Cassini captures sunlight shining off a shrinking sea on Titan
Sen—NASA's Cassini spacecraft has captured a glimpse of bright sunlight reflecting off Titan's north polar hydrocarbon seas. The newly released view showing Titan in infrared light was obtained by Cassini's Visible and Infrared Mapping Spectrometer (VIMS) on 21 August.
Cassini has captured, separately, views of the polar seas and the sun glinting off of them in the past, but this is the first time both have been seen together in the same view.
False-colour mosaic of infrared data by Cassini, released in 2013, reveals differences in composition of surface materials around hydrocarbon lakes at Titan. Image credit: NASA/JPL-Caltech/University of Arizona/University of Idaho
Titan is the only other place in the Solar System that we know has stable liquid on its surface, though its lakes are made of liquid ethane and methane rather than liquid water. Before Cassini's arrival at Saturn, scientists suspected that Titan might have bodies of open liquid on its surface.
Cassini found only great fields of sand dunes near the equator and lower latitudes, but located lakes and seas near the poles. While there is one large lake and a few smaller ones near Titan's south pole, almost all of Titan's lakes appear near the moon's north pole.
Near-infrared, colour mosaic from NASA's Cassini spacecraft shows the sun glinting off of Titan's north polar seas. Image credit: NASA/JPL-Caltech/University of Arizona/University of Idaho
The mirror-like reflection, known as the specular point, near the 11 o'clock position at upper left, is in the south of Titan's largest sea, Kraken Mare, just north of an island archipelago separating two separate parts of the sea.
This particular sunglint was so bright as to saturate the detector of Cassini's Visual and Infrared Mapping Spectrometer (VIMS) instrument, which captures the view. It is also the sunglint seen with the highest observation elevation so far. The sun was a full 40° above the horizon as seen from Kraken Mare at this time. Because it was so bright, this glint was visible through the haze at much lower wavelengths than before.
The southern portion of Kraken Mare (the area surrounding the specular feature) displays a "bathtub ring", a bright margin of evaporate deposits, which indicates that the sea was larger at some point in the past and has become smaller due to evaporation. The deposits are material left behind after the methane and ethane liquid evaporates, like the saline crust on a salt flat.
The highest resolution data from this flyby, the area seen immediately to the right of the sunglint cover the labyrinth of channels that connect Kraken Mare to another large sea, Ligeia Mare. Ligeia Mare itself is partially covered in its northern reaches by a bright, arrow-shaped complex of clouds made of liquid methane droplets, and could be actively refilling the lakes with rainfall.
The view contains real colour information, although it is not the natural colour the human eye would see. Red in the image corresponds to 5.0 microns, green to 2.0 microns, and blue to 1.3 microns. These wavelengths correspond to atmospheric windows through which Titan's surface is visible. The unaided human eye would see nothing but haze.