Cassini’s Radar And Vims Instruments Eye Impact Crater On Titan

The Cassini spacecraft has seen a 50-mile-diameter impact crater on Titan with different instruments on separate flybys, giving scientists new information on impact-crater formation on Saturn’s giant moon.

They’ve released a composite image of one of Titan’s most prominent impact craters as previously seen by Cassini’s radar and recently seen by its Visual and Infrared Mapping Spectrometer (VIMS).

The composite image is online at saturn.jpl.nasa.gov and at uanews.org.

The radar image was taken during the Cassini spacecraft’s Feb. 15, 2005 Titan flyby, and the VIMS images were taken during its April 16, 2005 Titan flyby, said Robert H. Brown of The University of Arizona, head of the VIMS experiment. Brown released the composite image at the European Geosciences Union meeting in Vienna, Austria, on Monday (April 25).

In radar, the crater and its ejecta blanket are bright. In radar, brighter surfaces mean rougher terrains, or else terrains tilted towards the radar. At VIMS infrared wavelengths, the crater appears dark and the ejecta blanket is bright, showing that the crust on the crater floor is different material than the ejecta.

“The composite image highlights the differences and similarities in how two instruments see the same thing,” Brown said. “It shows the power of combining instruments when you are trying to understand objects in the Saturnian system.”

VIMS is essentially a camera that takes pictures in 352 different colors at the same time. The colors cover the visible spectrum and into the infrared, or from three-tenths of a micron up to five and one-tenth microns. (A micron is one millionth of a meter.) Scientists can identify the chemical composition of the surfaces, atmospheres and rings of Saturn and its moons using VIMS.

Cassini began a 4-year-or-more exploratory tour of the Saturn system in July 2004. It has seen two impact craters on Titan so far.

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 radar instrument team is based at JPL, working with team members from the United States and several European countries. The visual and infrared mapping spectrometer team is based at the University of Arizona, Tucson.

This three-panel image shows one of Titan¹s most prominent impact craters in an infrared-wavelength image (left), radar image (center) and in the false-color image (right). The Cassini radar imaged this crater during Cassini¹s third flyby of Titan, on Feb. 15, 2005, (see PIA07368). The crater, located at 16 degrees west, 11 degrees north, is about 80 kilometers (50 miles) in diameter and is surrounded beyond that by a blanket of material thrown out of the crater during impact. In radar, brighter surfaces mean rougher terrains, or else terrains tilted toward the radar.

Two Titan flybys later, on April 16, the visual infrared mapping spectrometer on Cassini obtained images of the same crater. The panel on the left is an image at the 2.0 micron wavelength, showing that the crater has a dark floor and a small bright area in the center. The crater is surrounded by bright material, which has a very faint halo slightly darker than the surrounding dark material. Compare the radar image with the visual infrared mapping spectrometer image. Both the crater and the blanket of surrounding material (called ejecta) are bright at radar wavelengths; in the infrared, the crater itself is dark and this blanket of material is quite bright. In radar, the faint halo surrounding the blanket of material is quite similar in appearance to the rest of the ejecta blanket.

The right hand panel is a false-color visual infrared mapping spectrometer image of the crater at lower resolution. It shows the faint halo to be slightly bluer than surrounding material. That the material is bluer than its surroundings, while also being darker, suggests that the faint halo is somewhat different in composition. This suggests that the composition of Titan¹s upper crust varies with depth, and various materials were excavated when the crater was formed.

The same structure appearing so different to different instruments illustrates the importance of multiple instruments studying such phenomena. The Cassini spacecraft, being the most interdisciplinary spacecraft ever flown, strongly embodies such an approach.

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 radar instrument team is based at JPL, working with team members from the United States and several European countries. The visual and infrared mapping spectrometer team is based at the University of Arizona, Tucson.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. For more information about the visual and infrared mapping spectrometer visit http://wwwvims.lpl.arizona.edu/. Credit: NASA/JPL/University of Arizona