Slush on Europe
The most detailed imagery yet of Jupiter's moon Europa offers further evidence of the existence of slush beneath the bright moon's icy surface. There may even be liquid water on the moon. This is what planetary scientists from Brown University and NASA say after their analysis of the latest data from the Galileo spacecraft.
Europa is slightly smaller than our Earth's moon, but many times brighter. Its icy surface has fascinated scientists since the space shuttles of the Voyager missions flew through the Jovian system in 1979. Europa has a surface temperature of about -160 oC, so the moon could hold an ocean in its frozen state for several million years. However, some scientists now believe that the heat from the tidal forces exerted on Europa's ice sheet by Jupiter and the other moons may be sufficient to keep much of the water in the liquid state.
The latest images were taken by Galileo in December 1997 and have only recently reached Earth. They contain three key pieces of evidence showing that Europa can be squishy beneath the icy crust at shallow depths, and may be even warmer at greater depths. Clues include an oddly flat impact crater, chunky textured surfaces resembling icebergs, and gaps where new icy crust appears to have formed between ice sheets the size of continents.
Some of the new images show the flat center of Pwyll Crater. Impact marks and debris scattered over much of the moon indicate that a meteorite fell on Europa relatively recently (about 10-100 million years ago). The darker debris around the crater suggests that the impact brought deep material to the surface. But the crater's shallow basin and high mountain peaks may mean the surface ice was warm enough to collapse and fill in the deep hole, says Brown University's Geoffrey Collins.
A subsurface ocean warm enough to form slush could also explain the origins of a territory dubbed "Chaos Territory". It is riddled with broken and rounded blocks of crust the size of several city blocks. Between the jagged lumps, the new images show rough and swirling material that may have been trapped in the mud frozen by the extremely low surface temperatures.
Looking at Europa more globally, large sheets of ice appear to be sliding across the warmed interior of the moon. This process is very similar to the movement of the continental plates on Earth.
Recent images of Europa show that the darker, wedge-shaped gaps between the ice sheets share many similarities with new crust formation at mid-ocean ridges on Earth's ocean floor. The new crust bulging between the dividing plates on Europa, the researchers say, was formed from initially squishy ice, or possibly liquid water, that has frozen and fractured.
"All the evidence, taken together, supports the hypothesis that liquid or at least partially liquid water existed at several different subsurface locations in Europe in recent history at shallow depths," says James Head, professor of geosciences from Brown University and leader of a group of the Galileo research team. 'The combination of internal heat, liquid water and infalling organic material from comets and meteorites means that Europa has the key ingredients for life to emerge,' he explains."Europa, like Mars and Saturn's moon Titan, is a laboratory for studying the conditions that may have led to the formation of life in the solar system."
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