[X] My Assistant

[pioneer]

Is there any indication of tholin or oganic goo at the Huygens landing site or was it believed to be washed away by the methane rain?

[volcanopele]

Is there any indication of tholin or oganic goo at the Huygens landing site or was it believed to be washed away by the methane rain?

while it is believed based on DISR spectra that the dark regions are composed mostly of water ice, it does appear that there is some kind of darkening agent keeping the ice from being bright. Not usre what it is but presumably it is some kind of tholin or higher order hydrocarbon residue left before after the methane evaporates or drains down into the soil.

[Guest_BruceMoomaw_*]

Tholin on the river...

The very good full near-IR spectrum that Huygens took of Titan's surface from only 100 meters up shows that, above 1.6 microns, it closely matches water ice and is much darker than "hydrocarbon ice" (which Toby Owen described at the press conference as "frozen methane, ethane, and the like"). But Titan's surface is too warm for those compounds to exist as solid ice, anyway. This suggests that the unspecified "darkening agent" -- which Owen says darkens the other three peaks in the IR spectrum below the brightness of either water ice OR lightweight hydrocarbon ice -- is indeed goo made of heavier and more complex hydrocarbons and nitriles (or maybe even liquid methane, since I haven't yet seen the near-IR spectrum for that).

As he says, it's washed off the higher water-ice terrain by rain (or maybe by outflow from surface methane springs, althugh in that case I don't see how they could wash ALL the surface clean) and into the outflow channels and playas -- and then, after the liquid methane dries up there, a solid residue of dark organic sediment builds up on their bottoms. (By the way, as y'all might expect, the Huygens photos showing a dramatic albedo difference between light and dark regions have been dramatically contrast-stretched to bring out details -- the "light" areas have a real albedo of only about 20%, while the dark ones have 10-12%. That's still a pretty important difference, though. In fact, it's similar to the real albedo difference between the light and dark regions on the similarly stretched photos of Ganymede and Callisto that we're all so familiar with.)

[centsworth_II]

Hopefully, results from the gas chromatograph, mass spectrometer experiment will shed some light on exactly what complex hydrocarbons, or tholins, are present. I imagine this is the toughest of all the data collected by Huygens to interpret. I wonder how long it will be before results start coming out. At least, I hope more will be revealed about the tholin component of Titan.

[Guest_BruceMoomaw_*]

That you can count on -- very complex compounds have turned up in the ACP pyrolysis of cloud particles, and some organics heavier than methane were also volatilized out of the surface after landing by the GCMS' heated inlet (which was heated to fully 90 deg C). As you say, though, precisely identifying them is likely to take a while.

[Guest_BruceMoomaw_*]

By the way, as Jonathan Lunine said in his recent National Institute of Astrobiology lecture on the latest Huygens findings, the post-landing survival of the GCMS -- and its resulting surface analysis with that heated inlet -- was a real godsend. Without that, we would have been unable to nail down whether the channels were carved by liquid methane or ethane. And there is the possibility that the frequent exposure to the atmospherically generated organic goo on the surface to outbreaks of liquid water-ammonia mixture may have stimulated production of a lot of very complex prebiotic organics that don't exist at all in the atmosphere, which has been one of the biggest hoped-for scientific goals at Titan. If they are there, it's conceivable that even Huygens may be able to identify some of them. And since the GCMS (like the SSI package) jutted out of Huygens' bottom, I figured it would get smashed up if the probe hit even a moderately hard surface, which I expected it to do.

By contrast, the SSI experiments were something of a washout -- they worked beautifully, but since Huygens didn't land in actual liquid, all of them except the impact sensors may have been utterly useless. In fact, back in 1992, NASA's Space Studies Board recommended that Huygens carry no surface sensors except for impact sensors for precisely this reason. Except for the wave sensor and echo sounder, all of the other instruments were designed just to try and judge the composition of surface liquid by measuring its physical properties. It might have been more scientifically cost-effective to instead carry a heated core tube to allow the GCMS to carry out a really good surface-material analysis, a horizontal scanning mirror to allow the SLI to pan around at the landscape after landing, and maybe an anemometer and precipitation sensor for more post-landing weather data.

[Guest_BruceMoomaw_*]

Correction: it was a 1988 report in which the Space Studies Board recommended that Huygens carry no specific surface instruments except for impact accelerometers ( http://www7.nationalacademies.org/ssb/crafcassini88.html ).

[djellison]

"at most 15 minutes of available post-landing communication with the orbiter"

ARHGHGHAH

Ironically, a screw up forces a resdesign which gave us >6 times that. I wonder, if they'd have known about the dopper issue during PDR - would they have redesigned the misison as they have, or fixed the doppler issue's engineering. And if the former - would they then have considered some sort of modifications to instrumentation for the possibility of extended surface operations.

Doug

[Guest_BruceMoomaw_*]

I presume they would have done the latter -- LOTS simpler, and they'd have the same reasons that they had for initially designing the mission with a close flyby by Cassini the first time. Huygens was specifically designed as an atmospheric and descent-photo mission -- the nature of Titan's surface was so uncertain that it was hard even to come up with instruments that could cope with the full variety of possible surfaces (as indeed the SSI has just confirmed). But they DID want to ensure that they had the clearest possible communications during the final part of the descent (mostly to cope with the more rapid return of images then). So they designed a mission in which Cassini would be very close during the estimated time of the final stages of the descent, even though this meant that it would be completely out of touch with Huygens shortly after landing.

The logical thing (as I and the SSB said) would have been to go with the few instruments that would definitely have been workable no matter what kind of surface Huygens landed in: a core tube to collect surface material for GCMS analysis, and a mirror to let the DISR change its viewing direction after a landing. I wonder whether they went instead with the SSB package because they felt an obligation to let Britain in on the mission and this was the only experiment package Britain offered?