Astronomy Picture of the Day
October 29, 2012

Ontario Lacus
Ontario Lacus

NASA/JPL-Caltech/ASI/Proxemy Research and Dr Paolo C. Fienga/Lunar Explorer Italia/Italian Planetary Foundation for the additional process. and color.


This image-mosiac, obtained by the NASA - Cassini Spacecraft, shows the remnants of an ancient Southern Sea that used to sprawl out near the South Pole of Saturn's moon Titan; in fact, the dark Territory surrounding the black Feature visible in the middle of the frame, should indicate the ancient Shoreline of that Sea. Within the Basin, however, is the largest present-day Lake existing in Titan's Southern Hemisphere, such as Ontario Lacus. Ontario Lacus appears, as we wrote hereabove, as a solid black-colored Surface Feature and this circumstance tells us that is filled with liquid.


The single frames that form this picture were obtained by Cassini's Radar Instrument on July 2009 and January 2010; many of those radio-images were afterwards stitched together until they formed this mosaic. Scientists estimate that the ancient South Polar Titanian Sea (whose Ontario Lacus, in this perspective, is just a relatively small remnant) was possibly as large as about 300 by 170 miles (such as approx. 475 by 280 Km) across and likely less than a few hundred feet (meters) deep. Ontario Lacus, on the other hand, is about 80 by 235 Km across, and probably at least 30 feet (such as 10 meters) deep at its center. A few Scientists, in fact, speculate that Seas may have covered large parts of the Southern Hemisphere of Titan just less than some 50.000 years ago.


(note for the Readers: we, as IPF, honestly do not understand how and on which bases the aformentioned Scientists have speculated that the Southern Regions of Titan were covered by Seas just about 50.000 (and not 75.000, or 100.000, or - maybe - one Million) years ago. Estimates like this one (or even more complicated) require, in our opinion, heavy Science Data to support them and, at the time, such data are simply not available. However, what we are talking about here, is just a speculation, not a Scientific Truth, and so we shall consider it with interest, respect and benevolence, until proven right or wrong - a proof which, as you know, may never come. And that very likely - and unfortunately - shall not come in our lifetime...)


Titan, the Saturnian largest moon, is the only (known, so far) place besides Earth in our Solar System that hosts large open bodies of liquid. However, at the cold temperatures of Titan's Surface (such as about -290 degrees Fahrenheit. or 94 kelvins, or approx. -179° Celsius ), that liquid cannot possibly be water but, most likely, Methane and Ethane. Over one hundred Lakes and three Seas have been already seen at the North Pole of Titan, while the South Pole only has a few small Lakes. To this regards, Scientists have suggested that Cycles analogous to the so-called "Croll-Milankovitch Cycles" - which, on Earth, cause long-term cyclic transfer of Liquid Hydrocarbons from Pole to Pole, with the North Pole now containing the bulk of the liquids - may also occur on Titan. It is therefore possible that, some time less than about 50.000 years ago, the Titanian Cycle might have been reversed, suggesting that the South Polar Region should now contain (as it appears in this frame) just remnants (in the form of Lakes) of the once large Southern Seas.


This image-mosaic (which is an Original NASA - CASSINI Spacecraft radio image mosaic published on the NASA - Planetary Photojournal with the n. PIA 16166), since it is just a combination of Radio-Images of the Titanian Surface and NOT a real view of it, has been colorized, according to an informed speculation carried out by Dr Paolo C. Fienga (LXTT-IPF), in what they could reasonably be its possible Absolute Natural Colors (such as the colors that a human eye would perceive if someone were onboard the NASA - CASSINI Spacecraft and, once the thick layer of Titanian Hazes and Fogs shall have been completely overcome, looked down, towards the Surface of Titan itself), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team.



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