Scientists from the University of Cambridge and the MRC Laboratory of Molecular Biology, UK, have identified a group of exoplanets where the same chemical conditions that may have led to life on our planet exist.
This artist’s concept depicts one possible appearance of Kepler-452b, the first near-Earth-size world to be found in the habitable zone of star that is similar to our Sun. Image credit: NASA Ames / JPL-Caltech / T. Pyle.
The researchers 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.
“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, where the UV light powers a series of chemical reactions that produce the building blocks of life,” they said.
The team identified a range of planets where the UV light from their host star is sufficient 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. It brings us just a little bit closer to addressing the question of whether we are alone in the Universe,” said Dr. Paul Rimmer, a postdoctoral researcher at Cambridge’s Cavendish Laboratory and the MRC Laboratory of Molecular Biology.
Dr. Rimmer and colleagues plotted the amount of UV light available to planets in orbit around different 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.
Cool stars, on the other hand, do not produce enough light for these building blocks to be formed, except if they have frequent powerful solar flares to jolt the chemistry forward step by step.
Planets that both receive enough light to activate the chemistry and could have liquid water on their surfaces reside in what the researchers have called the abiogenesis zone.
Among the known exoplanets which reside in the abiogenesis zone are several planets detected by NASA’s Kepler Space Telescope — including Kepler 452b, an exoplanet that has been nicknamed Earth’s ‘cousin’ — although it is too far away to probe with current technology.
Of course, it is also possible that if there is life on other planets, that it has or will develop in a totally different way than it did on Earth.
“I’m not sure how contingent life is, but given that we only have one example so far, it makes sense to look for places that are most like us,” Dr. Rimmer said.
“There’s an important distinction between what is necessary and what is sufficient. The building blocks are necessary, but they may not be sufficient: it’s possible you could mix them for billions of years and nothing happens. But you want to at least look at the places where the necessary things exist.”
According to recent estimates, there are as many as 700 million trillion terrestrial planets in the observable Universe.
“Getting some idea of what fraction have been, or might be, primed for life fascinates me,” said co-author Professor John Sutherland, from the MRC Laboratory of Molecular Biology.
“Of course, being primed for life is not everything and we still don’t know how likely the origin of life is, even given favorable circumstances — if it’s really unlikely then we might be alone, but if not, we may have company.”
The team’s work is published in the journal Science Advances.
_____
Paul B. Rimmer et al. 2018. The origin of RNA precursors on exoplanets. Science Advances 4 (8): eaar3302; doi: 10.1126/sciadv.aar3302
