New research suggests that nitrous oxide, the chemical compound known as laughing gas that we use as a sedative and anaesthetic, could be a sign of life on planets beyond our solar system.
For astrobiologists, one question prevails among many that haunt humankind: Is there life beyond our planet?
While we have not directly observed “alien” life, scientists have been searching for water, organic matter, technology, or certain minerals and atmospheric gases to see whether there are any signs of past or present life in space where life could exist in the future.
However, almost all of these indicators, called biosignatures, are restricted to life as we know it. Our only point of reference is the Earth, so we search for life in space by searching for Earth-like conditions.
Researchers at the University of California, Riverside, joined by scientists from the NASA Goddard Space Flight Center and other institutions, suggest that nitrous oxide (N2O) has been off the radar as a potential biosignature gas because its concentration is currently low in Earth’s atmosphere.
“There’s been a lot of thought put into oxygen and methane as biosignatures. Fewer researchers have seriously considered nitrous oxide, but we think that may be a mistake,” said Eddie Schwieterman, lead-author of the paper and astrobiologist in UCR’s Department of Earth and Planetary Sciences.
N2O, better known as laughing gas, is a constituent of Earth's atmosphere that could be a viable evidence of life in exoplanets, or planets outside the solar system.
Abundance and detectability
One concern with considering N2O as a biosignature gas has been that it would be difficult to detect it from Earth with current technology.
With a direct link to the scarcity of the gas in Earth’s current atmosphere, this concern caused the gas to be seen as immaterial to scientific research.
However, Schwieterman suggests that “This conclusion doesn’t account for periods in Earth’s history where ocean conditions would have allowed for much greater biological release of N2O,” which would then leak into the atmosphere.
“Conditions in those periods might mirror where an exoplanet is today.”
Moreover, outside our solar system, there are stars like K-type and M-type dwarfs that produce a light spectrum that, compared to the sun, cannot effectively break up the N2O molecule.
Therefore, the researchers conclude, N2O could be found in detectable amounts in some exoplanets that harbour life.
A possible target for Webb
With the James Webb Space Telescope expected to collect data about the atmospheres of Earth-like planets revolving around the red dwarf star TRAPPIST-1, researchers suggest that one biosignature gas Webb should scan for is N2O.
“We wanted to put this idea forward to show it’s not out of the question we’d find this biosignature gas, if we look for it,” Schwieterman said.
The research team even determined how much of the gas would be produced by life in an Earth-like planet and estimated how much N2O the planet’s atmosphere would contain by modelling it orbiting around different types of stars.
“In a star system like TRAPPIST-1, the nearest and best system to observe the atmospheres of rocky planets, you could potentially detect nitrous oxide at levels comparable to CO2 or methane,” Schwieterman said.