# What aliphatic compounds were found on Ceres, and how where they identified?

Los Angeles Times's article NASA's Dawn mission finds life's building blocks on dwarf planet Ceres says;

While the scientists aren’t sure exactly what the compounds are, the fingerprint is characteristic of material containing carbon-hydrogen bonds, and may include components like methyl and methylene.

I've located the mentioned Science article Localized aliphatic organic material on the surface of Ceres but it is paywalled.

What was found? Is it some spectroscopic feature? Aliphatic compounds are hydrocarbons that are not aromatic. Is there a spectral feature that says "I am not aromatic" specifically, or does this just mean that aromaticity was not detected?

• Note, that's not quite right either, I checked the wiki page and some simple rings can be aliphatic, like C6H10. Cyclohexene. Ringed, but less stable, weaker bonds in the ring. I'll stop now. I'll stop posting now. – userLTK Feb 17 '17 at 4:38
• @userLTK Oh! I was hoping to get you to post more, not less! :) I thought you were already most of the way towards a good answer I could accept. The explanation was very helpful, so I thought that locking it in as an answer would be a good thing. Comments can be so "ephemeral", as demonstrated recently here ;) – uhoh Feb 17 '17 at 4:44
• I worry about posting an answer and getting some stuff wrong (like I did in the comment I deleted). If no one answers, I'll do some research and post something. I haven't read the pay-article either, but there's a few articles out on this so I read a little bit. – userLTK Feb 17 '17 at 6:03

OK, I did a bit of research on this. The LA Times article you quoted says something a little bit useful.

While the scientists aren’t sure exactly what the compounds are, the fingerprint is characteristic of material containing carbon-hydrogen bonds, and may include components like methyl and methylene.

Methyl means a carbon with at least 3 hydrogen bonded to it. Because carbon has 4 bonds, that 4th bond can be part of a chain, so a methyl group offers a very large body of molecules to choose from.

Methlyene is a carbon with 2 hydrogen.

The organic molecules that have been detected on Ceres are complex aliphatic compounds that seem to be almost tar-like in nature.

Tar is a pretty nonspecific term, tar-like even more so, but tar is made by cooking coal or wood without oxygen, so I would assume this implies it's not Oxygen rich. More "simple" complex hydrocarbon chains (and because "simple" complex is somewhat confusing, another way to say that it's probably mostly Cs and Hs in a fairly big molecule, probably 5, maybe 6 carbons minimum I would think, otherwise it would be too quickly sublimated into gas. Tar like aliphatic compounds would still be vulnerable to photo-disintegration by UV light from the sun, which is common enough on Ceres Surface, but would be high enough melting points to not evaporate somewhat rapidly like shorter chains would. That these compounds were found locally probably implies somewhat recent, localized hydro-thermal activity.

The Aromatic C-H bond and the Aliphatic C-H bond have different spectroscopy. Source.

There is a weak alkene CH stretch above 3000 cm-1. This comes from the C-H bonds on carbons 1 and 2, the two carbons that are held together by the double bond. The strong CH stretch bands below 3000 cm-1 come from carbon-hydrogen bonds in the CH2 and CH3 groups.

and

The IR spectrum for benzene, C6H6, has only four prominent bands because it is a very symmetric molecule. Every carbon has a single bond to a hydrogen. Each carbon is bonded to two other carbons and the carbon-carbon bonds are alike for all six carbons. The molecule is planar. The aromatic CH stretch appears at 3100-3000 cm-1 There are aromatic CC stretch bands (for the carbon-carbon bonds in the aromatic ring) at about 1500 cm-1. Two bands are caused by bending motions involving carbon-hydrogen bonds.

So, less than 3,000 cm wavelength implies what the LA-Times article said, Methyl and Methylene or CH3 and CH2 groups on fairly long chain carbon molecules, probably tar-like. But that's hundreds, perhaps thousands of molecules that fit those criteria, some with single bonds between carbons, some with double bonds, some maybe more complex and from all the articles I've read, they don't know which ones. They can't tell which hydrocarbons by orbiting spectroscopy, they can only see the signature of the CH3 and/or CH2 groups at the end of the chains.

To know which molecules, they'll need to test a sample. So, a mars-like rover is probably going to go to Ceres at some point.

Why this is interesting is that these molecules aren't that long lived on the surface of Ceres, because UV light form the sun destroys them and they're location implies they came from inside Ceres, probably by hydro-thermal activity. There's also ammonia rich clay and carbonate rich clay and those are 3 key ingredients to life. None of this is proof that there's life underground in Ceres, but the ingredients are all there (or mostly there). Warm water (below the surface - and Ceres has a lot of internal water based on it's density), and the basic building blocks. It's still a far cry from proof of life as nothing has been found on the surface of Ceres that doesn't exist in comets, other than the implication of underground liquid water. But having all the ingredients in the same place is interesting.

Small point to add, but the article above mention Ammoniated Clay and Carbonates. Both of those are building blocks. Neither is organic.

This is strengthened by the fact that the molecules are found together with carbonates and clays containing ammonia. These have been observed in many regions of Ceres

Carbonates are simple. A molecule or molecules bound to a CO3(2-) is a carbonate.

Ammoniated clay took some looking up, but I found this:

The orbiting Dawn spacecraft has a more ideal perch to observe how molecules on the dwarf planet’s surface reflect various wavelengths of light. It was in those wavelengths that Dawn investigator Carle Pieters and her colleagues spied the signature of ammoniated phyllosilicates, which are minerals similar to clays on Earth, mixed in with other materials.

Phyllosilicates are just clay or dissolved rock, with one or more OH- molecules. Ammoniated Phylosilicates, instead of having an OH- (Hydroxy group) have one or more NH2- (amides) or perhaps NH4+ (ammonium), which is a different charge so that wouldn't replace the OH but might still bond with silicates with hydro-thermal mixing.

• Wow beautiful summary! It will take me a day or sonto read through it all, but this certainly seems to be exactly what I was hoping for - and more! Reading about IR is always bumpy for me because of the swithch back and forth between wavelenght and wave number, especially mixed with "above" and "below". I think Dawn's spectrometer sees wavenumbers down to 2000 cm${}^{-1}$ which is the same as wavelengths up to (as long as) 5 $\mu$m. – uhoh Feb 18 '17 at 7:57