The image in the upper part of this table unveils the last radar data and altimetry data of Titan's surface obtained from the Cassini orbiter during its mission in the Saturn System. These radar data and altimetry data were acquired with the Radar Mapper of the Cassini spacecraft during the 127th targeted flyby of the Orange Moon performed on April 22, 2017 and called T-126. The Radar Mapper captured two radar views of Titan's surface presented in Figure A. Each portion is about 200 miles or 300 kilometers long. The radar view at right clearly shows a portion of a sea or a lake of hydrocarbons. Lakes or seas appear relatively dark and uniform. Brightness variations allow us to discern topographic or landscape features. Landscape elements will appear bright if they are rough, irregular or tilted toward the orbiter. On the other hand, landscape features which are smooth like lakes, seas, plains or plateaus will appear dark as opposed to mountains or hills.

The radar view found on the left part of Figure A reveals a portion of Titan's landscape which had already been observed during the first radar flyby of the Opaque Moon in 2004. One can notice bright, hilly terrains as well as darker plains. Planetologists are in a position to advance that there are no obvious evidence of changes in the appearance of the terrain in this area from the first radar view in 2004 to the final radar view of 2017. The radar view found on the right part of Figure A clearly shows the portion of the lake or sea Ligeia Mare where a transient bright feature called the "Magic Island" had been identified in several radar views during the Cassini mission. Was the Magic Island a transient island close to the coast ? The last radar view shows that the Magic Island is completely absent. It seems to have completely disappeared. Several hypotheses have been advanced to account for the presence of the enigmatic transient feature. It may have been related to a field of bubbles or strong waves.

The lower view of the image represents Figure B which reveals altimetry data in a region of lakes in the middle of both radar portions presented in Figure A. Altimetry data were obtained during the T-126 Flyby thanks to the Radar Mapper of the Cassini probe which switched to altimetry mode in order to perform a first-ever or last-ever measurement of the depths of several lakes that are located in the north polar region of Saturn's largest moon. The Cassini orbiter had to orientate its antenna straight down at the surface. Thus, the Radar Mapper measured the time delay between echoes from the surface of the pool of liquid and echoes from the bottom or floor of the lake. The graph of Figure B indicates variations in the depth, altitude or height of the terrain where the altimetry signal was sent. The radar view found in the lower part of Figure B corresponds to a radar portion of the area acquired during a previous radar flyby of the region where this altimetry campaign was performed. The yellow segment shows the area where the altimetry data were taken. Thus, we obtained altimetry data for eight small lakes located in the north polar region of Titan.

Although the altimetry data are still preliminary, the lakes whose topography has been studied here are believed to be approximately the same depth. The small pools of hydrocarbons may be about 100 meters or 328 feet deep. Are those lakes connected to a subsurface layer of liquid hydrocarbons comparable to a water table or aquifer ? That's a question researchers are seriously considering, at least for the north polar region of the giant moon. The second view from the upper part of the table corresponds to Figure A in higher resolution and the third view from the upper part of the table represents Figure B in higher resolution as well. Image Credit: NASA/JPL-Caltech/ASI .