For life to be present the three basic requirements are: 1) liquid water, 2) chemical building blocks, and 3) a source of energy. Europa is assumed to have all three. Europa is the fourth largest of Jupiter's 67 moons. Its icy crust shows evidence that it is frequently cracked open by tidal forces, and many cracks may be repeatedly pulled open and pushed together as Europa orbits Jupiter, pumping water from the sub-surface ocean up into the cracks. Greenberg proposed that ecosystems of bacteria and even multicellular life could live in these surface cracks, having just enough shelter from UV radiation and being supplied with heat and nutrients in the water pumped into the cracks. He even proposed that ultraviolet radiation striking Europas surface could free oxygen atoms from the ice, which could be absorbed into the sub-surface ocean via these cracks, and could oxygenate Europas ocean, allowing more complex life-forms to be supported. This moon of Jupiter might have life in a subsurface ocean

The presence of magnesium compounds on the surface of Europa suggests that water from the subsurface ocean reaches the surface through springs or vents. If this occurs these eruptions would deliver up ions and microbes from the ocean below. So, if there is life in Europa's subsurface ocean it could be scattered about the surface of the planet where landers or rovers might find it. This makes Europa a very interesting target in the search for extraterrestrial life. Some researchers believe that it is a much better target than Mars. NASA gives three pieces of evidence that strongly support the presence of Europa's subsurface ocean. 1) Magnetometer surveys done by the Galileo spacecraft discovered an induced magnetic field near Europa's surface. This suggest that a large body of conductive material (salty water) at a depth of 30 kilometers or less. 2) The surface of Europa has bands, ridges, fractures and multi- ringed impact structures that suggest the presence of mobile material below. 3) The surface of Europa has large-scale fractures and ridges similar to those that bound Earth's tectonic plates. These suggest a mobile layer below Europa's crust that supports it and allows it to move.

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A possible model of Europas interior An example of an orbiter passing over Europa The trailing hemisphere of EuropaInternal structure of Europa

Water from a subsurface ocean on Jupiter's moon, Europa, could reach the surface through seeps or erupt from hot water vents. This water would reveal the chemistry of the subsurface ocean and may contain microbes that live below. -Artist's concept image by NASA / JPL.

Europa has almost a complete absence of craters as well as almost no vertical relief. This interesting feature makes it difficult to find out the age of this moon.

Due to Europas smooth surface, it is the brightest moon is the solar system.

For centuries, the four largest moons of Jupiter didn't have actual names. Instead, Galileo gave each moon a number, from 1-4. Of the four large moons, Europa was believed to be the second closest to Jupiter, which is why Galileo also called it Jupiter II. It was Simon Marius who first proposed that the 4 moons should be given their current names.

H.W. QUESTION What kind of life forms do you think Europa would have?

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