Cassini Watches Mysterious Feature Evolve in Titan Sea
NASA's Cassini spacecraft is monitoring the evolution of a mysterious feature in a large hydrocarbon sea on Saturn's moon Titan. The feature covers an area of about 100 square miles (260 square kilometers) in Ligeia Mare, one of the largest seas on Titan. It has now been observed twice by Cassini's radar experiment, but its appearance changed between the two apparitions.
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| PIA18430: Mysterious Changing Feature in Ligeia Mare |
These three images, created from Cassini Synthetic Aperture Radar (SAR) data, show the appearance and evolution of a mysterious feature in Ligeia Mare, one of the largest hydrocarbon seas on Saturn's moon Titan. The views, taken during three different Cassini flybys of Titan, show that this feature was not visible in earlier radar images of the same region and its appearance changed between 2013 and 2014.
In the images, the dark areas represent the sea, which is thought to be composed of mostly methane and ethane. Most of the bright areas represent land surface above or just beneath the water line. The mysterious bright feature appears off the coast below center in the middle and right images.
The mystery feature had not been seen in preceding SAR observations of the region from 2007 to 2009. After its first appearance in early July 2013, it was not visible in observations by Cassini's Visible and Infrared Mapping Spectrometer, obtained later in July and in September 2013. Low-resolution SAR images obtained in October 2013 also failed to recover the feature.
This graphic and animation depicts a cross-section of the Saturnian moon Titan. Cassini scientists speculate there may be a layer of liquid water mixed with ammonia about 100 kilometers (62 miles) below the surface of Titan.
The assumption that Titan contains an internal ocean was generated from data gleaned from Cassini's Synthetic Aperture Radar during 19 separate passes over Titan between October 2005 and May 2007. Using data from the radar's early observations, the scientists and radar engineers established the locations of 50 unique landmarks on Titan's surface. They then searched for these same lakes, canyons and mountains in the reams of data returned by Cassini in its later flybys of Titan. What they found was prominent surface features seemed to shift from their expected positions by up to 31 kilometers (19 miles). Since the features could not have really moved, the apparent shift told the scientists and engineers that Titan was spinning about its axis in a previously unsuspected manner. The pre-Cassini model of Titan's spin accounted for the gravitational fields of Saturn and other nearby planets and moons but omitted other smaller less well understood effects. Since the observed spin of Titan does not fit this model, other influences, such as the seasonal changes in the motion of its atmosphere must also be important. It is difficult to explain how such relatively low energy phenomena could have such a pronounced influence on Titan's spin unless the moon's icy crust was decoupled from its core by an internal ocean. If the crust were decoupled from the core, atmospheric fluctuation alone could account the observed spin.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA's 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 radar instrument was built by JPL and the Italian Space Agency, working with team members from the United States and several European countries.
Image credit: NASA/JPL
Flybys are a major element of Cassini's tour. The spacecraft's looping, elliptical path around Saturn is carefully designed to enable occasional visits to the many moons in the system. All flybys provide an opportunity to learn more about Saturn's icy satellites, and encounters with giant Titan are actually used to navigate the spacecraft, changing its orbit or setting up future flybys.Cassini Solstice Mission: RADAR
Many of the most exciting encounters are "targeted" flybys, for which Cassini's flight path is steered so the spacecraft will pass by a specific moon at a predetermined distance, referred to as "closest approach." Cassini's targeted flybys have yielded incredible close-up views and many groundbreaking science results. Visits to Dione and Hyperion, for example, as well as the daring Oct. 2008 dives through the Enceladus plume, have provided some of the great highlights of the mission.
The Cassini Radar (RADAR) uses the five-beam Ku-band antenna feed assembly associated with the spacecraft high gain antenna to direct radar transmissions toward targets, and to capture blackbody radiation and reflected radar signals from targets.
RADAR Scientific Objectives:
RADAR Sensing Instruments:
- To determine whether oceans exist on Titan, and, if so, to determine their distribution.
- To investigate the geologic features and topography of the solid surface of Titan.
- To acquire data on non-Titan targets (rings, icy satellites) as conditions permit.
RADAR Instrument Characteristics:
- Synthetic Aperture Radar Imager [SAR] (13.78 GHz Ku-band; 0.35 to 1.7 km resolution)
- Altimeter (13.78 GHz Ku-band; 24 to 27 km horizontal, 90 to 150 m vertical resolution)
- Radiometer (13.78 GHz passive Ku-band; 7 to 310 km resolution)
- Mass (current best estimate) = 41.43 kg
- Peak Operating Power (current best estimate) = 108.40 W
- Peak Data Rate (current best estimate) = 364.800 kilobits/sec
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