The elements necessary for life are dispersed across the cosmos. While there is only known life on Earth, finding life elsewhere in the universe is a top priority for contemporary astronomy and planetary research.
We are two researchers who focus on astrobiology and exoplanets. We will soon be able to measure the chemical composition of atmospheres on planets orbiting other stars, in great part because of next-generation observatories like James Webb.
One or more of these planets may contain a chemical signature of life, it is hoped.
Habitable exoplanets
Where there is liquid water, such as in the oceans of Jupiter’s moon Europa or the underground aquifers underneath Mars, life may exist. However, it is extremely challenging to look for life in these locations because they are inaccessible, and finding life would necessitate sending a probe to return actual samples.
It’s possible that life will initially be discovered on planets orbiting other stars, as many astronomers think there’s a significant probability that it does.
The Milky Way galaxy alone contains an estimated 300 million potentially habitable planets, and some habitable Earth-sized planets are barely 30 light-years away from Earth. These planets are effectively the galactic neighbors of humanity.
Astronomers have so far found more than 5,000 exoplanets, hundreds of which may be habitable, by utilizing indirect techniques that gauge how a planet influences its neighborhood star. These observations can provide astronomers with data about an exoplanet’s mass and size, but not much more.
Looking for biosignatures
Astrobiologists will examine starlight that has reacted with a planet’s surface or atmosphere in order to find signs of life on a far-off planet. If life has altered the surface or atmosphere, the light may contain a “biosignature,” which is a telltale indicator.
Even though it supported basic, single-celled life, Earth had an atmosphere devoid of oxygen for the first half of its history. During this early period, Earth’s biosignature was incredibly weak. When a new family of algae emerged 2.4 billion years ago, that abruptly altered.
The photosynthetic mechanism utilized by the algae results in free oxygen, which is oxygen that isn’t chemically bound to any other element. Since then, light passing through Earth’s oxygen-rich atmosphere has carried a distinct and noticeable biosignature.
Certain wavelengths of light are more likely than others to remain trapped in the surface of a gas or material when the light bounces off its surface. The reason why objects have varied colors is due to the selective trapping of light wavelengths.
Because chlorophyll is particularly effective at absorbing light with the red and blue wavelengths, leaves are green. Red and blue wavelengths are absorbed as light strikes a leaf, leaving predominantly green light to reflect back into your eyes.
The precise makeup of the substance that the light interacts with determines the pattern of missing light. As a result, by measuring a planet’s particular color of light, astronomers can infer something about the makeup of the atmosphere or surface of an exoplanet.
Because these gases leave behind extremely distinct traces in light, such as oxygen or methane, this technique can be used to detect the existence of specific atmospheric gases linked to life. It could also be used to identify unusual hues on a planet’s surface.
On Earth, for instance, plants and algae use pigments like chlorophyll to collect particular wavelengths of light in order to carry out photosynthesis.
A sensitive infrared camera can be used to identify these pigments’ distinctive colors. This tint may indicate the presence of chlorophyll if it were to reflect off the surface of a far-flung planet.
Telescopes in space and on Earth
These minute variations in the light coming from an exoplanet with the potential to support life require a very large telescope to be able to detect them. The upcoming James Webb Space Telescope is the only telescope now able to accomplish such a feat.
James Webb took a scan of the spectrum of the gas giant exoplanet WASP-96b as it started its science operations in July 2022. The spectrum indicated the presence of water and clouds, although life is unlikely to exist on a planet the size and temperature of WASP-96b.
However, this preliminary evidence demonstrates that James Webb is able to recognize minute chemical traces in exoplanet light.
Webb will point its reflectors at TRAPPIST-1e in the upcoming months; it is only 39 light-years away from Earth and may be habitable.
By observing planets as they pass in front of their host stars and collecting starlight that reflects off the atmosphere of the planet, Webb can search for biosignatures. The telescope can only closely examine a few of the closest possibly habitable planets because Webb was not built to look for extraterrestrial life.
Additionally, it is limited to detecting changes in atmospheric concentrations of carbon dioxide, methane, and water vapor. Webb is unable to detect the presence of unbonded oxygen, which is the greatest indication for life, even though certain mixtures of these gasses may be suggestive of life.
The brilliant light of a planet’s host star will be blocked by advanced ideas for future, even more potent space telescopes to reveal starlight reflected back from the planet. To better view something in the distance, think of doing something akin to blocking the sun with your hand.
Small interior masks or big, exterior, umbrella-shaped spacecraft could be used in future space telescopes to accomplish this. Studying light reflecting off a planet is significantly simpler after the starlight is obstructed.
The Giant Magellen Telescope, the Thirty Meter Telescope, and the European Extremely Large Telescope are three more gigantic ground-based telescopes that will be able to look for biosignatures and are currently under development.
These telescopes might potentially be used to look for oxygen in the atmospheres of the nearest planets despite the disadvantage of Earth’s atmosphere distorting starlight due to their immense power compared to current telescopes on Earth.
Is it biology or geology?
Astrobiologists will only be able to identify significant biosignatures emitted by planets that have undergone a full transformation by life, even with the most potent telescopes in the ensuing decades.
Methane is a gas that is released by both cows and volcanoes, however most gases produced by terrestrial life can also be created by nonbiological processes. In addition to producing oxygen through photosynthesis, sunlight also breaks water molecules into oxygen and hydrogen.
When searching for extraterrestrial life, there is a good likelihood that astronomers will find some false positives. Astronomers must have a thorough understanding of a planet of interest to determine whether its geologic or atmospheric processes could resemble a biosignature in order to help rule out false positives.
The next wave of exoplanet research may be able to meet the standard for the remarkable evidence required to establish the reality of life. The James Webb Space Telescope’s first data release gives us a preview of the great advancements to come.
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