<p>I can give a rough answer to your question and some brief thoughts on the paper, and I invite correction from anyone smarter than me.   Your article talks about energy per mole, but energy of production on a daily basis would be a product of solar energy.</p>

<p>To produce hydrogen in Titan's atmosphere requires UV light, from this article, UV light of 1600 Angstroms (160 NM) <a href="http://www.astrobio.net/topic/solar-system/saturn/titan/the-missing-methane/" rel="nofollow">(Source)</a></p>

<p>Quote: </p>

<blockquote>
  <p>Methane is a carbon atom surrounded by four hydrogen atoms, and it can
  be broken apart by ultraviolet light at wavelengths of about 1600
  Angstroms. The fragments, or radicals, that are produced from this
  process are very chemically reactive. They’re things like CH, CH2, and
  in some cases CH3.</p>
</blockquote>

<p>Only a small percentage of the sun's light is in that range.   8%-10% of the sun's light is in the UV range, but maybe only 1%-2% in the upper UV3 range of 160 NM.  <a href="https://en.wikipedia.org/wiki/Sunlight#Composition_and_power" rel="nofollow">(Source)</a></p>

<p>The same Wiki article, using Saturn as a guide, Saturn receives between 13.4 and 16.7 Watts per square meter <a href="https://en.wikipedia.org/wiki/Sunlight#Intensity_in_the_Solar_System" rel="nofollow">(Source)</a>, so figure an estimate of 15 watts per square meter total solar energy, 1%-2% of that strong enough to pull a hydrogen atom off Methane, so 0.15 - 0.3 watts per square meter.   That might not sound like much, but on a moon the size of titan, that's a lot of square meters so the low wattage isn't a big deal.   That's a peak estimate though as some of the hydrogen would recombine with the CH3 it split from, some energy would likely be converted to heat, and perhaps the biggest problem, mentioned in the article above, a share of the hydrogen, perhaps the lion's share would simply be lost off the planet.</p>

<blockquote>
  <p>In the atmospheres of the giant planets, the hydrogen stays around
  because of the high gravity of those planets. Their atmospheres are
  primarily hydrogen anyway, and after the fragmentation occurs, the
  products sink into the deeper atmosphere, and methane is
  reconstituted. It’s a complete chemical cycle.</p>
  
  <p>On Titan, as far as we understand, that does not occur. Because the
  gravity is low, hydrogen should escape. The Voyager ultraviolet
  spectrometer saw a corona of hydrogen around Titan, which is a good
  indication that hydrogen is escaping. Now, if hydrogen is going away,
  the products that can be made from the methane are going to have a
  higher carbon to hydrogen ratio than methane itself, and you’re not
  going to be able to remake methane. So as far as we understand the
  photochemistry, Titan should be destroying methane and making more
  carbon-rich products, the simplest of which are acetylene – C2H2 – and
  ethane – C2H6. These are made directly from methane</p>
</blockquote>

<p>This is my problem with the article.  I don't see any way the hydrogen finds it's way down to the planet's surface to be used in the way the article suggests, life in the lakes of Titan.    It's an interesting idea and the people who wrote it are probably PHD educated and I'm not, but I suspect the majority of hydrogen produced high in Titan's atmosphere would remain high in it's atmosphere and over time, lost to the solar wind.</p>

<p>It does raise the question, because Titan should lose it's Methane over time, why does it still have so much Methane - a very good question.</p>

<p>Lets look at the timing.   <a href="https://en.wikipedia.org/wiki/Huygens_%28spacecraft%29" rel="nofollow">Huygens</a> landed on Titan January 14th, 2005.</p>

<p>Your article was written  14 January 2005; revised 18 April 2005</p>

<p>and here's an article from a few months later, November 2005.</p>

<p><a href="http://www.spaceref.com/news/viewpr.html?pid=18410" rel="nofollow">http://www.spaceref.com/news/viewpr.html?pid=18410</a></p>

<blockquote>
  <p>The origin of methane in Titan's atmosphere is a mystery because it
  gets broken down by sunlight and particle radiation from space in the
  upper atmosphere. If surface lakes and pools were the only source, all
  of Titan's methane would be lost by this mechanism in less than a
  hundred million years, a short time for a moon that's been around
  since the formation of the solar system 4.5 billion years ago.�
  Components of the methane molecules react with each other and
  atmospheric nitrogen. As they descend, they form larger and heavier
  molecules that comprise the orange haze that blankets the moon.
  Because Titan is very cold (292 degrees below zero F, or minus 180
  degrees Celsius) these heavy compounds condense and rain out on the
  surface.</p>
  
  <p>"We have determined that Titan's methane is not of biological origin,
  so it must be replenished by geologic processes on Titan, perhaps
  venting from a supply in the interior that could have been trapped
  there as the moon formed,"</p>
</blockquote>

<p>So, I'd chalk this one up to timing.   January-April 2005, life on Titan was a viable theory, which has since been de-theoried, or, whatever the correct term is.</p>

CC BY-SA 3.0
2015-07-31T09:35:08.003Z
2015-07-31T09:35:08.003Z
userLTK
<p>There is an interesting discussion about whether there could be life on Saturn's moon Titan. (For example <a href="https://www.youtube.com/watch?v=bbkTJeHoOKY" rel="nofollow">here</a>.) The life could use reaction of hydrogen and acetylene which are being produced by photolysis in Titan's atmosphere. I would like to know what total energy is available for such life per square meter per day, or at least how much hydrogen is produced in Titan's atmosphere per day. </p>

<p>There are some estimates in article <a href="http://astrobiology.jhu.edu/wp-content/uploads/2010/06/Icarus-2005-McKay.pdf" rel="nofollow">McKay and Smith, Icarus, 2005</a>, but I have problem translating the quantities they use for the estimate to total amount of hydrogen produced per unit of time or energy produced per unit of time.</p>

<life><titan>
Available energy for potential life on Titan
Irigi
# Available energy for potential life on Titan

(Asked by: username_0 on 2015-07-30)

There is an interesting discussion about whether there could be life on Saturn's moon Titan. (For example [here](https://www.youtube.com/watch?v=bbkTJeHoOKY).) The life could use reaction of hydrogen and acetylene which are being produced by photolysis in Titan's atmosphere. I would like to know what total energy is available for such life per square meter per day, or at least how much hydrogen is produced in Titan's atmosphere per day.

There are some estimates in article [McKay and Smith, Icarus, 2005](http://astrobiology.jhu.edu/wp-content/uploads/2010/06/Icarus-2005-McKay.pdf), but I have problem translating the quantities they use for the estimate to total amount of hydrogen produced per unit of time or energy produced per unit of time.

**Tags:** life, titan


---

## 1 answers

### Answer by username_1 on 2015-07-31. Score: 2 | Accepted answer

I can give a rough answer to your question and some brief thoughts on the paper, and I invite correction from anyone smarter than me. Your article talks about energy per mole, but energy of production on a daily basis would be a product of solar energy.

To produce hydrogen in Titan's atmosphere requires UV light, from this article, UV light of 1600 Angstroms (160 NM) [(Source)](http://www.astrobio.net/topic/solar-system/saturn/titan/the-missing-methane/)

Quote:

> Methane is a carbon atom surrounded by four hydrogen atoms, and it can
> be broken apart by ultraviolet light at wavelengths of about 1600
> Angstroms. The fragments, or radicals, that are produced from this
> process are very chemically reactive. They’re things like CH, CH2, and
> in some cases CH3.

Only a small percentage of the sun's light is in that range. 8%-10% of the sun's light is in the UV range, but maybe only 1%-2% in the upper UV3 range of 160 NM. [(Source)](https://en.wikipedia.org/wiki/Sunlight#Composition_and_power)

The same Wiki article, using Saturn as a guide, Saturn receives between 13.4 and 16.7 Watts per square meter [(Source)](https://en.wikipedia.org/wiki/Sunlight#Intensity_in_the_Solar_System), so figure an estimate of 15 watts per square meter total solar energy, 1%-2% of that strong enough to pull a hydrogen atom off Methane, so 0.15 - 0.3 watts per square meter. That might not sound like much, but on a moon the size of titan, that's a lot of square meters so the low wattage isn't a big deal. That's a peak estimate though as some of the hydrogen would recombine with the CH3 it split from, some energy would likely be converted to heat, and perhaps the biggest problem, mentioned in the article above, a share of the hydrogen, perhaps the lion's share would simply be lost off the planet.

> In the atmospheres of the giant planets, the hydrogen stays around
> because of the high gravity of those planets. Their atmospheres are
> primarily hydrogen anyway, and after the fragmentation occurs, the
> products sink into the deeper atmosphere, and methane is
> reconstituted. It’s a complete chemical cycle.
>
> On Titan, as far as we understand, that does not occur. Because the
> gravity is low, hydrogen should escape. The Voyager ultraviolet
> spectrometer saw a corona of hydrogen around Titan, which is a good
> indication that hydrogen is escaping. Now, if hydrogen is going away,
> the products that can be made from the methane are going to have a
> higher carbon to hydrogen ratio than methane itself, and you’re not
> going to be able to remake methane. So as far as we understand the
> photochemistry, Titan should be destroying methane and making more
> carbon-rich products, the simplest of which are acetylene – C2H2 – and
> ethane – C2H6. These are made directly from methane

This is my problem with the article. I don't see any way the hydrogen finds it's way down to the planet's surface to be used in the way the article suggests, life in the lakes of Titan. It's an interesting idea and the people who wrote it are probably PHD educated and I'm not, but I suspect the majority of hydrogen produced high in Titan's atmosphere would remain high in it's atmosphere and over time, lost to the solar wind.

It does raise the question, because Titan should lose it's Methane over time, why does it still have so much Methane - a very good question.

Lets look at the timing. [Huygens](https://en.wikipedia.org/wiki/Huygens_%28spacecraft%29) landed on Titan January 14th, 2005.

Your article was written 14 January 2005; revised 18 April 2005

and here's an article from a few months later, November 2005.

<http://www.spaceref.com/news/viewpr.html?pid=18410>

> The origin of methane in Titan's atmosphere is a mystery because it
> gets broken down by sunlight and particle radiation from space in the
> upper atmosphere. If surface lakes and pools were the only source, all
> of Titan's methane would be lost by this mechanism in less than a
> hundred million years, a short time for a moon that's been around
> since the formation of the solar system 4.5 billion years ago.�
> Components of the methane molecules react with each other and
> atmospheric nitrogen. As they descend, they form larger and heavier
> molecules that comprise the orange haze that blankets the moon.
> Because Titan is very cold (292 degrees below zero F, or minus 180
> degrees Celsius) these heavy compounds condense and rain out on the
> surface.
>
> "We have determined that Titan's methane is not of biological origin,
> so it must be replenished by geologic processes on Titan, perhaps
> venting from a supply in the interior that could have been trapped
> there as the moon formed,"

So, I'd chalk this one up to timing. January-April 2005, life on Titan was a viable theory, which has since been de-theoried, or, whatever the correct term is.


---

