Astrobiology is a science concerned with the search for life beyond Earth, as well as the origins, limits and future of life in the Universe. It is truly interdisciplinary in scope, encompassing astronomy, biology, chemistry, geophysics and many other disciplines. In my role I work as a bridge between astronomy and biology. My research focuses on using Earth as a template for exploring how life would interact with the atmospheres and surfaces of habitable exoplanets. This involves using Earth-like ecosystems as a basis for envisioning possible extraterrestrial biospheres by finding the overlaps between the environments life has adapted to on Earth (or to which evolutionary biology suggests that life could adapt given the right 'push') and the environments we predict for potentially habitable exoplanets. I then use these alien-but-familiar biospheres as components of climate or photochemistry models to simulate how less Earth-like life might be remotely detectable on specific, or hypothetical, exoplanets.
One aspect of this involves studying the impact stellar evolution may have on the biospheres of planets in the habitable zone of their star (the region around a star where temperatures are just right for liquid water to exist). These impacts include how life would adapt to changing conditions over geological time, how remotely detectable biosignatures would change and, ultimately, when all life on a planet would come to an end. Another aspect of my research involves investigating how frequently-flaring, active red dwarf stars would affect the biologically harmful ultraviolet radiation fluxes on any closely orbiting habitable zone rocky planets, as well as the mechanisms life could employ to survive such harsh environments.
It is important to know how the signs of life change over a planet’s habitable lifetime, or how they could differ for the full range of possible habitable environments that could exist on rocky exoplanets. Near-future habitable exoplanet discoveries will not all be similar to the present-day Earth. Some may host younger, simpler biospheres, others may host older, dying biospheres, while others may host more alien biospheres, hardened to high radiation levels, or other extremes. Different subsets of the distribution of possible habitable environments could lead to life that is very different to the life we see on Earth today. Consequently, these scenarios will produce very different sets of biosignatures. Knowing what signatures to look for from these worlds will increase the chances of confirming the presence of life on a planet beyond our solar system.
These types of project require the blending together of knowledge from a wide range of fields, such as stellar evolution, planetary geophysics, atmospheric physics, biological evolution, environmental biology and ecology. Putting strands of different science together in this way to imagine alien worlds leads to new and novel ideas, as well as some very interesting collaborations. Perhaps even more importantly, it can give us new perspectives on our own planet and the fragile interplay of life, geosphere and atmosphere that makes it not just habitable, but home.
The specifics of my research themes and associated publications are detailed in the Research Themes section below.
Earth is the only inhabited planet we know of, which makes it our only template for how a living world works. The geological record provides a guide to how a young habitable planet may look and how it may evolve with time. Earth today shows us how a middle-aged world with a rich biosphere operates. But what about the later stages of a living planet's lifetime? By looking at how stars like the Sun age, we can predict what conditions might be like on Earth millions, hundreds of millions and even billions of years from now. This gives us clues about what types of life could and could not live there and ultimately tells us how long a habitable planet can actually remain habitable.
Sunlight is an abundant energy source on Earth's surface that life very quickly figured out how to use as a fuel. On another habitable world, star light is likely to be an equally rich free energy source. So, if life were to evolve on another planet, it would not be surprising if it came up with something like photosynthesis to take advantage of this free food. Photosynthesis has the power to change atmospheric composition and vegetation itself has unique reflectance properties that can change the appearance of a planet's surface. By exploring how plant life might work on other worlds, we bring ourselves a step closer to knowing how to find some of the biggest fingerprints that life can leave behind on a planet.
Red dwarf stars (M type stars) are the most common type of star in the galaxy and most of the habitable planets we know about (to date) have red dwarf suns. So understanding how life would work in these systems is important for guiding our first biosignature-hunting missions. However, these stars, though cooler and fainter than the Sun, provide some interesting challenges for life as we know it in the form of large stellar flares and harsh ultraviolet radiation. Looking at how life on Earth copes under similar pressures can tell us a lot about what we may find on these alien worlds.
Questions at the boundaries between different scientific disciplines lead to some interesting research topics, including the origins of life, the survival of microbial life on the planets and moons of the Solar System, the search for intelligent life in the universe and even the ultimate fate of humanity and what it means to be an intelligent species with an understanding of the complexity of a living planet.