NASA Predicts Non-Green Plants on Other Planets
04.11.07
NASA scientists believe they have found a way to predict the color of plants on planets in other solar systems.
Green, yellow or even red-dominant plants may live on extra-solar
planets, according to scientists whose two scientific papers appear in
the March issue of the journal, Astrobiology. The scientists studied
light absorbed and reflected by organisms on Earth, and determined that
if astronomers were to look at the light given off by planets circling
distant stars, they might predict that some planets have mostly
non-green plants.
[You must be registered and logged in to see this link.] Image right:In the process of photosynthesis, plants convert energy from the sun
into chemical energy in the form of glucose, or sugar. The chlorophyll
in plants absorbs more blue and red light from sunlight, and less green
light. Chlorophyll is green, because it reflects green light more than
blue and red light.
Click image to enlarge. Credit: NASA Ames
"We can identify the strongest candidate wavelengths of light for the
dominant color of photosynthesis on another planet," said Nancy Kiang,
lead author of the study and a biometeorologist at NASA's Goddard
Institute for Space Studies, New York. Kiang worked with a team of
scientists from the Virtual Planetary Laboratory (VPL) at the
California Institute of Technology, Pasadena, Calif. VPL was formed as
part of the NASA Astrobiology Institute (NAI), based at the NASA Ames
Research Center in California’s Silicon Valley.
"This work broadens our understanding of how life may be detected on
Earth-like planets around other stars, while simultaneously improving
our understanding of life on Earth," said Carl Pilcher, director of the
NAI at NASA Ames. "This approach -- studying Earth life to guide our
search for life on other worlds -- is the essence of astrobiology."
[You must be registered and logged in to see this link.] Image left: This is an illustration of what plants may look like on different planets.
Click image to enlarge. Credit: Caltech illustration by Doug Cummings
Kiang and her colleagues calculated what the stellar light would look
like at the surface of Earth-like planets whose atmospheric chemistry
is consistent with the different types of stars they orbit. By looking
at the changes in that light through different atmospheres, researchers
identified colors that would be most favorable for photosynthesis on
other planets. This new research narrows the range of colors that
scientists would expect to see when photosynthesis is occurring on
extrasolar planets. Each planet will have different dominant colors for
photosynthesis, based on the planet’s atmosphere where the most light
reaches the planet’s surface. The dominant photosynthesis might even be
in the infrared.
"This work will help guide designs for future space telescopes that
will study extrasolar planets, to see if they are habitable, and could
have alien plants," said Victoria Meadows, an astronomer who heads the
VPL. The VPL team is using a suite of computer models to simulate
Earth-size planets and their light spectra as space telescopes would
see them. The scientists' goal is to discover the likely range of
habitable planets around other stars and to find out how these planets
might appear to future planet-finding missions.
Image left:The Hertzsprung-Russell diagram developed by 2 astronomers in 1912,
plots some of the characteristics of a large number of stars. They
plotted spectral class vs. luminosity (brightness) of a large sample of
stars. Our Sun's luminosity is 3.9 x 1026 Joules/s. The plot spans a
large range in luminosity from a fraction of our Sun's brightness (0.01
times) to (10,000 times) much greater the strength of our Sun. Stellar
surface temperatures range from 3,500 degrees Kelvin (K) (5,840
Fahrenheit (F)) to 50,000 K (89540 F). Our Sun is a G star. Credit: NASA
On Earth, Kiang and colleagues surveyed light absorbed and reflected by
plants and some bacteria during photosynthesis, a process by which
plants use energy from sunlight to produce sugar. Organisms that live
in different light environments absorb the light colors that are most
available. For example, there is a type of bacteria that inhabit murky
waters where there is little visible light, and so they use infrared
radiation during photosynthesis.
Image right:This SeaWiFS satellite image shows chlorophyll (which indicates ocean
plants) in the Earth's oceans. The Normalized Difference Vegetation
Index (NDVI) measures the amount and health of plants on land, while
chlorophyll a measurements indicate the amount of phytoplankton in the
ocean. Land vegetation and phytoplankton both consume atmospheric
carbon dioxide. Credit: SeaWiFS Project, NASA/Goddard Space Flight
Center, and ORBIMAGE
Scientists have long known that the chlorophyll in most plants on Earth
absorbs blue and red light and less green light. Therefore, chlorophyll
appears green. Although some green color is absorbed, it is less than
the other colors. Previously, scientists thought plants are not
efficient as they could be, because they do not use more green light.
According to scientists, the Sun has a specific distribution of colors
of light, emitting more of some colors than others. Gases in Earth's
air also filter sunlight, absorbing different colors. As a result, more
red light particles reach Earth's surface than blue or green light
particles, so plants use red light for photosynthesis. There is plenty
of light for land plants, so they do not need to use extra green light.
But not all stars have the same distribution of light colors as our
Sun. Study scientists say they now realize that photosynthesis on
extrasolar planets will not necessarily look the same as on Earth.
"It makes one appreciate how life on Earth is so intimately adapted to
the special qualities of our home planet and Sun," said Kiang.
[You must be registered and logged in to see this link.]Click image to enlarge Image above:This graph shows the intensity of light by color (wavelength) that
reaches the surface of Earth-like planets orbiting different types of
stars. From hotter to cooler, the star types are F, G, K, and M. Our
Sun is a G2 star (yellow line). A planet orbiting an F2 star (red line)
has more blue light at the surface, whereas Earth and the K2 star
planet receive more red light. Planets around M stars receive much less
visible light but much more infrared light. Atmospheric gases such as
ozone (O3), oxygen (O2), water vapor (H2O), and carbon dioxide (CO2)
absorb light at specific wavelengths, producing the pronounced dips
that astronomers might someday detect. Then in the diagram's horizontal
axis, mark the wavelengths from 0 to 0.4 microns as UV, 0.4 to 0.7 as
visible, and longer than 0.7 as infrared. Credit: NASA
NASA GISS is a leading center in the study of Earth’s past, present and
future climates, research that is vital for understanding how life
impacts and is impacted by the atmosphere on other planets. The NAI,
founded in 1997, is 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.
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