Written by Nancy Atkinson

January 13th, 2009

"What if another civilization had telescopes and spacecraft better than ours? Would Earth be detectable from another planet a few light-years away? Likewise, what will it take for us to detect life on an Earth-like planet within a similar distance? It's interesting to consider those questions, and now, there is data to help answer them. In December 1990, when the Galileo spacecraft flew by Earth in its circuitous journey to Jupiter, scientists pointed some of the instruments at Earth just to see how the old home planet looked from space. Since we knew life could definitely be found on Earth, this exercise helped create some criteria that if found elsewhere, would point to the existence of life there as well. But what if Earth's climate was different from what it is now? Would that signature still be detectable? And could potential biomarkers from extra solar planets holding climates much colder or warmer than ours be obvious? A group of researchers in France input some various criteria garnered from different epochs in Earth's history to test out this hypothesis. What did they find?

"One of the most telling of the criteria from the Galileo flyby revealing life on Earth was what is called the vegetation red edge –a sharp increase in the reflectance of light at a wavelength of around 700 nanometers. This is the result of chlorophyll absorbing visible light but reflecting near infrared strongly. The Galileo probe found strong for this evidence in Earth 1990.

"Luc Arnold and his team at the Saint-Michel-l’Observatoire in France wanted to determine some different parameters where plant life similar to Earth's would still be detectable via the vegetative red edge on an Earth-like planet orbiting a star several light years away. . . ." More: http://www.universetoday.com/2009/01/13/viewing-earth-as-an-extra-solar-planet/