The James Webb telescope could help astronomers spot extraterrestrial life

The ingredients for life are spread across the universe. While Earth is the only known place in the universe for life, detecting life beyond Earth is a… important 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 makeup of atmospheres of planets around other stars. The hope is that one or more of these planets will have a chemical signature of life.

A diagram with green bands around stars.
There are many known exoplanets in habitable zones — orbiting not too close to a star where the water is boiling, but not so far that the planet is frozen solid — such as marked green for both the solar system and the Kepler-186 galaxy with its planets labeled b , c, d, e and f. Image: NASA Ames/SETI Image: Institute/JPL-Caltech/Wikimedia Commons

Habitable exoplanets

To live could exist in the solar system where there is liquid water – such as the underground aquifers on Mars or in the oceans of Jupiter’s moon Europa. However, searching for life in these places is incredibly difficult, as they are hard to reach and detecting life would require sending a probe to return physical samples.

Greetings, Humanoids

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Many astronomers believe that there is a There is a high probability that life exists on planets orbiting other starsand it’s possible that’s true life will be found first.

Theoretical calculations suggest that there are about 300 million potentially habitable planets only in the Milky Way galaxy and several Earth-sized habitable planets within just 30 light-years of Earth — essentially humanity’s galactic neighbors. Until now, astronomers more than 5,000 exoplanets discoveredincluding hundreds of potentially habitable ones, using indirect methods that measure how a planet affects its nearby star. These measurements can give astronomers information about the mass and size of an exoplanet, but not much else.

A graph with two lines each with two peaks in the blue and red wavelengths.
Each material absorbs certain wavelengths of light, as shown in this diagram showing the wavelengths of light that are most easily absorbed by different types of chlorophyll. Image: Daniele Pugliesi/Wikimedia Commons, CC BY-SA

Looking for bio signatures

To detect life on a distant planet, astrobiologists will study starlight that interacting with a planet’s surface or atmosphere. If the atmosphere or surface has been transformed by life, the light may contain a clue, called a “biosignature.”

For the first half of its existence, the Earth had an atmosphere without oxygen, even though it harbored simple single-celled life. The Earth’s biosignature was very weak in this early era. That changed abruptly 2.4 billion years ago as a new family of algae evolved. The algae used a process of photosynthesis that produces free oxygen – oxygen that is not chemically bonded to any other element. Since then, Earth’s oxygen-filled atmosphere has left a strong and easily detectable biosignature on the light passing through it.

When light reflects off the surface of a material or passes through a gas, certain wavelengths of light are more likely to be trapped in the gas or material’s surface than others. This selective capture of wavelengths of light is why objects have different colors. The leaves are green because chlorophyll is particularly good at absorbing light in the red and blue wavelengths. When light hits a leaf, the red and blue wavelengths are absorbed, causing most of the 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. This allows astronomers to 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 recognize the presence of certain atmospheric gases associated with life – such as oxygen or methane – because these gases leave very specific signatures in the light. It can also be used to detect peculiar colors on a planet’s surface. For example, on Earth, the chlorophyll and other pigments that plants and algae use for photosynthesis capture specific wavelengths of light. These pigments produce characteristic colors which can be detected using a sensitive infrared camera. If you were to see this color reflecting off the surface of a distant planet, it might indicate the presence of chlorophyll.

Telescopes in space and on Earth

It takes an incredibly powerful telescope to detect these subtle changes in the light of a potentially habitable exoplanet. For now, the only telescope capable of such a feat is the new James Webb Space Telescope. Like began scientific operations in July 2022 James Webb read the spectrum of the gas giant exoplanet WASP-96b. The spectrum showed the presence of water and clouds, but life on a planet as big and hot as WASP-96b is unlikely to be found.

However, these early data show that James Webb is able to detect weak chemical signatures in light from exoplanets. In the coming months, Webb will focus his mirrors on TRAPPIST-1stan Earth-sized potentially habitable planet just 39 light-years from Earth.

Webb can search for biosignatures by studying planets as they pass in front of their host stars and record them starlight filtering through the planet’s atmosphere. But Webb wasn’t designed to look for life, so the telescope can survey only some of the closest potentially habitable worlds. It can also only detect changes in: atmospheric levels of carbon dioxide, methane and water vapor. While certain combinations of these gases can suggest lifeWebb is unable to detect the presence of unbound 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 parent star to reveal the starlight reflected from the planet. This idea is similar to using your hand to block out sunlight to better see something in the distance. Future space telescopes could use small, internal masks or large, external, umbrella-like spacecraft for this purpose. Once the starlight is blocked, it becomes much easier to study light reflecting off a planet.

There are also currently three massive ground-based telescopes under construction that will be able to search for biosignatures: the Giant Magellen Telescopethe Thirty meter telescope and the European extremely large telescope. Each is much more powerful than existing telescopes on Earth, and despite the handicap of Earth’s atmosphere that distorts the starlight, these telescopes could be able to survey the atmospheres of the nearest worlds for oxygen.

A cow and her calf are standing in a field.
Animals, including cows, produce methane, but so do many geological processes. Image: 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 detect strong biosignatures produced by worlds completely transformed 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 sunlight also produces when it splits water molecules into oxygen and hydrogen. There is a good chance astronomers will detect some false positives in search of the distant life. To rule out false positives, astronomers will have to understand an interesting planet well enough to understand whether it geological or atmospheric processes can mimic a biosignature.

The next generation of exoplanet studies has the potential to raise the bar of the extraordinary evidence needed to prove the existence of life. The first data release from the James Webb Space Telescope gives us an idea of ​​the exciting progress that will soon take place.The conversation

This article by Chris ImpeyUniversity Distinguished Professor of Astronomy, University of Arizonaand Daniel Apaiprofessor of astronomy and planetary sciences, University of Arizona has been reissued from The conversation under a Creative Commons license. Read the original article.


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