Martian Methane Reveals the Red Planet is not a Dead Planet
NASA has detected plumes of methane being emitted during the spring and summer, indicating that microoganisms may exist on Mars. The true test, other than finding the organisms, is to test for the level or deuterium in the methane. Living organisms prefer lighter isotopes so methane with less deuterium than the water released with it indicates it was formed through a biological process.
Scientists have determined that life can be detected from space, using data collected from the Galileo spacecraft. it indicated that, no matter earth's orientation and distance, chlorophyll-based vegetation generated a spike at 700-nm that doesn't exist on planets that we know don't have vegetation (that is, every other planet and moon in our solar system). It should be possible to detect this spike on planets around other suns, but there are significant technical challenges to overcome.