NASA’s Cassini spacecraft has capped 2013 with a spectacular new collection of Saturn photos showcasing the planet’s beauty, as well with its trademark rings and strange moons.
The newly released Saturn photos by Cassini include two views of Enceladus, Saturn’s sixth-largest moon. Enceladus is a winter-appropriate ice world. Geysers at its poles shoot ice particles into space, some of which make it into orbit around Saturn. Some of this space “snow” becomes part of Saturn’s E ring, Saturn’s second outermost ring that is made of microscopic particles.
Other images highlight Saturn’s largest moon, Titan. There are no jolly elves at Titan’s north pole; liquid methane and ethane seas appear as splotchy features near the moon’s poles. At the south pole, a high-altitude vortex swirls. The hazy orange atmosphere of Titan is thought to resemble the atmosphere of early Earth.
PASADENA, Calif. — The intensity of the jets of water ice and organic particles that shoot out from Saturn’s moon Enceladus depends on the moon’s proximity to the ringed planet, according to data obtained by NASA’s Cassini spacecraft.
The finding adds to evidence that a liquid water reservoir or ocean lurks under the icy surface of the moon. This is the first clear observation the bright plume emanating from Enceladus’ south pole varies predictably. The findings are detailed in a scientific paper in this week’s edition of Nature.
"The jets of Enceladus apparently work like adjustable garden hose nozzles," said Matt Hedman, the paper’s lead author and a Cassini team scientist based at Cornell University in Ithaca, N.Y. "The nozzles are almost closed when Enceladus is closer to Saturn and are most open when the moon is farthest away. We think this has to do with how Saturn squeezes and releases the moon with its gravity."
Cassini, which has been orbiting Saturn since 2004, discovered the jets that form the plume in 2005. The water ice and organic particles spray out from several narrow fissures nicknamed “tiger stripes.”
"The way the jets react so responsively to changing stresses on Enceladus suggests they have their origins in a large body of liquid water," said Christophe Sotin, a co-author and Cassini team member at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. "Liquid water was key to the development of life on Earth, so these discoveries whet the appetite to know whether life exists everywhere water is present."
For years scientists hypothesized the intensity of the jets likely varied over time, but no one had been able to show they changed in a recognizable pattern. Hedman and colleagues were able to see the changes by examining infrared data of the plume as a whole, obtained by Cassini’s visual and infrared mapping spectrometer (VIMS), and looking at data gathered over a long period of time.
The VIMS instrument, which enables the analysis of a wide range of data including the hydrocarbon composition of the surface of another Saturnian moon, Titan, and the seismological signs of Saturn’s vibrations in its rings, collected more than 200 images of the Enceladus plume from 2005 to 2012. These data show the plume was dimmest when the moon was at the closest point in its orbit to Saturn. The plume gradually brightened until Enceladus was at the most distant point, where it was three to four times brighter than the dimmest detection. This is comparable to moving from a dim hallway into a brightly lit office.
Adding the brightness data to previous models of how Saturn squeezes Enceladus, the scientists deduced the stronger gravitational squeeze near the planet reduces the opening of the tiger stripes and the amount of material spraying out. They think the relaxing of Saturn’s gravity farther away from planet allows the tiger stripes to be more open and for the spray to escape in larger quantities.
"Cassini’s time at Saturn has shown us how active and kaleidoscopic this planet, its rings and its moons are," said Linda Spilker, Cassini project scientist at JPL. "We’ve come a long way from the placid-looking Saturn that Galileo first spied through his telescope. We hope to learn more about the forces at work here as a microcosm for how our solar system formed."
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology, Pasadena, manages the mission for NASA’s Science Mission Directorate in Washington. The VIMS team is based at the University of Arizona in Tucson.
Cassini’s View of Saturn’s High North Saturn’s high north is a seething cauldron of activity filled with roiling cloud bands and swirling vortices. A corner of the north polar hexagon is seen at upper right. The image was taken on Aug. 25, 2008 at a distance of approximately 541,000 km (336,000 mi) from Saturn. Image scale is 29 km (18 mi) per pixel. Credit: NASA/JPL/SSI
Ganymede and Callisto are similar in size and are made of a similar mixture of ice and rock, but data from theGalileo and Voyager spacecraft show that they look different at the surface and on the inside. Just like Earth and Venus, Ganymede and Callisto are twins, and understanding how they were born the same and grew up to be so different is of tremendous interest to planetary scientists.
Ganymede and Callisto’s evolutionary paths diverged about 3.8 billion years ago during the Late Heavy Bombardment, the phase in lunar history dominated by large impact events. Impacts during this period melted Ganymede so thoroughly and deeply that the heat could not be quickly removed. All of Ganymede’s rock sank to its center the same way that all the chocolate chips sink to the bottom of a melted carton of ice cream. Callisto received fewer impacts at lower velocities and avoided complete melting. Ganymede is closer to Jupiter and therefore is hit by twice as many icy impactors as Callisto, and the impactors hitting Ganymede have a higher average velocity.
Itokawa is by far the smallest object featured on this blog, measuring only about 535 metres in length, and less than 300 metres in width and height. Its surface gravity is tiny (much less than a millimetre per second squared), so the spacecraft entered an orbit round the sun that was roughly parallel to the asteroid’s orbit, here about 7km away. So the rotation seen in the gif is Itokawa’s rotation, not the result of a camera orbiting around it.
Hayabusa later landed on the surface, collected some dust, and returned it to Earth for analysis. Google Images doesn’t seem to know of the photos near the surface, so I uploaded most of the good ones to an Imgur album here (edit: Google Images doesn’t recognise the photos I upload to it, but searching for ‘itokawa surface’ brings up some scattered results). I wouldn’t have guessed that a small asteroid would comprise lots of little rocks, just barely held together by their very weak gravity. But apparently such rubble piles are common.
Venus is the second closest planet to the Sun and has the highest surface temperature of any planet in our solar system, with an orbital period of about 225 Earth days. Because of its similar gravity and size, it is sometimes known as Earth’s “sister planet.” However, besides these two aspects, the two planets have almost nothing in common. With the densest atmosphere on any terrestrial planet in the solar system, the surface pressure on Venus is about 92 times that of Earth; the same pressure one kilometer beneath Earth’s oceans.
Even though Venus is comparatively much further away from the Sun than Mercury, it is the hotter planet with a surface temperature of around 462 °C; this is because of its dense atmosphere of greenhouse gases such as carbon dioxide and sulfur dioxide. One remarkable aspect of the atmosphere of Venus is the precipitation of liquid sulfuric acid. The surface geology of the planet has been observed by NASA for over twenty years now, and it is seen that there is extensive and violent volcanism at the surface.