Can a computer predict the evolution of alien worlds? Roger Highfield, Science Director, talks to a newly awarded scientist about his quest to simulate how planets evolve to study climate change on Earth and spur the search for alien life.
Since the dawn of human consciousness, people have gazed at the skies, wondering if we are alone in the universe.
Now, thanks to an ambitious computer model of Earth developed by a team led by biogeochemist Prof Benjamin J.W. Mills, we may have an extraordinary new tool to work out the possibilities for life here and elsewhere in the universe.
By reconstructing Earth’s ancient climate and atmospheric evolution over billions of years in a computer, Prof Mills and his team at the University of Leeds are studying how planets can make the transition from a barren world to one teeming with living things.
An artist’s conception of Kepler-452 b, compared with Earth in terms of size. Kepler-452 b is an ‘Earth-cousin’ that orbits a star like our sun in the habitable zone, where liquid water could exist. Source: Wikimedia Commons CC-BY-SA-4.0.
He has already used his computer model to study key moments in Earth’s evolution, notably the origins of a breathable atmosphere, and is now extending its use to see what would happen if we transplanted Earth to alien solar systems.
One aim would be to understand more fully the Goldilocks zone – the region around a star where the temperature is considered just right, not too hot and not too cold, for liquid water to exist on a planet’s surface, making it potentially habitable for life as we know it.
Another would be to understand the conditions for complex life to evolve, that is life with the potential to be intelligent.
In recognition of his work, Professor Mills has been recognised in the 2025 Blavatnik Awards for Young Scientists as the UK Laureate in Physical Sciences & Engineering, celebrated last week in awards funded by the Blavatnik Family Foundation and The New York Academy of Sciences.
His computer model is a descendant of James Lovelock’s simple ‘Daisyworld’ computer model, which is in the museum’s collections, and posits that daisies blanket the Earth, black ones absorbing light and warming the planet, white ones reflecting light and cooling it.
Printout of the Daisyworld programme developed by James Lovelock. Daisyworld was the computer model of how Gaia could work on a simplified planet: black daisies (represented by ‘#’) absorb light, warming the planet, while white daisies (shown by ‘.’) reflect light. Together they keep the planet’s temperature in balance.
The white flowers thrive when the world becomes warmer, the black ones when it becomes cooler. As the temperature rises, white daisies proliferate until they reflect so much light that the temperature starts to fall, causing the black daisies to multiply, and so on.
Originally developed as a simple model to show how the Earth and its life can interact to be self-regulating, Daisyworld can also show complex behaviour, such as tipping points.
By comparison, the Leeds computer model can simulate global climate in three dimensions, such as the circulation of the oceans and atmosphere, along with the effects of life, though ‘our model does stem from Daisyworld,’ he said.
However, the latest versions of these climate computer models are too big to run simulations over periods of billions of years. Instead, the Leeds team augmented this approach with artificial intelligence, which had been trained on data from movies, to fill in the gaps.
To interpolate between climate model predictions at routine intervals – to reveal patterns of heat, cold, rainfall and so on in ancient climates with various levels of oxygen, carbon dioxide or whatever – the team used an AI ‘emulator’ to fill in the blanks.
Water-worlds are common – exoplanets may contain vast amounts of water similar to Earth, artist concept. Credit: NASA
The initial version of their model extended an earlier type of ‘emulator’ first developed by Géosciences Environnement Toulouse, CNRS, Toulouse, France, to study ‘what if?’ climate scenarios. Prof Mills recently received funding from the European Research Council and UK Research and Innovation to create a second-generation model of how our planet works.
The Leeds team has used their Earth evolution model to study the evolution of our home world’s oxygen levels, which went from zero billions of years ago to a breathable atmosphere today. ‘Nobody had run this type of computer model that long, so it was really unclear what the processes were,’ he said.
Microbes began producing oxygen billions of years ago, but Earth’s atmosphere took 80% of its history to become breathable. The model reveals why: chemical cycling between continental crust, oceans, and atmosphere was a slow but essential process that paved the way for oxygen-producing plants and forests to elevate oxygen levels to where they are today.
The model can also shed light on a deeper issue. Despite record elevated temperatures on brief human timescales today, Earth’s climate is relatively cold – gaze back at our geological past and you find a lot of evidence of warm climates. ‘We have been trying to understand why the Earth is the temperature it is,’ he said.
The rare periods where it was cold enough to form permanent polar ice caps are associated with low levels of CO2 in the atmosphere reducing the greenhouse effect. The Leeds team used their model to explain these changes in CO2 levels in the atmosphere over the past 420 million years.
A key difference from previous models was that the Leeds model took account of the changing position of the continents. The model’s results best matched the observed geological records of temperature, CO2 levels and geography of ice caps when they included both the effects of rock weathering, which involves chemical reactions that remove CO2 from the atmosphere, and changes in CO2 released from volcanoes.
Their advanced Earth Evolution Models do not just reveal our own planet’s history – they can also provide a powerful framework for predicting the hospitability of alien worlds, for instance those orbiting a red dwarf star, which is cooler than our own sun.
By simulating the potential for the rise and fall of oxygen on exoplanets, for example, his team hopes to identify those with the right physical makeup or chemical signatures for habitability, as James Lovelock once did for Mars ,to help focus current efforts to find life on exoplanets.
They are interested in the most studied planetary system, aside from our own solar system, which lies about forty light-years away – the seven rocky exoplanets orbiting the TRAPPIST-1 star, all of which have the potential for water on their surface.
Illustration showing what the hot rocky exoplanet TRAPPIST-1 b could look like. TRAPPIST-1 b, the innermost of seven known planets in the TRAPPIST-1 system, orbits its star at a distance of 0.011 AU, completing one circuit in just 1.51 Earth-days. Source: NASA, ESA, CSA, J. Olmsted (STScI), T. P. Greene (NASA Ames), T. Bell (BAERI), E. Ducrot (CEA), P. Lagage (CEA)
Already their work suggests that, for complex life to emerge, such as animals, it is important for a world to have continents. Now they are asking how big those continents should be, how much water an alien planet needs, the impact of tidal locking (when the planet does not rotate) and even catastrophes. ‘I have just come out of a meeting with a master’s student where we were firing different sized asteroids at the model to see what happened to the biosphere,’ he added.
By doing this, they are trying to recreate the K–T extinction, the mass extinction of three-quarters of the plant and animal species on Earth, the one that heralded the decline of the dinosaurs and the rise of mammals.
Another application of the model is to help understand the possible impacts of geoengineering, the intentional alteration of the planetary environment to counteract climate change caused by human activity.
‘We are trying to simulate longer term geoengineered climates, up to 200 million years into the future,’ he said. By projecting climate change long into the future, this model may not only help us explore the possibilities for alien life but also reveal how long Earth’s biosphere can support life before climate change pushes it to the brink of extinction.
A new Space gallery will open in autumn 2025 in the Science Museum’s West Hall and will bring together many remarkable objects, including the Apollo 10 Command Module and Soyuz descent module.
Roger Highfield
Roger Highfield is the Science Director at the Science Museum Group, a member of the UK's Medical Research Council and a visiting professor at the Dunn School, University of Oxford, and Department of Chemistry, UCL. He studied Chemistry at the University of Oxford and was the first person to bounce a neutron off a soap bubble. Roger was the Science Editor of The Daily Telegraph for two decades, and the Editor of New Scientist between 2008 and 2011. He has written or co-authored ten popular science books, most recently Stephen Hawking: Genius at Work, and has had thousands of articles published in newspapers and magazines.
Roger has written 110 posts
Categorised
Sustainability, Our museum group, Science in the news