Cassini Finds New “Hot Spot”
Flybys of Saturn’s tiny moons Enceladus and Mimas by NASA’s Cassini spacecraft have found one of the moons to be the most reflective in the solar system and the other the most heavily cratered in the Saturnian system.
Enceladus, which scientists have long thought to be cold and dead, actually has a dynamic atmosphere and a warm polar region that suggests volcanic activity, said researchers studying the nearly white body.
Cassini flew within 109 miles of the surface of the tiny moon -- only 314 miles in diameter -- on July 14 and has been sending back data that has surprised researchers.
The moon’s south pole, like Earth’s poles, should be one of its coldest spots; researchers had predicted a temperature of about minus 324 degrees Fahrenheit. But infrared measurements indicate that it is actually the warmest spot on the moon at minus 261 degrees Fahrenheit, too warm to be accounted for by solar heating.
The find makes Enceladus only the third location in the solar system where “hot spots” associated with ongoing geological activity have been found. The other two are much larger: Earth and Jupiter’s volcanic moon Io.
A different instrument on the spacecraft also found a cloud of water vapor over the south pole, presumably produced by ice melting in the warmer region. The fact that water vapor persists in the atmosphere of this low-gravity world suggests that there is enough geological activity to replenish the water that escapes into space, said astronomer Torrance Johnson of the Jet Propulsion Laboratory in La Canada Flintridge.
Finally, the craft’s telescopes revealed large ice blocks, about 10 to 100 yards across, scattered around the polar region, a finding that “was not expected,” said imaging team member Peter Thomas of Cornell University. The blocks and other features “indicate that this region is young compared to the rest of Enceladus,” he said.
Cassini flew by Mimas on Tuesday, producing dramatic new images of the distinctive, 87-mile-wide, landslide-filled Herschel crater -- an indentation that makes the moon look like the Death Star from Star Wars.
The craft also provided the first close-ups of giant grooves on the opposite side of the moon that may have been produced when Mimas was struck by the object that created the Herschel crater.
