Titan: A Rainy Season Ahead?

by Paul Gilster on January 30, 2009

Rain seems to have been plentiful at Titan’s south pole. A new analysis of Cassini imagery compares the region in recent times with what it was about a year earlier, noting new features in areas many scientists believe to be lakes of liquid hydrocarbons. Adding to the conjecture is the fact that extensive cloud systems covered the region during this period, evidence for a large rainstorm amid changing seasons. All this comes from the almost global surface map Cassini’s Imaging Science Subsystem has been acquiring since April of 2004.

Have a look at some of this imagery, and keep an eye in particular on Ontario Lacus, at the bottom of each image, noting the difference in brightness.

cassini_lakes

Image (click to enlarge): The images on the left (unlabeled at top and labeled at bottom) were acquired July 3, 2004. Those on the right were taken June 6, 2005. In the 2005 images, new dark areas are visible and have been circled in the labeled version. The very bright features are clouds in the lower atmosphere (the troposphere). Titan’s clouds behave similarly to those on Earth, changing rapidly on timescales of hours and appearing in different places from day to day. During the year that elapsed between these two observations, clouds were frequently observed at Titan’s south pole by observers on Earth and by Cassini’s imaging science subsystem. Credit: NASA/JPL/Space Science Institute.

We now watch to see what happens as summer approaches in Titan’s northern ‘lake district.’ The Cassini team has released an updated map that includes near infrared images of a part of this area, adding to observations from other Cassini instruments that show greater amounts of liquid methane in the northern hemisphere than the southern. By all accounts, then, things should get active up north as the seasons progress. An active weather cycle with convective cloud systems and plentiful precipitation may well be the result, probably in amounts larger than we’ve documented so far in the south.

A Cassini news release covers the release of the latest map and goes on to point out an interesting fact: Although some of the northern lakes are quite large — Kraken Mare, if full, would be five times the size of Lake Superior — evaporation from the surface cannot account for the replenishment of the atmospheric methane lost through rainfall and surface deposition of haze particles. Elizabeth Turtle (Johns Hopkins Applied Physics Lab) explains:

“A recent study suggested that there’s not enough liquid methane on Titan’s surface to resupply the atmosphere over long geologic timescales. Our new map provides more coverage of Titan’s poles, but even if all of the features we see there were filled with liquid methane, there’s still not enough to sustain the atmosphere for more than 10 million years.”

That points to underground reservoirs of methane amidst a terrain filled with interesting organic chemistry. Even so, how long can this atmosphere persist? Another question is why we find liquids collecting in the polar regions and not at the lower latitudes. One thing on Cassini’s future agenda will be the study of clouds and temporary lakes near the equator as peak sunlight shifts in the spring and fall. For more, see Turtle et al., “Cassini imaging of Titan’s high-latitude lakes, clouds, and south-polar surface changes,” Geophysical Research Letters 36 (29 January 2009), p. L02204 (abstract).

Adam February 1, 2009 at 2:53

With all that methane weather Titan is definitely the “Earth of the Outer Solar System”. It may not harbour any life, but its abiotic processes are fascinating as they are. A long-duration mobile lander will teach us a lot. I’d love to see a Europa explorer too, but technologically that’s too much of an ask presently. Titan we can do and Europa will have to wait.

James M. Essig February 1, 2009 at 14:15

Hi Paul;

This article is most fascinating.

If Titan’s lakes can only sustain Titan’s atmosphere for 10 million years, it begs the question as to how much methane and other hydrocarbons Titan has below its surface and also whether or not there is any subsurface life on Titan that might somehow be generating the hydrocarbons.

Either way, planetary meteorology just became more interesting.

With all of these hydrocarbons, perhaps large solar sail or nuclear fission/nuclear fusion powered 20 km/second class cargo ships could carry the methane and/other hydrocarbons back to Earth for energy generation and as raw materials for manufacturing. Yet to be developed hydrocarbon materials perhaps stronger then the 450,000 PSI tensile strength Spectra which comprises modern body armour being used in Iraq and Afganistan by U.S. troops, might expedite the development of practical high mass specific reflectance beam sails that are very large and which can, as a result, accelereate large manned space craft to high gamma factors.

Either way, the discovery of such huge supplies of hydrocarbons on Titan Bodes well for future solar system wide human civilization including habitats, industry, scientific outposts, and transportation.

Thanks;

Jim

Adam February 2, 2009 at 2:20

Hi Jim

I think we can do without hydrocarbons from Titan for energy on Earth, Jim. To get serious about energy security we need to get out of burning stuff – it’s one of the least efficient ways of producing usable power.

And, in space, you need to crack an oxidiser out of combination with reductants to burn the hydrocarbons in the first place. There might be free peroxide on Mars, oxygen/ozone/peroxide on Europa (in the ice), and of course on Earth – all at the bottom of potential wells that need more energy input to climb than you can get out of the fuel mix. Methane has merit as a propellant in nuclear thermal rockets and it’s indefinitely storeable in space, being a pretty soft cryogen. But water is more abundant on small solar system bodies and might be propellant of choice.

James M. Essig February 4, 2009 at 2:39

Hi Adam;

Thanks for the above response.

About burning stuff, come to think of it, I must say I am in complete agreement with you.
The weather here in the Eastern United States seems to be getting freakier by the year. I do not know to what extent the weather pattern changes are cyclical or random, but they definately seem more extreme.

Perhaps the carbon or hydrocarbon materials in these other moons could be used in some sort of large scale insitu or almost insitu carbon based materials manufacturing. Materials that come to mind are artificial flawless diamond crystal materials with optimized carbon isotope ratios, carbon nanotubes, diamond cable, and the like. Producing these materials in very large quantities could be very useful for very large surface area solar or beam sails. Perhaps some sort of naontech can help in this regard.

Either way, there must be some use for all that carbon.

Regards;

Jim

MaDeR February 12, 2009 at 17:17

Essig, considering current technology and costs, transporting materials from Titan to Earth would be completely unfeasible and insanely costly, even in on surface of Titan was walled with pure, pure cocaine.

I noticed that many comments on this site have such unrealistic speak. Less SF books and movies, more sober view on so-called Reality.

ljk July 16, 2009 at 13:49

Evidence for condensed-phase methane enhancement over Xanadu on Titan

Authors: M. Ádámkovics, I. de Pater, M. Hartung, J. W. Barnes

(Submitted on 13 Jul 2009)

Abstract: We present evidence for condensed phase methane precipitation near Xanadu using nine nights of observations from the SINFONI integral-field spectrograph at the Very Large Telescope and imaging analysis with empirical surface subtraction. Radiative transfer models are used to support the imaging technique by simulating the spectrometer datacubes and testing for variations in both the surface reflectivity spectrum and atmospheric opacity.

We use the models and observations together to argue against artifacts that may arise in the image analysis. High phase angle observations from Cassini/VIMS are used to test against surface scattering artifacts that may be confused with sources of atmospheric opacity. Although changes in the surface reflectivity spectrum can reproduce observations from a particular viewing geometry on a given night, multiple observations are best modeled by condensed-phase methane opacity near the surface.

These observations and modeling indicate that the condensed-phase methane opacity observed with this technique occurs predominantly near Xanadu and is most likely due to precipitation.

Comments: accepted for publication in Planetary and Space Science; this http URL

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Cite as: arXiv:0907.2255v1 [astro-ph.EP]

Submission history

From: Mate Adamkovics [view email]

[v1] Mon, 13 Jul 2009 21:08:43 GMT (4138kb,D)

http://arxiv.org/abs/0907.2255

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