Titan Review article Options

[rlorenz]

I'm fascinated by the radar images of the lakes in your Titan review.Unfortunately, the radar images don't give any indication on the appearance of the liquid.Does it appear dark, orange, blue... from a human eye?

Some dark and uniform patches located on the "white snow" of Iapetus made me think they were pools of hydrocarbons, similar to what we might find on Titan. Do you think that the idea is relevant?

Lakes - get asked this a lot. Dunno. Probably like one of those 'Random_City at night' postcards - black.
Since the lakes are at the poles, its often nighttime. Sun and saturnshine is always low on the horizon, never
high in the sky, and only red light filters down to the ground. If you brought your own white light with you,
depends. Pure methane would look blueish - like Neptune - because of the methane absorptions in red. But
if there is a lot of reddish tholin suspended in it, maybe brownish (wine-dark sea?). So mostly black

White snow - even stuff like benzene (for example) at liquid nitrogen temperatures is white. I think
maybe anthracene is yellow (maybe Juramike can explain how things get dark/colored?). Soot of course is
black. I don't think we can rule out any of these of Titan (or Iapetus, for that matter..)

[rlorenz]

Great article, thanks for sharing it here. ......
No No ! The lesson is quite otherwise. Post here before publication and take advantage of the free nit-picking service.

Interesting idea. Though if you post here, why bother publishing anyway....?

Someone at AGU suggested getting T-shirts made

"Mars - The Second Most Titan-Like Planet in the Solar System"

[ngunn]

"Mars - The Second Most Titan-Like Planet in the Solar System"

I'm not sure - Thinking about the atmosphere as a fraction of planetary mass I think Earth and Venus would claim places one and two there.

How about "Mars - the second most Moon-like planet in the Solar System"?

[vjkane]

Pure methane would look blueish - like Neptune - because of the methane absorptions in red. But
if there is a lot of reddish tholin suspended in it, maybe brownish (wine-dark sea?).

Ralph -

In all the discussions of Titan missions, has anyone discussed putting a "lander" in the one of the lakes to study their composition?

All -

At the AGU conference, there was a poster proposing that the "land" area around the lakes might be a lot like the karst regions of Earth where the liquid has eroded the surface into dramatic shapes. It would be beautiful to see, but I can't imagine an engineering team ever agreeing that such an area would be safe to land in. ("What part of cliffs and unsafe don't you understand?...)

[Mongo]

In all the discussions of Titan missions, has anyone discussed putting a "lander" in the one of the lakes to study their composition?

I would love a "Pioneer Venus" style mission with at least five Huygens-style landers plus an orbiter, with each lander directly sampling one of the major terrain units:

1) the bright terrain as seen at Xanadu
2) the dark brown equatorial dune fields
3) the dark blue channel deposits
4) the very bright, possibly volcanism-related deposits as seen north of Hotei Arcus
5) the north-polar liquid hydrocarbon "oceans" (or Ontario Lacus, depending on approach geometry)

If there were room in the budget for a balloon in addition to this, it would be great, but I have a feeling that even these five landers would be a budget-buster.

Bill

[scalbers]

Or could we suggest elements of the Vega Venus missions that included a balloon?

http://en.wikipedia.org/wiki/Vega_program

[vjkane]

Or could we suggest elements of the Vega Venus missions that included a balloon?

My understanding is that the challenge at Titan is communications. If you build a single large balloon or lander, you can put the antenna, transmitter, and power system to communicate directly with Earth. If you do lots of landers, balloons, or combinations, then you need a relay orbiter. The second craft by itself appears, from my readings of the cost estimates, to cost ~$2B, probably less if you strip all the instruments off.

I could envision a mission that had several landers and the flyby carrier could act as the relay. Such missions have been proposed for Venus where the lander life is short. I don't know if such a mission would be considered worth while by the scientific community at Titan. Having seen how much more is learned from a lander when scientists have time to plan samples, etc, they may feel that a single longer lived lander would contribute more than a number of short lived landers.

I like your list of proposed landing sites.

[dburt]

How about "Mars - the second most Moon-like planet in the Solar System"?

Currently agree. As has been stated by others, Mars resembles what the Moon might look like with mostly frozen water and a thin atmosphere. (Of course, Mercury might ultimately finish ahead of Mars in the race for Moon resemblance.)

-- HDP Don

[Juramike]

White snow - even stuff like benzene (for example) at liquid nitrogen temperatures is white. I think
maybe anthracene is yellow (maybe Juramike can explain how things get dark/colored?).

Sure - I'll take a stab at it.

For organic molecules, things with molecular pi-orbital systems will absorb UV light. The electrons in the pi-systems get pushed up to an excited state. The UV photon goes in and excites the pi-cloud, then goes zipping off in another direction. Other photons just pass right through. Net result: UV gets absorbed.

The more extended and conjugated the pi-system, the lower the energy UV photons that can get absorbed.

Benzene has a UV peak absorbance at 210 nm. It looks white to our eyes, but is really absorbing some UV light. Put a bit of benzene on a phosphorescent silica background, and hit it with a UV light at 210 nm, and you'll see the black spot where the light didn't get through to the phosphorescent background. (At 254 nm the absorbance is kinda weak.)

(Chemists use this trick every day when monitoring reactions by TLC (thin layer chromatography). The bulk of compounds synthesized have extended aromatic or heteroaromatic rings. When there's no UV absorbance, like in aliphatic molecules, then chemists have to "do the dip" in order to stain the TLC using a reactive stain. [Still other chemists inject reaction crudes directly into the LCMS and clog up the instrument for everybody esle - these are bad chemists])

The more extended the pi-system, the lower the energy gap between the occupied and unoccupied pi-orbitals. Fusing aromatic rings together, or sticking certain functional groups in conjugation with the aromatic pi-system, all cause a shift to longer wavelengths. (Carboxyl, alkene, oxy, thio, halo - stuff like that), So things like napthyl, and anthracene (more and more benzenes in a line) make the maximum aborbance longer.

If you shift the UV absorbance into longer wavelengths, eventually you start absorbing in the visible spectrum. Remove blue light, and things look more yellow.

So the more extended the pi-system in a molecule, the yellower it looks.

Aside from the wavelength shift, there is also the effect of changing the extinction coefficient with certain functional groups, this can really amplify the absorbance exponentially. Check out the bathochromic shift (longer wavelength) and extinction coefficient jump for anthracene:

Benzene - lamba max = 255 nm (extinction coeff = 230) [much bigger absorbance hump near 210]
Naphthalene - lambda max = 314 (extinction coeff = 250)
Anthracene - lambda max = 380 (extinction coeff = 9000)

[In my advisor's group in graduate school, there was a guy in the next lab making large molecules resembling C60. As the aromatic system got larger, the compounds went from yellow, to an intense brick red. The guy's name was Rudiger Faust, and I strongly recommend his book "World Records in Chemistry" as a gift for anyone with even a slight hint of chem nerd in them.]

It does NOT take very much polymeric aromatic impurity to make things look highly colored. (Extreme case being black).

Most reactions always give a little black or highly colored aromatic goo that needs to be purified away. In my experience most reaction mixtures or slightly impure products (when things go good) always seem yellow. It's a rare and special day when someone gets a blue or green color in their reaction or product. (And we usually stand around and go "Pretty!")

Titan's surface and lakes are most likely highly colored. (Remember that black is a color).

-Mike

[nprev]

...Mike, you just freakin' amaze me sometimes...well, frequently. That was the best sixty-second semester of organic chem I ever had; what a gold mine! Thank you!!!

[rlorenz]

(we identified the same 5 terrain types as possible targets, btw)
Problem with this concept are (1) that this would mean having 5 sets of expensive chemical analysis
payloads (2) that in a battery-limited lifetime of a few hours (remember you need to stay warm
as well as functioning) it is difficult to be sure that you will acquire the surface sample you want
(3) Huygens-style landing might not be viable on cryovolcanic terrain, or Xanadu
(4) short-duration landers do not get long-term science like meteorology, seismology, magnetometry,
changing illumination, rotation state determination

I would love a "Pioneer Venus" style mission with at least five Huygens-style landers plus an orbiter, with each lander directly sampling one of the major terrain units:

1) the bright terrain as seen at Xanadu
2) the dark brown equatorial dune fields
3) the dark blue channel deposits
4) the very bright, possibly volcanism-related deposits as seen north of Hotei Arcus
5) the north-polar liquid hydrocarbon "oceans" (or Ontario Lacus, depending on approach geometry)

If there were room in the budget for a balloon in addition to this, it would be great, but I have a feeling that even these five landers would be a budget-buster.

Bill

[rlorenz]

Sure - I'll take a stab at it.
<snip>

Mike - that was great. For your next assignment, explain why hydrolyzed tholins are
fluorescent (see Icarus paper by Hodyss et al a couple of years ago..)

[djellison]

And bonus points if it involves anything on Youtube.

[rlorenz]

In all the discussions of Titan missions, has anyone discussed putting a "lander" in the one of the lakes to study their composition?

Yes. Indeed, my 'class' in the short course preceeding the International Planetary Probe Workshop
in Bordeaux in June considered just such a concept

Things to consider, though
1. it's been hard enough to argue that the lakes are indeed lakes (and it would be even harder to
argue that they will still be lakes when the follow-on mission gets there : if methane, they
might evaporate seasonally) so optimizing the payload for lakes specifically is a bold choice.
2. I'd argue that while the lake chemistry may be exceedingly interesting in perhaps not-understood
ways (e.g. see the NRC Limits to Organic Life report many threads ago) the known path to pyrimidines,
amino acids etc is via hydrolysis of tholins in impact melt sheets and cryolava flows. If you had the
capability you might land at and sample the edge of such a flow. A lower-tech alternative is to
argue the dune sands are likely to contain some component of such material, since the sand has been
transported over some distance anyway (and the non-hydrolysis part of such sands is unknown and
interesting anyway)

[Mongo]

(we identified the same 5 terrain types as possible targets, btw)
Problem with this concept are (1) that this would mean having 5 sets of expensive chemical analysis
payloads (2) that in a battery-limited lifetime of a few hours (remember you need to stay warm
as well as functioning) it is difficult to be sure that you will acquire the surface sample you want
(3) Huygens-style landing might not be viable on cryovolcanic terrain, or Xanadu
(4) short-duration landers do not get long-term science like meteorology, seismology, magnetometry,
changing illumination, rotation state determination

It sounds like the biggest problem would be the short lifetime of a battery-powered lander, combined with the limited power available and the lack of choice about where the lander touches the surface. Not to mention that the probe would be duplicated four or five times, and the same mass budget could presumably send a much more capable single payload.

The other option would be some form of dirigible balloon, with ducted fan(?) for some degree of directional control, that mainly stays in the troposphere with occasional descents to the surface for samples. It would have to be powered by RTGs or perhaps a nuclear reactor, which should also allow enough power for a direct link to Earth, eliminating one link in the communication chain (although the bit rate may be higher if an orbiter can relay its transmissions).

The orbiter would have to be the highest priority in my opinion, as it would provide at a reasonable cost considerably better radar and optical coverage than Cassini, as well as a possible telecom capability if there is budgetary room for a surface probe. Most of the (very valid) objections to the Huygens-style landers suggest that any surface/atmospheric probe must be nuclear-powered, as well as having airborn capability -- and indeed would spend almost all its Titan time well above the surface. This is discussed in far more detail in the OPAG reports.

The combination of orbiter and dirigible balloon would be very expensive, though. This is one time that a collaboration with ESA and perhaps other space agencies would be helpful (if ITAR allows it). The additional administrative workload would be difficult, but I think that the increased mission capability would be worth it. Of course I am not the one who would have to shoulder the extra workload.

Bill