components of life spread all over the universe. While Earth is the only known place in the universe where life exists, the discovery of extraterrestrial life is The main objective From modern astronomy And the planetary science.

We are two scholars who study outer planets And the 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. Hopefully, one or more of these planets will have a chemical fingerprint for life.

Habitable outer planets

life It may exist in the solar system Where there is liquid water – such as aquifers on Mars or in the oceans of Jupiter’s moon Europa. However, the search for life in these places is very difficult, as it is difficult to reach and detect life requires sending a probe to return the physical samples.

Many astronomers believe that there is a file Good chance of life on planets orbiting other starsAnd this could be the place Life will be found first.

Theoretical calculations indicate that there is something close 300 million potentially habitable planets In the Milky Way alone and Many habitable planets the size of Earth Within only 30 light-years from Earth – essentially humanity’s neighbors in the galaxy. So far, astronomers have done it Discover more than 5,000 exoplanetsincluding hundreds of potentially habitable ones, using indirect methods which measures how a planet affects its nearby star. These measurements can provide astronomers with information about the mass and size of an exoplanet, but no more than that.

Looking for bio signatures

To discover life on a distant planet, astrobiologists will study existing starlight Interact with the planet’s surface or atmosphere. If the atmosphere or surface is transformed 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 it hosted simple, single-celled life. The Earth’s vital footprint was quite faint during this early era. That suddenly changed 2.4 billion years ago When a new family of algae evolved. The algae used photosynthesis that produces free oxygen – oxygen that is not chemically bound to any other element. From that time on, Earth’s oxygen-filled atmosphere left a strong and easily detectable vital imprint on the light passing through it.

When light bounces off the surface of a material or passes through a gas, certain wavelengths are more likely to remain trapped in the gas or surface of the material than others. This selective fit of the wavelengths of light is the reason for the different colors of objects. Leaves are green because chlorophyll is particularly good at absorbing light in the red and blue wavelengths. When light hits the paper, the red and blue wavelengths are absorbed, leaving mostly green light bouncing back into your eyes.

The pattern of lost light 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 that comes from a planet.

This method can be used to identify the presence of certain atmospheric gases associated with life – such as oxygen or methane – because these gases leave very specific signals in the light. It can also be used to detect strange colors on the surface of a planet. On Earth, for example, plants chlorophyll and other pigments and algae in photosynthesis use specific wavelengths of light. These dyes Distinctive color production It can be detected using a sensitive infrared camera. If you see this color reflecting off the surface of a distant planet, it probably indicates the presence of chlorophyll.

Telescopes in space and on Earth

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 telescope James Webb Space Telescope. as it is Scientific operations began In July 2022, James Webb conducted a cute reading 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 host life.

However, these early data show that James Webb is able to detect faint chemical signals in light from exoplanets. In the coming months, Webb was set to turn her mirrors toward TRAPPIST-1ea potentially habitable Earth-sized planet only 39 light-years from Earth.

Webb can search for biometric fingerprints by studying and capturing planets as they pass in front of their host stars Starlight that flows through the planet’s atmosphere. But Webb was not designed to search for life, so the telescope is only able to examine a few of the closest potentially habitable worlds. It can also detect changes made to Levels of carbon dioxide, methane and water vapor in the atmosphere. While certain combinations of these gases It might suggest lifeWebb is unable to detect the presence of unbound oxygen, which is the strongest indication of life.

Pioneering concepts for future space telescopes, and even more powerful, include plans to block the bright light of Earth’s host star to detect starlight reflected from the planet. This idea is similar to using your hand to block out sunlight to better see something from a distance. Future space telescopes could use small indoor masks or a large, parachute-like outer spacecraft to do this. Once the starlight is blocked out, it is much easier to study the light bouncing off a planet.

There are also three massive ground-based telescopes currently under construction that will be able to search for biometric fingerprints: Giant Magellan TelescopeThe Thirty meters telescope and the european very large telescope. Each is much more powerful than the telescopes on Earth, and although obstructed by Earth’s atmosphere distorting starlight, these telescopes may be able to explore the atmospheres of the nearest worlds in search of oxygen.

Is it biology or geology?

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

Unfortunately, most of the gases released by terrestrial life can also be produced through non-biological processes – cows and volcanoes release methane. Photosynthesis produces oxygen, but sunlight also does so when it splits water molecules into oxygen and hydrogen. there A good chance for astronomers to spot some false positives When searching for a distant life. To help rule out false positives, astronomers will need to understand an interesting planet well enough to understand if it is. Geological or atmospheric processes can mimic a biosignature.

The next generation of exoplanet studies has the potential to transcend the level of Unusual evidence Need to prove the existence of life. The first release of data from the James Webb Space Telescope gives us a sense of the exciting progress that is coming soon.

Chris EmbiDistinguished University Professor of Astronomy, University of Arizona And the Daniel AbayProfessor of astronomy and planetary sciences, University of Arizona

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