IT SOUNDS like a zen koan. If a tree on an alien world falls, would we notice? of the University of Oxford and Adam Wolf of Princeton University think we just might.
They say the shadows cast by trees would change the amount of light a planet reflects as it orbits its star. When the planet is behind its star as seen from Earth 鈥� as the moon is during its full phase 鈥� the trees would cast little shadow, while at other points in its orbit the shadows would grow longer. Future telescopes should be able to search for these changes ().
of the NASA Goddard Institute for Space Studies in New York City says steep mountains could mimic the effect. But Wolf notes that less than 1 per cent of Earth鈥檚 surface has a slope of 45 degrees or more.
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