Aug 2, 2018 - Science

Scientists target exoplanets where life could form as it did on Earth

Artist's concept above shows the Pluto system from the surface of one of its smaller moons 2015. Photo: Universal History Archive/UIG via Getty Images

A team of U.K.-based scientists have identified a group of planets outside our solar system that have similar chemical conditions that likely led to the formation of life on Earth.

The big picture: The scientists found a collection of planets with the potential to host water that also have stars positioned to potentially provide ideal conditions of both light and temperature that could set off the necessary chemical reactions to form life.

The new study, published this week in the journal Science Advances, represents one of several emerging approaches to narrowing down the list of candidate planets that could host life.

According to past research, life emerges from molecular precursors that include elements like lipids and amino acids that can go on to form DNA and RNA — necessary components to comprise life forms. However, such molecules can only emerge through specific conditions, including being exposed to ultraviolet (UV) light, the study found.

How they did it: With the goal of discovering which conditions are most important for developing the chemical building blocks to forming life, the scientists from the University of Cambridge and the Medical Research Council Laboratory of Molecular Biology conducted laboratory experiments to determine the speed at which the building blocks of life form through combinations of water, along with hydrogen cyanide and hydrogen sulfite ions. They varied the exposure to ultraviolet light as well as temperatures.

What they found: According to the study, experiments that were conducted while exposed to UV light kickstarted the chemical reactions necessary to form life, while the experiments run in the absence of such radiation could not form such compounds.

Upon discovering the ideal conditions of both light and temperature that cause RNA to form, the scientists identified the area around stars that display such conditions: The "abiogenesis zones." This area is defined in the study as "the zone in which a yield of 50% for the photochemical products is obtained, adopting the current UV activity as representative of the UV activity during the stellar lifetime and assuming a young Earth atmosphere."

  • The team then located exoplanets believed to be able to support water on the planet's surface, and matched those located within a star's abiogenesis zone.
  • The study notes that, among planets with high gas content that can also support water, "there is a tantalizing possibility that some of their larger moons may be primed for life."

Why it matters: "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 Paul Rimmer, the lead author of the study and an astrophysicist at Cambridge University, in a press release.

Sarah Rugheimer, an astronomer and astrobiologist who was not involved in the study, explained the significance of UV light: "UV has a bit of bad reputation in the origins community, and for good reason, it can break apart molecules and can be harmful for life as we know it," she told Axios.

"However it is also becoming increasingly clear that UV can drive some prebiotic pathways thought necessary for the origin of life," she said. "Ultimately we will need to measure the UV radiation of the host star to better understand the atmosphere and conditions for life on an exoplanet."

What they're saying: Stephen Kane, associate professor of astronomy and planetary astrophysics at the University of California, Riverside, who was not involved in the new study, said the methods used in this study differ from other approaches to finding exoplanets that might host life.

"Thus far calculations have concentrated on geophysical and climate considerations, in particular the potential presence of liquid water on the surface," he told Axios.

"The biological considerations expressed in this work are a natural progression for determining criteria for habitability and will hopefully provide a significant aid in selecting target planets in the search for biosignatures."

The bottom line: While this study does not prove life on other planets exists or will develop, it may make it easier for scientists to sort through the growing list of exoplanets in order to narrow down the candidates most likely to host life.

The study also cautions that it's possible that life on other planets could develop in a completely different way than it did on Earth.

"There’s an important distinction between what is necessary and what is sufficient," Rimmer said in the press release.

"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."
— Paul Rimmer, astrophysicist at Cambridge University
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