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Posted by baalke on April 11, 2007, 12:53 pm
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Caltech News Release
Embargoed until 6:00 AM PDT, Wednesday, April 11, 2007
Some Earth-like Worlds May Have Foliage of Colors Other Than Green,
Researchers Say
PASADENA, Calif.--In the next decade, when scientists are able to
study Earth-sized worlds around other stars, they may find that
foliage on some of the planets is predominantly yellow-or orange, or
red. It all depends on the color of the star the planet orbits and
the stuff that makes up the planet's atmosphere.
That's the conclusion of researchers from the Virtual Planetary
Laboratory, a NASA-funded initiative at the California Institute of
Technology, who are announcing today results from a series of
comprehensive computer models for guiding the future search for plant
life on other worlds. Two related papers on what to expect out of
photosynthesis are being issued in the journal Astrobiology.
Determining the range of possible colors is important because
scientists need to know what to look for when they begin getting
spectra of light from faraway Earth-sized planets, says lead author
Nancy Kiang, a biometeorologist at NASA's Goddard Institute for Space
Studies, and currently a visitor at Caltech's Spitzer Science Center.
"The dominant color of photosynthesis could be yellow, or orange, or
maybe red," Kiang explains. "I think it is unlikely that anything
will be blue--and, of course, green plants are also a possibility,
since that's what we have here."
"What makes this study unusual is the highly interdisciplinary method
by which planetary scientists, atmospheric scientists, biologists,
and others have pooled their efforts in modeling the possible spectra
of light available to plants on Earth-like planets orbiting around
other stars," says Vikki Meadows, an astrobiologist at Caltech and
lead scientist of the Virtual Planetary Laboratory. Because the study
requires data about everything from the type of photons given off by
a main-sequence star in a particular stage of its life, to the depth
of water that an aqueous plant might prefer, a huge variety of
information is required.
"No single astronomer or biologist or atmospheric scientist could
have attacked this problem individually to get the simulation," says
Meadows, who is herself an astrobiologist whose original academic
training was in astronomy. "So these papers are truly
interdisciplinary pieces of work."
The researchers focused on the way plants use light for energy to
produce sugar--which is pretty much the definition of
photosynthesis--because photosynthetic pigments must be adapted to
the available light spectrum. The available light spectrum at a
planet's surface is a result of both the light from the parent star
and filtering effects of gases in the atmosphere. For example, ozone
absorbs ultraviolet light so that not much reaches Earth's surface.
"It turns out that the spectrum of the number of particles of light
is what is important, and on Earth there are more particles in the
red," Kiang explains. "This could explain why plants here on Earth
are mainly green."
On Earth, plants absorb blue light because it is energetic, and red
light because the photons are plentiful. There is more than enough
energy from the blue and red in sunlight, so plants do not really
need more. Therefore, they reflect away relatively more green light,
which is why plants appear green to us.
A planet orbiting a star with the size and temperature roughly like
our sun, and with Earth's particular mix of oxygen and what-have-you,
would tend to have plants that like to soak up light in blue and red
and less in green. But the situation could be different on other
planets, where other colors of the spectrum might predominate. In
those cases, another color like red might not be so useful, and the
plants would mostly appear red.
There are many other factors, such as the role not only ozone plays
but also carbon dioxide and water vapor, how the stellar radiation
creates chemical reactions in the atmosphere, whether the star is
prone to solar flares, how much water is on the planet, how much
light gets to the surface, what gases are produced by the plants
themselves, and so on. This is why a complex computer model was
necessary.
Also, one might wonder what things could live on a planet with very
little ozone, for example, where radiation would be a daily assault
on living organisms, and energetic particles from solar winds would
be like deadly microscopic bullets. Meadows says the modelers have
taken such scenarios into consideration, and they think that there
might be a "sweet spot" a few to tens of feet below the surface of
the water where life is protected from UV radiation.
"We found that the sweet spot could be up to nine meters underwater
for a planet orbiting a star significantly cooler than our sun, and
photosynthesis could still take place," she says. "Something with a
floatation capability could be protected from solar flares and still
get enough photons to carry on."
In short, the new model provides a powerful tool for looking for life
on other worlds, Meadows says.
"We once thought that planets around other stars were exceedingly
rare," she explains. "But every time telescopes have gotten better,
we've been able to find more and more Jupiter-sized planets. So
there's no reason to think that there aren't a huge number of Earth-
sized planets out there as well.
"We may not find anything like ourselves, but it's possible that
bacterial life is prevalent on these Earth-like planets," Meadows
adds. "If we have the environment for life to exist, then we think
that it's likely that life will emerge in these conditions."
The other authors of the two papers are Antigona Segura-Peralta,
Giovanna Tinetti, Martin Cohen, Janet Siefert, and David Crisp, all
of the Virtual Planetary Laboratory, Govindjee, of the University of
Illinois, and Robert Blankenship, of Washington University.
The Virtual Planetary Laboratory was formed as part of the NASA
Astrobiology Institute, which was founded in 1997 as a partnership
between NASA, 12 major U.S. teams, and six international consortia.
NAI's goal is to promote, conduct, and lead integrated
multidisciplinary astrobiology research and to train a new generation
of astrobiology researchers.
For related images, please visit
http://www.nasa.gov/centers/goddard/news/topstory/2007/spectrum_plants.html.
Contact:
Robert Tindol
tindol@caltech.edu
(626) 395-3631
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Posted by robert casey on April 11, 2007, 5:44 pm
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baalke@earthlink.net wrote:
> Caltech News Release
> Embargoed until 6:00 AM PDT, Wednesday, April 11, 2007
>
> Some Earth-like Worlds May Have Foliage of Colors Other Than Green,
> Researchers Say
>
A few plants on Earth are purple instead of green. Which would mean
that they suck up the green light in sunlight, instead of red and blue.
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Posted by bae on April 12, 2007, 8:31 pm
Please log in for more thread options >baalke@earthlink.net wrote:
>
>> Caltech News Release
>> Embargoed until 6:00 AM PDT, Wednesday, April 11, 2007
>>
>> Some Earth-like Worlds May Have Foliage of Colors Other Than Green,
>> Researchers Say
>
>A few plants on Earth are purple instead of green. Which would mean
>that they suck up the green light in sunlight, instead of red and blue.
They aren't purple *instead* of green, they are purple *as well as* green.
They producce anthocyanin pigments which make the green of chlorophyll
less visible to our eyes. Anthocyanins aren't photosynthetic pigments.
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