Ultraviolet light may have played a critical role in the emergence of life on Earth and could be a key to finding life elsewhere in the universe, a study led by an Indian-origin scientist at Harvard suggests. The study found that red dwarf stars might not emit enough ultraviolet (UV) light to kick-start the biological processes most familiar to our planet.
For example, certain levels of UV might be necessary for the formation of ribonucleic acid, a molecule necessary for all forms of known life. “It would be like having a pile of wood and kindling and wanting to light a fire, but not having a match,” said Sukrit Ranjan of the Harvard-Smithsonian Center for Astrophysics (CfA) in the US.
“Our research shows that the right amount of UV light might be one of the matches that gets life as we know it to ignite,” said Ranjan. Researchers focused on red dwarf stars, which are smaller and less massive than the Sun, and the planets that orbit them. Recently, several planetary systems with potential habitable zones, where liquid water could exist, have been discovered around red dwarfs including Proxima Centauri, TRAPPIST-1, and LHS 1140.
Using computer models and the known properties of red dwarfs, the researchers estimate that the surface of rocky planets in the potentially habitable zones around red dwarfs would experience 100 to 1,000 times less of the UV light that may be important to the emergence of life than the young Earth would have. Chemistry that depends on UV light might shut down at such low levels, and even if it does proceed, it could operate at a much slower rate than on the young Earth, possibly delaying the advent of life.
“It may be a matter of finding the sweet spot,” said Robin Wordsworth of the Harvard School of Engineering and Applied Science. “There needs to be enough ultraviolet light to trigger the formation of life, but not so much that it erodes and removes the planet’s atmosphere,” said Wordsworth, co-author of the study published in The Astrophysical Journal. Previous studies have shown that the red dwarf stars in systems such as TRAPPIST-1 may erupt with dramatic flares in UV.
If the flares deliver too much energy, they might severely damage the atmosphere and harm life on surrounding planets. On the other hand, these UV flares may provide enough energy to compensate for the lower levels of UV light steadily produced by the star, researchers said.