[ad_1]
The natural history of the Earth can now serve as a guide for astronomers to identify exoplanets. About 500 million years ago, this planet had a different light signature due to the dominance of the moss. About 300 million years ago, ferns were dominant and mature forms of plants reigned today – changing the light signature of the planet. Credit: Jack O. Malley-James / Wendy Kenigsberg / Brand Communications
By examining the natural history and evolution of the Earth, astronomers may have found a template for plant footprints – borrowing from changing eras of flora – to determine the age of habitable exoplanets.
"Our models show that the signature of the Earth's reflectance increases with the surface of our planet, but also with the age of our planet," said co-author Jack O-Malley-James, researcher associated with the Carl Sagan Institute of Cornell University. The research, "The red-bordered biosignature of vegetation through time on earth and exoplanets", published online in astrobiology.
The geological record of the last 500 million years shows that the Earth's surface has changed dramatically from an ice cover to huge forests spread over the ground. For most of the beginnings of our planet, terrestrial plants did not exist, but the plants eventually spread to the surface of the Earth. The first plants, mosses, show only a weak plant signature difficult to find at a distance for astronomers compared to modern trees.
"We use the Earth's history as the key to finding life in the universe," said co-author Lisa Kaltenegger, associate professor of astronomy at Cornell University and director from the Carl Sagan Institute. "Our work shows that when plants evolved on Earth, the signal of vegetation that reveals their presence has become stronger, making older exoplanets really interesting places to look for vegetation."
Exoplanets can be desiccated, arid with clear skies and endless cactus forests, or warm jungle worlds covered with rainforests. "Over interstellar distances, these places could be the best targets for spotting vegetation," said Kaltenegger.
When NASA's Galileo mission left Earth for Jupiter in 1989, Cornell astronomer Carl Sagan asked the spacecraft's instruments to look at Earth to see how light reflected on a rich, inhabited planet. The December 1990 observations revealed a significant increase in the reflectance between the red spectrum and the infrared spectrum, just beyond the limits of human vision, due to vegetation.
"The signal that Galileo detected for the Earth was similar to what the observations of an exoplanet might look like in another star system, but, of course, Galileo was much closer to us," said O-Malley-James.
"Observing an exoplanet is harder, but telescope technology is becoming more and more efficient at pinpointing tiny signals," said O-Malley-James. "And taking into account the changing landscapes of the Earth in our models will facilitate the detection of future vegetation on other worlds."
Kaltenegger said: "Looking at how life has changed Earth's biosignatures over time helps us determine which planets are most likely to show the strongest signs of life, ultimately giving us the best chance of determine life. "
Explore more:
Astronomers assemble "light footprints" to unravel the mysteries of the cosmos
More information:
Jack T. O. Malley-James et al., Red-bordered vegetation biosignature through time on Earth and exoplanets, astrobiology (2018). DOI: 10.1089 / ast.2017.1798
Source link
