It’s sad to beg, but sadder is to beg over and over again, until exhausting our audience… It’s my case, I admit. It’s my fault. In my quest to increase the number of followers of the ASTROMOL’s Facebook account (wink-wink), I embarked on a smelly adventure in which I promised articles about stinky gases if I overcame every challenge. The first, “Flatulence in Space (I)”,was published in August 2015. January 2016 saw the birth (or, rather, smelled the birth) of “Flatulence in Space (II)” and, since there are no two without three, we tried again. The last one was hard, but we’ve made it. And since I do what I promise, here’s the third (and who knows if the last one, snif) deliver of “Space Flatulences”. Don’t cry for me 😉
“Nature never ceases to amaze us.” As if it were the script of a documentary, I see myself pronouncing this phrase as I choose the title of this report. I know it’s a little scatological, but it’s totally true: let’s talk about some of the gases that are in our flatulence. Watch out, in our flatulence there’s not just gas, there are more things, but we’re not going to talk about those. The compounds that give farts that smell (not all smell the same, it will all depend on what we have ingested) are well known. And some of them are also in space. Now you’ll understand why I, who usually talk about Astrophysics and Astrochemistry, get into these issues.
Hydrogen sulfide and carbonyl sulfide are the two pestilent compounds we have already talked about in this series. But today we do not bring sulfide, today we bring methyl mercaptan or methanethiol (CH3SH), a second cousin of methanol (CH3OH), which replaces sulfur (S) with oxygen (O). This mercaptan, from the thiol family, is a colorless gas that smells of rotten cabbage (although, in truth, I’ve never smelled a rotten cabbage, anyone with experience? Comments, please).
It appears to be in numerous plant and animal tissues and occurs in some processes of bacterial breakdown of proteins from methionine (as Wikipedia faithfully tells us), that is, a zombie would stink of CH3SH. It’s in the poop and farts (and in the stinky breaths) but, pay attention, it’s also in our brains (I see the joke coming) and in the blood.
There are also some cheeses that contain it and smell like this, to methyl mercaptan (you have an example in the Beaufort’s cheese) because of the action of some unleashed microorganism. Swamps emanate this smelly compound, but exposure would only be dangerous if we talk about industrial issues (and yet the danger of methyl mercaptan is not demonstrated). It is used as a precursor to pesticides, in the manufacture of plastics and feed, to break down wood in paper factories and is added to jet aircraft fuels.
Methanethiol is one of the gases added to the butane (remember that butane smells nothing) so that we get the olfactory alarms in case of leakage. (That reminds me of an olfactory fire alarm designed for deaf people who let out a wasabi spray. This research won an Ig Nobel Prize in 2011).
What about space?
Methyl mercaptan was detected in 1979 by Linke and collaborators in Sagittarius B2, a molecular cloud of the galactic center known to be one of the most productive massive star formation areas in the galaxy. So, we could already say that it had been detected in the interstellar medium.
Subsequent studies also detected the presence of methyl mercaptan towards the hot core of G327.3-0.6, a region of massive stars formation (this was the first time that methanethiol was found outside the galactic center).
It was also detected in the cold molecular cloud B1 (this cloud is located in the so-called First Hydrostatic Core stage, formed when the collapse phase at the star’s birth stage is stopped. We had already spoken before about this detection).
And, very recently, methyl mercaptan has been found in the protostar IRAS 16293-2422. Its finding suggests that there may be entire families of Sulphur-carrying molecules that have not yet been detected in protostars and would form from CH3SH.
It has been searched in other environments but, so far, has not yet been detected. Although there are proposals to use it as a biomarker when researching the surface of Mars. As a result of a biological process (you know, farts and so on) this, and other compounds of its kind, can help find signs of life on Mars or in the atmospheres of exoplanets. The linked work above explains that methanethiol may be involved in the origin of life in places with hydrothermal activity at low temperatures caused by serpentinization (a process that consumes water and releases heat). This process could take place on Mars, in icy oceans of moons or satellites, and in other smaller bodies, as well as on Earth.
Thus, detecting the presence of methyl mercaptan could be a tool for detecting signs of life. Although, honestly, we return to the usual: detecting a particular compound that we associate with the presence of life does not necessarily imply that there is life. There are many processes, in addition to farts, that can lead to the formation of methyl mercaptan. In this series of “flatulence in space” we always get to the same point: the origin of life.
And this because, dear friends, it seems that life, although it can be wonderful, sometimes stinks. 😉
Image 1: Space-filling model of the methanethiol molecule. Credits: Ben Mills.
List of molecules detected in space on the astrochymist web.
The methyl mercaptan on the “astrochymist” website.
Information on the toxicity of methyl mercaptan on the “Agency for Toxic Substances and Disease Registry” website of the Centers for Disease Control and Prevention (Atlanta, USA). Public Health Summary.
Originally published in Spanish on the Naukas website: “Flatulencias espaciales (III)” (2016/05/10).