Titan Rocks

By Phil Plait | September 21, 2005 10:24 pm

On Monday of this week, I had the pleasure of attending a talk by NASA scientist Chris McKay. Back in January 2005, a lander called Huygens (pronounced “HOY-gens”) touched down on the surface of Titan, Saturn’s biggest moon. It was an incredible achievement! McKay is a co-investigator on an instrument onboard Huygens. He came to my university to talk about that weird moon. Whenever I hear a good talk, I try to walk away with one cool thing I learned. This time I really did, and now I’m gonna share it with you.

Titan is big, as moons go. It’s 50% wider than our Moon, and 80% more massive. That means it’s less dense than our Moon. The Moon is mostly rock, and so Titan must be mostly material less dense than that. We know there’s a lot of water ice out there in that part of the solar system, so it’s a good bet that Titan has a lot of it.

But Titan is cold. Really cold: -180 C! At that temperature, ice gets very hard, like rock on Earth.

Now let me digress for a second. Titan has an atmosphere. It’s mostly nitrogen (like Earth’s!) with about 10% methane. At that temperature and pressure, it’s possible for methane to exist as a liquid, too. So methane can rain down from the air as a liquid, collect in depressions, and flow like water does on Earth.

Still with me? Great! Now look at this awesome picture:

That’s the surface of Titan, as seen by a camera on Huygens. The flat rock to the left of center is about 15 cm (6 inches) across, and the rounder one next to it is roughly 4 cm (1.5 inches) across. Now, those aren’t rocks: they’re ice! Like I said, on Titan, ice is like rock. To be honest, it’s not certain those are ice; some instruments on Huygens indicated they are, others said they aren’t. I suspect they are covered with some sort of material on their outside which is throwing off the instruments, but I’m no expert. Still, it seems likely they are mostly ice.

But look how round they are! Almost as if they’re eroded. It’s known also that there are riverbed-like features not far from the rocks, and the plain they sit in looks a lot like a dry stream bed. Could this have been the site of running liquid methane?

There’s more, and this is totally cool: there is an accelerometer on board Huygens, an instrument which measures how hard the probe was decelerated as it fell to the surface. When it hit, it measured that as well. If the surface had been solid rock, then the accelerometer would get a big spike as the probe smacked into the surface, and that’s it. If it hit a liquid, then you’d get up-and-down wiggles as it bobbed in the liquid.

But what the accelerometer showed was that the impact had a big spike, and then a single rebound. This is not what you’d expect from a solid or liquid surface, but just what would happen if it hit something gloppy like mud.

Mud! It seems as if it recently rained methane where Huygens hit. The methane would flow down, like a river, and drain into a basin someplace. As this happens many times over millions of years, the “rocks” of water ice erode and get round. But every time, just after it rains, the ground is soggy.

Did Huygens land right after a rain, maybe only a few months after a wet season? No one knows, and McKay only speculated. But what an amazing thought! We have a rainy season here in northern California, and if an alien probe landed here in, say, April, and plopped into the mud that causes Mrs. Bad Astronomer and me such grief in the garden every spring, they might get a reading much like we got from Huygens. But while ours has silicon, oxygen, dirt, and biological organic compounds in it, Titan’s mud has methane, ethane, and simple hydrocarbons… all at a seasonal 94 Kelvin.

So that’s my one thought from the talk: a billion miles away, but maybe Titan is not so alien after all.

I’ve said it before, and I’m sure I’ll say it many times hence: I love this stuff!


Comments (27)

  1. I love this stuff too! This morning my newspaper had a story about a couple of gullies that have appeared on the surface of Mars since the last time the orbiter camera took a photo in 2003, probably evidence of seismic activity.

    Marsquakes and Titanic monsoons… we’re not the only ones with wild weather.

  2. Stuart

    At one talk I went to, John Zarnecki (planetary scientist who works with Huygens) said that before going into the ‘mud’ or ‘wet sand’, the probe may have hit an ice pebble – perhaps like one of those in the picuture. From what I heard, there was a very soft top layer, perhaps a pebble and then the ‘wet sand’.

    Another of the instruments detected a sudden increase in methane just after landing. It is thought that this methane had evaporated from the surface after a relatively hot Huygens lander had landed on it! So not only did it land on ‘mud’ but it started ‘steaming’ (OK, change water vapour for methane and that analogy works).

  3. HawaiiArmenian

    What are the chances, that instead of “mud” or “sludge”, Huygens landed in some type of complex organic goo? I’m no astrochemist, but I suspect that with the molecules present in Titan’s atmosphere and surface (nitrogen, ethane, methane, along with perhaps other hydrocarbons), it’s possible for pre-biotic conditions to be formed, similar to that of early earth’s, but in deep freeze. Although I suspect that the molecular detector would have recognized these compounds if they existed.
    Also, considering the natural process in the formation of organic compounds, is there any evidence for lightening in Titan’s atmosphere? If this is the case, coupled with the ubiquitous presence of simple hydrocarbons, we might be in for greater surprises then we expected.

  4. slinted

    Dr. McKay will be doing another talk, on much the same material I’d imagine, in San Francisco, free and open to the public at the Randall Museum on Tuesday September 27th.

    http://www.randallmuseum.org/content_images/FallFlyer05.pdf (page 6)

  5. Cool stuff indeed. A place with liquid methane, rain, lakes, rivers… wow.

  6. nimzo64

    This is cooool. It was over 25 years ago when I read Kurt Vonnegut’s scifi book “The Sirens of Titan. ” Ever since then, I have maintained an interest in that wonderful moon with an atmosphere (as well as an interest in all of Vonnegut’s work). I have always wondered what the surface would be like etc. Now we have some answers!!

    …oh yeah, has anyone speculated on the possibility that Huygens landed on the Flying Spaghetti Monster. His Noodly Appendage is close to the consistency of mud. I hope this isn’t so, my life would be empty without Him.

  7. Huygens is definitely not to be pronounced like “Hoygens”. In my country the Netherlands (where Huygens was born and raised, and where many schools and streets are named after Huygens) a question like “Do you know HOY-gens?” is very likely to be answered with: “WHO????”.

    So impress your friends and do a short lesson on how to pronounce Huygens by visiting the webpage that I just found: http://frank.harvard.edu/~paulh/misc/huygens.htm

    Those of you who are interested in the history of astronomy might enjoy visiting Huygens web at http://www.phys.uu.nl/~huygens/ . Here you can read English translations of Huygens’ orginal papers in which he described his discoveries and observations of the Saturnian system. Note the peculiar anagram in the end of one of his papers!

  8. tsg

    “Huygens is definitely not to be pronounced like ‘Hoygens’.”

    I just listened to the mp3 and there’s no way in hell you’re getting Americans to say it like that. We don’t have letters for half those sounds.

    You’ll have to settle for “Hoygens” although I suppose “Howgens” would be closer.

  9. Sam

    That mp3 was interesting to hear. I’ve read many times, from many popular science folk, that Huygens is pronounced “Hoy-gens.” (I think that’s even how Carl Sagan pronounced it on Cosmos episodes.) I guess noone took the time to see how it was really pronounced.

    Just goes to show, a million people can tell you something and it takes nothing away from the chance that they’re all flat out wrong ūüėČ

    It sounds like it’s pronouced “Howkunts” with more emphasis on the “h” than the “k.”

  10. Sam

    Oops, I meant “Howkhunts” with more emphasis on the “h” than the “k.”

  11. The Galaxy Trio

    Beche-la-mer, I’m not sure a marsquake counts as “weather”. :)

    Hey, I tease.

    But there is the, um, “theory” that some weather can cause quakes. Here in the wonderous paradise of So. Cal. there is a common belief that “Santa Ana” conditions (when we get hot, dry katabatic winds from the high desert) can trigger quakes. Several years ago we did seem to have a run of tremors for a while that correlated with hot days, but I don’t think anyone has even proposed a causality model. It was just cooincidence.

    Not so fun in the summer, but Santa Ana conditions in the winter can make a grown man weep with joy. That’s the kind of weather that makes people live here despite all the problems.

  12. Yes, it sounds like “HOWchh-hoontz”, where “chh” is the growled noise with the tongue in the back of the throat, like in Hebrew (“challa” and “Channukkah”).

    Interesting, but I have no idea how to make that clear in a written blog. :-)

  13. Doug

    Pronouncing Huygens: hey, what do you expect? We don’t really know
    how to pronounce “Halley”, and it’s English! And back to Dutch, most people
    mispronounce the last name of Vincent, the 19th century Dutch artist who cut off an ear.

    Yes, the pictures and descriptions of Titan make it looks so terrestrial. I have to keep reminding folks: the rocks are ICE. The rain is METHANE.
    It’s freaking COLD. Some of the pictures during Huygens descent look even
    more terrestrial. But it’s a methane bay washing up on an ice-rock shore!
    Cool! Yes, literally!

  14. Tim G

    Send a helicopter.

    This idea has been kicked around for a while.

    The atmospheric pressure on the surface of Titan is 1.5 times that of Earth, but it is so cold that its density is about five times as great. The surface gravity is around one seventh that of Earth. Therefore, a helicopter would require one seventh the thrust and one thirty-fifth the power in a hover.

    While resting on the ground, the helicopter’s radiothermal generators would recharge its batteries or capacitors.

  15. Palliard

    I was looking forward to the landing of Huygens years before it actually happened… and I must say, I wasn’t disappointed. Of all the models that were proposed for the surface of Titan, the one that is actually real seemed the least likely at the time. Too “earthlike”, many would say. All I can say now is… wow!

    And I have heard the helicopter idea bandied about before. On the surface, it seems pretty obvious: low gravity + dense atmosphere = aircraft. And something like a Draganflyer would be able to hover and wait for commands from over an hour away, given enough batteries. I don’t think anybody has yet really addressed overcoming the cryogenic temperatures involved, however. Keeping your robotic helicopter operating at 94K for any great length of time would be no small feat, I’m thinking. I’m reminded of Stanislaw Lem’s “The Three Electroknights”, for those of you familiar with it.

  16. Sriram

    really cool stuff i wish i was there in titan…

  17. aiabx

    What has struck me about all the planets and moons we have landed on is how, er, normal they look. Our moon looks strange, but evrywhere else looks like a rocky desert somewhere on earth. I guess science fiction always led me to expect spires of ice and ringed planets hanging in a dark blue sky, and I’m intrigued by the apparent normalcy of it all.
    -Andy B

  18. M.A.DeLuca

    Alright, now this is really cool. But if you’ll pardon my ignorance and unwillingness to do a simple Google search, why does the photo have such a strong sepia tint? Is that a true-color view, or is it the result of some peculiarity of the camera’s design? Or is it just really old and faded? Does the next one in the sequence show an old-time Titan Civil War soldier uncomfortably staring into the camera?

  19. Tim G. Says:
    ” Send a helicopter. The atmospheric pressure on the surface of Titan is 1.5 times that of Earth, but it is so cold that its density is about five times as great. The surface gravity is around one seventh that of Earth. Therefore, a helicopter would require one seventh the thrust and one thirty-fifth the power in a hover. ”

    Hmmm, high pressure and density, low temperature and gravity; sounds like the perfect combination for a hot air balloon. Well, a hot nitrogen-methane balloon. Remember that “hot” is relative. Maybe just the heat from the spacecraft’s instruments would be enough, if captured in some light rigid canopy, to float the system and let it travel around looking down at the surface.

  20. james

    Halley -> Haw-lay ( say it with a raised eyebrow and a sneer, you uncultured louts!)

    Also, would the Tyrell corporation have sounded so cool in Blade Runner if it had been pronounced T’rll ? (It’s welsh, all one syllable)

  21. Stuart

    M.A.DeLuca, I’m pretty sure that the pictures from the surface of Titan were taken with a black-white camera. The colouring was applied later to give a ‘realistic’ view of the surface. The colours actually come from the spectrometer measurements (one of the other instruments on-board) so are probably about right.

  22. Nigel Depledge

    Another nice piece, BA. I’ve been following the progress of both the Cassini orbiter and the Huygens lander at the ESA’s website.

    What a fantastic heap of data they’ve sent back. And the mission hasn’t even reached its half-way point yet.

    I have a vague memory of either reading or hearing somewhere that people not brought up speaking Dutch physically cannot make some of the sounds in the Dutch language. I think the guttural in the back of the throat is one of them (or maybe the only one).

    A lot of English visitors to Scotland have a similar problem, being unable to distinguish between the words “lock” and “loch” (or being unable to pronounce the two distinct sounds as two separate sounds).

  23. NelC

    There was a meme floating around the British media a decade or so back, criticising British sci-fi series for filming their alien locations in quarries and gravel pits.

    The thing is, most of the planets and moons we’ve landed probes on are gravel pits. Our Moon: dark grey dust and gravel. Mars: orange sand and gravel. Venus: orange, half-melted gravel. Titan: orange, icey gravel. The makers of Dr Who and Blake’s Seven got it more right than they realised. The only thing they got wrong was the colour….

  24. LarrySDonald

    I just reread this, kind of as a starting point to more info on Titan. Dunno how interesting this is, but here’s what happened..

    I saw it about the time it was written, though knowing next to nothing about Titan I just thought “Yeah, ok, that’s pretty damn cool but it’s just some moon right? Perhaps I’ll read more about it later” and moved on. At about the same time, I started reading Pale Blue Dot by Sagan. It was form ’94, so a bit dated fact wise but I really like his stuff so I’ve been working my way through his books. It had quite a lengthy musing on Titan, the so-far data, how it was gathered (probably the main point) and so forth. It seemed *really* facinating, but of course woefully little was known. It did say that there were plans to put a craft in orbit along with a lander though, doing more serious data gathering by local radar and IR as well as mesurements from the lander. I instantly thought “hey, cool, I wanna see that”. Then it mentioned that it was (hopefully) going to be launched about ’97 and shoud take about seven years to get there. Hey, that’s like.. last year. Hey wait, I saw a picture from Titan on the BA Blog! That must have been the lander! Cha-ching, jackpot, I *don’t* have to wait ‘cos I’m reading outdated material and they’re there! Not that I’m a huge fan of instant gratificantion, but it’s nice when it happens to you.

  25. dre

    i’m a little late adding to the discussions, but i’m surprised at how much the very dutch huygens, when properly pronounced, sounds like the very english hawkins. any etymologists out there? connections?

  26. Burgersoft777

    Not as late as I am….but I didn’t come to pronounce Huygens. I am here to enthuse about this treasure box of a world. Titan has great promise as a staging post and a manufacturing plant for almost anything you could dream up. Its a Bonanza world. A ripe plumb ready for exploitation.
    If we go anywhere it likely that Titan will be place we go.

  27. 7

    I say that we exploit it too.
    But let us make our plans to do it with the best grammar possible, if you please.

    In all seriousness though, I really love this stuff. I can’t believe how far we’ve come, and how far we get to continue in going. A moon in the Saturn system…I mean that is really cool.


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