Cassini Reveals Depths of Titan’s Lakes & Seas
Saturn’s largest moon, Titan, continues to put on a show for the Cassini spacecraft as its moves toward northern summer. In a recent flyby, Cassini sounded the depths of Titan’s largest sea, Kraken Mare, and discovered new transient features similar to the previously observed “Magic Island” (http://www.nasa.gov/jpl/cassini/saturn-moon-titan-20131212.html).
The findings are being presented this week by Cornell University planetary scientist Alexander Hayes at the Division for Planetary Sciences Meeting of the American Astronomical Society held in Tucson, Arizona.
On August 21st, 2014, Cassini set out to measure the depth of Kraken Mare and characterize the sea state of both Kraken and Ligeia Mare. Using the techniques developed to sound the depths of Ligeia Mare in May 2013 (http://www.nasa.gov/jpl/cassini/saturn-moon-titan-20131212.html), the Cassini Radar Team has isolated reflections from a 40 km (25 miles) segment of Kraken Mare’s seafloor. These bottom echoes were found in a shallow region near the mouth of a drowned river valley that feeds the sea and showed distinctive double-peaked returns indicating shallow depths of 20-35 m (65-115 ft). For the remainder of the 200 km (125 mile) shore-to-shore track across the sea, the seafloor was not observed. This means that the liquid was either too deep (> 200 m [650 m]) or too absorbing (much more absorbing than Ligeia Mare). The altimetry data from dry land in and around Kraken Mare showed relatively steep slopes leading up to the sea, consistent with, but not necessarily evidence for, deep liquid. Cassini scientists are still analyzing the data to determine the liquid’s absorptivity, which is intimately related to its composition, but the shallow depths, as compared to the 160 m (525 ft) depth of central Ligeia Mare, make this calculation difficult. Applying these techniques to the 2008 altimetry data over Ontario Lacus, the largest lake in Titan’s south polar region has, for the first time, revealed depths of 20-40 m (65-130 ft) in the lake’s southern areas.
In addition to measuring depths of Kraken, Cassini re-observed a mysterious transient feature, dubbed Titan’s “Magic Island,” first seen in July 2013 (http://www.nasa.gov/jpl/cassini/cassini-watches-mysterious-feature-evolve-in-titan-sea). Observations obtained starting two weeks after the initial discovery of the “Magic Island” did not show evidence for the bright features. The data acquired in August 2014, however, reveal that bright features are again present at the location of the original “Magic Island,” but that their appearance has evolved since the initial discovery. It is unclear whether the features have been continuously present since July 2013, and were in some way not detectable in the interim, or if the two observations indicate distinct transient events. Currently, the most likely candidates are waves, bubbles, or floating debris.
In an exciting development, two new transient “Magic Island” features were also observed in Kraken Mare during the August 2014 observation. Unlike the Ligeia transients, however, the Kraken Mare transients were observed within several hours of observations acquired by Cassini’s Visible and Infrared Mapping Spectrometer (VIMS). The VIMS data show a 5-micron-bright detection at the same location as the radar transients. This detection is similar to returns interpreted as specular reflections from waves or wet ground. These observations require the transient feature to be located at the surface of the liquid and support explanations including waves and wet floating debris. Combined, these new observations demonstrate that Titan’s polar seas are dynamic and exciting environments that will certainly continue to surprise and astonish us for the remaining years of the Cassini mission. Cassini is scheduled to observe the Ligeia features again in January 2015.
PIO Contact:
Syl Kacapyr
+1 607-255-7701, cell: +1 607-339-6450
vpk6@cornell.edu
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and ASI, the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. The VIMS team is based at the University of Arizona in Tucson. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the US and several European countries.
More information about Cassini and its mission:
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