Grandiose Canyons on a Saturn Moon, Filled With Liquid Methane

Aug 16, 2016

By Kenneth Chang

Deep, narrow canyons on Titan, Saturn’s largest moon, are flooded with liquid methane and other hydrocarbons, radar data from NASA’s Cassini spacecraft has found.

Titan, the Saturn moon with a diameter one and a half times that of Earth’s moon, is a surprisingly complex world. It has three large seas, a thick covering of haze and clouds, and surface contours carved by erosion — despite temperatures of about minus 300 degrees Fahrenheit (minus 184 Celsius).

“For many things, it is similar to our planet,” said Valerio Poggiali of the University of Rome, and a member of the Cassini spacecraft mission’s radar team. “That is why we consider Titan really a laboratory for a deeper understanding of our home planet.”


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3 comments on “Grandiose Canyons on a Saturn Moon, Filled With Liquid Methane

  • @OP – link – In an article published Tuesday in the journal Geophysical Research Letters, Mr. Poggiali and his colleagues reported that they had spotted three reflections from the radar signal. The first came from the radar bouncing off the edges of the canyon.

    The second was a bright reflection, like a glint off a mirror. This they interpreted as the liquid surface, and tellingly the height of the surface in the main channels was the same as that of the sea, even more than 100 miles away. For the dark material to be that flat and that reflective, it almost certainly had to be the same liquid as in the sea. (The smaller tributaries were at higher elevations, suggesting that they were flowing downhill into the larger rivers.)

    It has been understood for some years now, since the earlier Cassini images, that Titan has seas, river valleys, and methane rain. This has added detail showing long estuaries or fjords.

    The newly described canyons in Titan’s north polar regions are about half a mile wide and 790 to 1,870 feet deep, with slopes greater than 40 degrees. Earlier observations by Cassini had spotted channels branching off Ligeia Mare, the second largest of Titan’s seas, adding to the exotic features observed on the moon’s surface.

    This raises the interesting question of angles of rest in low gravity.
    Studies on experiments and studies of dunes on Mars suggest that angles of rest do not vary much with low gravity (when compared to those on Earth), but some short low gravity experiments conducted on diving aircraft have suggested they can change in low gravity.

    This link explains some experiments and observations:-

    http://onlinelibrary.wiley.com/doi/10.1002/grl.50586/full
    These measured values of dynamic angle of repose of ~30–31° and ~33–34° match the expected range of 30° to 35° found both from laboratory experiments and measurements of terrestrial dunes [Cooke et al., 1993, and references therein] and are certainly not 5° to 7° lower than terrestrial values as predicted by Kleinhans et al. [2011]. These results support the hypothesis that the dynamic angle of repose is independent of gravity. It is possible that some other factor, such as static charge between grains, could be counteracting a real decrease in the dynamic angle of repose due to low gravity. However, we believe this is improbable both because such a counteracting force would be unlikely to produce results this congruent with our expectations of the angle being independent of gravity and because the requisite interparticle forces would strongly inhibit the saltation required to produce the observed dune migration.

    [17] To be more technically accurate, this discussion should be framed in terms of θstop as was mentioned earlier. In this case, we still observe that Martian and terrestrial dunes exhibit the same range of angles on their lee slopes. Assuming similar thicknesses of granular flow in both cases, which seems reasonable given that the granular materials should be basically similar, that the overall landform morphology is the same, and that the sand fluxes are comparable [Bridges et al., 2012b], it would seem that the parameter θstop is mostly independent of gravity.

    [18] The results of Kleinhans et al. [2011] were used by Horgan and Bell [2012] to argue against the role of CO2 frost in forming dune gullies in the north polar sand sea of Mars [Hansen et al., 2011]. However, our results show that these slope angles should not be altered by the low-gravity environment, and we also note that Martian dune gullies have been directly observed to form only when there is CO2 frost on the ground, at least in the southern hemisphere [Diniega et al., 2010; Dundas et al., 2012]. Preliminary results of monitoring the northern dunes through the most recent summer also do not show gully formation (C. Hansen, personal communication, 2012).

    It may be that the 40° slopes on Titan may be “frost” related, rather than gravity related, or may be the result of flowing liquid undercutting and eroding harder material. It could also be an effect of flowing “warmer” liquid thawing and undercutting frozen material.
    As water is a rock, and CO2 is unlikely to be involved, at the temperatures on Titan, the nature of this possible “frost” is not clear to me.

    @OP – Titan, the Saturn moon with a diameter one and a half times that of Earth’s moon, is a surprisingly complex world. It has three large seas, a thick covering of haze and clouds, and surface contours carved by erosion — despite temperatures of about minus 300 degrees Fahrenheit (minus 184 Celsius).

    On Earth, the dynamics of climate arise from the transformations of water between its liquid, ice and vapor phases. On Titan, the chilly conditions are close to where methane can similarly coexist as liquid, ice and vapor, and that generates similar climate and geological phenomena.

    4 Conclusions

    [20] By measuring the dynamic angle of repose of sand on Mars using the slip faces of active Martian sand dunes in Nili Patera, Herschel Crater, and Gale Crater, we are able to conclude that the dynamic angle of repose of dry granular material is, as was long suspected, independent of gravity. Since grain flows on dune slip faces are likely similar on the Earth and Mars, the more technically accurate parameter θstop is also shown to be independent of gravity. Our data do not allow us to directly examine the relationship between the static angle of repose and decreasing gravity; however, previous results from landers and rovers have been interpreted as indicating that the static angle is also independent of gravity. Finally, our results showing that the slip faces in Nili Patera are on average 3° steeper than those in Herschel and Gale craters indicate that the sand grains at Nili Patera are likely rougher than those at Herschel and Gale. This is interesting as we are thus able to learn about grain textures from orbital imagery.



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  • Meanwhile:- The Juno Probe has been taking pictures of Jupiter’s poles, which have now been released by NASA.

    http://www.bbc.co.uk/news/science-environment-37259937

    The US space agency (Nasa) has released spectacular new images of Jupiter acquired by its Juno probe.

    The pictures show the swirling clouds of the gas giant at both its poles – views that no previous mission has managed to acquire in such detail.

    Juno captured the data last weekend as it made its first close approach to the planet since going into orbit in July.

    The flyby took the spacecraft just 4,200km above Jupiter’s multi-coloured atmosphere.

    The 6MB of data downlinked to Earth from the encounter is still being analysed, but principal investigator Scott Bolton said new things were already obvious.

    “First glimpse of Jupiter’s north pole, and it looks like nothing we have seen or imagined before. It’s bluer in colour up there than other parts of the planet, and there are a lot of storms,” the Southwest Research Institute scientist explained in a Nasa statement.

    “There is no sign of the latitudinal bands or zones and belts that we are used to – this image is hardly recognisable as Jupiter.

    “We’re seeing signs that the clouds have shadows, possibly indicating that the clouds are at a higher altitude than other features.”

    The probe’s Jovian Infrared Auroral Mapper (JIRAM) has acquired unique views of Jupiter’s southern aurora.

    Earth telescopes have tried but failed to get such images.

    And Juno’s Radio/Plasma Wave Experiment (Waves) has recorded the blizzard of particles moving through the planet’s super-strong magnetic field.

    Juno’s quest is to investigate the secrets of the Solar System by explaining the origin and evolution of its biggest planet.

    The spacecraft’s remote sensing instruments will look down into the giant’s many layers and measure their composition, temperature, motion and other properties.



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