If life does exist anywhere else in the universe, it may only be fleeting. Now scientists are researching how signs of life might look on dying planets.
Astronomers have discovered hundreds of distant alien planets in the past two decades. Future missions could detect potential signs of life called biosignatures on those worlds, such as oxygen or methane in their atmospheres.
Astrobiologist Jack O'Malley-James at the University of St. Andrews in Fife, Scotland and his colleagues noted that biosignatures of life on Earth have not remained the same over time, but have altered considerably over its history. This led the researchers to speculate about how Earth and other planets might look in the future.
"Astrobiology as a field seems to put a lot more focus on the origins of life and how to find life beyond Earth, but less emphasis is put on the end of life, which is what got me interested in finding out more about how biospheres on other planets might meet their ends, and by extension, how long we could expect to detect life on a habitable planet over the course of its habitable lifetime," said O'Malley-James, the lead author of the study.
The scientists were testing a computer model of the climates and biospheres — the overall life — of possible exoplanets.
"That was when the idea came about to run this model forward in time to see when all water and all life would disappear from the planet," O'Malley-James said.
The Sun is a middle-aged star, currently about 4.6 billion years old. In the later stages of its evolution, about 2 billion to 3 billion years from now, the Sun will grow much hotter, leading to much higher surface temperatures on the future Earth and thus far harsher environments for any last life to grow and survive on the planet.
The research team modeled the biosignature gases Earth's biosphere would generate up to 2.8 billion years from the present.