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Posted by: rlorenz Dec 14 2007, 05:02 PM

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

Posted by: ugordan Dec 14 2007, 05:13 PM

Posted by: volcanopele Dec 14 2007, 05:42 PM

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.

Posted by: djellison Dec 14 2007, 06:02 PM

I assume the D is for Danger?



Doug

Posted by: remcook Dec 14 2007, 06:07 PM

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

Posted by: rlorenz Dec 16 2007, 03:57 PM

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)

Posted by: djellison Dec 16 2007, 04:29 PM

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

Posted by: Mongo Dec 16 2007, 04:30 PM

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

Bill

Posted by: Floyd Dec 16 2007, 05:21 PM

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

Posted by: nprev Dec 16 2007, 06:45 PM

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

Posted by: Rob Pinnegar Dec 16 2007, 06:54 PM

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

Posted by: Webscientist Dec 16 2007, 08:12 PM

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?

Posted by: JRehling Dec 16 2007, 11:08 PM

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.

Posted by: Stu Dec 16 2007, 11:55 PM

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!

Posted by: ngunn Dec 17 2007, 10:06 AM

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.

Posted by: rlorenz Dec 17 2007, 01:37 PM

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..)

Posted by: rlorenz Dec 17 2007, 01:43 PM

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"

Posted by: ngunn Dec 17 2007, 03:19 PM

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"?

Posted by: vjkane Dec 17 2007, 04:53 PM

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?...)

Posted by: Mongo Dec 17 2007, 06:46 PM

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

Posted by: scalbers Dec 17 2007, 07:30 PM

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

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

Posted by: vjkane Dec 17 2007, 07:46 PM

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.

Posted by: dburt Dec 17 2007, 08:04 PM

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

Posted by: Juramike Dec 17 2007, 08:34 PM

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

Posted by: nprev Dec 17 2007, 08:58 PM

...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!!!

Posted by: rlorenz Dec 18 2007, 12:22 AM

(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

Posted by: rlorenz Dec 18 2007, 12:24 AM

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..)

Posted by: djellison Dec 18 2007, 12:29 AM

And bonus points if it involves anything on Youtube.

Posted by: rlorenz Dec 18 2007, 12:33 AM

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)

Posted by: Mongo Dec 18 2007, 12:58 AM

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

Posted by: Juramike Dec 18 2007, 04:26 AM

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

Posted by: ngunn Dec 18 2007, 11:40 AM

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.

Posted by: rlorenz Dec 18 2007, 01:59 PM

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.

Posted by: vjkane Dec 18 2007, 05:05 PM

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.

Posted by: Mongo Dec 18 2007, 05:55 PM

So personal cheques directly to Ralph Lorenz are out?

Posted by: dvandorn Dec 18 2007, 06:31 PM

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

-the other Doug

Posted by: vjkane Dec 18 2007, 07:42 PM

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

Posted by: rlorenz Dec 18 2007, 08:13 PM

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.

Posted by: rlorenz Dec 18 2007, 08:16 PM

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

Posted by: dvandorn Dec 18 2007, 08:42 PM

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

Posted by: Mongo Dec 18 2007, 08:59 PM

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.

Posted by: tty Dec 18 2007, 10:09 PM

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.

Posted by: ngunn Dec 18 2007, 10:24 PM

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. . .

Posted by: vjkane Dec 18 2007, 11:58 PM

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

Posted by: NMRguy Dec 19 2007, 01:14 PM

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?

Posted by: rlorenz Dec 19 2007, 02:35 PM

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.

Posted by: ngunn Dec 19 2007, 02:57 PM

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.

Posted by: NMRguy Dec 19 2007, 03:14 PM

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.

Posted by: JRehling Dec 19 2007, 10:24 PM

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.

Posted by: ngunn Dec 19 2007, 10:38 PM

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".

Posted by: vjkane Dec 20 2007, 01:17 AM

My suspicion is that Enceladus' jets are simple geology and orbital stressing without the connection to the solid core to provide all the building blocks of life (and I'll state up front that this is strictly an armchair observation). Titan, on the other hand, is endlessly fascinating with many processes and environments.

Posted by: ugordan Dec 20 2007, 08:34 AM

I get the same feeling myself. Cold faithful? More like Sterile faithful if you ask me.

Posted by: djellison Dec 20 2007, 08:52 AM

It's simple. The Enceladus plumes are indeed, a very interesting feature. Titan is an interesting world. It's not even a contest in my eyes. Sadly, my cheque book isn't big enough.

Doug

Posted by: belleraphon1 Dec 20 2007, 12:50 PM

Nature is rarely simple. Too soon to declare Enceladus sterile....................

Enceladus has much to teach us about how small ice/rock worldlets (yes, I will use that word here) behave..... clues to some of the activity being glimpse on Kuiper Belt bodies perhaps....

But if a choice has to be made...... TITAN should win!!!!! No argument there.

Craig

Posted by: Matt Dec 27 2007, 10:12 PM

Worldlets.....well put, I like it; I only wish I'd thought of it before you.

But what's the critical size?

Anything below 600km is a worldlet?

Ralph I read your 'Lifting Titan's Veil' book just before Cassin/huygens reached Saturn and enjoyed it very much, it really whetted the appetite, and am looking forward to reading the new book.

I knew Titan was going to turn out to be an interesting world....but this is ridiculous.

Posted by: nprev Dec 27 2007, 10:41 PM

Yeah. You guys are right. We know enough about the Solar System now to say with a high degree of confidence that Titan's the only other place that has dynamic surface processes that even remotely approach (in terms of complexity) those of Earth. (Who knows what's happening on the "surfaces", if any, of the gas giants, but doesn't matter; we can't find out with current technology anyhow.)

Titan's gotta be the Cassini XM focus, and also that of all foreseeable outer-planet investigation.

Posted by: belleraphon1 Dec 28 2007, 02:40 PM

Nprev....

I would not go that far. There many mysteries begging answers and further exploration.

I have to say that my choice for the next flagship mission should be the Europa Explorer. The technology is mature for a mission like that, and we need another orbiter at Jupiter to make up for the loss of downlink due to Galileo's high gain antenna problem. The Jupiter system and Europa, have much to teach us.

The tech to do a decent follow on to CASSINI at Titan (balloons, landers,etc.,) just is not here as yet. Outer planet missions take a LONG time to reach their destinations, and so, for selfish reasons, if any outer planet mission is going to happen before I hit my 70's (which is not really a bad thing, I may be retired from my day job by then and able to devote more attention), it needs to be started now.

That being said, I earnestly hope to be around for the next Titan (Enceladus) explorer, after CASSINI has done it's work!

And Matt, thanks for the compliment on the term worldlets.... actually, I think Poul Anderson might have invented that first. As for what size object deserves that word, well.... even Itokawa has it's mysterious gravel shores, and to stand on that surface, watch the stars spin, I can well imagine exclaiming "My Wor(l)d"!!!

Craig

Posted by: nprev Dec 28 2007, 03:31 PM

Well, I was less than clear (again) in what I meant (sorry!)

Europa certainly needs & deserves attention, but frankly I'm not completely convinced that achieving major scientific objectives--confirmation of an ocean, ice thickness sounding, global high-res photographic coverage, plume search/monitoring--can't be accomplished via one or more Discovery missions in the relatively near term. We pretty much know what to look for at Europa and indeed throughout the entire Galliean satellite system. What we don't know is whether we can get to that putative ocean via any practical technology, but again that seems like something that could be determined on less than a Flagship-class level of effort. I think that the answer to that question is key for planning all future Europa exploration.

On the other hand, we've already landed on Titan; we know that we can conduct in situ exploration using reasonable evolutes of current technology, which becomes a trade-off between transit time/launch costs and science return. (Side note: this is why I still wish that there was an ongoing, organized effort by JPL or somebody to identify particularly favorable outer-planet launch opportunities). Titan is quite possibly at least as geochemically complex as Earth (with an outside chance of being more so). Therefore, to me, it seems as if there is a lot more science to be done at Titan than anywhere else in the Solar System

Posted by: ugordan Dec 28 2007, 04:12 PM

We're straying to the old Jovian-Saturnian system debate once again, which seems to come down to personal preference biasing everyone's opinions so we'll never all agree on what should be explored first.

I'd be interested in hearing how you envision a Discovery mission getting to Jupiter and doing any global coverage of Europa of the type you proposed? All the more importantly since IIRC the Delta II is being retired and causing the more expensive Atlas V to be used. Forgive me, but sending Discovery missions (which were all pretty much confined to a bit outside of Mars' orbit) to Jupiter seems like a far-fetched idea. Is there any document I missed that discusses such possibilities? We've had discussions about even New Frontiers missions being inadequate for in-depth Europa investigation.

Posted by: nprev Dec 28 2007, 05:28 PM

The strategy I envision is sort of a "one-note pony" theme; maybe two or three instruments per mission designed to answer a specific research question, that's it. Core assumption is that the launch vehicle is the vast majority of cost (and, yeah, the demise of the Delta II is a huge blow... ...hopefully new LVs from the independent launch enterprises like SpaceX will prove both more capable and less costly over time.)

Posted by: vjkane Dec 28 2007, 06:37 PM

I've been looking into readily accessible information on mission costs. A Discovery mission to Jupiter -- beyond perhaps a single, simple flyby -- seems impossible. The Juno mission is close to $1B with a limited (although not cheap) instrument set, a spinning spacecraft, solar power, and limited radiation hardening. I can't think of any mission that could come in at half the budget that could do useful science at Jupiter. The only idea that seems possible is a single Io flyby, and I have my doubts about that.

Posted by: vjkane Dec 28 2007, 06:43 PM

I made the sad realization recently that the next Flagship mission would arrive at its target someplace between by 65th and 70th birthday. The decisions NASA/ESA/JAXA will make in the next couple of years will result in the only Flagship missions I can count on still being alert enough to care about. It made the decisions very personal.

For me, this is an avocation (but one that has persisted since I saw the first Viking surface image on the front page of my newspaper so long ago), but for the scientists, all but the youngest realize that this is their one shot at a mission that will return data during their professional careers. This is what happens when we wait ~20 years between Flagship new starts.

Posted by: nprev Dec 28 2007, 08:33 PM

Kind of why I'm prodding this, also acknowledging that my odds of seeing another Flagship aren't great (about to turn 45 here); I want more!!!

One of the reasons for the cost caps seems to be best stated as "deprivation drives innovation". I don't really agree with that idea, but if the paradigm can indeed be effectively utilized then hopefully the planetary science community can do so.

EDIT: May have strayed too far into the policy & strategy region over the last few posts. Admins, please do what you feel is appropriate...

Posted by: lyford Dec 28 2007, 08:39 PM

By then the pain of waiting may be assuaged by the instant brain implant direct to sensor download link that JPL will providing the members of UMSF.com in 2025

Posted by: JRehling Dec 28 2007, 08:40 PM

I think the key question, which may come down more to faith than evidence, is: How much more favorable is the very best spot on Europa for landed exploration than the best spot we now know of? Is it possible that if we sent a lander to the best spot we know of now that it would land in an area that last received salty/silty flooding ten million years ago, but if we looked harder we would find a spot that last received salty/silty flooding ten years ago? Or 100? Or... whatever?

This is the main value proposition for a Europa orbiter. If Europa is basically homogeneous on a regional scale (obviously, on a local scale, it is not), then we will gain comparatively little from orbital reconnaissance in detail. But if there is one special place (or 10 or 20 of them) where we get better access to the ocean below (either in terms of a very thin spot in the ice for direct access, or just a much fresher patch of surface ice), then there is tremendous value in mapping the hell out of Europa at great resolution before sending something up there [down there] for a taste.

There's no doubt that Europa is going to be vastly more isotropic than Titan. Chromatically, Europa is almost a two-color world, with every spot on the surface distinguished by how much dark stuff is in the ice, and a simple metric that probably correlates with that would be the age of every spot. Think of the Earth -- we have crust that is millions of years old, and we have crust that is 26 years old (Mt. St. Helens) or as fresh as yesterday. But those new areas are very small, and wouldn't turn up after just a few flybys.

Titan will be wonderfully more complex than Europa, and is an irresistible target for future flagship missions, and if there were only going to be one more outer solar system mission ever, I would consider Titan the best choice. But as part of a sequence, I think it makes more sense to visit Europa next, then Titan, and then possibly Europa for the mission after that. Or, to direct the competition elsewhere, I might say that when we have gone further down the road of exhausting possible flagship missions to Mars, that Europa might merit some or most of the "astrobiology" coffer that Mars is now monopolizing.

Posted by: belleraphon1 Dec 28 2007, 09:00 PM

ugordan... yes I kinda felt my original note really should have been in the OPAG thread. And you are right, we all have our own bias..... I do not see going back to Jupiter unless Europa is the utlimate focus.

I cannot see how to explore the outer solar system at less than $1billion. And if you are going to spend that kind of money, you cannot justify a Discovery class mission style that looks at just a small aspect of the scientific questions that beg data.

We can all hope for a day when nanobots can be launched, driven by nuclear rockets, on fast direct trajectories to there outer
destinations. For now we have to work with chemical rockets hurling heavy payloads.

I would love to see further exploration of all the outer planets (Uranus and Neptune beg to be orbited and probed). But the reality is, if we are going to launch any new outer planet mission soon, the technology and TIME is right to go back to Jupiter/Europa.

In the mean time, CASSINI will continue to refine our picture of Titan and Enceladus. We have a chance to watch seasons change on a world as complex as Earth. Let's enjoy the ride!

nprev, I love Titan, too!!!

Craig

Posted by: vjkane Dec 28 2007, 09:34 PM

John, as usual, nails the subject, at least as I see it.

In our lifetimes (or at least mine), we won't have the technology or money to have a probe melt all the way through the ice to reach Europa's ocean. Given this, an Europan lander has to find a place that (1) has subsurface material at or very, very close to the surface and (2) can be landed on with a high probability of the lander surviving. To me, this is the goal of the Europa orbiter -- find those sweet spots. Hence, the orbiter has to have a robust (read heavy, power hungry, and bit intensive) instrument suite to find those spots.

I think the goal of a Europa lander is far enough out that I would not favor a Europa-only mission. (Plus there is every chance that the sweet spot for landing doesn't exist: where surface material is near the surface, if such places exist, the terrain may be impossible to land in. If this is the only justification for the mission, it is easy to get skunked.) If the Europa orbiter also does *a lot* of Jovian science, too, then I could favor this mission. Europa plus a dedicated Ganymede campaign, plus Io studies (with a big camera) and maybe a flyby or two, plus Jupiter atmospheric studies, plus maybe magnetospheric studies starts to sound pretty interesting.



Again, I agree with John. The Europa mission technology has more than a decade of technology development. A Titan mission will be far more robust with a decade of technology development. So, even though it means that I am not likely to see the final mission(s) in the sequence, I think that Jupiter now, then Titan (with that decade of technology development so it's the best damn mission the money can buy!!!), then back to Europa if the Europa orbiter found those sweet spots for landing. This is the manager in me speaking.

But if there is only to be one outer planet flagship mission, do Titan! It is the most interesting body in the outer solar system, in my opinion. This is the (armchair) explorer in me speaking.