Cassini Gets New Views of Titan's Land of Lakes

[K^2]

Methane is not as good of a solvent as water.

The same thing that makes water a better solvent at typical Earth temperatures, the hydrogen bonds, also makes it unusable at low temperatures. Methane is a better choice for cryogenic life.

as if some of you never learned organic chemistry in your lives...

I say let's search for helium life on the Sun. When life gives you lemons...

The thing about organic chemistry is that it's all about organic compounds at typical temperatures. When you drop down to 90K, you have to make sure that your intermolecular bonds are much weaker. That means you have to get away from any polar molecule and use a non-polar solvent. Since you obviously slept through all of your other chemistry courses, including physical chemistry and quantum chemistry, I'll remind you that the main requirement for bio-chemistry is ability to change reaction rates with very small changes in temperatures or concentrations. That means, your intermolecular forces need to be dominated by a bond that's comparable to energy at relevant temperature. At 300K the hydrogen bonds are it, and that makes water an ideal solvent. At 90K you are looking at much weaker bonding. Something like dipole-dipole interactions are likely to replace hydrogen bonds. And that means that a non-polar solvent, such as methane, is going to be quite sufficient.

[nhnifong]

Are there any membranes comparable to lipid bi-layers that can be constructed with dipole-dipole interactions?

[mdatspace]

snip

But there is something else in the favor of Europa: Tidal heating. Titan gets most of its internal heat by radioactive decay. Said heat depletes over time. Europa has radioactive decay and tidal heating. Looking at their surfaces, I think it is easy to judge which one has been more active. Titan is constantly resurfaced by erosion and deposition, covering up older features. Europa has only been resurfaced through endogenic processes, not to mention the differences within.

While titan has a subsurface ocean, it likely does not get as much heat or nutrients as Europa, as there are likely subsurface vents spewing heat and nutrients every day and night.

Edited October 27, 2013 by mdatspace

[K^2]

Are there any membranes comparable to lipid bi-layers that can be constructed with dipole-dipole interactions?

I'd be shocked if there weren't. You just need a molecule that interacts with itself on one end a bit stronger than it does with methane, and you need it not to freeze solid at 90K.

While titan has a subsurface ocean, it likely does not get as much heat or nutrients as Europa

We aren't talking about subsurface oceans. We are talking about the seas and lakes of methane on the surface. And the nutrient for potential life there would be acetylene, which is quite abundant and renewable thanks to solar radiation.

[mdatspace]

We aren't talking about subsurface oceans. We are talking about the seas and lakes of methane on the surface. And the nutrient for potential life there would be acetylene, which is quite abundant and renewable thanks to solar radiation.

But is it better chemistry than a subsurface ocean? No. It is abundant and renewable, but that says nothing about its use to life. It is easy to see how much oceans do when it comes to life.

[lajoswinkler]

The same thing that makes water a better solvent at typical Earth temperatures, the hydrogen bonds, also makes it unusable at low temperatures. Methane is a better choice for cryogenic life.

The thing about organic chemistry is that it's all about organic compounds at typical temperatures. When you drop down to 90K, you have to make sure that your intermolecular bonds are much weaker. That means you have to get away from any polar molecule and use a non-polar solvent. Since you obviously slept through all of your other chemistry courses, including physical chemistry and quantum chemistry, I'll remind you that the main requirement for bio-chemistry is ability to change reaction rates with very small changes in temperatures or concentrations. That means, your intermolecular forces need to be dominated by a bond that's comparable to energy at relevant temperature. At 300K the hydrogen bonds are it, and that makes water an ideal solvent. At 90K you are looking at much weaker bonding. Something like dipole-dipole interactions are likely to replace hydrogen bonds. And that means that a non-polar solvent, such as methane, is going to be quite sufficient.

Methane is by all means quite similar to a noble gas and behaves like an ideal gas. Methane molecule behaves like a tiny ball. Its tetrahedral structure ensures the force vectors arising from the small electronegativity differential are nullified. I do not see it as CH₄, is see it as a ball with a name CH₄ written on it.

I am quite aware of the biochemical requirements, thank you. What you don't realize is that the energy to break apart one C-H bond in methane is 435 kJ mol^-1. I'd like to see that in a cryogenic environment, and please, no enzyme talk. It's ridiculous.

If you can give any, even remotely solid, hypothetical mechanism for that, I would consider it as a possibility.

Until then, I see your arguments as "it's space and anything can happen in space because it's not Earth" and therefore you can proceed working on liquid helium life, too.

Are there any membranes comparable to lipid bi-layers that can be constructed with dipole-dipole interactions?

Biological membranes work using a combination of hydrophobic bonds (pseudoforces arising from the tendence of surrounding water to lower its energy state by binding together and excluding other nonpolar stuff) and hydrogen bonds from the polar parts of the lipid molecules. Hydrogen bonds are a special case of Keesom forces (dipole-dipole) so I'm not sure where are you getting at with this question. Can you clarify it?

[K^2]

Methane is by all means quite similar to a noble gas and behaves like an ideal gas. Methane molecule behaves like a tiny ball. Its tetrahedral structure ensures the force vectors arising from the small electronegativity differential are nullified. I do not see it as CH₄, is see it as a ball with a name CH₄ written on it.

Yeah, so all interactions with it are on the order of 1-2 kJ/mol. So maybe as little as 1/10th of water. At temperatures less than a third of terrestrial, that's quite normal. Keeping in mind that we have thermophiles at up to 400K with water as solvent, 90K for methane seems like an extreme range of a warm environment. So long as all of your organics is going to be non-polar and dipole-dipole interactions replace hydrogen bonds this is just the right temperature range.

You are still thinking in terms of interactions you want at 300K+. For 90K, methane is just what you want.

I am quite aware of the biochemical requirements, thank you. What you don't realize is that the energy to break apart one C-H bond in methane is 435 kJ mol^-1. I'd like to see that in a cryogenic environment, and please, no enzyme talk. It's ridiculous.

If you can give any, even remotely solid, hypothetical mechanism for that, I would consider it as a possibility.

For starters, I'm not sure why you'd want to break C-H bonds. The building material we are considering is acetylene, which already has just one hydrogen bound to a carbon. So at worst, we need to break C-C bonds, which is considerably easier, especially if you start with a triple bond there.

But ok, I'll bite. Lets talk about the C-H bond. You insist that it's necessary to be able to break it for biosynthesis. 435kJ/mol is 4.5eV per bond. At 300K you are going to get 0.013 eV per C-H bond from thermal excitation. At 90K you'll have 0.0039eV.

So to break the C-H bond at 90K, you have to supply 4.496 eV of energy, and at 300K you have to supply 4.487 eV. Are you seeing a lot of difference? Because I don't.

Let me put it another way. Temperature at which average energy will exceed 4.5eV per bond is going to be over 100,000K. So it make absolutely no difference if you compare that to 90K or 300K. You have to do something creative with it if you want to break the bond.

So it's your turn. Why don't you go into details of how this C-H bond is broken at 300K and try to explain what it is that prevents it from happening at 90K.

[nhnifong]

[Scotius]

Scoot over nhnifong. And pass the 'corn, willya?