Hello IBH students, alumni, and professors!
Dr. Cheng contacted me in regards to writing a post for the IBH Student Highlight section. I’ll be writing about a little intro on astrobiology and astrochemistry. So, naturally, the first couple questions that will probably arise are “What is astrobiology exactly?” and “What is astrochemistry?”
In regards to astrobiology, the first idea that might pop up in your head is that it is the study of extraterrestrial life. That is partially correct. NASA had a separate term for that back in the day (i.e. exobiology), but it never really caught on seeing as that we only know of terrestrial life so far. While astrobiology would involve studying ET, the field is much bigger than that.
Astrobiology includes the study of the origin of life here on Earth and for the search for extraterrestrial organisms in our solar system and beyond. It tests the limits of what life is capable of. As you might imagine, the field is pretty interdisciplinary. The University of Illinois was awarded an astrobiology grant relatively recently (see here:http://astrobiology.illinois.edu). The team consisted of biologists, chemists, geologists, physicists, and astronomers.
Each field plays its role. Geologists are usually tasked with unlocking Earth’s geological code and identifying biosignatures, which are mineral depositions that can be traced exclusively to biotic origins. The nasty thing about Earth’s geological historical record is that it does not contain much information about life’s origins. That’s where the chemists and physicists come in: they try to determine how life might form using bottom-up approaches. Put another way, they try to recreate life or prebiotic molecules from simple starting materials. That is a definitely a difficult job to do when you do not have the recipe (i.e. geological history).
Physicists also team up with astronomers to search for more exoplanets, search for hints of life on said exoplanets, and search for life in the solar system. At the moment, our ability to search for life outside the solar system is extremely limited. Our best hope is to identify atmospheres that “look” like Earth’s spectroscopically. Humanity cannot do that well right now, but things may be different when the James Webb telescope is finally launched and put into orbit (see this: http://www.jwst.nasa.gov). In regards to our own solar system, geology-chemistry-physicist-astronomer hybrids called planetary scientists design space missions that record the physical and chemical characteristics of planetary bodies including astrobiologically relevant ones like Mars, Europa, and Enceladus.
So where do biologists fit in within astrobiology? Biologists study the origin of life from a top-down approach, they study extremophiles (organisms that, as the name suggests, love extreme physical and/or chemical environments), and put constraints on where life might actually exist.
In studying the origin of life, biologists are responsible for unraveling the genomes of “primitive” bacterial and archaeal species and deducing what the Last Ultimate Common Ancestor, or LUCA, may have looked like. While LUCA itself was probably quite complex with fully operational ribosomal machinery and the works, knowing how such an organism looked like might give the necessary constraints for the aforementioned chemists/physicists trying to solve the origin of life problem from the bottom-up approach. This is not universally accepted, but it is the prevailing school of thought at the moment.
As mentioned, biologists also study extremophiles. A recent infamous example of this includes the GFAJ-1 microbe from Mono Lake, CA where the study’s authors thought that the bacteria was utilizing arsenic in its DNA backbone. Long story short, they’re not. This led to a number of controversies. However, the study of extremophiles is usually not so dramatic. The best example of this is the study of the thermophile Thermus aquaticus which led to the development of the popular technique called the polymerase chain reaction (PCR). The bacteria’s enzymes are able to withstand high heat and are thus perfect for surviving the high temperature required to denature DNA and to assemble nucleotides. Other examples of interesting extremophiles include electrophiles that can accept electrical currents as source of energy and other bacteria that can produce electricity given a source of organic nutrients. Applications for the latter include the development of microbial fuel cells.
Lastly, biologists also put constraints on where life might be found. This is helped a lot by the previously mentioned extremophile work, but biophysicists also come into play here. These types of biologists put physical constraints to what is actually possible. For example, biophysicists poked holes in the paper that claimed GFAJ-1 uses some arsenic instead of phosphorus in its DNA backbone. They did this by showing that the resulting structure would be thermodynamically unstable and break apart. Similarly, they put limitations on what life requires in order to exist in various environments.
So far, astrobiologists can agree on three basic items necessary for life: (1) a liquid solvent (not necessarily water), (2) a source of nutrients, and (3) a source of free energy. Within our solar system, Mars, Europa, Enceladus, and Titan all meet the aforementioned criteria. Personally, I find moons like Europa and Enceladus most exciting, astrobiologically speaking, because both contain subsurface oceans so, in a way, they are the most “Earth-like” since our planet really is more ocean than it is earth.
A moon like Titan or dwarf planets like Pluto are exciting for different reasons altogether and they finally bring me to the topic of astrochemistry, the study of chemical reactions that occur in space. The reasons why Titan and Pluto are exciting are because of their large amounts of nitrogen and presence of primordial molecules like methane. Titan’s atmosphere is denser than Earth’s and its composition is thought to be similar to early Earth’s. I previously mentioned that we do not have a terrestrial geological record of the origin of life, but I never said anything about an extraterrestrial record. ☺ The problem is getting there. Titan’s atmospheric chemistry is very exciting as it is laced with simple organic building blocks like CO2, CO, and CH4. The atmospheric reactions lead to the formation of large molecules called tholins, a nonspecific group of organic chemicals that could be important in forming prebiotic molecules.
Tholins are also formed on the dwarf planet Pluto where methane laced nitrogen ices exist on the surface. This is important because such ices could have existed closer to the inner solar system before solar fusion began in the Sun and temperatures were much lower. The thinking then goes that some important prebiotic molecules may have formed in space first before raining down on Earth in the form of comets. Time will only tell.
So what are some of the opportunities that I had with astrobiology/astrochemistry? My astrobiology experiences began at the University of Illinois where I worked in Dr. Bruce Fouke’s geomicrobiology laboratory. My main project there involved working on an artificial hot spring with the goal of seeing how microbes affect calcium carbonate deposition in a controlled environment. As an undergraduate, I had two internships at NASA: the first was also at a geomicrobiology laboratory and the second was in something called planetary protection. While the latter does sound like a Men In Black type of job, the protection portion is usually meant for other planetary bodies nowadays. In short, NASA does not want terrestrial microbes to start colonizing astrobiologically relevant sites like Mars or Europa.
The project I most enjoyed working on was at JPL with the planetary protection division. It involved enumerating the amount of bioburden found within spacecraft materials. We used what one of my mentors called „classical techniques” like counting colonies, but also „modern techniques” like qPCR and epifluorescent microscopy to quantify the amount of spores within spacecraft materials. We also had the opportunity to work with a cryogenic mill…it is always fun to grind down material meant to survive the harsh conditions of outer space into a fine powder. ☺
After working on some more biology-related projects, I moved towards astrochemistry. My Master’s research had a number of projects, but the most relevant one to biology involved the chemistry of Pluto-analogue ices. Here we created a gas mixture consisting of a carbon source (CO or CH4), H2O, and N2 to simulate the Pluto-Charon system. We then irradiated the gas mixtures and deposited the products on a 6 Kelvin coldfinger where we were able to identify products using IR spectroscopy. At this point, the ices consisted mostly of nitrogen. Now, nitrogen is interesting because it can be used as a matrix material that separates out reactive species in the solid phase. So, in short, it can trap and accumulate reactive species. Our goal was then to show that with the right sublimation steps we would be able to form new products and trap them in a water ice. We were able to show that, but I’ll leave the details for another day as the work still isn’t published. So in addition to the direct irradiation of ices on Pluto and other planetary bodies, chemicals can also form in relatively large amounts through simple processes like sublimation. The other thing that we formed were the aforementioned tholins! While we did not characterize most of the tholins, these molecules are interesting because they are large organic molecules and many are prebiotically relevant. While Pluto has not officially been confirmed to have tholins yet, the red haze observed by New Horizons is mostly likely due to tholins.
I’m taking a little break from school, but I hope to continue with astrochemistry for my PhD work and work exclusively on tholins!
I hope that the information mentioned here was both informative and inspirational. If you do get hooked by astrobiology, my only major career recommendation would be to not make it your only gig. Funding for space sciences is capricious and life is a lot more fun when you are getting paid for doing what you love! All the scientist types mentioned here do research within other fields so just remember that you do not have to “settle” for one thing or another.
If you have questions on how to get started in astrobio/chem, you can send me an e-mail here: email@example.com
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