Ontario Lacus: Awash on Titan

by Paul Gilster on July 31, 2008

Remember those oceans of methane we thought might exist on Titan? They were an exciting thought (I recall hypothetical images of the Huygens probe bobbing in such an ocean at the end of its journey, before we knew what it would actually land on). It’s exciting to confirm that liquid does exist on Titan’s surface in the form of liquid hydrocarbons, with a positive identification of ethane. At least one of the large lakes the Cassini orbiter has found there contains the substance, but we also know that numerous other lake-like areas exist beneath the smog.

Image: The Imaging Science System aboard NASA’s Cassini orbiter took the image, left, of Ontario Lacus in June 2005. (Image credit: NASA/JPL/Space Science Institute.) Cassini’s Visual and Infrared Mapping Spectrometer took the image, right, of Ontario Lacus in December 2007. This view, taken at 5-micron wavelengths from 1,100 kilometers (680 miles) away, shows the part of the lake that is visible on Titan’s sunlit side. What appears to be a beach is seen at the lower right of the image, below the bright lake shoreline. (Credit: NASA/JPL/University of Arizona).

The news should come as no major surprise, just as discovering water ice on Mars is momentous but at the same time long anticipated. But in both cases making the detection has been tricky, on Titan because atmospheric hydrocarbons make observing a challenge. Cassini managed the feat with its visual and infrared mapping spectrometer (VIMS) nonetheless, and we now know that Ontario Lacus, a bit larger than Lake Ontario on Earth and imaged in late 2007 on Titan’s south polar region, is awash. More in this JPL news release.

“Detection of liquid ethane confirms a long-held idea that lakes and seas filled with methane and ethane exist on Titan,” said Larry Soderblom, a Cassini interdisciplinary scientist with the U.S. Geological Survey in Flagstaff, Ariz. “The fact we could detect the ethane spectral signatures of the lake even when it was so dimly illuminated, and at a slanted viewing path through Titan’s atmosphere, raises expectations for exciting future lake discoveries by our instrument.”

And note this, from VIMS principal investigator Robert H. Brown (University of Arizona):

“It was hard for us to accept the fact that the feature was so black when we first saw it. More than 99.9 percent of the light that reaches the lake never gets out again. For it to be that dark, the surface has to be extremely quiescent, mirror smooth. No naturally produced solid could be that smooth.”

Thus we learn more about a hydrological cycle based on methane, with ethane and other hydrocarbons created by the breakdown of atmospheric methane by sunlight. Other evidence of the cycle seems glaringly obvious, in the form of channels evidently carved by fluids, along with evidence of rain and evaporation. Indeed, Ontario Lacus, ringed by a gradually more exposed beach, seems to be evaporating as we watch. Seasonal change in this dynamic environment should be fascinating to monitor as, in a few years, Titan’s north pole emerges into sunlight.

{ 6 comments }

Adam July 31, 2008 at 18:01

Titan might have quite an extensive groundwater system of methane/ethane trapped in the regolith which wold explain a lot. The complicated erosional terrain of Xanadu is also indicative of intense rainfall occasionally – makes for quite a varied climate and perhaps needs more than a few polar lakes as a source. A base there will be a must eventually, though it seems too inhospitable for terrestrial life to really thrive even in biospheres.

ljk July 31, 2008 at 19:44

Coupling convectively driven atmospheric circulation to surface rotation: Evidence for active methane weather in the observed spin rate drift of Titan

Authors: Jonathan L. Mitchell

(Submitted on 30 Jul 2008)

Abstract: A large drift in the rotation rate of Titan observed by Cassini provided the first evidence of a subsurface ocean isolating the massive core from the icy crust. Seasonal exchange of angular momentum between the surface and atmosphere accounts for the magnitude of the effect, but observations lag the expected signal by a few years.

We argue this time lag is due to the presence of an active methane weather cycle in the atmosphere. An analytic model of the seasonal cycle of atmospheric angular momentum is developed and compared to time-dependent simulations of Titan’s atmosphere with and without methane thermodynamics. The disappearance of clouds at the summer pole suggests the drift rate has already switched direction, signaling the change in season from solstice to equinox.

Comments: 16 pages, submitted to ApJ

Subjects: Astrophysics (astro-ph); Space Physics (physics.space-ph)

Cite as: arXiv:0807.4778v1 [astro-ph]

Submission history

From: Jonathan Mitchell [view email]

[v1] Wed, 30 Jul 2008 04:00:12 GMT (109kb)

http://arxiv.org/abs/0807.4778

Enzo July 31, 2008 at 21:12

Titan gives me the impression of a world where only the poles are cold enough to have permanent methane/ethane lake, especially in the winter hemisphere (currently north). Ontario Lacus is the only identified lake at the south pole and it seems to be evaporating as well. Maybe, during spring/autumn there are precipitations at lower latitudes as the poles swap roles. That would also justify the erosion visible at lower latitude and the dry river beds seen by Huygens.
Mine is pure uninformed speculation as I’m no meterologist.

Enzo July 31, 2008 at 21:16

And I forgot to add that most of the methane clouds are currently seen at the poles, like in this picture :
http://photojournal.jpl.nasa.gov/catalog/PIA10434

I seem to remember that methane clouds were seen at the south pole as well in one of the first flybys, much more rarely at lower latitudes.

James M. Essig July 31, 2008 at 23:16

Hi Folks;

I am greatly pleased by the finding of the ethane lake on Titan as I am sure we are all.

Perhaps a settlement could be built on Titan even if it is enclosed in a highly regulated biosphere.

One obvious thing that comes to mind is the use of the liquid hydrocarbons on Titan as a fuel source for manned chemical rocket vessels plying the depths of the solar system, a source of construction materials for space based structures such as for any future ultra-strong, ultra-tough structures made from massed produced carbon nano-tubes or nanotech self assembly mechanisms that produce structures out of pure diamond, and the like.

Another possibility is to use these vast reserves of low atomic number element based materials as fusion fuel for interstellar space faring manned craft.

It is really anyone’s guess as to how deep this discovered lake is. With a surface area of 7,800 square miles, obviously an average depth of 1 mile would put the fuel volume at 7,800 cubic miles. However, the depth of the lake might be much deeper in certain places and there appears to be numerous similar lakes on the surface of Titan.

I read an article today in my copy of the latest issue of “Science News” about artificial base pairs in artificially assembled “DNA” in a laboratory environment wherein at least some of the base pair molecular units where of compounds other than A, T, G, C. These new forms of DNA were more resistant to enzymes and some even had triple molecular bonds for increased sturdiness. The point is that perhaps DNA like organic and even biological compounds could develop even in the super cold oceans of Titan. I would throw a party if even some primitive life forms were discovered on Titan.

Thanks;

Jim

ljk October 5, 2008 at 23:59

Clathration of Volatiles in the Solar Nebula and Implications for the Origin of Titan’s atmosphere

Authors: Olivier Mousis, Jonathan I. Lunine, Caroline Thomas, Matthew Pasek, Ulysse Marboeuf, Yann Alibert, Vincent Ballenegger, Daniel Cordier, Yves Ellinger, Francoise Pauzat, Sylvain Picaud

(Submitted on 1 Oct 2008)

Abstract: We describe a scenario of Titan’s formation matching the constraints imposed by its current atmospheric composition. Assuming that the abundances of all elements, including oxygen, are solar in the outer nebula, we show that the icy planetesimals were agglomerated in the feeding zone of Saturn from a mixture of clathrates with multiple guest species, so-called stochiometric hydrates such as ammonia hydrate, and pure condensates.

We also use a statistical thermodynamic approach to constrain the composition of multiple guest clathrates formed in the solar nebula. We then infer that krypton and xenon, that are expected to condense in the 20-30 K temperature range in the solar nebula, are trapped in clathrates at higher temperatures than 50 K. Once formed, these ices either were accreted by Saturn or remained embedded in its surrounding subnebula until they found their way into the regular satellites growing around Saturn.

In order to explain the carbon monoxide and primordial argon deficiencies of Titan’s atmosphere, we suggest that the satellite was formed from icy planetesimals initially produced in the solar nebula and that were partially devolatilized at a temperature not exceeding 50 K during their migration within Saturn’s subnebula.

The observed deficiencies of Titan’s atmosphere in krypton and xenon could result from other processes that may have occurred both prior or after the completion of Titan. Thus, krypton and xenon may have been sequestrated in the form of XH3+ complexes in the solar nebula gas phase, causing the formation of noble gas-poor planetesimals ultimately accreted by Titan.

Alternatively, krypton and xenon may have also been trapped efficiently in clathrates located on the satellite’s surface or in its atmospheric haze.

Comments: Accepted for publication in The Astrophysical Journal

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0810.0308v1 [astro-ph]

Submission history

From: Olivier Mousis [view email]

[v1] Wed, 1 Oct 2008 22:39:32 GMT (304kb)

http://arxiv.org/abs/0810.0308

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