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domingo, 5 de mayo de 2013

NASA - Dwarfed Wavemaker-- Enceladus shows


Enceladus as viewed from NASA's Cassini spacecraft.


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05/02/2013 12:00 AM EDT

Like a proud peacock displaying its tail, Enceladus shows off its beautiful plume to the Cassini spacecraft's cameras. Enceladus (313 miles, or 504 kilometers across) is seen here illuminated by light reflected off Saturn. This view looks toward the Saturn-facing side of Enceladus. North on Enceladus is up and rotated 45 degrees to the right. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 18, 2013. The view was acquired at a distance of approximately 483,000 miles (777,000 kilometers) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 173 degrees. Image scale is 3 miles (5 kilometers) per pixel. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo. For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org. Credit: NASA/JPL-Caltech/Space Science Institute




Enceladus as viewed from NASA's Cassini spacecraft.
Enceladus as viewed from NASA's Cassini spacecraft.
Enceladus [en-SELL-ah-dus] is one of the innermost moons of Saturn. It is quite similar in size to Mimas, but has a smoother, brighter surface. Enceladus reflects almost 100 percent of the sunlight that strikes it. Unlike Mimas, Enceladus displays at least five different types of terrain. Parts of Enceladus shows craters no larger than 35 km in diameter. Other areas show regions with no craters, indicating major resurfacing events in the geologically recent past. There are fissures, plains, corrugated terrain and other crustal deformations. All of this indicates that the interior of the moon may be liquid today, even though it should have frozen aeons ago. It is postulated that Enceladus is heated by a tidal mechanism similar to Jupiter's moon Io. Enceladus is perturbed in its orbit by Saturn's gravitational field and by the large neighboring satellites Tethys and Dione.
Because Enceladus reflects so much sunlight, the surface temperature is only -330 degrees Fahrenheit (-201degrees Celsius).
Since early 2005, the Cassini-Huygens Mission to Saturn has uncovered many mysteries about Enceladus. Below is a discovery timeline for this intriguing moon.
February and March 2005
Enceladus has an atmosphere:
The Cassini spacecraft makes two trips by Enceladus.
  • Cassini's magnetometer discovers an atmosphere around Enceladus, evidence that gases may be originating from the moon's surface or interior.
  • The cosmic dust analyzer records thousands of hits from tiny particles of dust or ice, possibly coming from a cloud around the moon or from the adjacent E ring.
  • The science teams plan to go back for a closer look.
July 2005
Warm fractures on Enceladus:
Cassini flies within 175 km (109 miles) of Enceladus, the closest it comes to any of Saturn's moons.
  • The imaging team sees unusual geology on the moon's southern pole, including house-sized ice boulders and evidence of recent geological activity.
  • The visual and infrared mapping spectrometer determines that the large dark cracks, called "tiger stripes," at the south pole are very young and seem to have a continual supply of fresh ice.
  • The composite infrared spectrometer shows that the south pole is much warmer than expected, suggesting an internal heat source.
  • The ion and neutral mass spectrometer and the ultraviolet imaging spectrograph detect water vapor in the atmosphere, which appears to come from a localized source.
  • The cosmic dust analyzer detects a large increase in the number of particles near Enceladus, confirming that Enceladus is the source of Saturn's E ring.
November 2005
Spray above Enceladus:
  • Cassini's visual and infrared mapping spectrometer measures the spectrum of the plumes originating from the south pole of the icy moon, capturing a very clear signature of small ice particles.
  • The imaging team produces the first pictures of the plume of icy material streaming from Enceladus' south pole, possible evidence of Yellowstone-like geysers fed by reservoirs of liquid water.
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Just the Facts

Orbit Size (semi-major axis):  238,037 km
Mean Radius:  252.1 km
Volume:  67,113,076 km3
Mass:  107,944,591,230,692,000,000 kg
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