A Conversation for Peer Review

A87949345 - Titan (Moon)

Post 1

A. N. Ulriksen

Entry: Titan (Moon) - A87949345
Author: A. N. Ulriksen - U15002585

First entry on this site! I'm a bit new to HTML, so hopefully the formatting is okay.

A87949345 - Titan (Moon)

Post 2

Dmitri Gheorgheni - Not Banned in China

Hi! That looks good to me. So does the entry. smiley - smiley Informative, conversational, and gets right to the heart of what we really want to know: where can I find a planet I can fly on? smiley - winkeye

A87949345 - Titan (Moon)

Post 3

Tavaron da Quirm - Arts Editor

smiley - smiley A great Entry! Informative, good to read and a good length.

There's only one thing I noticed: In the 1st paragraph of the last section you say 'scientists think there could already be life on the planet.' You should correct planet to moon. smiley - winkeye

A87949345 - Titan (Moon)

Post 4


Welcome to h2g2 – and thank you for enthusiastically writing an entry already! Definitely a great start – make sure you stick around!

I'm also impressed to see you getting stuck in using HTML (our version's called GuideML) – had you wanted to know about how to write superscript numbers, for example squared or cubed, then you can use ² for ^2 and ³ for ^3, but for other numbers over 3 you can have 23, instead of ^23. But don't get bogged down in the minor details if you're not interested as it is perfectly clear what you mean.


A87949345 - Titan (Moon)

Post 5

A. N. Ulriksen

Thanks for catching that!

A87949345 - Titan (Moon)

Post 6

A. N. Ulriksen

Thanks for the kind comments, everyone! I changed "planet" to "moon" in that one paragraph, and will now see if I can change the HTML to have the exponents show up.

I'm really glad to see that this site has such a supportive community. smiley - smiley

A87949345 - Titan (Moon)

Post 7

Dmitri Gheorgheni - Not Banned in China

Yeah, we're pretty well behaved, most of the time. smiley - rofl Come join in the conversations in the h2g2 Post - A87942667 this week.

A87949345 - Titan (Moon)

Post 8

SashaQ - happysad

Thank you for this Entry - it will be an excellent addition to the Edited Guide once it has finished going through Peer Review smiley - ok Informative and entertaining smiley - biggrin

I like your way with words smiley - ok "a bit like saying that you want to live in a dry-ice freezer." "even just jumping up and down would be quite the experience." - superb phrases smiley - biggrin

I just had one question:

I can visualise the shape of Titan from your description but I can't visualise what "bedrock of water ice" is - can you say a bit more about that? Ah, I see later that there is liquid on the surface - the water ice is mostly covered by the oceans but 40% of the water ice rises above the level of the oceans, is that right?

A87949345 - Titan (Moon)

Post 9

Gnomon - time to move on

Hi A.N.

Is there an easily understood reason why Titan retains an atmosphere but our own moon doesn't? They both have similar surface gravity. I was always told it was the lack of gravity that caused the moon's atmosphere to gradually drift off into space. Why does that happen everywhere except Titan?

One tiny tweak:

"Nasa" should be "NASA".

A87949345 - Titan (Moon)

Post 10

A. N. Ulriksen

Thanks for the compliments! I’ll admit I had a lot of fun writing this article. smiley - smiley

Also thanks for pointing out parts where the article might get confusing (and thanks, Gnomon, for catching the NASA typo. I thought I revised it last time, but I guess I must have forgotten to actually fix it. Whoops!).

Anyway, you guys both asked really good questions. I’d like to give the disclaimer that I’m not an astronomer (I’m just extremely enthusiastic about space, haha) so it’s definitely possible I might get stuff wrong, but I’ll try to answer your questions based on what I’ve researched and my understanding of this topic.

A87949345 - Titan (Moon)

Post 11

A. N. Ulriksen

First of all, I figured it’d probably be easier for you to visualize Titan if I gave you visuals. smiley - smiley

With that in mind, here’s a neat diagram I found of the current theory regarding Titan’s layers:

And here is a photo of Titan’s surface (the icy ground is yellow, and the methane lake and rivers are colored in blue):

There’s also this video on Youtube of Huygen’s brief landing on Titan which renders what the probe saw on the moon’s surface. Pretty neat stuff (sadly no aliens as far as I can tell, though it’s possible I just didn’t spot them): https://www.youtube.com/watch?v=9L471ct7YDo

Now, here’s my understanding of why the layers are the way they are. I’d like to apologize in advance since it’s pretty long:

The way I view it is that Titan’s layers are a lot like Earth’s, except that they’re formed using different materials. Earth’s crust is mostly made out of rock, but if you dig far enough beneath this you’ll find a lot of magma, which is basically just rock that has been heated to the point of liquefaction.

The same thing happens on Titan, just with water (mixed with salts and some other things) instead of rock. On the surface it’s too cold for water to exist in a liquid state, so all the water just solidifies. So you get a “ground” that’s really just a lot of ice, with a coating of various hydrocarbons and some lakes and rivers of methane since it’s cold enough for methane to exist in a liquid state.

Dig several kilometers into the icy crust of Titan, however, and the temperature begins to increase (much like on Earth as you begin to hit the mantle). Eventually it’s warm enough that the water no longer can maintain its solid state, so the ice melts away into a huge underground ocean of (extremely salty) water.

Swim to the bottom of this ocean and this is where things officially start to get weird. This is because the ocean floor is made of ice, too, but the temperature there is really hot. What gives?

This probably requires some extra explanation. See, the normal Earth way to make ice is to lower the temperature of water until it reaches its freezing point. This causes the water molecules to stop moving around so much and begin to clump together, which is what’s happening on Titan’s surface. But if you don’t have a low enough temperature, you can also cheat and make ice another way: just put enough pressure on the water molecules until they’re forced to stick together like they’re at some awkward family reunion.

This is what happens to the water molecules on Titan that are closer to the core. You don’t really see this kind of ice on Earth because the pressure isn’t high enough on Earth’s surface, where most of Earth’s water lies. (As a side note, outside the Solar System you can find some really weird planets that are made up largely of this kind of pressure-formed ice, like Gliese 436 b, which is known for being really hot and having a ton of this “burning ice” on its surface).

Anyway, in summary: Titan has a giant underground ocean that is sandwiched between layers of two different kinds of ice—one type on the crust that is formed through low temperatures and one closer to the core that is formed through extreme pressure. It also happens to have oceans, lakes, and rivers made out of liquid methane/ethane, but these are all on the surface and located above that first layer of ice (kind of like how Earth has a bunch of water oceans that are separate from the “ocean” of magma beneath its surface). Beneath all this water is Titan’s core, which makes up most of the moon’s mass and is composed of silicate.

Let me know if this made sense! If it did I’ll try to add a similar (though perhaps briefer) explanation to the article itself so that I can hopefully clear things up for other people. smiley - smiley

A87949345 - Titan (Moon)

Post 12

A. N. Ulriksen

You’re right to think that it’s pretty weird that Titan is the only moon in our Solar System to have a dense atmosphere! To be fair, Titan is a good bit further from the Sun than our moon, meaning that it is both colder than the moon (so gas particles are slower on Titan and less likely to achieve escape velocity) and subjected to less solar wind (the main culprit in the disappearance of Mars’s atmosphere, among others). So Titan probably does have a somewhat easier time holding on to any stray gases than our poor, atmosphere-less moon. This in itself, however, doesn’t really explain why Titan has an atmosphere 60% thicker than Earth’s while similarly distant and massive moons (such as Triton, Ganymede, or Europa) can call themselves lucky if they can form even a single, wispy cloud.

Anyway, I looked into this a bit after reading your question since I wasn’t too sure about the answer. As it turns out, astronomers aren’t too sure why Titan has such a lush atmosphere, either, so we are both in good company.

There are some theories, of course—one of them states that it’s possible that Titan got most of its atmosphere from a few comet impacts that transformed the ammonia ice present in the comets into copious amounts of Nitrogen. Presumably, the greater gravitational force of Jupiter would have meant that similar comet impacts on Ganymede and Callisto would have been much more devastating than those that hit Titan, so comet impacts on those moons would have vaporized their atmospheres rather than helping to build them up like what (theoretically) occurred on Titan.

There are some notable flaws in this theory, though—first of all is the fact that data collected on what comets are made up of and data regarding the composition of Titan’s atmosphere don’t really match up, so scientists are starting to doubt that Titan’s atmosphere could have been made up entirely of comet residue. The second problem is that Titan has a lot of methane, and the amount of methane in its atmosphere doesn’t seem to be decreasing. Methane tends to react quickly and form other organic substances, so clearly Titan must be replenishing the methane in its atmosphere somehow in a way that’s more consistent than just patiently waiting around for another comet to hit it.

A more current theory states that it’s likely that Titan has some chemical reactions going on beneath its surface that is constantly regenerating its Nitrogen and Methane-rich atmosphere. We’ll probably have to wait some years before we get any concrete evidence pointing to what exactly that process entails, though. (Of course everyone has their fingers crossed that extraterrestrial lifeforms might play a role, but it seems to be the least likely possibility at this moment. Guess we’ll have to see...)

A87949345 - Titan (Moon)

Post 13

Gnomon - time to move on

Thanks AN. It's clear that you've considered this issue, and it is probably too complex to put into the Entry, which is after all a simple guide. We don't want to confuse the readers, so it's probably best not to mention the issue of why Titan is the only moon with an atmosphere.

A87949345 - Titan (Moon)

Post 14

A. N. Ulriksen

You make a good point! I think there's a lot of stuff I could add, but you're right that it's probably best not to get too sidetracked. smiley - smiley

A87949345 - Titan (Moon)

Post 15

SashaQ - happysad

Thanks for those links - the video of the probe landing was particularly impressive, but the image of the methane lakes in the landscape of ice does clarify indeed smiley - ok

That is a good comparison of the structure of the Earth compared to the structure of Titan, so Earth has bedrock made of rock, but Titan has 'bedrock' that is water ice, I see smiley - ok

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