life test for planets

Date: Sat Jan 26 2002 - 00:04:35 MST

<<Planet reveals telltale signature of plant life

15:34 25 January 02
Will Knight

Astronomers have identified a telltale signature of plant life in light
reflected from a planet for the first time - but the planet is Earth.
Researchers at the Haute Provence Observatory in France collected light from
Earth that had bounced back down from the shadowed side of the Moon.

The discovery provides a low-cost way to simulate the way that light might be
reflected from a distant planet that had vegetation similar to the Earth's.
This cannot be done with satellites in low Earth orbit because of the way the
atmosphere affects the reflection of light.

    Plants alter the Earth's relfection (Photo: NASA)

"It's curious that no-one thought of doing this before," says Jean Schneider,
of the Paris Observatory, who helped interpret the data. The signature of
plants in the light is clear, he says: "There is a lack of reflection below
725 nanometres."

The Earth reflects less light than would be expected below this wavelength
because plants absorb that part of the Sun's spectrum during photosynthesis.
The team believes this approach could help identify vegetation on distant
planets orbiting other stars.

Alien plant life

But Schneider points out that vegetation on another planet could be very
different to that on Earth. "There are some bacteria on Earth that are
photosynthetic, but have a much higher reflectivity," he says.

The new observations examined all of the Earth's light from a distance for
the first time. The spectrum is most intense in the range that represents
blue light, showing that the Earth is, indeed, a "blue planet".

Plants themselves reflect more infrared light than visible light, but humans
can only see the green light they reflect.

The French observations were made in April 2001 and analysis detected the
vegetation signature in December 2001. In July that year another team from
Steward Observatory in Arizona made related observations.

15:34 25 January 02>>


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