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JWST has shown that it can detect life signatures on exoplanets

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The conversationThe ingredients for life are spread throughout the universe. While Earth is the only known place in the universe with life, detecting life outside of Earth is a main goal from modern astronomy and planetary science.

We are two scientists studying exoplanets and astrobiology. Thanks in large part to next-generation telescopes like James Webb, researchers like us will soon be able to measure the chemical composition of the atmospheres of planets around other stars. The hope is that one or more of these planets will have a chemical signature of life.

There are many known exoplanets in habitable zones – orbits not too close to a star where the water boils off but not so far away that the planet is frozen solid – as marked in green for both the solar system and the Kepler-186 Star system with its planets labeled b, c, d, e and f. Credit: NASA Ames/SETI Institute/JPL-Caltech/Wikimedia Commons

Habitable exoplanets

life could exist in the solar system where there is liquid water – like in the aquifers on Mars or in the oceans of Jupiter’s moon Europa. However, finding life in these locations is incredibly difficult as they are difficult to reach and detection of life would require sending a probe to return physical samples.

Many astronomers believe there is good chances that life exists on planets orbiting other starsand it’s possible that’s where Life is found first.

Theoretical calculations suggest that it is around 300 million potentially habitable planets alone in the Milky Way and several habitable Earth-sized planets within just 30 light-years from Earth—essentially humanity’s galactic neighbors. So far, astronomers have discovered over 5,000 exoplanetsincluding hundreds of potentially habitable, with indirect methods which measures how a planet affects its nearby star. These measurements can give astronomers information about an exoplanet’s mass and size, but not much more.

Each material absorbs specific wavelengths of light, as illustrated in this chart, which shows the wavelengths of light most easily absorbed by different types of chlorophyll. Photo credit: Daniele Pugliesi/Wikimedia Commons, CC BY-SA

In search of biosignatures

To discover life on a distant planet, astrobiologists will study the available starlight interacts with a planet’s surface or atmosphere. If the atmosphere or surface has been altered by life, the light can contain a clue called a “biosignature.”

For the first half of its existence, the earth had an oxygen-free atmosphere, although it supported simple, unicellular life. Earth’s biosignature was very weak during this early era. That changed suddenly 2.4 billion years ago when a new family of algae evolved. The algae use a process of photosynthesis that produces free oxygen – oxygen that is not chemically bound to another element. From that point forward, Earth’s oxygen-filled atmosphere has left a strong and easily detectable biosignature on light passing through it.

When light bounces off the surface of a material or travels through a gas, certain wavelengths of light are more likely to remain trapped in the surface of the gas or material than others. This selective trapping of light wavelengths is why objects have different colors. Leaves are green because chlorophyll absorbs light in the red and blue wavelength range particularly well. When light hits a leaf, the red and blue wavelengths are absorbed, leaving mostly green light to bounce back into your eyes.

The pattern of missing light is determined by the specific composition of the material with which the light interacts. Because of this, astronomers can learn about the composition of an exoplanet’s atmosphere or surface by essentially measuring the specific color of light coming from a planet.

This method can be used to detect the presence of certain atmospheric gases associated with life – such as oxygen or methane – as these gases leave very specific signatures in the light. It could also be used to detect particular colors on a planet’s surface. On Earth, for example, the chlorophyll and other pigments that plants and algae use for photosynthesis capture specific wavelengths of light. These pigments produces characteristic colors which can be detected with a sensitive infrared camera. If you were to see this color reflected off the surface of a distant planet, it would possibly indicate the presence of chlorophyll.

Telescopes in space and on earth

The James Webb Space Telescope is the first telescope capable of detecting chemical signatures of exoplanets, but it is limited in its capabilities. Photo credit: NASA/Wikimedia Commons

It takes an incredibly powerful telescope to detect these subtle changes in light coming from a potentially habitable exoplanet. Currently, the new telescope is the only telescope capable of such a feat James Webb Space Telescope. How it is started scientific operation In July 2022, James Webb took a reading of The Spectrum of Gas giant exoplanet WASP-96b. The spectrum showed the presence of water and clouds, but a planet as large and hot as WASP-96b is unlikely to host life.

However, these early data indicate that James Webb is able to detect faint chemical signatures in the light of exoplanets. In the coming months, Webb will be turning his mirrors towards TRAPPIST-1ea potentially habitable planet the size of Earth, just 39 light-years from Earth.

Webb can search for biosignatures by examining planets as they pass in front of their host stars and capturing them Starlight penetrating the planet’s atmosphere. But Webb wasn’t designed to look for life, so the telescope can only study some of the nearest potentially habitable worlds. It can also only detect changes to Carbon dioxide, methane and water vapor in the atmosphere. While certain combinations of these gases can suggest lifeWebb is unable to detect the presence of free oxygen, which is the strongest signal for life.

Leading concepts for future, even more powerful space telescopes include plans to block the bright light from a planet’s host star to reveal starlight reflected off the planet. This idea is similar to using your hand to block the sunlight to get a better look at something in the distance. Future space telescopes could use small, internal masks or large, external, umbrella-like spacecraft to do this. Once starlight is blocked, it becomes much easier to study light reflected off a planet.

There are also currently three huge, ground-based telescopes under construction that will be able to search for biosignatures: the Huge Magellan Telescopethe Thirty meter telescope and the European Extremely Large Telescope. Each is far more powerful than existing telescopes on Earth, and despite the handicap of Earth’s atmosphere, which distorts starlight, these telescopes may be able to probe the nearest worlds’ atmospheres for oxygen.

Animals, including cows, produce methane, but so do many geological processes. Photo credit: Jernej Furman/Wikimedia Commons, CC BY

Is it biology or geology?

Even with the most powerful telescopes of the coming decades, astrobiologists will only be able to see strong biosignatures originating from worlds completely altered by life.

Unfortunately, most of the gases released by terrestrial life can also be produced by non-biological processes – cows and volcanoes both release methane. Photosynthesis produces oxygen, but so does sunlight as it splits water molecules into oxygen and hydrogen. There is a good chances that astronomers will spot some false positives in search of distant life. To avoid false positives, astronomers need to understand a planet of interest well enough to know if it is a planet geological or atmospheric processes could mimic a biosignature.

The next generation of exoplanet studies has the potential to break the bar extraordinary evidence needed to prove the existence of life. The first data release from the James Webb Space Telescope gives us a glimpse of the exciting advances to come.The conversation

Chris Impeydistinguished university professor of astronomy, University of Arizona and Daniel ApaProfessor of Astronomy and Planetology, University of Arizona

This article is republished by The conversation under a Creative Commons license. read this original article.

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