The ingredients for life are scattered throughout the universe. While Earth is the only known place in the universe with life, detecting life beyond Earth is a main goal of modern astronomy Y planetary science.
We are two scientists who study exoplanets Y 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 have a chemical signature of life.
There are many known exoplanets in habitable zones, orbits not too close to a star that water boils, but not so far away that the planet freezes over, as indicated by green for both the solar system and the Kepler-186 star system. with their planets. labeled b, c, d, e, and f. Image credit: NASA Ames/SETI Institute/JPL-Caltech/Wikimedia Commons
habitable exoplanets
life could exist in the solar system where there is liquid water, such as 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.
Many astronomers believe that there is a Good chance that life exists on planets orbiting other stars.and it might be there life will be found.
Theoretical calculations suggest that there are about 300 million potentially habitable planets in the Milky Way galaxy alone and several habitable Earth-sized planets within just 30 light years of Earth, essentially humanity’s galactic neighbors. Until now, astronomers have discovered more than 5,000 exoplanetsincluding hundreds of potentially habitable ones, using indirect methods that measure how a planet affects its nearby star. These measurements can give astronomers information about an exoplanet’s mass and size, but not much else.
Looking for biosignatures
To detect life on a distant planet, astrobiologists will study the light from stars that have interacted with the surface or atmosphere of a planet. Whether the atmosphere or the surface was transformed by life, the light can carry a clue, called a “biological signature.”
For the first half of its existence, Earth sported an oxygen-depleted atmosphere, even though it supported simple, single-celled life. Earth’s biosignature was very weak during this early era. That abruptly changed 2.4 billion years ago when a new family of algae evolved. The algae used a process of photosynthesis that produces free oxygen, oxygen that is not chemically bound to any other element. Since then, Earth’s oxygen-filled atmosphere has left a strong and easily detectable biosignature in light passing through it.
When light bounces off the surface of a material or passes through a gas, certain wavelengths of light are more likely to remain trapped on the surface of the gas or material than others. This selective capture of wavelengths of light is the reason why objects have different colors. 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, leaving the green light to bounce back into your eyes.
The pattern of stray light is determined by the specific composition of the material with which the light interacts. Because of this, astronomers can learn something about the composition of an exoplanet’s atmosphere or surface, in essence, by measuring the specific color of light coming from a planet.
This method can be used to recognize the presence of certain atmospheric gases that are associated with life, such as oxygen or methane, because these gases leave very specific signals in light. It could also be used to detect peculiar colors on a planet’s surface. On Earth, for example, 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 saw this color reflecting off the surface of a distant planet, it would potentially signify 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 its capabilities are limited. Image Credit: NASA/Wikimedia Commons
An incredibly powerful telescope is needed to detect these subtle changes in light coming from a potentially habitable exoplanet. For now, the only telescope capable of such a feat is the new James Webb Space Telescope. as it started science operations in July 2022, James Webb did a spectrum reading of the 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 harbor life.
However, these early data show that James Webb is capable of detecting faint chemical signatures in light from exoplanets. In the coming months, Webb is ready to turn the mirrors on himself. TRAPPIST-1ea potentially habitable Earth-sized 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 capturing starlight filtering through the planet’s atmosphere. But Webb wasn’t designed to search for life, so the telescope can only peer at a few of the closest potentially habitable worlds. It can also only detect changes in atmospheric levels of carbon dioxide, methane and water vapor. Although certain combinations of these gases can suggest lifeWebb cannot detect the presence of unbound oxygen, which is the strongest sign of life.
Leading concepts for even more powerful future space telescopes include plans to block the bright light from a planet’s host star to reveal starlight reflected from the planet. This idea is similar to using your hand to block sunlight to better see something in the distance. Future space telescopes could use small internal masks or large, external, umbrella-shaped spacecraft to do this. Once starlight is blocked, it becomes much easier to study the light that bounces off a planet.
There are also three huge ground-based telescopes currently under construction that will be able to search for biosignatures: the Giant Magellan Telescopethe thirty meter telescope and the European Extremely Large Telescope. Each is far more powerful than existing telescopes on Earth, and despite the disadvantage that Earth’s atmosphere distorts starlight, these telescopes could probe the atmospheres of nearby worlds for oxygen.
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Is it biology or geology?
Even using the most powerful telescopes for decades to come, astrobiologists will only be able to detect strong biosignatures produced by worlds that have been completely transformed by life.
Unfortunately, most of the gases released by terrestrial life can also be produced by non-biological processes: cows and volcanoes release methane. Photosynthesis produces oxygen, but sunlight does too, when it splits water molecules into oxygen and hydrogen. There’s a there’s a good chance astronomers will spot some false positives looking for the distant life. To help rule out false positives, astronomers will need to understand a planet of interest well enough to know if its geological or atmospheric processes could mimic a biological signature.
The next generation of exoplanet studies has the potential to raise the bar for extraordinary evidence necessary 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 to come.
Chris ImpeyUniversity Distinguished Professor of Astronomy, university of arizona Y daniel paiProfessor of Astronomy and Planetary Sciences, university of arizona
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