A startling result from the Cassini mission has just been announced: Titan, Saturn’s giant moon, may have an ocean of water and ammonia under its surface.
The Cassini probe does more than return hauntingly beautiful images. It is equipped with a sort of radar that allows it to map the topographical features of Saturn’s moons. This allows scientists to make accurate studies of the moons’ surfaces, including that of Titan. This in turn gives scientists an excellent set of landmarks, allowing them to study physical characteristics of the moons, including their rotation period.
Titan’s period is well-studied, and Cassini has visited Titan many times. Astronomers used the known landmarks and rotation period of Titan to predict what they will see with each visit… and they found landmarks like lakes and mountains that were far afield of where they were expected, as much as 30 kilometers (19 miles). A solid body will rotate as such, making these features very predictable. If the landmarks weren’t where they should be, then it must mean that Titan isn’t a solid body.
The more detailed story is that the crust, the surface layer of the moon must be decoupled, separate, from the interior. The only way for that to be is for there to exist a liquid layer between the surface and the core. Titan is far too cold and is comprised of the wrong material to have a hot mantle like the Earth does. Instead, scientists think it has an ocean 100 km below its frozen surface. Given the composition of the surface and the known density of Titan, they suspect it is made of liquid water and ammonia. The crust floats over this chilly liquid, and as winds blow on the surface the crust drifts, causing the predictions of landmark locations to be off.
The surface of Titan is loaded with what we call simple organic molecules: ethane, methane, and more. It is shocking, to say the least, to consider what would happen when you mix liquid water and organic compounds. Could there be life swimming deep under the surface of that planet-sized moon?
At the moment — and for the foreseeable future — there is no way to know. The ocean, if it exists, has not yet been confirmed, so we don’t want to put the cart before the horse. A lot of hard work lies ahead for those who study this distant world — seasonal variations in the positions of Titan’s landmarks would indicate that it is indeed the atmosphere blowing over the surface that is changing the rotation of the crust itself, and that in turn would give much credence to the idea of an underground ocean.
If this does pan out, then we will have to add yet another object in our solar system to the short list of worlds where liquid water can and does exist. And given the near-certainty of liquid water below the surface of Enceladus, Saturn will be able to proudly claim at least two them.
March 20th, 2008 at 3:28 pm
Wow.
Just…wow.
Time to recalibrate the upper end of my Coolness Scale(tm) again.
March 20th, 2008 at 3:31 pm
I think you got that a bit wrong BA. You say that Titan might have an ocean of liquid water/ammonia under its crust. I’d say, “Titan might have an area of its upper mantel comprised of molten water.”
It’s entirely semantic, but it does change how you look at it. After all, from Earth’s point of view Venus has flows of molten rock on its surface. From Titan’s point of view Earth has flows of molten water on its surface. What a piping hot place that Earth must be! From Triton’s point of view Titan has flows of molten methonal on its surface. “What an incredibly hot place Titan is!”, say aliens living on Triton (if there were any).
So I wouldn’t call this an ocean any more than I’d think someone from Venus would be correct to say that Earth has oceans of liquid rock under its surface.
March 20th, 2008 at 3:34 pm
Oh man oh man — let’s go there, now!
March 20th, 2008 at 3:40 pm
The Solar system just gets more and more awesomer, doesn’t it?
March 20th, 2008 at 3:42 pm
WOW!!! OMG…
this is so… great, why should we go to mars!
I want my JIMO back and SIMO to go with it!
March 20th, 2008 at 3:42 pm
Wait — liquid water and ammonia? Titan has a vast subsurface ocean comprised of window cleaner?
March 20th, 2008 at 3:46 pm
I get a tingly feeling each time there is a possibility of life teeming under surfaces of planets
March 20th, 2008 at 4:05 pm
JediBear, my first thought was along those lines too. A whiff of that ocean would smell like a common household cleaner.
Man, this solar system gets stranger every discovery we make. To paraphyrase a quote attributed to the late Arthur C. Clark, “not only is the solar system stranger than we imagine, it’s stranger than we can imagine.”
March 20th, 2008 at 4:05 pm
There are just too many cool things being discovered by science these days. I’m going to have to go woo so life can be dull. This is only temporary, of course.
March 20th, 2008 at 4:10 pm
Hm. Wonder if there’s tectonic activity to go with that crust motion. It’s not obvious from the article whether the crust moves as a single object (which is just detached from the core), or whether different parts move at different speeds.
March 20th, 2008 at 4:29 pm
You can just hear the Titanians saying ’suck on that, Rhea, with your so-called ring’.
Gopher, I see it the opposite way round to you: Earth *does* have an ocean (of molten iron, not rock, which is only molten in a few places) deep below the surface. And there’s evidence the solid core beneath that rotates at a different speed to the rocky part of the planet. There’s evidence for non-synchronous rotation on Europa and Ganymede, too.
March 20th, 2008 at 4:43 pm
Cool news, but… am I imagining things (or getting mixed up with Enceladus), because I thought we already suspected an ocean below the surface of Titan?
March 20th, 2008 at 4:49 pm
Water and the possibility of life? As someone else once said: “There be whales on board!”
March 20th, 2008 at 4:54 pm
“not only is the solar system stranger than we imagine, it’s stranger than we can imagine.”
Not only was it not Arthur C. Clarke who said that, apparently (at least according to Wikipedia) it wasn’t even that other Arthur, Sir Arthur Eddington.
http://en.wikiquote.org/wiki/Arthur_Stanley_Eddington
The article goes on to speculate that it’s a distortion of what J. B. S. Haldane said about the Universe.
March 20th, 2008 at 5:14 pm
This may be a silly question, but when you say that the period of Titan is well known, I wonder how it is measured independently of the motion of surface features?
March 20th, 2008 at 5:34 pm
Looks like the poor orbiting dirtball we call our Moon is the only giant moon without any liquid close to its surface; Jupiter’s Galilean moons minus Io and Titan have probably all water oceans; Io itself has plenty of liquid sulfur and lava; Neptune’s Triton in turn may have other substances such as liquid nitrogen.
Looks like the price of getting a large companion was that it came bone dry: the collision that created our Moon took care of any volatiles it could have had.
March 20th, 2008 at 5:41 pm
I vote we re-name Titan “Windex” (Window cleaner here in Canada – not sure if you boys have that putrid stuff in the States.)
March 20th, 2008 at 5:41 pm
If Titan does have a subterranean (sun-titanian?) ocean, why hasn’t it all frozen solid? Titan is tidally locked with saturn, so where does it get the heat to keep all that water from freezing?
March 20th, 2008 at 5:50 pm
Alfredo, that’s a good question. When he spoke of Titan’s period, in context I think her meant its orbital period is well-known [whereby it's been possible to accurately navigate past it several times]. The orbital periods of the satellites can be determined to great precision from right here on Earth, whereas their spin periods aren’t easily measurable from here. So one of the things being attempted with Cassini’s radar has been to measure the several moons’ rotation rates.
I gather that this has been very reliable for the other moons in the system, but anomalously not so much for Titan. Assuming all the data have been reduced properly (maybe they haven’t; Phil mentions that much work remains), this implies that the surface isn’t rotating at a constant rate.
March 20th, 2008 at 5:53 pm
Alfredo – my reading is that what is new is that the rotation period is slightly irregular as measured using surface features, and the theory being put forward for test is that the surface winds can advance or retard the motion of this floating crustal layer. A reason to keep the Cassini extended mission as extended as possible, since the relevant cycle time would be Saturn’s seasons.
March 20th, 2008 at 5:53 pm
Titan’s internal heat could be generated by tidal flexing as it repeatedly goes from periapsis to apoapsis and back again.
March 20th, 2008 at 6:14 pm
What is the supposed composition of the highland areas? any suggestion of rocky crust- or is it all various ices?
March 20th, 2008 at 6:15 pm
@Max Faginon
>If Titan does have a subterranean (sun-titanian?) ocean, why hasn’t it
> all frozen solid?
If I had to guess, I would say the ammonia could be the key to that one, acting as a kind of antifreeze maybe?
March 20th, 2008 at 6:48 pm
I want to out on a limb here and make a wild prediction: Life will eventually be discovered on Mars, Europa, Titan, and more.
And I was thinking that before I read this…
Pure speculation, of course. But I’ll take bets.
March 20th, 2008 at 6:50 pm
Nemo, I’ll even grant that there has been evidence of intelligent life, on Mars, for over 30 years.
March 20th, 2008 at 7:53 pm
OK… native life.
March 20th, 2008 at 8:02 pm
“OK… native life.”
I used that one on a poor schmuck a few months back who insisted that, as a matter of principle, there can be no life elsewhere. You wouldn’t believe how long I was able to yank his chain, all with a couple of commas.
March 20th, 2008 at 9:03 pm
Uh…
Could the astronomers reading this ease up on their fascinating scientific breakthroughs for a few days?
I haven’t had time to fully digest the BA article on gamma ray bursts before this breakthrough came down the pipe-line.
For crying out loud. I’ve been trying to write a paper this week, and I can’t keep up with all of this new information. By the time I’ve got around to reading one planet-shattering discovery, those pesky astronomers have gone and made another ten discoveries. Something has to give, and I don’t think it should be my schedule.
So please- if you discover intelligent life on another planet or find a way of exceeding the speed of light, can you kindly schedule your announcements in the future at reasonably paced intervals so I can keep up. I can just about handle one breakthrough per week- any more and I start to get swamped.
If I’m being completely honest, I still haven’t got around to learning relativity- and that news is a *century* old. Enough! Go take a vacation, or catch up on some movies. The universe will still be there when you get back.
March 20th, 2008 at 9:21 pm
Methane marshes on top, and an ammonia-water ocean below? Criminy, and I thought Earth was weird.
March 20th, 2008 at 10:49 pm
Wow. This one I totally don’t understand. Is the ocean “free floating”, kind of like a snow globe with a smaller solid globe inside it? Or more of a muddy layer? Without the outer crust being a solid impermeable layer, or the crust being something less dense than water, like pumice, how does the water stay underground? We all know that there is plenty of groundwater on earth, but a lot of it is on the surface. Wouldn’t the water make it’s way to the top and settle in depressions of the surface? So how does this work on Titan?
Even if we sent a probe there, would we ever be able to drill down 100 km to reach the ocean? All the drilling on earth is done with big rigs, lots of pipe, lots of bits and lots of workers. Could a robot do it?
I know if we can send a crack team of oil rig drillers to drill a hole on an asteroid, I know we can send one to Titan!
March 20th, 2008 at 10:50 pm
Chrsitian, tell me about it. I can’t keep up– literally. There was a story about Mars today I didn’t write about, and there’s more cool stuff I have hardly looked at yet.
March 21st, 2008 at 12:11 am
If an ocean is sandwiched between core and outer icy shell, what would happen during a major impact event? Forget melting, etc. I’m just talking about the giant pressure wave that would be generated.
Mightn’t that have a rather deleterious effect on any lifeforms present (noting though that microorganisms on earth with an outer macromolecular sheath CAN take a lot of pressure- but this much?)?
Jess Tauber
March 21st, 2008 at 3:10 am
I’m with you all the way Christian (and Phil) I’m trying to cram for my final exam and the Scientists keep moving the goalposts! Stop the solar system please I need to catch up! It just keeps getting curiouser and curiouser and awesomer and awesomer by the day.
March 21st, 2008 at 4:46 am
[...] usual, Phil Plait at Bad Astronomy has the scoop. A startling result from the Cassini mission has just been announced: Titan, [...]
March 21st, 2008 at 6:31 am
Titan always struck me as kind of … mushy. How I envy the explorers of this bizarre world in the distant future.
March 21st, 2008 at 6:52 am
[...] 21, 2008 in Physics But Titan, Saturn’s giant moon, may be. [...]
March 21st, 2008 at 9:50 am
Titan is a very cool world. In the physical sense, too, of course — its albedo of 0.3 gives it an equilbrium temperature of 82 K, and the surface temperature is 94 K. It has a greenhouse effect due to methane, brief nitrogen-methane pairs, and, weirdest of all nitrogen-nitrogen pairs. Nitrogen isn’t a greenhouse gas at the temperatures we’re used to, but it is on Titan.
Plus the haze high in its atmosphere gives it an antigreenhouse effect — the haze absorbs sunlight but allows infrared to pass through it, thus lowering the temperature of the ground. The Titan greenhouse effect of 21 K should bring the temperature up to 103 K at the surface, but the antigreenhouse effect takes 9 K off that, leaving us with 94 K.
Then you have the 1.467 bar surface pressure — the closest atmospheric pressure to Earth of any known world in the solar system. You’d need serious heating systems to move around there in a space suit, but air pressure would not be a problem. I don’t know how fierce the wind would be, but I suspect not very — Titan rotates only once in 15 days, since it’s tidally locked to Saturn. There’s a high atmosphere level that “superrotates,” as there also is on Venus, but that doesn’t much affect ground conditions.
I’m sorry they didn’t get a good atmosphere breakdown from Huygens. I was waiting for percentage figures to come through like we got when Viking landed on Mars in 1976. Everyone had expected Martian air to be high in argon, as much as 25-28%; it was a surprise when argon turned out to be only 1.6% of Martian air. We know Titan has mostly nitrogen, argon of less than 12%, and methane somewhere in the 3-6% range, but I want better figures than that. I hope they send more landers with better instruments in the future.
And the landforms are awesome. I wonder what color it all is in human vision? Makes me think of the landscapes that flashed by during Dave Bowman’s FTL trip in 2001, where Kubrick took Earth landscapes and gave them bizarre colors just to make them look alien.
March 21st, 2008 at 3:56 pm
Titan’s oceans shouldn’t be too surprising. Back in the early 1970s John Lewis worked out that the radioactives in the silicate component of the moons would be enough to melt much of the icy mantles – ever since people have been arguing over whether solid state convection would chill the mantles out or not. Convection is a much more efficient heat transport process than conduction, but the rheological properties (i.e. ability to flow under pressure) of large amounts of ice are hard to model and study experimentally, so lots of guesswork was needed to work out whether the ice mantles of the moons would be frozen or still liquid.
Looks like experiment has come down on the side of liquid under all that ice. Above the ocean will be a layer of convecting ice – imagine great balloons of “warm” ice floating up through the crust, just like granite batholiths in Earth’s crust. Below the ocean will be a layer of high-pressure ice phases (ammonia freezes solid at 300 K when under 10,000 bars of pressure), and below that will be the muddy core. When we have more seismological data from Titan we might learn if its silicate core has differentiated into rock and metal.
March 21st, 2008 at 4:28 pm
I think if there is water under the surface of Titan it is frozen water. That doesn’t mean there isn’t a liquid ocean under the surface. It just means it isn’t water. That’s where the ammonia comes in since at normal tempatures ammonia is a gas, however it is one of thoes gasses that becomes a liquid at lower tempatures. That’s why we are talking about windex instead of water here. I don’t know what windex does to make the ammonia a liquid.
March 22nd, 2008 at 4:15 am
Correct me if I’m wrong (wouldn’t surprise me), but the organic compounds on the upper layers of Titan’s atmosphere are tholins, right? And when tholins are mixed with liquid water or ammonia, they produce amino acids? With that in mind, is there any way that tholins could be mixed in with subsurface oceans of water or ammonia?
Because if there is, and they’re producing amino acids, that’d be the coolest thing EVER. Get a dedicated lander to Titan, stat!
April 28th, 2008 at 9:19 pm
[...] I knew it all along. I saw it with my scrying glass. [...]