The study of exoplanets has exploded in the past three decades. Since the discovery of the first exoplanet in 1992, scientists have confirmed the existence of more than 5,000 more. Planets have turned out to be much more abundant than scientists thought, and it is believed that every star is orbited by at least one planet. As technology advances, so does our ability to study worlds beyond our own solar system. For the first time in history, telescopes may even be advanced enough to detect biosignatures on other planets. Biosignatures are forms of evidence suggesting the existence of life on a planet, which are generally believed to exist in the form of atmospheric composition. For example, the presence of large amounts of oxygen or methane may indicate that biological processes are taking place. Recently, however, scientists have proposed a new biosignature Infrared radiation be reflected plants.
Plants and light
Plants are one of the most abundant life forms on Earth Soil. About 32% of the earth’s surface is covered with plants and plants make up 80% of the total biomass on earth. Plants are so abundant that most Earth biosignatures are a direct result of plants and how they have changed the chemistry of our world. Plants are responsible for most of the earth oxygen through the process of photosynthesis, in which plants use sunlight and water to produce energy, releasing oxygen as a by-product. While photosynthesis absorbs sunlight, it also reflects some of it. Plants largely absorb the light in the visible part of the electromagnetic spectrum while reflecting infrared light. By reflecting infrared light, plants can prevent overheating. This phenomenon is called the Vegetation Red Edge (VRE), and some scientists believe it could be used in detecting plants on alien worlds.
Comparing Earthshine to other worlds
While the idea of observing infrared light reflected from other worlds sounds simple, it’s a bit more complicated than that. First, it can be difficult to determine whether the infrared radiation is actually being reflected by plants or whether there is some other process involved. To get an idea of what a plant-filled planet would look like, scientists analyzed the light reflected by our world, the earth. The Earth itself does not emit much of its own light, but rather reflects the Earth’s light Sun into space. This light is called Earthshine, and scientists often examine the light reflected from our world to study our planet’s biosignatures. One way to do this is to study the light reflected from the Moon because of earthquake. By analyzing Earthshine reflected from the moon, scientists can analyze the chemical composition of us atmosphere, as well as what percentage of earthshine is the result of plants reflecting infrared radiation. Data suggests that the overall change in Earthshine due to plant life is about 2%, which may not seem like much, but it’s large enough that if other planets have similar amounts of plant life, it could be detectable. While comparisons between Earth and exoplanets use a host of assumptions, they can still be a useful tool in predicting what extraterrestrial biosignatures might look like. Then scientists compared Earthshine to some known exoplanets to predict what their VRE would look like, assuming that plant life on those worlds behaves like vegetation on Earth and exists in similar abundances. The resulting data can be used to search for plants on other worlds.
An age-old question
For as long as humans have known that the stars are other suns, we’ve wondered if we’re alone in this vast universe. As technology advances and telescopes become more powerful, humanity will likely have the means to detect life on other planets in the not-too-distant future. Telescopes like James Webb are already revolutionizing our understanding of exoplanets, and future telescopes will be designed with the ability to study exoplanet atmospheres in such detail that biosignatures are likely to be detected. The answer to the question of whether we are alone in the universe could very well be within reach.