The James Webb telescope has proven it can detect signs of life in alien atmospheres!

Although the Earth is the only known place in the universe where there is life, the discovery of life outside of it is the main goal of modern astronomy and planetary science.

Chris Impey, Distinguished Professor of Astronomy at the University, and Daniel Abbey, Professor of Astronomy and Planetary Science at the University of Arizona, teach exoplanets and astrobiology. Largely thanks to next-generation telescopes like James Webb, researchers like them will soon be able to measure the chemical composition of planetary atmospheres around other stars.

Life can exist in the solar system where there is liquid water, such as in aquifers on Mars or in the oceans of Jupiter’s moon Europa. However, the search for life in these places is very difficult, as they are difficult to access, and the detection of life requires sending a probe to return physical samples.

Many astronomers believe that there is a strong possibility that life could exist on planets orbiting other stars, and that this is probably where life first originated.

Theoretical calculations show that there are about 300 million potentially habitable planets in the Milky Way alone, and many more habitable Earth-sized planets only 30 light-years from Earth – galaxies in the neighborhood of humanity.

So far, astronomers have discovered more than 5,000 exoplanets, including hundreds of potentially habitable planets, using indirect methods that measure how a planet affects its closest star. These measurements may provide astronomers with information about the exoplanet’s mass and size, but little more.

To detect life on a distant planet, astrobiologists will study starlight that has interacted with the planet’s surface or atmosphere. If the atmosphere or surface is altered by life, the light may carry a clue called a “biosignature”.

During the first half of its existence, the Earth had an atmosphere without oxygen, although simple single-celled life existed on it. The biometric footprint of the Earth in this early era was very weak. The situation changed dramatically 2.4 billion years ago, when a new family of algae appeared.

And the algae used a process of photosynthesis that produced free oxygen—oxygen that is not chemically bonded to any other element. Since that time, the earth’s oxygenated atmosphere has left a strong and easily detectable life imprint on the light passing through it.

When light reflects off the surface of a material or travels through a gas, certain wavelengths are more likely to remain in the gas or on the surface of the material than others. This selective matching of the wavelengths of light is what causes the different colors of objects. And the leaves are green because chlorophyll is especially good at absorbing light in red and blue wavelengths. When light hits the paper, the red and blue waves are absorbed, leaving mostly green light reflected back into your eyes.

The nature of light loss is determined by the specific composition of the material with which the light interacts. For this reason, astronomers can learn something about the composition of an exoplanet’s atmosphere or surface by measuring the specific color of light coming from the planet.

This method can be used to detect the presence of certain atmospheric gases associated with life, such as oxygen or methane, because these gases leave very specific fingerprints on light. It can also be used to detect strange colors on a planet’s surface.
On Earth, for example, chlorophyll and other pigments and algae used in photosynthesis use light at specific wavelengths.

These pigments produce characteristic colors that can be detected with a sensitive infrared camera. And if you see this color reflecting off the surface of a distant planet, it probably indicates the presence of chlorophyll.

It takes an incredibly powerful telescope to detect these subtle changes in light from a potentially habitable exoplanet. Currently, the only telescope capable of such a feat is the new James Webb Space Telescope.

When James Webb began his science career in July 2022, he measured the spectrum of the gas giant exoplanet WASP-96b. The spectrum showed the presence of water and clouds, but a large, hot planet like WASP-96b is unlikely to harbor life.

However, these early data show that James Webb is able to detect faint chemical signals in the light of exoplanets.

In the coming months, the telescope will point its mirrors at TRAPPIST-1e, a potentially habitable Earth-sized planet just 39 light-years from Earth.

James Webb can search for biometrics by studying planets as they pass in front of their stars and capturing starlight as it streams through the planet’s atmosphere. But Webb wasn’t designed to search for life, so the telescope can only explore a few nearby potentially habitable worlds.

It can also detect changes in the levels of carbon dioxide, methane, and water vapor in the atmosphere. Although certain combinations of these gases may indicate the presence of life, the James Webb telescope cannot detect the presence of unbound oxygen, which is the strongest sign of life.

Pioneering concepts for future and even more powerful space telescopes include plans to block out the bright light of Earth’s parent star to detect starlight reflected off the planet. This idea is like using your hand to block out sunlight so you can see things better from a distance.

And future space telescopes could use small internal masks to do this, or a large parachute-like spacecraft. Once the starlight is blocked, it becomes much easier to study the light bouncing off the planet.

Also currently under construction are three massive ground-based telescopes that will be able to search for biometric fingerprints: the Giant Magellanic Telescope, the Thirty Meter Telescope and the European Very Large Telescope. Each of them is much more powerful than telescopes on Earth, and although the Earth’s atmosphere distorts the light of stars, these telescopes can probe the atmospheres of nearby worlds in search of oxygen.

Even with the most powerful telescopes in the coming decades, astrobiologists will only be able to detect powerful biosignatures produced by worlds completely altered by life.

Unfortunately, most of the gases emitted by terrestrial life can also be produced by non-biological processes – cows and volcanoes emit methane. Photosynthesis produces oxygen, but sunlight also produces it when it splits water molecules into oxygen and hydrogen.

And there’s a good chance astronomers will find some false positives when looking for distant life. To rule out false positives, astronomers need to study an interesting planet well enough to understand whether its geological or atmospheric processes can mimic a biosignature.

And the next generation of exoplanet research could overcome the huge barrier of evidence needed to prove the existence of life. The first release of data from the James Webb Space Telescope gives us a glimpse of the exciting progress that is coming soon.

Source: Science Alert.