I've done my own version of a diagram of Titan's hydrological cycle (attached,) the original (also attached) being on p12 of Dr Ralph Lorenz's great book Saturn's Moon Titan: Owners' Workshop Manual. Can anyone take a look and see if I've got it right please? Im particularly concerned about what I've put in the big text box about what happens to methane diffusion when it's hit by UV rays.

Looks like H₂ and H escape to space, and other components are broken down and fall back to the surface, but I'm not sure.
It's for a graphic design project
Cheerz
GIAN🙂XXX

(SCIENCE AGE ABOUT 12)

Just now, Gian said:

I've done my own version of a diagram of Titan's hydrological cycle (attached,) the original (also attached) being on p12 of Dr Ralph Lorenz's great book Saturn's Moon Titan: Owners' Workshop Manual. Can anyone take a look and see if I've got it right please? Im particularly concerned about what I've put in the big text box about what happens to methane diffusion when it's hit by UV rays.

Looks like H₂ and H escape to space, and other components are broken down and fall back to the surface, but I'm not sure.
It's for a graphic design project

Your graphic states "and are then converted into nitriles".

This could well be the case, but the formation of nitrile and further carbon-nitogen compounds requires a catalyst, normally a copper salt on earth but UV light will also do.

Bearing in mind the weakness of the UV light on Titan, I wonder what the convertion rate is ? A few % perhaps.

Sorry I have no further information at the moment, you will need to look it up.

Perhaps @exchemist or @sethoflagos or @chenbeier might add more.

19 minutes ago, studiot said:

Sorry I have no further information at the moment, you will need to look it up.

Perhaps @exchemist or @sethoflagos or @chenbeier might add more.

Thanks, I've also contacted Prof Lorenz, but I wanted everyone here's take too🙂

11 hours ago, studiot said:

Your graphic states "and are then converted into nitriles".

This could well be the case, but the formation of nitrile and further carbon-nitogen compounds requires a catalyst, normally a copper salt on earth but UV light will also do.

Bearing in mind the weakness of the UV light on Titan, I wonder what the convertion rate is ? A few % perhaps.

Sorry I have no further information at the moment, you will need to look it up.

Perhaps @exchemist or @sethoflagos or @chenbeier might add more.

The strength of the CN triple bond in nitriles (the main ones of interest are acetonitrile and amino acetonitrile) are considerable more resistant to UV photolysis than their corresponding carboxylic acid whatever the UV intensity happens to be.

In cold dense molecular clouds where UV input is extremely low, their half lives are of the order 10^8 years whereas that for acetic acid is perhaps a tenth of that.

Since they are precursors of amino acids such as glycine, they are significant in the production of a number of biologically important compounds within galaxies.

13 hours ago, Gian said:

I've done my own version of a diagram of Titan's hydrological cycle (attached,) the original (also attached) being on p12 of Dr Ralph Lorenz's great book Saturn's Moon Titan: Owners' Workshop Manual. Can anyone take a look and see if I've got it right please? Im particularly concerned about what I've put in the big text box about what happens to methane diffusion when it's hit by UV rays.

Looks like H₂ and H escape to space, and other components are broken down and fall back to the surface, but I'm not sure.
It's for a graphic design project
Cheerz
GIAN🙂XXX

(SCIENCE AGE ABOUT 12)

Regarding your ( c ) , if a free radical is formed it will be CH₃• rather than CH₃⁻, and the hydrogen released will be H• rather than H+. The dot denotes an unpaired electron, which makes the species reactive. There is no charge separation in free radical reactions so both species are uncharged. CH₃• is known as a methyl radical. A pair of these certainly combine to give ethane, C₂H₆. However the formation of acetylene, HC≡CH, would need further explanation. I could imagine methyl radicals removing H from ethane, perhaps, but 4 would have to be removed before you reached acetylene so this route seems a bit doubtful. Is there a further explanation in Lorentz's book for how acetylene is formed?

Edited July 5, 2025Jul 5 by exchemist

I found this rather interesting paper which goes into the reactions in Titan’s atmosphere in some detail: https://pubs.acs.org/doi/10.1021/acsearthspacechem.2c00041

It seems one route for acetylene formation involves the methylene radical CH2, in its triplet state, i.e. with 2 unpaired electrons. Two of these can produce acetylene plus hydrogen, apparently. But the chemistry of Titan’s atmosphere is clearly very complex. One key feature is it is a reducing atmosphere, i.e. with no oxygen present. It is this that allows all these hydrocarbon fragments to form and react with one another.

Edited July 5, 2025Jul 5 by exchemist

2 hours ago, exchemist said:

Regarding your ( c ) , if a free radical is formed it will be CH₃• rather than CH₃⁻, and the hydrogen released will be H• rather than H+. The dot denotes an unpaired electron, which makes the species reactive. There is no charge separation in free radical reactions so both species are uncharged. CH₃• is known as a methyl radical. A pair of these certainly combine to give ethane, C₂H₆. However the formation of acetylene, HC≡CH, would need further explanation. I could imagine methyl radicals removing H from ethane, perhaps, but 4 would have to be removed before you reached acetylene so this route seems a bit doubtful. Is there a further explanation in Lorentz's book for how acetylene is formed?

Thanks, so the CH₄ (methane) doesn't change into an an anion, but into CH₃• which is a "methyl radical?"🙂

Just now, Gian said:

Thanks, so the CH₄ (methane) doesn't change into an an anion, but into CH₃• which is a "methyl radical?"🙂

Exactly. See my later post and the link to the paper. It’s pretty complicated but you can see the sort of thing that goes on.

22 hours ago, studiot said:

Your graphic states "and are then converted into nitriles"...

7 hours ago, exchemist said:

Exactly. See my later post and the link to the paper. It’s pretty complicated but you can see the sort of thing that goes on.

11 hours ago, sethoflagos said:

The strength of the CN triple bond in nitriles ...

Dear Messrs Exchemist, Studiot & Sethoflagos
I've had this from Dr Lorenz, and although it's mostly above my head I think I can follow it enough so I'll use this in my graphic,

Lorenz, Ralph D.<Ralph.Lorenz++++++>

Gian

You’ve almost got it, but strictly it’s like this   (I would say your wording ‘heavy organics.. .converted into nitriles’ is not quite correct)

 UV & electrons   break CH4 into bits   -  CH, CH2, CH3, H

Electrons  also break N2 into bits   N

 These fragments can recombine    (the following equations sum up what could actually be several steps, which may or may not involve excited states, ions/electrons or third molecules that soak up energy, but are simplified for explanation)

 H + H -> H2

CH + CH  ->  C2H2  (acetylene)

CH3 + CH3 -> C2H6  (ethane)

N + CH2 + CH  -> C2H3N  (acetonitrile)

And so on to C6H6 (benzene) and many more complicated hydrocarbons (C,H compounds) and nitriles (C,H,N compounds)

 The H2 escapes to space. Everything else eventually ends up on the surface

Ralph

Hope this makes sense to everyone and additional comments appreciated
Cheerz

GIAN🙂XXX

11 minutes ago, Gian said:

Dear Messrs Exchemist, Studiot & Sethoflagos
I've had this from Dr Lorenz, and although it's mostly above my head I think I can follow it enough so I'll use this in my graphic,

Lorenz, Ralph D.<Ralph.Lorenz++++++>

Gian

You’ve almost got it, but strictly it’s like this   (I would say your wording ‘heavy organics.. .converted into nitriles’ is not quite correct)

 UV & electrons   break CH4 into bits   -  CH, CH2, CH3, H

Electrons  also break N2 into bits   N

 These fragments can recombine    (the following equations sum up what could actually be several steps, which may or may not involve excited states, ions/electrons or third molecules that soak up energy, but are simplified for explanation)

 H + H -> H2

CH + CH  ->  C2H2  (acetylene)

CH3 + CH3 -> C2H6  (ethane)

N + CH2 + CH  -> C2H3N  (acetonitrile)

And so on to C6H6 (benzene) and many more complicated hydrocarbons (C,H compounds) and nitriles (C,H,N compounds)

 The H2 escapes to space. Everything else eventually ends up on the surface

Ralph

Hope this makes sense to everyone and additional comments appreciated
Cheerz

GIAN🙂XXX

Yup, that's a simplified free radical reaction scheme showing the same basic idea as the more complicated ones in the paper.

On 7/5/2025 at 6:37 PM, Gian said:

 UV & electrons   break CH4 into bits   -  CH, CH2, CH3, H

Electrons  also break N2 into bits   N

 These fragments can recombine    (the following equations sum up what could actually be several steps, which may or may not involve excited states, ions/electrons or third molecules that soak up energy, but are simplified for explanation)

 H + H -> H2

CH + CH  ->  C2H2  (acetylene)

CH3 + CH3 -> C2H6  (ethane)

N + CH2 + CH  -> C2H3N  (acetonitrile)

And so on to C6H6 (benzene) and many more complicated hydrocarbons (C,H compounds) and nitriles (C,H,N compounds)

 The H2 escapes to space. Everything else eventually ends up on the surface

See what is happening here from a particular perspective:

UV photolysis (and 'electrolysis') is creating a survival advantage to those molecular species that are less susceptible to their effects and/or less exposed to them due to their depth in the atmosphere; the remainder being more prone to being broken down back into simpler species:

Gravitation is creating a survival advantage for larger, denser molecular species by drawing them deeper into the atmosphere where they are better shielded from UV radiation and/or being lost to space.

Add to these the 2nd Law of Thermodynamics which creates by purely statistical means, a survival advantage for molecular species that are new to the mix or existing in very low concentrations due to the higher entropy of more diverse mixtures.

The overall effect of UV on a 'primitive' atmosphere can hence be seen as the spontaneous generation of an ever-increasing diversity of increasingly complex UV-resistant molecular species.

The origin of species by natural selection?

It's so very similar isn't it. And for my money, was very much a significant part of life's earliest origins here on earth.

2 hours ago, sethoflagos said:

See what is happening here from a particular perspective:

UV photolysis (and 'electrolysis') is creating a survival advantage to those molecular species that are less susceptible to their effects and/or less exposed to them due to their depth in the atmosphere; the remainder being more prone to being broken down back into simpler species:

Gravitation is creating a survival advantage for larger, denser molecular species by drawing them deeper into the atmosphere where they are better shielded from UV radiation and/or being lost to space.

Add to these the 2nd Law of Thermodynamics which creates by purely statistical means, a survival advantage for molecular species that are new to the mix or existing in very low concentrations due to the higher entropy of more diverse mixtures.

The overall effect of UV on a 'primitive' atmosphere can hence be seen as the spontaneous generation of an ever-increasing diversity of increasingly complex UV-resistant molecular species.

The origin of species by natural selection?

It's so very similar isn't it. And for my money, was very much a significant part of life's earliest origins here on earth.

Interesting POV. +1