July 24, 2006 | David F. Coppedge

Titan’s Land-o’-Lakes Found

The Cassini spacecraft has found features that look like methane lakes in the northern latitudes of Titan (see JPL press release).  The large dark patches, some about 30 miles across with rounded edges, appear to be associated with fluid channels.  Radar echoes cannot determine for sure whether the surface is liquid (dark means smooth, light means rough); the dark features could represent dry lakebeds like those found by the Huygens Probe.  Still, the surfaces appear extremely flat, although some of them may show evidence of waves.  Since these large, rounded dark features did not appear at equatorial latitudes, a comparison with the south pole at a future flyby will be instructive.  The radar images were obtained during the T16 flyby on Saturday, July 22.  Amateur enthusiasts are abuzz with excitement and interpretations at Unmanned Spaceflight, and Emily at the Planetary Society is sure they are lakes, comparing them to other lakes in the solar system.  They could be calderas from cryovolcanism – or just remnants of long-gone lakes.  A report on Science Now says the dark areas show higher temperatures, as would be expected from liquids, and reside north of 70° where methane rains would more likely occur.
    Another Titan story comes from the European Space Agency.  By analyzing interference patterns in the radio signal from the Huygens probe to the Cassini orbiter, researchers calculated that the surface the probe landed on is covered with pebbles 5-10cm in diameter.
    Also from the Saturn system, another view of Enceladus was released, paired with the moon Rhea.  Taken from 2.5 million miles away, the jets of Enceladus (en-SELL-a-dus) are clearly visible (see 07/11/2006 story).  A processed image was released July 21 allowing details of the outer plume to be shown feeding the E-ring.  The next close flyby won’t be till March 12, 2008 near the end of the prime mission (see timeline).  Since Enceladus has proven extraordinarily interesting, it will doubtless become a prime target for any extended mission if the spacecraft continues its nine-year record of good health.
    Heads Down:  Cassini is now increasing its inclination over the next few orbits (plot, the 180-degree transfer).  By fall through spring, we should get unprecedented views looking down over Saturn’s rings from high overhead.  This will provide a welcome change of view after months of seeing the rings as thin lines (example).  The edge-on views have reminded us that, for all their vast extent, the rings are only about 100m thick.  The new vantage point, showing the ring system’s full breadth and detail of color and structure (example) is sure to inspire artists and poets as well as scientists (see overhead diagram).

Titan appears to be showing a distinct regional difference between the equator and the poles.  Being cooler, the poles may be condensing out more of the liquid methane and ethane that is believed to be constantly produced in the upper atmosphere.  The current radar SAR image strip represents only a tiny fraction of Titan’s surface, so it is impossible to say if this region with its dark patches represents much of the polar regions or not.  The last two radar passes have been exceptionally intriguing (see also the July 19 press release about the April 30 flyby).  Titan presents a few familiar landscapes, but many unique ones.  Impact craters are rare, and there are no high mountains (as detected on the smaller moons like Iapetus).  It’s going to take awhile to sort all this out.  Too much theorizing too early might spoil the fun of discovery.

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