the most likely place to look for life. However, any mission we send to Europa to find life would have to be very careful to be sterilized as any microbes hitching a ride from Earth would contaminate any detection techniques used on Europa to search for life.

Just recently, Europa was found possibly to experience plate tectonics, much like Earth. Slabs of ice may slide under each other, creating "Europa-quakes", much like earthquakes experienced on Earth as continental plate slide under and above each other. More information about plate tectonics can be found on space.com's article about Europan plate tectonics.

Artist's Concept of Plate Tectonics on Europa

Credit: Noah Kroese, I.NK

Close-up view of possible plate spreading on the surface of Europa

Credit: NASA/JPL

 

Martian Canals?

Hubble Image of Mars (Mercator Projection)

 

By the mid 19th century, telescopes had improved enough that surface features on Mars could be easily observed and examined. In 1877, Italian astronomer Giovanni Schiaparelli noted what he thought were long straight lines on the surface which he named after rivers on Earth and identified them on maps he drew of Mars as "canali" which is Italian for channels or grooves. English speakers misinterpreted canali as canals and thought that the channels on Mars were artificial, created by Martians (which is the correct term for someone from Mars - if there were such a creature).

Schiaparelli Map of Martian "canals"

Percival Lowell Map of Martian "canals"

The Martian canals led rise to a plethora of science fiction which believed that Mars was inhabited by intelligent creatures including "War of the Worlds" by H.G. Wells and "The Martian Chronicles" by Edgar Rice Burroughs (who also created Tarzan the Apeman). 

As telescopic resolution improved with new technology, it became clear that the channels on Mars were not artificial, but were created naturally in the ancient past by running water. In a previous post, we learned that water once flowed freely on the surface, but as the atmosphere was stripped away, allowing the planet to cool and the air pressure to drop, surface water no longer exists on Mars.