When people find out that I’m an astrobiologist – that is, my work concerns the search for life on other planets, amongst other things- invariably, the first question is, “Have you found any yet?”
So, to start, I’d like to say for the record, that no, I haven’t (believe me, you would have heard about it if I had). But while that goal remains unattained, astrobiologists have still made astounding discoveries about life in the universe – and the finding of truly alien life may not be that far off.
I think the reason people find my field of research so fascinating is because it tackles some very foundational questions. How did life originate? Under what conditions can it survive? Where else might we find it? And what might it look like when we do? Because of the scale of these questions, astrobiology isn’t really a single field, per se – but rather a collections of many different disciplines (including, but not limited to, astronomy, geology, chemistry, biology, and planetary science), all trying to come up with answers.
In order to determine the likelihood of finding life elsewhere in the universe, we first must know how easy or difficult it is for life to emerge in the first place. This is the realm of the prebiotic chemists, who focus on how living systems can develop from simple chemistry (sometimes poetically referred to as abiogenesis). There are different theories as to how this happened – some scientists suggest that RNA, a molecule similar to DNA that has the capability to reproduce itself may have been the forerunner to life as we know it; others suggest that metabolic processes, or the creation of simple bubble-like “protocells” set the stage for life. It should be noted that these theories are not necessarily mutually exclusive – it has been suggested that life may have originated independently multiple times on Earth, competed and merged with each other, and finally gave rise to the biosphere we know today.
I should note that a general assumption about life in the universe is that it’ll most likely be similar to us, biochemically speaking. The foundations of Earth biochemistry are carbon (due to the fact that it can easily form complex molecules) and water (which is particularly good at dissolving molecules, and appears to be abundant through the universe). The latter was considered so key to life as we know it that, for a period of time, the motto of NASA’s astrobiology program was “Follow the Water” (this is also why there’s so much buzz whenever NASA announces the detection of liquid water elsewhere in our solar system). With that said, more exotic biochemistries – using silicon instead of carbon, for example, or using ammonia or methane instead of water – have also been proposed.
In addition to how life comes into being, we also must know how many places are available for it to live. One approach to this question is studying the abundance of habitable planets in the universe. Exoplanets – planets found around stars other than our sun- have been discovered to be staggeringly common. The Kepler space telescope mission, in particular, has found dozens of potentially Earth-like worlds, many located in the “Goldilocks zone” of their main star (where the temperature is “just right” for liquid water to exist on the surface).
We don’t know necessarily know if these planets are actually inhabitable or not (though we hope to answer that with future missions, such as the James Webb Space Telescope and Transiting Exoplanet Survey Satellite; I’m particularly fond of the latter since it shares my name), but these early findings are certainly promising.
Another angle on the question of habitability is studying the conditions on which life can survive – especially in environments that seem extreme and inhospitable to us. As it turns out, life is extraordinarily hardy, with organisms, known as extremophiles, making their homes in even incredibly harsh surroundings. From microbes living in the superheated water of hydrothermal systems to radiation-eating fungi discovered in the ruins of Chernobyl , it appears that life is amazingly adaptable. While most extremophiles are microbes, there are some more complex organisms that hold this distinction as well – my particular favorite being the iceworm, a glacier-dwelling invertebrate that is so well adapted to the cold that it will literally melt if its temperature is raised too high above freezing.
So, having established how life might originate and where it might survive, the next question is how might we detect it? This brings us to one of the primary areas of research in astrobiology – the identification and detection of biosignatures. Biosignatures are simply the chemical and physical traces left by living systems on their environment. A classic example is the presence of both methane and oxygen in the Earth’s atmosphere – since methane isn’t chemically stable in those conditions, some process must actively be producing it (incidentally, methane isn’t stable on Mars, either – which is why there was such excitement when very low levels of it were detected by the Curiosity mission). Biosignatures can also include microfossils or other geological traces left by microbes, and spectral lines in the light reflected off a planet indicating the presence of chlorophyll.
Related to biosignatures is probably the most famous aspect of astrobiology – the search for technosignatures. As the name suggests, these are indicators of the presence of a technological civilization. SETI, the Search for Extraterrestrial Intelligence, is the most well known effort to locate signs of an advanced aliens, but it is not the only one- there also astrobiologists keeping their eyes peeled for everything from signs of astroengineering (constructions the size of stars) to potentially looking for the lights of alien cities in the spectral signatures of planets. A find of this sort is the holy grail of astrobiology – after all, as exciting as an alien microbe might be, we’rd really prefer something we could talk to. It’s worth noting, though, it is statistically unlikely that any other alien civilization is at the same technology level as us, and may be much further advanced on the Kardashev scale, so they may not be as interested in what we have to say.
Are we alone? Where did we come from? These are just some of the questions astrobiologists hope to answer. And, even better, you can help the astrobiology community answer them, too! The field has been a pioneer in the use of citizen science – recruiting assistance from everyday people. Projects include SETI@Home (a screensaver that uses your computer’s idle processing power to search for signals in SETI radio data) and Planet Hunters (a website where users can help detect planets around other stars).
So, if you find the search for life in the universe as thrilling and fascinating as I do, then feel free to join in the fun! Who knows- you might just find help us find something.
And I’d finally have a good answer for “Have you found any yet?”
Tessa is a 28 year old PhD student, and perhaps the world’s only queer trans astrobiologist. A nerd going way back, her interests include science fiction, space exploration, sustainability, science communication, and feminism and gender. Her hobbies also include horseback riding, playing the flute, social dancing, knitting, and occasional attempts at writing fiction. She currently resides in Tempe, AZ with her even nerdier fiancee and a mastiff mix who thinks he’s a lapdog. She tweets occasionally @spacermase.