Kepler 452b
Study suggested exoplanets near sun-like stars could have life. Pictured, one possible appearance of the planet Kepler-452b, the first near-Earth-size world to be found in the habitable zone of a star that is similar to our sun. NASA/JPL-Caltech/T. Pyle

The search for potentially habitable exoplanets has been on for years. Scientists identified a number of Earth-like worlds that are far enough from their host stars to have liquid water and possibly life. However, as there are thousands of planets, with many in these so-called habitable or “goldilocks” zone, there is not enough information to launch a mission and zero in on a particular world.

Now, a new work looking at the fundamental chemistry required to kick-start primordial life has given us new insights into where to look.

Back in 2015, a group of researchers theorized that cyanide, a deadly poison, played a critical role in triggering the series of processes that formed basic and then complex life on Earth.

They conducted a series of experiments suggesting carbon from meteorites crashing on Earth reacted with nitrogen to form hydrogen cyanide, which then reacted with several other chemicals in the presence sunlight to produce the building the blocks of cells, including precursors to lipids, amino acids, and nucleotides.

The study drew immediate attention from researchers at Cambridge, England, who decided to apply that hypothesis into exoplanetary conditions.

"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," Paul Rimmer, one of the authors of the study, said in a statement. "I started out measuring the number of photons emitted by their lamps, and then realized that comparing this light to the light of different stars was a straightforward next step."

First, the researchers determined how much ultraviolet (UV) energy would be required for the job. For this, they conducted two experiments — with and without UV light — and witnessed the behavior of hydrogen cyanide and sulfite ions in water.

"We wanted to see how much light it would take for the light chemistry to win out over the dark chemistry," Didier Queloz, senior author of the study, added.

While the work conducted in dark didn’t produce any viable results, the test in lights, as demonstrated in 2015, produced compounds capable of kick starting the cycle of life. The researchers then compared that data with the light emitted by different stars and came to the conclusion that any star, which is as hot as the sun, can give away sufficient UV light to trigger the series of processes required for life on planets in its proximity.

Cooler stars might not be a strong match for such reactions, unless they’re emitting powerful flares from time to time, the group added.

Planets in the Abiogenesis zone
Diagram of confirmed exoplanets within the liquid water habitable zone Paul Rimmer

This basically means exoplanets sitting in the habitable zone of hot, sun-like stars could have both — water as well as the chemistry required for life. Many exoplanets identified by the Kepler mission sit in this so-called “abiogenesis zone,” including Kepler 452b — the exoplanet NASA dubbed as Earth’s “cousin” three years ago.

These worlds are still too far to be explored by an individual space mission, but NASA’s recently launched TESS exoplanet hunter and futuristic James Webb Space Telescope could provide more insight into these planets, including the possibility of life on or below their surface.

The study titled, "The origin of RNA precursors on exoplanets," was published Aug. 1 in the journal Science Advances.