Thursday, September 10, 2009

Thoughts on Titan Mare Explorer

John R. passed along these thoughts (posted with his permission) in response to the blog posts about a proposed Titan Mare Explorer (TIME) ( and

Here's a link to a large image of a watery horizon on a cloudy day on Earth:

Makes me think we might want to pass on the imagery.

The chemical analysis is a must, and sounding for depth is too easy not to do, but I seriously wonder the value of a single depth measurement. As I understand it, the weight of water ice under liquid methane would be fairly low in Titan's gravity, so I wonder if the lake bottom might be very heterogeneous, making a point measurement like that sort of arbitrary. A single altimetry track provided by radar, if some wavelength could penetrate the liquid, would be infinitely more useful.

Even the chemical analysis will leave us wondering about anisotropies. The Earth's oceans vary in salinity by a factor of about 1.5 from one location in open water to another. And here's an interesting map of salinity for Lake Pontchartrain.

All of which is just to flag, mindful of the Galileo Probe's experience at Jupiter, the risk of anisotropies and the impact that has on the value of collecting data. Clearly, the value is still there, and we'd love to have it in hand, but it undermines the meaningfulness of the data to some extent, as long as we're comparison-shopping billion-dollar missions.

Editorial Thoughts: These issues emphasize, in my mind, the value of TIME being able to make measurements over months, which its plutonium power source would allow. That would allow it to examine the surface conditions under varying weather conditions (assuming they vary meaningfully over a few months). If the winds or currents can push the lander (raft? boat?) over a meaningful transect of the surface, then there would be more chances to sample compositional heterogeneity. This would also be useful for depth sounding. I wonder if the probe could be designed so that the structure above the surface would be more likely to catch the wind?

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