A tiny moon
of Saturn, no larger than England, is changing researchers notions about
which celestial bodies can support geologic activity. New, closer images of
Enceladus have confirmed that a plume, noticed in previous images, is indeed
an enormous geyser emanating from visible cracks in the moons surface.
In this color-enhanced image, an enormous
plume emanating from fractures on Saturns moon Enceladus appears backlit
by the sun. Astronomers were surprised to find geologic activity on the small
moon, which is seven times smaller than Earths moon. Image courtesy of
NASA/JPL/Space Science Institute.
NASAs Cassini spacecraft first revealed the plume-like feature in images taken in January and February last year. But according to Carolyn Porco, Cassini imaging team leader at the Space Science Institute in Boulder, Colo., speculation remained that the feature was an artifact of the camera. Following a special Cassini mission in November to take a closer look, however, the images confirmed it without question, Porco says.
The moon and its plume look similar to a comet and its tail, which forms from vapor created when sunlight warms the icy body. Enceladus, however, does not receive much sunlight. Instead, pressurized vapor on Enceladus emanates from below the surface and shoots out like a jet through vents the team calls tiger stripes, Porco says. She describes the vapors composition of small icy particles to be like the finest powder you might ski on in Utah. The cause of the pressurized geyser, Porco says, is due to an internal source of heat on the moon, either from flexing tides or from radioactive material.
Small bodies such as Earths moon, which is 3,476 kilometers in diameter, typically lose their internal heat shortly after formation, rendering them geologically dead. Porco says that even though she was not surprised to find geologic activity on Enceladus, she finds it thrilling to see geologic activity on another body especially a moon only 480 kilometers in diameter, with a geyser as tall as the moon is wide. Finding activity on such a small body, Porco says, has torqued our ideas around about how geologic activity can come about.
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