Scientists have identified a group of planets outside our solar system that have the same chemical conditions that could have led to life on Earth.
The researchers, from the University of Cambridge and the Medical Research Council Laboratory of Molecular Biology (MRC LMB), found that the chances for life to develop on the surface of a rocky planet like Earth are connected to the type and strength of light given off by its host star.
Published in the journal Science Advances, the study suggests stars which give off sufficient ultraviolet (UV) light could kick-start life on their orbiting planets in the same way it likely developed on Earth.
Apparently, UV light powered a series of chemical reactions that produced the building blocks of life in the lead up to the creation of what we know as our planet today.
It brings us just a little bit closer to addressing the question of whether we are alone in the universe
The researchers identified a range of planets where the UV light from their host star was sufficient enough to allow these chemical reactions to take place, and that lie within the habitable range where liquid water can exist on the planet's surface.
"This work allows us to narrow down the best places to search for life," said Dr Paul Rimmer, the postdoctoral researcher, and the paper's first author. "It brings us just a little bit closer to addressing the question of whether we are alone in the universe."
The new paper is the result of an ongoing collaboration between the Cavendish Laboratory and the Medical Research Council Laboratory of Molecular Biology (MRC LMB), bringing together organic chemistry and exoplanet research. It builds on the work of Professor John Sutherland, a co-author on the current paper, who studies the chemical origin of life on Earth.
Stars around the same temperature as our sun emitted enough light for the building blocks of life to have formed on the surfaces of their planets
"I came across these earlier experiments, and as an astronomer, my first question is always what kind of light are you using, which as chemists they hadn't really thought about," added Rimmer.
"I started out measuring the number of photons emitted by their lamps, and then realised that comparing this light to the light of different stars was a straightforward next step."
The two groups performed a number of laboratory experiments to measure how quickly the building blocks of life can be formed from hydrogen cyanide and hydrogen sulphite ions in water when exposed to UV light. They then performed the same experiment in the absence of light.
"There is chemistry that happens in the dark: it's slower than the chemistry that happens in the light, but it's there," added senior author Professor Didier Queloz.
The same experiment run in the dark with the hydrogen cyanide and the hydrogen sulphite resulted in an inert compound which could not be used to form the building blocks of life, while the experiment performed under the lights did result in the necessary building blocks.
The researchers then compared the light chemistry to the dark chemistry against the UV light of different stars. They plotted the amount of UV light available to planets in orbit around these stars to determine where the chemistry could be activated.
They found that stars around the same temperature as our sun emitted enough light for the building blocks of life to have formed on the surfaces of their planets, and that both receive enough light to activate the chemistry. This, they concluded, means they could have liquid water on their surfaces, and thus life within them.
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