March 17, 2011
This series of images from NASA's Cassini spacecraft shows changes on the surface of Saturn's moon Titan, as the transition to northern spring brings methane rains to the moon's equatorial latitudes. Some of the most significant changes appear within a period of only a couple of weeks.
The brightest objects seen in these images are methane clouds in the troposphere, the lowest part of the atmosphere, which are most visible on the left of panel B, the lower half of panel C, and the right of panel D. Surface features appear in shades of gray. These images show changes (outlined area) along the southern boundary of a dune field near the equator named Belet. Dark Belet occupies most of the top of these images. (Belet looks dark because it is made from different materials than neighboring areas.)
Titan's equatorial latitudes are mostly arid. However, scientists interpret the changes seen in these images to be evidence of methane rain wetting the surface. Scientists have monitored the brightness of Titan's surface, including this area, for years and have ruled out other possible causes of the changes. In these images, some of the dark areas grow larger and then recede within weeks. The maximum extent of the changes is shown with a blue outline.
Years ago, images from the European Space Agency’s Huygens probe and the Cassini radar instrument revealed dry channels near the equator (see Mosaic of River Channel and Ridge Area on Titan
and Xanadu: Rivers Flowed onto a Sunless Sea). The new observations suggest the climate here is similar to that in the southwestern United States, where infrequent rain carves washes and riverbeds.
Titan's weather has been changing with the seasons, and storms now are more common at low latitudes, such as those observed here. An arrow-shaped storm cloud several hundred kilometers (miles) across was observed on Sept. 27, 2010. See Titan's Arrow-Shaped Storm for an image of that storm. See The Rite of Spring
to learn how the sun's illumination of the Saturnian system changed during the transition to spring in the northern hemispheres and to fall in the southern hemispheres of the planet and its moons. See Titan's Moving Mid-Latitude Clouds to learn more about Titan's changing weather.
The first image in this montage, panel A on the left, was taken early in the Cassini mission on Oct. 22, 2007, and shows how this region had appeared before the storms. The second image, panel B, was taken on Sept. 27, 2010. The huge arrow-shaped cloud is just out-of-frame to the left in panel B. The arrow-shaped cloud was quickly followed by extensive changes on the surface that can be seen in panel C, an image captured on Oct. 14, 2010. These changes cover an area of 500,000 square kilometers (193,000 square miles), roughly the combined area of Arizona and Utah in the United States.
The wet terrain can still be seen about a month after the storm in panel D, which was taken on Oct. 29, 2010. But by Jan. 15, 2011, which was the date of panel E, the area mostly appears dry and bright, with a much smaller area still dark, i.e. wet.
These images were re-projected, and the view in each is centered on terrain at 19 degrees south latitude, 251 degrees west longitude. Images in panels A, B, D, and E were taken with the Cassini spacecraft narrow-angle camera using a spectral filter sensitive to wavelengths of near-infrared light centered at 938 nanometers. The image in panel C was taken with the Cassini wide-angle camera using the same filter. The views were obtained at a range of distances from approximately 211,000 kilometers (131,000 miles) to 1.85 million kilometers (1.15 million miles) from Titan. Scale is about 7 kilometers (4 miles) per pixel in these re-projected images.
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 in Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.