What would plants look like on another world? Scientists imagined that on a moon with low gravity and a thick atmosphere, vegetation could grow to the size of hot air balloons. Some plants could "tower" or "float" half a mile (800 meters) above the surface.

The illustration was made for the National Geographic Channel documentary Extraterrestrial, a look at what life on other worlds might really look like. Visit the Channel's Extraterrestrial Web site for a video excerpt, more images, and an interactive feature.

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