If you travel into deep space and look back at Earth through a sophisticated telescope, you could measure what’s called the vegetation red edge (VRE). The vegetation red edge is a mixture of red and infrared light that is reflected by plants on Earth’s surface. Because of clouds, ice masses, and large oceans, the vegetation red edge on Earth is actually fairly small and difficult to measure. If you went millions of years back in history, it would be even harder to see. Today’s terrestrial plants give off a more red and infrared light than the mosses and ferns that evolved earlier in earth’s history.
While it may be too late to use this measurement to ascertain if Earth supports life, it could be useful elsewhere. Jack T. O’Malley-James and Lisa Kaltenegger from Cornell University recently proposed measuring the VRE of planets orbiting stars in regions that may be able to support life. Through a series of models, they determined that some life-harboring planets, particularly older planets that could have become covered in jungle or desert, are likely to have particularly large and easy to measure VRE signals. It may seem surprising that deserts would give off a large VRE signal, but cacti have one of the strongest vegetation red edge signal of all modern plants, thanks to their adaptations for water retention.
While the researchers hope that measurements of the vegetation red edge will be able to infer the presence or absence of vegetation on distant planets, they warn that this method will not be able to determine things like the type of vegetation or its distribution over the planet. Additionally, planetary features like cloud coverage, highly reflective ice sheets, and oceans diminish the intensity of VRE signal, increasing the difficulty of detection.
Managing Correspondent: Emily Kerr
Media coverage: Earth’s history could be used to spot plant life on alien worlds