News & blog Are We Alone in the Universe? Q&A with Sarah Rugheimer Written by Alan Barker, Freelance Writer, British Science Festival We know that ultraviolet radiation can give us sunburn. But it can also be traced back to the origins of life itself. Dr Sarah Rugheimer, at the University of Oxford, uses UV to look for signs of life on exoplanets – planets orbiting stars beyond our solar system. Dr. Rugheimer is delivering the Rosalind Franklin Award Lecture at this year’s British Science Festival. She spoke to Alan Barker about her work. Dr Sarah Rugheimer, at the University of Oxford, uses UV to look for signs of life on exoplanets It seems like one of the ultimate questions: is there life beyond the Earth? Yes, this single question is why I get out of bed in the morning. We’ve been asking the question for a long time. We have, but with no real prospect of finding objective evidence. And then, back in the 1960s, the SETI project started to look for evidence of intelligent life. No luck so far. The radios have been silent. We’ve heard no ‘Hello Earthlings’ call from the cosmos! But life doesn’t need to be using technology for us to detect it. You know that picture of the Earth taken from Voyager 1 in 1990 – Carl Sagan’s pale blue dot? I love that image. It shows us what our planet might look like to an alien astronomer. And she could tell that life was on our planet, because in Earth’s reflected light she’d see signatures of oxygen and methane. 'Pale Blue Dot' (Source: NASA) Why would they betray the existence of life? Because together these two gases wouldn’t exist on a lifeless world. On Earth, they’re produced in combination by microbial life. Without a constant, high flux of both gases from biological processes, oxygen would quickly destroy methane and they would be removed from the atmosphere. Geology alone wouldn’t produce detectable concentrations of these gases. It’s the combination of oxygen and methane in an atmosphere that constitutes a strong biosignature – one possible sign that life is present. So you look for that particular combination in an exoplanet’s atmosphere? It’s our best hope of finding life outside our solar system, though there are other biosignature gases. Such as? Nitrous oxide: laughing gas, you may have had it at the dentist. Dr. Clara Sousa-Silva at MIT recently proposed phosphine as a potential biosignature gas on a world without oxygen. There are others: dimethyl sulphide, for instance, and methyl chloride. And how do you look for these biosignatures? You’d look at the light from a planet. A spectrum is basically a light fingerprint. Just as every person has a unique fingerprint, so light interacts with different gases in an atmosphere to create a unique spectrum of those molecules. How does ultra-violet light fit into all this? I model how these biosignatures change, depending on the host star’s temperature and activity. Stars come in many sizes and have different UV environments. High energy UV light breaks apart some biosignatures, but the same UV radiation fosters the reactions that form biosignature gases like ozone – and we use ozone as a proxy for oxygen, since it’s easier to detect. It can’t be easy detecting any light from a planet so far away. It’s not. A star like our Sun outshines an Earth-like planet by a factor of over a billion. For every billion photons we get from a star, we get just one from that habitable planet. It’s a bit like trying to detect a firefly while staring directly into a spotlight. And imagine that the spotlight is in the US, and you’re observing from the UK. That’s how difficult it is. Is it possible? Not yet. But we are close and that’s what’s exciting. NASA plans to launch the James Webb Space Telescope in 2021 and large ground-based observatories will also be coming online in the 2020s. These telescopes will have the capacity to detect biosignatures from a few of the closest habitable exoplanets. It is extremely difficult to detect light from far away planets How does your work contribute to these projects? My work simulates what these spectra would look like. Just because some biosignatures are more abundant in an atmosphere that doesn’t mean they’re easier to detect. When we’re building these telescopes, it’s vital to ensure that we’re looking at the right wavelengths of light, and that we’re observing for long enough and at a high enough resolution to tease out these spectral fingerprints. How optimistic are you that we’ll find these biosignatures? Well, there are probably 40 billion earth-like planets in our galaxy alone. And we know of billions of galaxies, right? But it’s no good just speculating. Is life a cosmic imperative, popping up on every habitable planet in the universe? Or is it exceedingly rare, arising only under the strictest of conditions? We just don’t know. But for the first time in human history, we have the scientific capability to answer this question. And whatever the answer is, it’s going to have far-reaching consequences for how we view ourselves in a cosmic context. So we might be the last generation of lonely earthlings? I hope so! Sarah Rugheimer delivers Are We Alone in the Universe? at the British Science Festival on Tuesday 10 September at 11:00. Read more about her lecture and book tickets here.