In our last inspirational scientist blog, Dr Andrew Conway Morris, MRC Clinician Scientist at the University of Cambridge, told us how he developed a test to diagnose pneumonia. In the sixth instalment of the series Dr Ed Gillen describes his work searching for life on exoplanets.
‘By detecting planets orbiting other stars (exoplanets) we can learn about planetary systems, how they form and evolve, and maybe one day discover signs of life on another planet like the Earth’
Searching the night sky
If you look up on a cloudless night, you can see about 4,500 stars in the night sky. However, these are only the brightest stars in the sky – there are many, many more. In our galaxy, the Milky Way, we estimate there are around 100 thousand million stars…and we think there are billions of galaxies in the universe. That’s a lot of stars!
Our own star, the Sun, hosts a planetary system around it (the Solar System), which contains eight planets including the Earth. Although we do not believe that every star in our galaxy has planets orbiting it, we do think that there may be as many planets as there are stars. By detecting planets orbiting other stars (exoplanets) we can learn about planetary systems, how they form and evolve, and maybe one day discover signs of life on another planet like the Earth.
Exoplanets
Over the last 25 years, we have discovered more than 4,000 exoplanets and expect to find many more. We have discovered that exo-planetary systems come in all shapes and sizes. For example, we have found planets like Jupiter that orbit their stars in only a few days (our own Jupiter takes 12 years to orbit the Sun). We have found tightly packed systems of several planets that all orbit their star in less time than it takes Mercury to complete one orbit of the Sun. Perhaps most surprising of all is that planets with sizes between those of the Earth and Neptune are the most common, yet we have no such planets in the Solar System.
Measuring for signs of life on exoplanets
I am an astronomer who searches for exoplanets to determine their properties, better understand planetary systems, and maybe one day detect signs of life on a planet outside our solar system. I search for planets using the ‘transit’ method: if, as seen from Earth, a planet passes in front of (transits) its star during its orbit, the planet blocks out some of the star’s light, which causes the star to appear slightly fainter while the planet passes in front of it. This repeats with every orbit of the planet.
We can estimate the orbital period and size of the planet from how often these dips occur and by how much the star appears to get fainter. We can then measure the mass of the planet by taking spectra of its star and measuring the Doppler shift in the star’s spectral lines, which is caused by the gravitational pull of the planet as it orbits. Finally, we can study the atmosphere of the planet: when the planet transits its star, a small amount of the star’s light passes through the planet’s atmosphere on its path to reach us.
Molecules in the planet’s atmosphere leave ‘fingerprints’ on this light, which we can identify and use to understand the composition of the planet’s atmosphere. Currently, this is possible for gaseous planets like Jupiter and Neptune, but we hope to be able to do the same for Earth-like planets in the not too distant future and, who knows, maybe even detect signs of life.
Choosing science
I always enjoyed science at school, and found astronomy fascinating. However, becoming a scientist is something that came from pursuing the subjects I enjoyed most, rather than something I set out to become. At school, my favourite subjects were physics and ancient history. I decided to do physics at university and took as many astronomy options as I could, and graduated with a degree in physics with astronomy. From there, I began a PhD and enjoyed it enough to pursue exoplanet research as a career…and I’m still enjoying it today.
How to become a professional scientist
Follow the subjects you enjoy most, maintain a sense of curiosity about how the natural world and wider universe works, and remember that, through scientific research, you can help improve that world. You might already know the specific area on which you want to focus or it may be that this only becomes apparent over time, but you will find your passion. You can make a difference. Finally, science is a very international discipline, so it’s offers great opportunity to travel, and to work in other countries and experience different cultures.
About the author
Dr Ed Gillen is an astronomer and exoplanet scientist. He spent five years in Cambridge as a postdoctoral researcher. Dr Gillen is now a Lecturer at Queen Mary University of London. He is also a visitor in the Physics Department at Cambridge. Dr Gillen is a keen advocate of exoplanets and is always happy to engage with the public about astronomical topics.
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