Written by Alan Barker, Freelance Writer, British Science Festival 

Dr Sarah Rugheimer is looking for signs of life on exoplanets – planets orbiting stars beyond our solar system. And she has some remarkable ways of doing it. Dr. Rugheimer – currently Hugh Price Fellow at Jesus College, Oxford – delivered the Rosalind Franklin Award Lecture at this year’s British Science Festival. Alan Barker was there.

Dr. Rugheimer delivered the Rosalind Franklin Award Lecture at this year’s British Science Festival.

Do you believe that life exists elsewhere in the universe? Nearly everyone at Dr Sarah Rugheimer’s Award Lecture did. I certainly raised my hand.

We so don’t want to be lonely.

Do the math. Our galaxy contains perhaps 40 billion Earth-like planets. And Hubble’s Ultra Deep Field images are filled with unimaginable numbers of galaxies. Surely, life must be abundant. And surely, we should look for it.

This image from Hubble’s Ultra Deep Field shows about 5,500 galaxies (Credit: NASA)

Dr Rugheimer has thought long and hard about the task. Running through her Award Lecture was the deep theme that in science, to paraphrase Richard Feynman, you must take great care not to fool yourself. And she’s not looking for heptapods; she’d be happy with evidence of microbes.

So, how to find the evidence?

First, find a suitable planet. We could look – and are doing so – at our own solar system; and since 1992, we’ve found over 4,000 exoplanets, circling other stars. Dr Rugheimer introduced us to TRAPPIST-1, a promising system of at least seven planets circling a star only 39 light years away. Life seems to need a surface, so we’d look for rocky planets; and it almost certainly needs water, which is a useful solvent for chemical reactions and – luckily – is abundant in the universe.

TRAPPIST-1 (Credit: NASA)

Second, look for biosignatures. The most likely would probably be a combination of oxygen and methane. In the 1960s, as Sarah explains in a recent New Scientist article, astronomers realised that, unless they were being pumped continuously into an atmosphere, these two gases would quickly destroy each other. A lifeless planet might contain one or the other; but only a planet teeming with life would have an atmosphere containing both.

To find that combination, we’d use spectra. The light from a host star alters as it passes through a planet’s atmosphere; the effects come out in the spectra, recorded as squiggly lines on a graph. (You can see some examples from Sarah’s own work here.) TRAPPIST-1 might give us no fewer than three candidate planets for this technique; in the words of the TRAPPIST-1 website, they “are the most optimal currently at our disposal.”

But capturing the light is tough. Imagine trying to detect a firefly, in front of a spotlight, 6,000 miles away. Dr Rugheimer reckons that capturing spectra from an exoplanet is several hundred times tougher.

The technological hurdles are being overcome. NASA’s James Webb Space Telescope is scheduled to launch in 2021; its relatively low-resolution observations will help quantify what Dr Rugheimer called ‘abundances of molecules’. Ground-based telescopes, including the European Southern Observatory’s Extremely Large Telescope, due to start operating in Chile in 2025, will give us hi-res information, allowing astronomers to distinguish individual compounds and even isotopes. That news, Sarah told us, blew her away: she never dreamed that such accuracy would be possible in her lifetime.

The second hurdle is interpreting the spectra. And once more, the potential for fooling yourself looms large. Most stars in our galactic neighbourhood are M stars: small red dwarfs, cool, faint and long-lived. And one in four of them may have habitable planets. (TRAPPIST-1 is a red dwarf.) But M stars are volatile, and their activity can wreak havoc with biosignatures.

The planet shown here, fourth from the TRAPPIST-1 star, is in the habitable zone (Credit: NASA-JPL/Caltech)

Which is where Dr Rugheimer’s work fits in. She models how high-energy ultraviolet radiation alters biosignatures, breaking some apart and fostering the reactions that might form others. Her work will help the new telescopes, when they come online, to observe at the right wavelengths, at the right resolution, for the right length of time.

Sarah’s key takeaway: you need multiple gases to assert the possible presence of life. When the announcement comes – as, she told us, it surely will – that we’ve discovered oxygen on an exoplanet, we’ll need to exercise caution. We must not let our sense of loneliness fool us.

And even if we can assure ourselves that we’ve found life, will we be satisfied? Perhaps the discovery will make us feel even more lonely. Who knows? The most remarkable thought conjured by her remarkable lecture is that, maybe, in a few years’ time, we’ll be in a position to answer that question.

Alan Barker is a writer, trainer and coach specialising in communication skills. He has been working with the British Science Association since 2015. Alan’s webinar, Storytelling for Scientists, is on the 3M YouTube channel.