[X] My Assistant

[Guest_AlexBlackwell_*]

Scientists Solve the Mystery of Methane in Titan's Atmosphere
By Lori Stiles, UANews.org
March 1, 2006

Scientists Solve the Mystery of Methane in Titan's Atmosphere
By Lori Stiles, UANews.org
March 1, 2006

This refers to the Tobie et al. paper in the March 2, 2006, issue of Nature.

[Guest_BruceMoomaw_*]

Judging from the LPSC abstracts, Tobie's is actually only one of several rival theories. The most interesting thing about his theory, if it's true, is that it's a violation of the usual Principle of Historical Mediocrity as applied to solar system history. He explicitly states that Titan started outgassing major amounts of methane only about 300 million years ago -- and that for all of its history before then, it was radically different.

What might be called the Great Ammonia Mystery -- why Titan seems to show evidence of it, but Enceladus and the other smaller moons don't -- seems to be one of the biggest new mysteries uncovered by Cassini, and I'll be putting a summary of the whole swarm of new LPSC and EGU abstracts on the subject in this section soon. It may be connected on some ways with the origin of Titanian methane.

[volcanopele]

We may have at least a preliminary answer to one of their test very soon thanks to Monday's Titan pass that included some Radio Science doppler experiments. From the paper:

"If a subsurface ammonia–water ocean and a rocky core are present, as predicted by our model, Titan's tidal secondary potential Love number k2 should be higher than 0.3 and its moment of inertia factor C/MR2 should be lower than 0.33; these quantities should be measured by the Radio Science Subsystem later in the mission"

[Guest_AlexBlackwell_*]

We may have at least a preliminary answer to one of their test very soon thanks to Monday's Titan pass that included some Radio Science doppler experiments. From the paper:

"If a subsurface ammonia–water ocean and a rocky core are present, as predicted by our model, Titan's tidal secondary potential Love number k2 should be higher than 0.3 and its moment of inertia factor C/MR2 should be lower than 0.33; these quantities should be measured by the Radio Science Subsystem later in the mission"

It's possible but very tough with just the T11 data. I think RSS won't be comfortable with a Love number until all the gravity data come in (i.e., T22, T33, and T38).

[volcanopele]

It's possible but very tough with just the T11 data. I think RSS won't be comfortable with a Love number until all the gravity data come in (i.e., T22, T33, and T38).

It makes wonder though if they could at least place some constraints with just the T11 data. they may not have a number they are comfortable with, I perfectly understand that.

[Guest_AlexBlackwell_*]

It makes wonder though if they could at least place some constraints with just the T11 data. they may not have a number they are comfortable with, I perfectly understand that.

Yes, my understanding is that the stand-alone T11 gravity data can give a rough, first-order estimate for k2, perhaps enough for hypothesis testing. On the other hand, T11 by itself should give pretty good estimates for the other gravity coefficients: GM, C20, and C22.

[hendric]

Yes, my understanding is that the stand-alone T11 gravity data can give a rough, first-order estimate for k2, perhaps enough for hypothesis testing. On the other hand, T11 by itself should give pretty good estimates for the other gravity coefficients: GM, C20, and C22.

Is there a good reference on the net for what these variables mean?

[remcook]

a start...

http://www.spenvis.oma.be/spenvis/ecss/ecss04/ecss04.html

I'll try to find some pictures..

edit - some pictures on spherical hramonics

http://commons.wikimedia.org/wiki/Spherical_harmonic
http://cfauvcs5.harvard.edu/lana/fun/spheres.htm

[The Messenger]

Judging from the LPSC abstracts, Tobie's is actually only one of several rival theories. The most interesting thing about his theory, if it's true, is that it's a violation of the usual Principle of Historical Mediocrity as applied to solar system history. He explicitly states that Titan started outgassing major amounts of methane only about 300 million years ago -- and that for all of its history before then, it was radically different.

What might be called the Great Ammonia Mystery -- why Titan seems to show evidence of it, but Enceladus and the other smaller moons don't -- seems to be one of the biggest new mysteries uncovered by Cassini, and I'll be putting a summary of the whole swarm of new LPSC and EGU abstracts on the subject in this section soon. It may be connected on some ways with the origin of Titanian methane.

Evidence of ammonia acting in the past, or current evidence of ammonia? The paper is a little ballsy, since the gravity runs could either support or debunk it.

[Guest_AlexBlackwell_*]

Evidence of ammonia acting in the past, or current evidence of ammonia? The paper is a little ballsy, since the gravity runs could either support or debunk it.

Most scientists appreciate a testable hypothesis: indeed, I wish more papers were just as "bal[l]sy" and not wishy-washy with "maybe this, maybe that."

[The Messenger]

Most scientists appreciate a testable hypothesis: indeed, I wish more papers were just as "bal[l]sy" and not wishy-washy with "maybe this, maybe that."

Agreed. Ballsy was meant as a compliment

[Guest_AlexBlackwell_*]

Agreed. Ballsy was meant as a compliment

That's the way I interpreted it, though perhaps "courageous" would have been a more politically correct adjective

[Guest_AlexBlackwell_*]

Yes, my understanding is that the stand-alone T11 gravity data can give a rough, first-order estimate for k2, perhaps enough for hypothesis testing. On the other hand, T11 by itself should give pretty good estimates for the other gravity coefficients: GM, C20, and C22.

From the Cassini Significant Events Report for for 02/23/06 - 03/01/06:

The focus then shifted to the Radio Science Subsystem (RSS). This was the first of four coordinated gravity field passes - the others occurring in T22, T33, and T38 - to determine the low degree coefficients of Titan's gravity field. This knowledge may help to answer the question of whether Titan possesses an internal ocean. The four passes require disparate geometries: two of these flybys must occur when Titan is near periapse along its orbit around Saturn and two flybys - of which T11 was one - must occur when Titan is close to its apoapse. For each of these two pairs, one flyby must be on a nearly equatorial orbit with respect to Titan as was T11, and the other on an orbit with an inclination as large as possible. Radio Science also had two Gravity Science Enhancement (GSE) passes occurring after the flyby. The GSE passes are crucial to de-correlate Titan's mass from the distance at closest approach.

I guess this is why I'm a little hesitant about even a rough, first order estimate for Titan's Love number based on one flyby. On the other hand, maybe, as you suggest, some constraints on k2 could be placed, unless the number RSS generates is really flaky. We'll see.