Life on Earth requires water. When scientists look for life in other places, they look for signs of water. And they now say they have found them on a moon of Saturn.
The American spacecraft Cassini passed close to Enceladus [en-SELL-ah-dus] in February of two thousand five. Cassini captured images of what appears to be material shooting away from the moon.
The leader of the team studying the pictures of Enceladus is Carolyn Porco of the Space Science Institute in Boulder, Colorado. She says the finding could change the way scientists look at conditions for life in the solar system.
Scientists considered several possible causes for the jet of material seen in the pictures from Cassini. But they found the most likely was that water was shooting out of Enceladus. They describe these jets as geysers, just like the boiling water that shoots out of the ground in places like Yellowstone National Park.
The main difference between Yellowstone’s geysers and those of Enceladus is temperature. Geysers on Earth are caused by heat below the ground. Ground water enters these areas, begins to heat and shoots through openings in the ground.
Scientists believe the geysers on Enceladus are only about zero degrees Celsius — just above freezing. This may seem cold to us. But on Saturn’s icy moon, zero degrees is very hot.
Scientific measurements show that Enceladus is very cold — about two hundred degrees below the freezing point of water. But measurements by Cassini have shown that some parts of Enceladus are much warmer — only one hundred sixty-degrees below freezing.
Scientists suggest that even warmer temperatures may exist below the surface of the moon. If there is liquid water, it would be much warmer than the surrounding ice. This could cause the liquid water to explode out of openings in the surface, causing the picture that Cassini captured.
How could water exist on such a cold world? Planetary scientists have developed theories that liquid oceans exist on several icy worlds. Two moons orbiting the planet Jupiter, Callisto and Europa, are good candidates.
Information gathered by the Voyager and Galileo space vehicles suggests that powerful forces are at work under the surfaces of these moons. The strong force of gravity from Jupiter may make underground temperatures on Callisto and Europa warm enough to melt water.
But there is a closer example of liquid water hidden under ice right here on Earth. Ten years ago, Russian and British scientists confirmed the existence of a lake in the coldest part of the world — Antarctica. It is called Lake Vostok. It lies under four thousand meters of ice.
There are several theories for why water in the lake remains liquid. One is that warmth from the Earth has melted the ice. Another is that pressure from the huge weight above the ice caused it to melt. Whatever the reason, Lake Vostok has led some scientists to believe some moons of Jupiter and now Saturn could have whole oceans hidden under their icy surface.
Cassini will get another close look at Enceladus in two thousand eight.
Taken from voaspecialenglish.com