GLINT OF SUNLIGHT CONFIRMS LIQUID IN NORTHERN LAKE DISTRICT OF TITAN
NASA’s Cassini Spacecraft has captured the first flash of sunlight reflected off a lake on Saturn’s moon Titan, confirming the presence of liquid on the part of the moon dotted with many large, lake-shaped basins.
Cassini scientists had been looking for the glint, also known as a specular reflection, since the spacecraft began orbiting Saturn in 2004. But Titan's northern hemisphere, which has more lakes than the southern hemisphere, has been veiled in winter darkness. The sun only began to directly illuminate the northern lakes recently as it approached the equinox of August 2009, the start of spring in the northern hemisphere. Titan’s hazy atmosphere also blocked out reflections of sunlight in most wavelengths. This serendipitous image was captured on July 8, 2009, using Cassini’s visual and infrared mapping spectrometer.
This image will be presented Friday, Dec. 18, at the fall meeting of the American Geophysical Union in San Francisco.
“This one image communicates so much about Titan -- thick atmosphere, surface lakes and an otherworldliness,” said Bob Pappalardo, Cassini project scientist, based at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “It’s an unsettling combination of strangeness yet similarity to Earth. This picture is one of Cassini’s iconic images.”
Titan, Saturn’s largest moon, has captivated scientists because of its many similarities to Earth. Scientists have theorized for 20 years that Titan’s cold surface hosts seas or lakes of liquid hydrocarbons, making it the only other planetary body besides Earth believed to harbor liquid on its surface. While data from Cassini have not indicated any vast seas, they have revealed large lakes near Titan’s north and south poles. In 2008, Cassini scientists using infrared data confirmed the presence of liquid in Ontario Lacus, the largest lake in Titan’s southern hemisphere. But they were still looking for the smoking gun to confirm liquid in the northern hemisphere, where lakes are also larger. Katrin Stephan, of the German Aerospace Center (DLR) in Berlin, an associate member of the Cassini visual and infrared mapping spectrometer team, was processing the initial image and was the first to see the glint on July 10th. “I was instantly excited because the glint reminded me of an image of our own planet taken from orbit around Earth, showing a reflection of sunlight on an ocean,” Stephan said. “But we also had to do more work to make sure the glint we were seeing wasn’t lightning or an erupting volcano.” Team members at the University of Arizona, Tucson, processed the image further, and scientists were able to compare the new image to radar and near-infrared-light images acquired from 2006 to 2008. They were able to correlate the reflection to the southern shoreline of a lake called Kraken Mare. The sprawling Kraken Mare covers about 400,000 square kilometers (150,000 square miles), an area larger than the Caspian Sea, the largest lake on Earth. It is located around 71 degrees north latitude and 337 degrees west latitude. The finding shows that the shoreline of Kraken Mare has been stable over the last three years and that Titan has an ongoing hydrological cycle that brings liquids to the surface, said Ralf Jaumann, a visual and infrared mapping spectrometer team member who leads the scientists at the DLR who work on Cassini. Of course, in this case, the liquid in the hydrological cycle is methane rather than water, as it is on Earth. “These results remind us how unique Titan is in the solar system,” Jaumann said. “But they also show us that liquid has a universal power to shape geological surfaces in the same way, no matter what the liquid is.” The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The visual and infrared mapping spectrometer team is based at the University of Arizona, Tucson.
On January 27, 2009, soaring over the south pole in a high inclination orbit,
the VIMS instrument aboard the Cassini spacecraft took these pictures of
Saturn's aurora shining in infrared light. The spacecraft was about
1,100,000 kilometers (~683,000 miles) above the surface of the planet
when the images were taken.
Each image took about 68 minutes to aquire because a long exposure time was needed to bring out the dim light coming from the aurora. The images were taken about 5 hours apart and we can see the change in viewing angle as the spacecraft's orbit takes it from a high latitude toward Saturn's equator.
The false color images were put together using data from three wavelengths of infrared light. For red we used a wavelength of 5.02 microns. At this wavelength, Saturn shines from within so we can see all areas of the planet, even the shadowed parts. For the green we used 3.95 microns and for blue, 3.66 microns. The aurora shine most brightly at these wavelengths and parts of Saturn where the sun is shining also show as blue-green areas.
The aurora circle the pole at high latitudes (-70 to -80 degrees in this case) and we hope to learn more about their structure and behavior from such images.
Click on the image to see a larger version.
Flying over the unlit side of Saturn's rings, the Cassini spacecraft captures Saturn's glow, represented in brilliant shades of electric blue, sapphire and mint green, while the planet's shadow casts a wide net on the rings.
This striking false-color mosaic was created from 25 images taken by Cassini's visual and infrared mapping spectrometer over a period of 13 hours, and captures Saturn in nighttime and daytime conditions. The visual and infrared mapping spectrometer acquires data simultaneously at 352 different wavelengths, or spectral channels. Data at wavelengths of 2.3, 3.0 and 5.1 microns were combined in the blue, green and red channels of a standard color image, respectively, to make this false-color mosaic.
This image was acquired on Feb. 24, 2007, while the spacecraft was 1.58 million kilometers (1 million miles) from the planet and 34.6 degrees above the ring plane. The solar phase angle was 69.5 degrees. In this view, Cassini was looking down on the northern, unlit side of the rings, which are rendered visible by sunlight filtering through from the sunlit, southern face.
On the night side (right side of image), with no sunlight, Saturn's own thermal radiation lights things up. This light at 5.1 microns wavelength (some seven times the longest wavelength visible to the human eye) is generated deep within Saturn, and works its way upward, eventually escaping into space. Thick clouds deep in the atmosphere block that light. An amazing array of dark streaks, spots, and globe-encircling bands is visible instead. Saturn's strong thermal glow at 5.1 microns even allows these deep clouds to be seen on portions of the dayside (left side), especially where overlying hazes are thin and the glint of the sun off of them is minimal. These deep clouds are likely made of ammonium hydrosulfide and cannot be seen in reflected light on the dayside, since the glint of the sun on overlying hazes and ammonia clouds blocks the view of this level.
A pronounced difference in the brightness between the northern and southern hemispheres is apparent. The northern hemisphere is about twice as bright as the southern hemisphere. This is because high-level, fine particles are about half as prevalent in the northern hemisphere as in the south. These particles block Saturn's glow more strongly, making Saturn look brighter in the north.
At 2.3 microns (shown in blue), the icy ring particles are highly reflecting, while methane gas in Saturn's atmosphere strongly absorbs sunlight and renders the planet very dark. At 3.0 microns (shown in green), the situation is reversed: water ice in the rings is strongly absorbing, while the planet's sunlit hemisphere is bright. Thus the rings appear blue in this representation, while the sunlit side of Saturn is greenish-yellow in color. Within the rings, the most opaque parts appear dark, while the more translucent regions are brighter. In particular, the opaque, normally-bright B ring appears here as a broad, dark band separating the brighter A (outer) and C (inner) rings.
At 5.1 microns (shown in red), reflected sunlight is weak and thus light from the planet is dominated by thermal (i.e., heat) radiation that wells up from the planet's deep atmosphere. This thermal emission dominates Saturn's dark side as well as the north polar region (where the hexagon is again visible) and the shadow cast by the A and B rings. Variable amounts of clouds in the planet's upper atmosphere block the thermal radiation, leading to a speckled and banded appearance, which is ever-shifting due to the planet's strong winds.
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 was designed, developed and assembled at JPL. The Visual and Infrared Mapping Spectrometer team is based at the University of Arizona, where this image was produced. For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov/home/index.cfm. Credit: NASA/JPL/University of Arizona
Massive Mountain Range Imaged on Saturn's Moon Titan
This composite image shows a massive mountain range running just south of Titan's equator. The tallest mountains ever seen on Titan -- coated with layers of organic material and blanketed by clouds -- have been imaged on Saturn's moon Titan by NASA's Cassini spacecraft.
"We see a massive mountain range that kind of reminds me of the Sierra Nevada mountains in the western United States. This mountain range is continuous and is nearly 100 miles long," said Dr. Bob Brown, team leader of the Cassini visual and infrared mapping spectrometer at the University of Arizona, Tucson.
During an Oct. 25 flyby designed to obtain the highest resolution infrared views of Titan yet, Cassini resolved surface features as small as 400 meters (1,300 feet). The images reveal a large mountain range, dunes, and a deposit of material that resembles a volcanic flow. These data, together with radar data from previous flybys, provide new information on the height and composition of geologic features on Titan.
Near the wrinkled, mountainous terrain are clouds in Titan's southern mid latitudes whose source continues to elude scientists. These clouds are probably methane droplets that may form when the atmosphere on Titan cools as it is pushed over the mountains by winds.
The composition of dunes that run across much of Titan is also much clearer. "The dunes seem to consist of sand grains made of organics, built on water-ice bedrock, and there may also be some snow and bright deposits," Brown said.
Two views of an area riddled by mountain ranges that were probably produced by tectonic forces. Titan is a complex place and scientists are uncovering the secrets of the surface, one flyby at a time.
|This high-resolution (with a maximum resolution of 1.2km) color image from VIMS shows an example of Titan's longitudinal dunes. The dunes were first seen and identified in RADAR. This image represents the first view of the dunes in reflected light. Though not true color as the human eye would see, the image represents real color information with red assigned to 2.7um, green to 2.0um, and blue to 1.3um. The VIMS image was taken during the T4 encounter with Titan on 2005 March 31. Below is a RADAR map of precisely the same area as the VIMS map above. Though the linear features are visible in the RADAR swath, they do not appear as strongly as do dunes nearer to the equator.|
|These two pictures were made from the data of 5 image cubes of Titan. These cubes were obtained by the VIMS instrument during the T17 flyby, which occurred on September 7, 2006. The data of Titan was taken as the spacecraft was flying away from the moon. The color scheme used in the images is designed to show different aspects of Titan and specifically to highlight clouds. Pink/red colors correspond to the organic haze that exists throughout Titan's atmosphere, but is most noticeable near the limb. Green corresponds to light coming from Titan's surface. Blue/white corresponds to clouds of liquid methane between 10 and 30 kilometers above Titan's surface. There are clouds at Titan's south pole during this flyby (near the limb at about 7:00 as seen in this image). There are also extensive cloud systems along the 40 degree South latitude line that extend from the limb to the terminator as seen by Cassini. Observations such as these hold promise for measurements of Titan's winds and for studying the formation and evolution of Titan's storm systems.|
CASSINI IMAGE SHOWS SATURN DRAPED IN A STRING OF PEARLS
Saturn appears dressed to the nines, "wearing" a strand of "pearls" in a stunning infrared image from the Cassini spacecraft that showcases a meteorological phenomenon.
The image, acquired by Cassini’s visual and infrared mapping spectrometer, shows Saturn lit by its own internal, thermal glow. Clearly visible is a 60,000-kilometer-long (37,000 miles) string of bright “pearls,” which are actually clearings in Saturn’s deep cloud system.
The image is available at: http://www.nasa.gov/cassini , http://saturn.jpl.nasa.gov , and http://wwwvims.lpl.arizona.edu .
The findings are being presented today at the Division for Planetary Sciences Meeting of the American Astronomical Society held in Pasadena, Calif.
More than two dozen cloud clearings appear at Saturn's north latitude. Each clearing follows another at a regular spacing of about 3.5 degrees in longitude. This is the first time such a regular and extensive train of cloud clearings has been observed, indicating that they may be a result of a large planetary cloud formation or wave that might encircle the whole planet.
Scientists plan to continue observing this phenomenon over the next few years to try to learn more about Saturn’s deep circulation systems and meteorology.
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 Cassini-Huygens mission for NASA’s Science Mission Directorate, Washington. The Cassini orbiter was designed, developed and assembled at JPL. The visual and infrared mapping spectrometer team is based at the University of Arizona.
|This false-color mosaic of Saturn shows deep-level clouds silhouetted against Saturn's glowing interior. The image was made with data from Cassini's visual and infrared mapping spectrometer, which can image the planet at 352 different wavelengths. This mosaic shows the entire planet, including features like Saturn's ring shadows and the terminator, the boundary between day and night. The data were obtained in February 2006 at a distance of 1.6 million kilometers (1 million miles) from directly over the plane of Saturn's rings, which appear here as a thin, blue line over the equator. The image was constructed from images taken at wavelengths of 1.07 microns shown in blue, 2.71 microns shown in green, and 5.02 microns shown in red. The blue-green color (lower right) is sunlight scattered off clouds high in Saturn's atmosphere and the red color (upper left) is the glow of thermal radiation from Saturn's warm interior, easily seen on Saturn's night side (top left), within the shadow of the rings, and with somewhat less contrast on Saturn's day side (bottom right). The darker areas within Saturn show the strongest thermal radiation. The bright red color indicates areas where Saturn's atmosphere is relatively clear. The great variety of cloud shapes and sizes reveals a surprisingly active planet below the overlying sun-scattering haze. The brighter glow of the northern hemisphere versus the southern indicates that the clouds and hazes there are noticeably thinner than those in the south. Scientists speculate that this is a seasonal effect, and if so, it will change as the northern hemisphere enters springtime during the next few years. Full-Res TIFF|
|The active cloud systems on Saturn at multiple levels in the atmosphere are revealed in this close-up view by the Visual Infrared Mapping Spectrometer (VIMS) onboard the Cassini Orbiter. By fading between images simultaneous acquired at two distinctively different wavelengths -- 0.95 um and 5.1 um -- the three-dimensional nature of Saturn's major two cloud layers above the 3-bar level can be visualized. In this daytime view of Saturn's south tropical region near 30 degrees S. latitude, ammonia (NH3) clouds near the 1-bar pressure level are seen reflecting sunlight (blue, representing 0.95 um). By contrast, the red view obtained at 5.1 um predominantly shows a different cloud layer near the 3-bar level composed of ammonia hydrosulfide (NH4SH), and are created at depth by the chemical reactions of ammonia (NH3) with hydrogen sulfide (H2S). Saturn's indigenous thermal radiation, generated at depth near the 8-bar level, is used to backlight the deep clouds. Thus, these clouds are seen in silhouette against the glow of Saturn's interior and show up as dark features. These deep-level cloud systems, discovered by Cassini/VIMS, reveal a large array of dynamical processes, including convection and planetary waves, some 60 km underneath the ammonia clouds. In some places, clouds appear to extend vertically throughout the 1-3 bar region, and can be discerned in both the blue and red images. These systems are likely convective cells which mix both cloud layers together as the cells rise some 60 km in altitude from depth. These Cassini/VIMS images were acquired from 347,000 km above Saturn's ammonia cloudtops and have a spatial resolution of 173 km per pixel.|
|This movie is composed of 5 image cubes of Titan obtained by the VIMS instrument during the 2006 September 7 T17 flyby of Titan as the spacecraft was flying away from the moon. The color scheme is designed to show different aspects of Titan in a clear way, and specifically to highlight clouds. Pink/red colors correspond to the organic haze that exists throughout Titan's atmosphere, but is most noticable near the limb. Green corresponds to light coming from Titan's surface. Blue/white corresponds to clouds of liquid methane between 10 and 30 kilometers above Titan's surface. There are clouds at Titan's south pole during this flyby (near the limb at about 7:00 as seen in this image). There are also, however, extensive cloud systems along the 40 degree South latitude line that extend from the limb to the terminator as seen by Cassini. During the movie you can see the western cloud group dissipating, and the eastern clouds moving eastward and a little bit north. Observations such as these hold promise for measurements of Titan's winds and for studying the formation and evolution of Titan's storm systems.|
|These two images depict Titan as seen by VIMS after the T16 closest approach on July 22, 2006. The color images were generated using the 5 micron wavelength for red, the 2 micron wavelength for green and the 1.2 micron wavelength for blue. The clouds, circled in the lower image, are of the type seen previously and reported by Griffith et al. in Science. The image shows the clouds spreading out along the 40 degree South latitude line.|
|This false-color image of Saturn was constructed by combining 3 images at three different infrared wavelengths (see top panel). The image at the left was taken at 1.3 um wavelength, where both Saturn and it's rings strongly reflect light. The center image was taken at 2.4 um wavelength where the rings strongly reflect light, but Saturn, because of the methane in it's atmosphere, absorbs most of the light. The third image was taken at a wavelength of 5 um where, because they are composed of almost pure water ice, the rings absorb almost all the light, and Saturn, because its interior is warm, glows. Assigning each of the three images to blue, green and red, respectively, results in the beautiful, false-color, composite image below.|
|This false color image of Saturn, taken on June 30, 2006, shows an area of the planet with shadows of the rings across the upper portion and the lower portion illuminated by sunlight. The upper area, in the ring shadow, would be black in visible light but glows red in the infrared because Saturn is warm inside. This light from the interior shines out through the clouds giving us a look at some of the interesting atmospheric structure. This is a false color composite with blue at 0.91 microns, green at 2.25 microns, and red at 5.01 microns. The distance from Cassini to Saturn center in this image is 335,000 km.|
This is a two-image-cube composite of VIMS' view of a crescent Titan as Cassini approached for the T16 flyby on 2006 July 22. Colors are mapped to spectral windows where the surface is visible, R=5um, G=2um, B=1.26um.