How The James Webb Space Telescope will See Oxygen in Alien Atmospheres

The Cosmic Companion
Jan 6 · 4 min read

As astronomers examine the atmospheres of planets orbiting other stars, a new method of detecting oxygen, developed at the University of California Riverside, could provide evidence for worlds that may harbor life.

Astronomers currently know of more than 4,000 exoplanets, orbiting stars other than our own Sun. Many of these are found in the habitable — or Goldilocks — zone around their parent stars, where temperatures are neither too warm, nor too cold, for water to pool on their surface, potentially forming rivers, lakes, and oceans. However, no one has yet found a world where life has taken hold.

Here on Earth, the presence of lifeforms has filled our atmosphere with vast concentrations of oxygen — around 20 percent — far more than our planet would possess, were it devoid of life. This oxygen is the result of photosynthesis, carried out by algae, plants, and cyanobacteria.

Astronomers may soon be able to detect oxygen in the atmospheres of distant exoplanets. This could be the signs of life — or heating that could doom large water worlds like this one. Image credit: Simulation by The Cosmic Companion/Created in Universe Sandbox.

Because of this, some astronomers are hoping that abnormal levels of oxygen might act as a telltale sign of life — even primitive life — on other worlds. Using the upcoming James Webb Space Telescope, researchers at UC Riverside believe they have developed a new technique capable of seeing signs of oxygen molecules colliding with each other in the atmospheres of distant worlds.

“Before our work, oxygen at similar levels as on Earth was thought to be undetectable with Webb. This oxygen signal is known since the early 1980s from Earth’s atmospheric studies but has never been studied for exoplanet research,” said Thomas Fauchez of NASA’s Goddard Space Flight Center.

Wanted: Alive or Dead

Conceptual image of water-bearing (left) and dry (right) exoplanets with oxygen-rich atmospheres. Crescents are other planets in the system, and the red sphere is the M-dwarf star around which the exoplanets orbit. The dry exoplanet is closer to the star, so the star appears larger. Image credit: NASA/GSFC/Friedlander-Griswold

As oxygen molecules collide, they block a percentage of the infrared light that would normally be recorded from being seen by telescopes. Examination of the patterns recorded in the data can determine the chemical composition of the alien atmosphere.

Researchers at NASA and UC Riverside collaborated together, calculating the amount of this infrared light that would be blocked by collisions.

One challenge (and opportunity) with this study is that life is not the only source of atmospheric oxygen. Many chemical reactions also produce oxygen as a byproduct. Under some conditions, this gas can build up, making it appear that life could exist, even when the world is barren of life.

The James Webb Space Telescope will be able to carry out observations of exoplanets with the extreme precision needed to test the atmospheres of alien worlds searching for the telltale signs of life. Video credit: James Webb Space Telescope.

The new detection process is capable of finding oxygen in the atmospheres of exoplanets, regardless of whether life exists on the world, or if the gas is created thought chemical or geological processes.

Water worlds which come too close to their Sun, or buildup heat from a runaway greenhouse effect (like what happened on Venus) can lose their oceans to space. When this happens, radiation breaks apart the water molecules, into hydrogen and oxygen. The hydrogen, being the lightest of all elements, quickly escapes to space, leaving behind oxygen. This gas can build up, creating the illusion that lifeforms might populate the planet.

“Oxygen is one of the most exciting molecules to detect because of its link with life, but we don’t know if life is the only cause of oxygen in an atmosphere. This technique will allow us to find oxygen in planets both living and dead.” Edward Schwieterman, an astrobiologist at UC Riverside stated.

Other techniques will be required to scour the data, looking for worlds where the gas is the result of life, or chemical and geological causes.

The James Webb Space Telescope, due for launch in March 2021, will be the first spacecraft capable of studying the atmospheres of exoplanets in great detail. The NASA-designed spacecraft is expected to discover thousands of new alien worlds during its operational lifetime.

This novel method of finding oxygen in the atmospheres of distant worlds was profiled in the journal Nature Astronomy.

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