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It's the rise of greenery and plants that has paved the way for the planet to support a vibrant mix of life-forms ranging from humans to dinosaurs, among others. Looking for this same process in extraterrestrial worlds, especially in ancient planets, could be a way to search for life and perhaps even a new home outside the solar system.
According to a new study, the Earth's vegetative history could open avenues to search for habitable exoplanets. In a new article, scientists define the "red edge of vegetation", which means that the Earth is very effective at reflecting a good amount of light in the near infrared.
"We use the Earth's history as a key to finding life in the universe," said Lisa Kaltenegger, co-author of the research, Cornell University, in a statement. "By examining how life has changed Earth's biosignatures over time, it helps us determine which planets are most likely to show the most powerful signs of life, giving us the best chance of successfully locating life, if it's there. "
According to the Cornell Report, over the last 500 million years, the surface and geology of the Earth have changed dramatically. It has gone completely from ice to expanses of vast forests. However, during most of the Earth's history, the landmass was not dominated by plants, but once they began to take root, they completely covered the major part of the planet. Mosses were the first terrestrial plants, but they have a weak vegetation signature compared to modern trees. It may therefore be difficult to search for them from astronomers.
"Our models show that the reflectance signature of the Earth's vegetation increases with the coverage of the surface of our planet, but also with the age of our planet," said co-author Jack O & # 39; Malley-James, of the Carl Sagan Institute of Cornell.
Exoplanets – planets of different stars – could be thirsty and arid, they could have clear skies and endless cactus forests, or even be hot jungle worlds covered with rainforests, Kaltenegger explains. Over interstellar distances, she says, such planets could be the best targets for spotting vegetation.
In 1989, NASA launched the Galileo to Jupiter and Carl Sagan asked the space agency to spin the spacecraft to see the Earth, to understand how light was reflected on the planet, Earth being the only place known to support life. According to the December 1990 report, the observations were made and revealed a distinctive reinforcement of the reflectance between the red spectrum and the infrared – near infrared spectrum – this wavelength of light exceeds the limits of human vision and is caused by vegetation.
"The signal detected by Galileo for the Earth was similar to what could be the observations of an exoplanet in another star system, but, of course, Galileo was much closer to us," said O & # 39; Malley James.
Observing an exoplanet is more difficult and far away, but telescope technology, he said, is beginning to detect even the smallest signals. In addition, taking into account the changing landscapes of the Earth in current models, it will be easier to detect vegetation in other worlds, in the near future, he explained.
The paper entitled "The biosignature of the red edge of vegetation over time on Earth and exoplanets" was first published in the Astrobiology Journal.
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