This just out. Not earth-shattering, but colorful - maybe handy as an up-to-date
Titan intro

http://www.jhuapl.edu/techdigest/td2702/lorenz.pdf

Well, I guess the secret is out. The ISS camera is actually a space station attached to Cassini. So while Ralph and the others have to wait for there data to be played back, a group of us and I are actually in orbit around Saturn in our nice, comfortable station.

I assume the D is for Danger?



Doug

Yeah that Space Station also makes its appearance in the New Solar System (I think) book

edit - it was the encyclopedia of te solar system

Hmm. So nice of you all to speak in such glowing terms about the content as a
whole rather than getting hung up on a typo........
Note to self - stop posting to UMSF, just causes grief.

The ISS mistranslation did not originate with me - I just checked my manuscript -
must have got introduced in typesetting. But I should have caught it at the
proofing stage.

(Doug - must be D for Deathwish)

Hand on heart - I've been keeping it ready for today so I can read it in chunks while waiting for videos to render out for a work project - and it's bloody good. I'm out of the loop with Titan in a major way - it's orange, it's fuzzy, it's probably sticky - that's about it. This piece is pitched perfectly at the enthusiast who needs the Titan 101. Almost reminds me of the kids news show Newsround...not the kids bit, but the way it explains the indepth facts, whilst educating enough on the go to put them in context. Not easy.

Nicely done

"Plotting updates on
its location on a wall-chart map of Titan could become
a daily activity in schools"

You KNOW that's Tesheiners job, right? Purveyor of virtual pins+strings.

Doug

You know that we're just teasing. I personally thought that the article was a good basic introduction to Titan for newcomers.

Bill

Ralph, I really enjoyed the article--keep up the excellent work. Don't let the nitpickers at UMSF get you down--most UMSF readers just enjoy a good read and don't comment one way or another. Definitely keep posting.
-Floyd

Great article, Ralph; certainly a call to arms for future missions. Thanks for sharing it with us!

Nice article. I picked up a few things from it that I didn't know before today.

I bought in 2004 "Lifting Titan's Veil".It's of course the reference for Titan and I will reread it very soon to compare with what we know now ( presented in Titan revealed).

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?

Great synopsis. The points regarding the diversity of the chemistry were new to me.

I think the comment about mobility and exploration is dead-on, and the map of a possible groundtrack got my imagination going. I think I would expect greater return from a two-balloon mission than one lander + one balloon.

I'm reminded of how the original plan for Mariner 8 and 9 intended to place one in an orbit producing high phase angle imagery and the other into an orbit providing low phase angle imagery, so that the two data sets would complement one another. The failure of Mariner 8 spoiled this plan, but it was an interesting strategy.

So I wonder about a two-balloon mission that placed the two balloons not only at different latitudes, but also different altitudes. A lot of the diversity of Titan correlates with latitude, and a single balloon would run the hazard of permanently missing some of that diversity, even if it lasted a very long time.

So, off the cuff, I am thinking about a mission with an equatorial balloon that begins its mission at around 20 km altitude, and a polar balloon (preferably northern, at around 80-85N) at around 3-5 km. The northern lake districts provide diversity that would be interesting to probe extensively. The low altitude would mean narrower imaging noodles, so we would be rooting for it to complete many laps. Meanwhile, the equatorial balloon would have wider imaging at lower resolution. If it does have an extremely extended lifetime, it might be desirable to drop its altitude after it had circumnavigated Titan a few times. As for the polar balloon, it would be nice to have it migrate eventually to the mid latitudes, but this may not be possible. The balloons might be flown until they fail, or their mobility could be sacrificed in order to provide a "lander" somewhere. With two, we could split the difference, keeping one flying indefinitely while landing another.

At the end of a mission like this, we would have a lot of ground-truthing of most of Titan's interesting terrain types. We could select some high-value targets for the initial entry points (with much of what followed being left to the chance of circulation patterns). Of course, an orbiter would provide comprehensive mapping at resolutions intermediate between the balloons' and Cassini's. At the end, we'd have a rough global map, with enough ground-truthing to feel like we know the place pretty well. Then if we send another lander, we'd know where we want to send it. Right now, picking which places on Titan's surface NOT to explore if we only sent 1 or 2 landers feels like choosing which of your children you love least.

Great intro to the wonders and mysteries of Titan, Ralph. There's a lot there I can use - if it's ok? - in my Outreach talks in schools here in the UK. Titan really is second only to Mars on my personal "Most Fascinating Worlds in the Solar System" list.

You do know people weren't criticising but just josh'n with ya, right? I've lost count of the number of times I've been sniggered at for putting rising or setting Suns in MER panoramas where they've no right to be, it's all just part of the UMSF fun!

Great article, thanks for sharing it here. In advocating further exploration of Titan after Cassini I almost dare to believe you will be pushing on an open door. This world is the perfect challenge for 21st century science. Yes, big spending will be required, but it will be science that ordinary people can relate to (unlike string theory or 'dark energy'). Mars is our new Wild West, Titan our new Antarctica. Exciting times.



No No ! The lesson is quite otherwise. Post here before publication and take advantage of the free nit-picking service.

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..)

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"

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"?

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?...)

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

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

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

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.

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

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

...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!!!

(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

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..)

And bonus points if it involves anything on Youtube.

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)

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

More pi system fun. When pi-systems get really extended they can allow multiple modes of accessible pi system excited states. So instead of the simple pi-->pi* from above post, you get pi-->pi*1-->pi*2 + hv. So instead of the same color light going off in a different direction, you get a different color light being emitted. So it will look brighter in that color. The new color corresponds to the energy gap between the excited states.

[Sometimes when we do UV based TLC described above, instead of a black dot against the phosphorescent background, we get a spot that "glows back at ya". Usually this is bluish, but other fun colors are often seen as well. IIRC, anthracene will glow back at ya blue when illuminated with a 254 nm UV lamp (or it might be at 210 nm - more things seem glowy at shorter wavelengths)]

Usually the reradiated wavelength is specific (and tunable) for the molecule. This trick is used to identify certain materials and uhhh, bodily fluids [How many time have we seen them whip out the tunable light source at a crime scene on "CSI"?]

[[A lot of ion channel assays use a really cool trick with fluorescence. Biologists use a fluorescent compound (call it a red glower) that floats on the outer surface of the cell membrane (it's got a lot of charged functional groups that won't let it pass through the membrane bilyer). Biologist then add another fluorescent compound that has an acidity close to pH of the cell environment. There is another fluorescent compound (call it a blue glower) that will protonate and lock up to one side of the membrane, which ever one has the lower pH. Under normal conditions of cell polarization the blue glower is on the inside membrane far from the red glower. You zap with a laser at the right wavelength that excites only the red glower and it glows "red". But when the membrane (via ion channels) is depolarized with an active compound, the ionic gradient shifts, the blue glowing free-floating compound switches to the same side of the membrane as the red glowing compound. Because of their proximity, the excited red molecule can now transfer fluoresence energy to the blue glower. So when you zap a depolarized membrane with the laser to excite the red molecule, it gets excited, tranfers energy to the blue glower and you get a "blue" glow instead of "red". So now you can figure the cells polarization state by measuring color red = normal, blue = depolarized. This nifty trick is called fluorescence resonance energy transfer (FRET) and is used all the time in biological and chemical assays. And the fluorescent dyes used are usually big aromatic compounds with heteroatoms liberally sprinkled in the ring system.

Check out (cool diagrams): http://en.wikipedia.org/wiki/FRET

Why do they go through all this effort? Because one of the most common problems with screening compounds with a single-flourescence assay is that you get all sorts of false positives.

It seems a whole bunch of polyaromatic compounds are out there in nature just waiting to glow back at ya and mess up your single-flourescence assay. The double-flourescence trick gets around these impostors.]]

So with all sorts of aromatics dripping down from the atmosphere, a UV light on Titan would be a really psychedelic experience.

-Mike

Fascinating, Mike. But you've got me wondering if a UV light source is absolutely necessary. Could there be chemical reactions going on that produce the coloured lights directly? Would a cryovolcanic eruption produce a cold firework display? Would a violent rainstorm be accompanied by strange glows? I guess you'd have to be underneath the haze to observe such phenomena if they occur.

OK. right there you took the thread away from discussing the next Flagship into 'someday, wouldnt it be
nice'

You can debate the readiness of an RTG dirigible, but reactors are not presently on the cards.

btw - ITAR doesnt *prevent* anything, it just necessitates paperwork. Clean interfaces help.

Leaving aside the question of power source, designing a system that can touch down repeatedly with a high probability of survival is really hard. Winds could easily blow you around at low altitudes. When you start your descent, you will be over point x, but as you descend the winds may take you to very dangerous point y, and you are too far away for real time control from Earth.

I'm not an engineer, but it might be easier to have a balloon that drops small landers (although once they have to carry heavy instruments like a mass spectrometer, they may not be so small...) at interesting points.

In a side conversation with Ralph L, he pointed out that there are many, many mission options. The hard part is to nail down the science goals and establish the budget. Once that is done, the engineers can apply their creativity.

So send your checks to NASA and letters to Congress.

So personal cheques directly to Ralph Lorenz are out?

And remember, folks, this comes from someone who was a lot closer to the JIMO debacle than most of us.

-the other Doug

Beer leaves fewer auditable tracks, and regardless of the outcome, you had a beer and good company.

You could buy 'Titan Unveiled' when it comes out in April. I think my
royalties work out at about the price of a beer per copy.

Actually I stayed well clear of that one (thankfully). I was, however, on the NRC panel that
contemplated it and other such missions

http://www.nap.edu/catalog.php?record_id=11432

That still makes you closer and more knowledgeable than most (if not all) of the rest of us about the specific issue of flying full-scale nuclear reactors on outer planet probes, Ralph.

Sure, it's possible. The technical challenges and risks are just a little higher than can be overcome at the moment, I think.

-the other Doug

Oh, I intend to. I had bought "Lifting Titan's Veil" as soon as it came out in HC, so that's one beer worth of royalties already.

I couldn't agree more. Landing a dirigible in any sort of wind is quite tricky even with a live crew, real time control and a landing team on the ground.

Lowering an instrument package on a cable might be barely feasible in flat terrain. If the wind is reasonably steady and not too strong an autopilot could probably hold the dirigible more or less still. However if the probe got stuck the only option would be to cut the wire.

April. And there was I hoping that 'later this year' might still happen. (I see it's already up on Amazon.) Never mind, you can count on an April beer from me. And the rest of us here would definitely be too much for one night, so we'd better stagger those purchases. . .

I just pre-ordered my copy. I hope it publishes on time so I can bring it with me on my vacation.

So perhaps I can ask a question about the currently orbiting flagship?

In your very nice review, you state the following (below). I have heard a number of proposals for an XXM and this option would certainly allow for the longest observation window in the Saturn system. I know we can only have limited discussion about the possible XXM when we haven't yet finished the nominal mission, but is the "low-maintenance cycler orbit" a long term Cassini mission goal or YOUR preferred orbit evolution?

Well, you can ask, but as I have said before, I have a policy of not discussing ongoing
implementation issues, spacecraft crises etc. I can say the following, however..

First, recognize that formally speaking, even the XM is not yet approved. (Though this was the
first item on the outer solar system list of the old Decadal survey). So all this is hypothetical
until that happens.

Of all the things to do in the Saturnian system, I think it is safe to say there was some consensus
that studying the seasonally-changing system for as long as possible (i.e. longer duration, even
at the expense of lower activity) is scientifically important, more so than any specific goal.

Finally, I'd say the Cassini scientists have learned to trust the orbit wizards at JPL. Rather than
specifying lots of orbit petals in great detail and overconstraining the problem, we scientists
just say, 'Make us a pretty flower' (and after some thought) 'some big petals and a few small
ones, and a few that stick up above the plane if you can'. So the orbit designers know we
like Titan, know we like looking down on the rings, know we like enceladus etc. and will work
their magic. A Titan-Enceladus cycler may be the most efficient solution (at least for
part of XXM), or it may not be. It does have some obvious attributes, and is 'catchy' in the
sense that it sounds efficient, has a name that people 'get' instantly. A cycler by definition is in
the ring plane, so some ring/aurorae observations would suffer, so I doubt that all of XXM would
be a cycler.

While possibly good for Cassini XXM, a Titan-Enceladus cycler would be a poor substitute for
a Titan orbiter in a future mission - remember Titan and Enceladus are 3x further apart
than are the Earth and the Moon, so the cycler spends most of its time between them, rather
than at either one.

Wouldn't it also preclude repeated RADAR passes over Titan's polar wetlands? That must be one of the priority targets for long term observation surely.

This is more along the lines of the reply that I was expecting, so thanks for the additional insight.

IIHO, the Saturn system really could use a longer duration observation campaign if only because the seasonal effects are so much stronger at Saturn than at Jupiter. Having a good set of eyes in the system will out-perform anything we have here on the ground.

But that being said, there’s always the trade-off between getting as much science done as possible today and saving resources in order to observe at a later date. Engineering, budgetary, and random constraints always put uncertainty on the “later date”. You guys are the experts, so keep on trucking and good luck with the real policy decisions that allow so much great work to be done in the first place.

A purely equatorial orbit would preclude RADAR obervations of Titan's poles. But you could get a direct polar flyby by tipping the orbit around Saturn by only 0.14 degrees. That shouldn't take a lot of fuel. The bigger problem is that Titan's gravity will do things to the orbit after that, so you need two burns if you want just one such flyby, and then return to the equatorial orbit.

The polar regions are fairly small, and it won't take long to map them -- it's looking for change that will merit repeat coverage, and I think most of the science would come from checking them just twice -- as early as possible, and as late as possible.

Spot on, as usual. But why is it that I find Titan's lakes more interesting than the jets of Enceladus? It's the liquid thing. I keep harking back to that very early post by (I think) Vexgizmo - "Show me the water".