[X] My Assistant

[elakdawalla]

Jonathan Lunine just gave a presentation in a press conference at DPS in Cambridge where he argued that "Titan is perhaps the most Earthlike place in the solar system in terms of the balance of physical processes modifying its surface." He mentioned channels, windblown features, possible lakes, evidence of tectonism, highlands and lowlands. Then he showed a pair of very interesting graphs, which he kindly gave to me, demonstrating how Titan sits in a very Earth-like "Sweet Spot" in the solar system.

The first graph has a plot of mass (normalized to Earth) on the y axis and distance from the Sun (in AU) on the X axis, and contains Venus, Earth, and Mars:



Lunine said that Venus is too close to the Sun so too hot for liquids; Mars is cool enough for liquids but its mass is too low to sustain widespread geologic activity over geologic time scales. So Venus has endogenous volcanism but little evidence of surface modification by liquids; Mars has lots of surface modification, little present endogenous geologic activity. Earth is balanced in between....and so, onto his next graph, is Titan.

Next he shows this graph. Note the axes have changed slightly to mass normalized to Titan and log of distance from the Sun, and he puts on Ganymede, Titan, and Triton, and voila, they map out the same space as Venus, Earth, and Mars on the previous graph:



He argues that Titan sits in an Earth-like "Sweet Spot" and that that's why it's so interesting. Ganymede (and similar Callisto) are like "baked Titans" and Triton (and similar Pluto) is too small for intrinsic geologic activity.

This may be a cartoon with lots of exceptions but I thought it was interesting. But I thought it would be more interesting to plot as many bodies as we can think of on one graph, and draw on distances from the Sun at which you'd expect to see interesting liquids, and see what patterns we can find. (Note someone asked Lunine where Europa would fall, and he said that there are lots of exceptions in the outer solar system because tidal heating messes up the solar distance-surface temperature relationship.) I don't have time to do this though and was wondering if anyone else wanted to have a go at playing with patterns in the solar system.

Emily

[The Messenger]

Aside from being vaguely corny (akin the the harmonies of the planets) there is a big missing tooth: No ammonia. So what Lunine has constructed is a relationship that struck a strong enough cord to be echoed in the general press, but one that is not based upon observational facts. In other word, Lunine is perpetuating an unsupported myth.

This is annoying, because there are enigmatic factual data emerging from Titan that are all but incomprehensable. This is a great puzzle, but don't expect 'sweet spot' analogies based in part on wishful thinking to help resolve it: Use the data and the chemicals we see, not what has been predicted or imagined.

No one can, at present, explain how the stratified equatorial atmosphere observe from Cassini could produce the vertical shear rates necessary to explain the Doppler patterns observed during Huygens descent.

That's the big story.