Life needs more than a rocky planet able to support liquid water in order to develop just like it did on Earth. According to a 2015 study by researchers at the Medical Research Council (MRC) in Cambridge, U.K., it also needs ultraviolet light to kick-start a series of chemical reactions that lead to the formation of the three key ingredients in ribonucleic acid (RNA) — a close relative of DNA.
RNA is thought to be the first molecule of life able to carry information and to further the interaction of other molecules, thereby facilitating its own multiplication, notes Space.com.
Per the 2015 research, conducted by Prof. John Sutherland of the MRC’s Laboratory of Molecular Biology (LMB), UV light sparks the creation of the building blocks of life by fostering a reaction between hydrogen cyanide and other chemicals, producing the precursors to lipids, amino acids, and nucleotides.
All these “are essential components of living cells,” explains the University of Cambridge. In fact, this is how scientists believe life evolved here on Earth — from hydrogen cyanide mixed in our atmosphere by the combination of nitrogen and asteroid-delivered carbon.
Once released onto the planet’s surface, UV light coming from the sun powered its interaction with other elements, creating “the primordial soup from which all life on Earth originated,” notes the university.
The same recipe for making RNA precursors could hold true on alien planets orbiting in the habitable zone of their host stars, argues a new study, published today in the journal Science Advances.
The new work builds on Sutherland’s past findings and pinpoints a dozen of exoplanet candidates where life could have started just as it did on our planet. On the list are three exoplanets in the nearby TRAPPIST-1 system — TRAPPIST-1e, f, and g, the last of which might also have an atmosphere, as the Inquisitr previously reported. Other candidates include Kepler-452b and LHS 1140b, a super-Earth discovered last April, per the Inquisitr.
These are all rocky bodies residing in their star’s habitable zone, or “Goldilocks zone,” and are also showered with sufficient amounts of UV light to make possible the chemical reactions necessary for churning the building blocks of life.
Study lead author Dr. Paul Rimmer, affiliated with both the Cavendish Laboratory at Cambridge University and the MRC LMB, chimed in on the results.
“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.”
The exoplanets were selected following a rigorous list of criteria, including their size, the distance from their parent star and the amount of light they receive.
Once Rimmer noticed that UV light was essential to the production of RNA precursors, as discovered by Sutherland, he began calculating which stars with a similar temperature as our sun give off the same kind of UV light.
“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,” Rimmer said. “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.”
Since cooler stars don’t emit enough UV light to power the RNA-forming reaction unless they experience frequent flares, a temperature similar to that of the sun was the first of the prerequisites, explains Cambridge University.
Rimmer’s team started looking for exoplanets orbiting those stars that were both in the “Goldilocks zone” and in the size range of less than 1.4 times the radius of Earth. This is the reason why the closest and most famous exoplanet, Proxima b, didn’t make the cut, despite its documented potential to host life, as reported by the Inquisitr.
‘Light Chemistry’ Vs ‘Dark Chemistry’
To test out their theory, Rimmer and Sutherland devised a series of experiments meant to replicate the conditions on a sulfur-rich young planet blasted by various amounts of UV light. This helped them calculate the minimum requirement of ultraviolet radiation needed to spark the creation of RNA.
The tests revealed that, although some chemical reactions still go on in the dark, hydrogen cyanide and hydrogen sulphite ions in water only give rise to the building blocks of life when exposed to UV light.
“There is chemistry that happens in the dark: it’s slower than the chemistry that happens in the light, but it’s there,” said study senior author Prof. Didier Queloz, also from the Cavendish Laboratory. “We wanted to see how much light it would take for the light chemistry to win out over the dark chemistry.”
Of the listed exoplanets where life could ignite the same way it did on Earth, the strongest contender so far is Kepler-452b, hailed as Earth’s “cousin” and the exoplanet most similar to our home, the Inquisitr reported at the time of its discovery in 2015.