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Exoplanets - Planets Beyond Our Solar System


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NASA's Spitzer First to Crack Open Light of Faraway Worlds


NASA's Spitzer Space Telescope has captured for the first time enough light from planets outside our solar system, known as exoplanets, to identify signatures of molecules in their atmospheres. The landmark achievement is a significant step toward being able to detect possible life on rocky exoplanets and comes years before astronomers had anticipated.

"This is an amazing surprise," said Spitzer project scientist Dr. Michael Werner of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "We had no idea when we designed Spitzer that it would make such a dramatic step in characterizing exoplanets."

Spitzer, a space-based infrared telescope, obtained the detailed data, called spectra, for two different gas exoplanets. Called HD 209458b and HD 189733b, these so-called "hot Jupiters" are, like Jupiter, made of gas, but orbit much closer to their suns.

linked-image
Image above: NASA's Spitzer Space Telescope was recently used to
capture spectra, or molecular fingerprints, of two "hot Jupiter" worlds
like the one depicted here. This is the first time a spectrum has ever
been obtained for an exoplanet, or a planet beyond our solar system.
Image credit: NASA/JPL-Caltech
+ Animation and caption
+ Related images and briefing materials


The data indicate the two planets are drier and cloudier than predicted. Theorists thought hot Jupiters would have lots of water in their atmospheres, but surprisingly none was found around HD 209458b and HD 189733b. According to astronomers, the water might be present but buried under a thick blanket of high, waterless clouds.

Those clouds might be filled with dust. One of the planets, HD 209458b, showed hints of tiny sand grains, called silicates, in its atmosphere. This could mean the planet's skies are filled with high, dusty clouds unlike anything seen around planets in our own solar system.

"The theorists' heads were spinning when they saw the data," said Dr. Jeremy Richardson of NASA's Goddard Space Flight Center, Greenbelt, Md.

"It is virtually impossible for water, in the form of vapor, to be absent from the planet, so it must be hidden, probably by the dusty cloud layer we detected in our spectrum," he said. Richardson is lead author of a Nature paper appearing Feb. 22 that describes a spectrum for HD 209458b.

In addition to Richardson's team, two other groups of astronomers used Spitzer to capture spectra of exoplanets. A team led by Dr. Carl Grillmair of NASA's Spitzer Science Center at the California Institute of Technology in Pasadena, Calif., observed HD 189733b, while a team led by Dr. Mark R. Swain of JPL focused on the same planet in the Richardson study, and came up with similar results. Grillmair's results will be published in the Astrophysical Journal Letters. Swain's findings have been submitted to the Astrophysical Journal Letters.

A spectrum is created when an instrument called a spectrograph splits light from an object into its different wavelengths, just as a prism turns sunlight into a rainbow. The resulting pattern of light, the spectrum, reveals "fingerprints" of chemicals making up the object.

Until now, the only planets for which spectra were available belonged in our own solar system. The planets in the Spitzer studies orbit stars that are so far away, they are too faint to be seen with the naked eye. HD 189733b is 370 trillion miles away in the constellation Vulpecula, and HD 209458b is 904 trillion miles away in the constellation Pegasus. That means both planets are at least about a million times farther away from us than Jupiter. In the future, astronomers hope to have spectra for smaller, rocky planets beyond our solar system. This would allow them to look for the footprints of life -- molecules key to the existence of life, such as oxygen and possibly even chlorophyll.

"With these new observations, we are refining the tools that we will one day need to find life elsewhere if it exists," said Swain. "It's sort of like a dress rehearsal."

Spitzer was able to tease out spectra from the feeble light of the two planets through what is known as the "secondary eclipse" technique. In this method -- first used by Spitzer in 2005 to directly detect the light from an exoplanet for the first time (http://www.spitzer.caltech.edu/Media/releases/ssc2005-09/index.shtml) -- a so-called transiting planet is monitored as it circles behind its star, temporarily disappearing from our Earthly point of view. By measuring the dip in infrared light that occurs when the planet disappears, Spitzer can learn how much light is coming solely from the planet. The technique will work only in infrared wavelengths, where the planet is brighter than in visible wavelengths and stands out better next to the overwhelming glare of its star.

In the new studies, Spitzer's spectrograph, which measures infrared light at a range of wavelengths, stared at the two transiting planets as they orbited their stars. This allowed the astronomers to subtract the spectra of the stars from the spectra of the planets plus their stars to obtain spectra of the planets alone.

"When we first set out to make these observations, they were considered high risk because not many people thought they would work," said Grillmair. "But Spitzer has turned out to be superbly designed and more than up to the task."

Previous observations of HD 209458b by NASA's Hubble Space Telescope revealed individual elements, such as sodium, oxygen, carbon and hydrogen, that bounce around the very top of the planet, a region higher up than that probed in the Spitzer studies and a region where molecules like water would break apart. To do this, Hubble measured changes in the light from the star, not the planet, as the planet passed in front. The observations indicated less sodium than predicted, which again supports the idea that the planet is socked in with high clouds.

Astronomers hope to use Spitzer for additional studies of transiting exoplanets, which are those that cross in front of their stars from our point view. Of the approximately 200 known exoplanets, 14 are transiting. At least three of these in addition to HD 209458b and HD 189733b are candidates for obtaining spectra. Further spectral studies of HD 209458b and HD 189733b will also yield more information about the planets' atmospheres.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA. Spitzer's infrared spectrograph was built by Cornell University, Ithaca, N.Y. Its development was led by Dr. Jim Houck of Cornell.

For artist's concepts and more information, visit http://www.nasa.gov/spitzer and www.spitzer.caltech.edu/Media.

Tabatha Thompson
NASA Headquarters, Washington
202-358-3895

Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673

2007-020


Source: NASA - Missions - Spitzer - News
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NASA's Spitzer Marks Beginning of New Age of Planetary Science


For Release: February 22, 2007

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NASA's Spitzer Space Telescope has for the first time captured the light from two known planets orbiting stars other than our Sun. The findings mark the beginning of a new age of planetary science, in which "extrasolar" planets can be directly measured and compared.

"Spitzer has provided us with a powerful new tool for learning about the temperatures, atmospheres and orbits of planets hundreds of light-years from Earth," said Dr. Drake Deming of NASA's Goddard Space Flight Center, Greenbelt, Md., lead author of a new study on one of the planets.

"It's fantastic," said Dr. David Charbonneau of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass., lead author of a separate study on a different planet. "We've been hunting for this light for almost 10 years, ever since extrasolar planets were first discovered." The Deming paper appears today in Nature's online publication; the Charbonneau paper will be published in an upcoming issue of the Astrophysical Journal.

So far, all confirmed extrasolar planets, including the two recently observed by Spitzer, have been discovered indirectly, mainly by the "wobble" technique and more recently, the "transit" technique. In the first method, a planet is detected by the gravitational tug it exerts on its parent star, which makes the star wobble. In the second, a planet's presence is inferred when it passes in front of its star, causing the star to dim, or blink. Both strategies use visible-light telescopes and indirectly reveal the mass and size of planets, respectively.

In the new studies, Spitzer has directly observed the warm infrared glows of two previously detected "hot Jupiter" planets, designated HD 209458b and TrES-1. Hot Jupiters are extrasolar gas giants that zip closely around their parent stars. From their toasty orbits, they soak up ample starlight and shine brightly in infrared wavelengths.

To distinguish this planet glow from that of the fiery hot stars, the astronomers used a simple trick. First, they used Spitzer to collect the total infrared light from both the stars and planets. Then, when the planets dipped behind the stars as part of their regular orbit, the astronomers measured the infrared light coming from just the stars. This pinpointed exactly how much infrared light belonged to the planets. "In visible light, the glare of the star completely overwhelms the glimmer of light reflected by the planet," said Charbonneau. "In infrared, the star-planet contrast is more favorable because the planet emits its own light."

The Spitzer data told the astronomers that both planets are at least a steaming 1,000 Kelvin (727 degrees Celsius, 1340 Fahrenheit). These measurements confirm that hot Jupiters are indeed hot. Upcoming Spitzer observations using a range of infrared wavelengths are expected to provide more information about the planets' winds and atmospheric compositions.

The findings also reawaken a mystery that some astronomers had laid to rest. Planet HD 209458b is unusually puffy, or large for its mass, which some scientists thought was the result of an unseen planet's gravitational pull. If this theory had been correct, HD 209458b would have a non-circular orbit. Spitzer discovered that the planet does in fact follow a circular path. "We're back to square one," said Dr. Sara Seager, Carnegie Institution of Washington, Washington, co-author of the Deming paper. "For us theorists, that's fun."

Spitzer is ideally suited for studying extrasolar planets known to transit, or cross, stars the size of our Sun out to distances of 500 light-years. Of the seven known transiting planets, only the two mentioned here meet those criteria. As more are discovered, Spitzer will be able to collect their light -- a bonus for the observatory, considering it was not originally designed to see extrasolar planets. NASA's future Terrestrial Planet Finder coronagraph, set to launch in 2016, will be able to directly image extrasolar planets as small as Earth.

Shortly after its discovery in 1999, HD 209458b became the first planet detected via the transit method. That result came from two teams, one led by Charbonneau. TrES-1 was found via the transit method in 2004 as part of the NASA-funded Trans-Atlantic Exoplanet Survey, a ground-based telescope program established in part by Charbonneau.

Artist's concepts and additional information about the Spitzer Space Telescope are available at http://www.spitzer.caltech.edu/Media.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center, at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA. For more information contact Nancy Neal Jones, Goddard Space Flight Center, 301/286-0039; or David Aguilar, Harvard-Smithsonian Center for Astrophysics, 617/495-7462.

Dolores Beasley
Headquarters, Washington
(Phone: 202/358-1753)

Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone: 818/354-4673)

jpl2005-050
ssc2005-09


Source: NASA/CalTech - Spitzer- Newsroom Edited by Waspie_Dwarf
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The Language of Planetary Light

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Credit: NASA/JPL-Caltech/D. Charbonneau (Harvard-Smithsonian CfA)

and NASA/JPL-Caltech/D. Deming (Goddard Space Flight Center)

This graph of data from NASA's Spitzer Space telescope shows changes in the infrared light output of two star-planet systems (one above, one below) located hundreds of light-years away. The data were taken while the planets, called HD 209458b and TrES-1, disappeared behind their stars in what is called a "secondary eclipse." The dip seen in the center of each graph represents the time when the planets were eclipsed, and tells astronomers exactly how much light they emit.

Why a secondary eclipse? When a planet transits, or passes in front of, its star, it partially blocks the light of the star. When the planet swings around behind the star, the star completely blocks its light. This drop in total light can be measured to determine the amount of light coming from just the planet.

Why infrared? In visible light, the glare of a star overwhelms its planetary companion and the little light the planet reflects. In infrared, a star shines less brightly, and its planet gives off its own internal light, or heat radiation, making the planet easier to detect.

By observing these secondary eclipses at different infrared wavelengths, astronomers can obtain the planet's temperature, and, in the future, they may be able to pick out chemicals sprinkled throughout a planet's atmosphere. The technique also reveals whether a planet's orbit is elongated or circular.

This strategy will not work for all known extrasolar planets. It is ideally suited to study those Jupiter-sized planets previously discovered to cross, or transit, between us and the Sun-like stars they orbit, out to distances of 500 light-years. NASA's Spitzer Space Telescope was the first to successfully employ this technique.

The data of HD 209458b were taken by Spitzer's multiband imaging photometer using the 24-micron array. The data of TrES-1 were taken by Spitzer's infrared array camera using the 8-micron array.

Source: NASA/CalTech - Spitzer- Newsroom

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Blinded by the Light

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Credit: NASA/JPL-Caltech/R. Hurt (SSC)[/color]

This artist's concept shows what a fiery hot star and its close-knit planetary companion might look close up if viewed in visible (left) and infrared light. In visible light, a star shines brilliantly, overwhelming the little light that is reflected by its planet. In infrared, a star is less blinding, and its planet perks up with a fiery glow.

Astronomers using NASA's Spitzer Space Telescope took advantage of this fact to directly capture the infrared light of two previously detected planets orbiting outside our solar system. Their findings revealed the temperatures and orbits of the planets. Upcoming Spitzer observations using a variety of infrared wavelengths may provide more information about the planets' winds and atmospheric compositions.

In this figure, the colors represent real differences between the visible and infrared views of the system. The visible panel shows what our eyes would see if we could witness the system close up. The hot star is yellow because, like our Sun, it is brightest in yellow wavelengths. The warm planet, on the other hand, is brightest in infrared light, which we can't see. Instead, we would see the glimmer of star light that the planet reflects.

In the infrared panel, the colors reflect what our eyes might see if we could retune them to the invisible, infrared portion of the light spectrum. The hot star is less bright in infrared light than in visible and appears fainter. The warm planet peaks in infrared light, so is shown brighter. Their hues represent relative differences in temperature. Because the star is hotter than the planet, and because hotter objects give off more blue light than red, the star is depicted in blue, and the planet, red.

The overall look of the planet is inspired by theoretical models of hot, gas giant planets. These "hot Jupiters" are similar to Jupiter in composition and mass, but are expected to look quite different at such high temperatures. The models are courtesy of Drs. Curtis Cooper and Adam Showman of the University of Arizona, Tucson.

Source: NASA/CalTech - Spitzer- Newsroom

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Absence of Water in Distant Planet's Atmosphere Surprises Astronomers


The Harvard-Smithsonian Center for Astrophysics press release is reproduced below:

Release No.: 07-03
For Release: Embargoed until 10:00 am PST/1:00 pm EST, February 21, 2007


linked-image

Astronomers have measured the first-ever infrared spectrum of two planets orbiting distant Sun-like stars. The planet HD 189733b, shown here in an artist's rendering, appears to be missing common molecules like water and methane. Astronomers speculate that these molecules are present but hidden behind a high layer of silicate clouds.
Credit: David A. Aguilar (CfA)


Cambridge, MA - A team of astronomers led by Carl Grillmair (Spitzer Science Center) and David Charbonneau (Harvard-Smithsonian Center for Astrophysics) announced today that they have directly measured the first spectrum from a known planet orbiting a distant star. Two other teams made a similar measurement of a different extrasolar planet. Taken together, this pioneering work opens a new field of planetary exploration, allowing astronomers to directly analyze the atmospheres of worlds beyond our solar system.

"In a sense, we're getting our first sniffs of air from an alien world," said Charbonneau. "And what we found surprised us. Or more accurately, what we DIDN'T find surprised us."

"We expected to see common molecules like water, methane, or carbon dioxide," explained Grillmair. "But we didn't see any of those. The spectrum was flat, with no molecular fingerprints that we could detect."

The planet studied by Charbonneau and his colleagues is known as HD 189733b. It orbits a star slightly cooler and less massive than the Sun located about 60 light-years from Earth in the direction of the constellation Vulpecula. It is the closest known "transiting" planet to Earth.

HD 189733b is a type of planet known as a "hot Jupiter." It orbits very close to its star, completing one revolution every 2.2 days. Its mass and physical size are both slightly larger than Jupiter. At a distance of only three million miles from its star, HD 189733b is heated to a broiling temperature of 1700 degrees Fahrenheit.

HD 189733b was selected for study because it periodically crosses in front of and behind its star. When transiting in front, the planet partially eclipses the star and blocks a small portion of the star's light. Similarly, the system dims slightly when the planet disappears behind its star since the star blocks the planet's light. By observing this "secondary eclipse," astronomers can tease out the faint signal of the planet from the overwhelming light of the nearby star.

The team studied HD 189733b using the Infrared Spectrograph instrument aboard NASA's Spitzer Space Telescope. Spitzer detects infrared light, or light beyond the red end of the visible light spectrum.

When light is split into a rainbow-like spectrum, certain atoms or molecules can leave "fingerprints" in the spectrum. Those fingerprints tell astronomers what molecules are there, just as crime scene investigators use real fingerprints to determine what person was in the area.

Missing Fingerprints

Theoretical calculations by different teams unanimously predicted that water vapor should be the most obvious spectral feature. However, the fingerprint of water was missing from HD 189733b. Astronomers also expected a prominent signature of methane, but that was missing as well.

"The most fundamental thing we predicted was wrong," said Grillmair.

Since planet formation works the same way everywhere, and since the molecules in question should be just as abundant on a distant world orbiting a Sun-like star as they are in our solar system, astronomers speculate that something is hiding the molecules from sight.

One clue comes from the spectrum of a second planet, HD 209458b, which orbits a different star. That spectrum, obtained by a team led by Jeremy Richardson (NASA's Goddard Space Flight Center), shows hints of silicates - molecules containing silicon and oxygen. Such molecules form rocks on the Earth, but on the scorching-hot worlds studied with Spitzer, silicates exist as tiny dust grains that can form clouds.

"We think that both planets may be cloaked in dark silicate clouds," said Charbonneau. "These worlds are blacker than any planet in our solar system."

The best way to clear up the mystery is to study additional "hot Jupiters" to determine if they show similar signs in their atmospheres. Astronomers also will continue to study HD 189733b and HD 209458b in more detail.

"Right now, it's a puzzle," said Charbonneau. "With a few more puzzle pieces, the picture should become clearer."

The Grillmair/Charbonneau study of HD 189733b will be published in an upcoming issue of The Astrophysical Journal Letters. The Richardson study of HD 209458b is being published in the February 22 issue of the journal Nature. A third team led by Mark Swain (NASA's Jet Propulsion Laboratory) also has submitted a study of the spectrum of HD 209458b to The Astrophysical Journal Letters.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center, Pasadena, Calif. JPL is a division of California Institute for Technology, Pasadena.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Source: CfA Press Release
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How to Pluck a Spectrum From a Planet

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This diagram illustrates how astronomers using NASA's Spitzer Space Telescope can capture the elusive spectra of hot-Jupiter planets. Spectra are an object's light spread apart into its basic components, or wavelengths. By dissecting light in this way, scientists can sort through it and uncover clues about the composition of the object giving off the light.

To obtain a spectrum for an object, one first needs to capture its light. Hot-Jupiter planets are so close to their stars that even the most powerful telescopes can't distinguish their light from the light of their much brighter stars.

But, there are a few planetary systems that allow astronomers to measure the light from just the planet by using a clever technique. Such "transiting" systems are oriented in such a way that, from our vantage point, the planets' orbits are seen edge-on and cross directly in front of and behind their stars.

In this technique, known as the secondary eclipse method, changes in the total infrared light from a star system are measured as its planet transits behind the star, vanishing from our Earthly point of view. The dip in observed light can then be attributed to the planet alone.

To capture a spectrum of the planet, Spitzer must observe the system twice. It takes a spectrum of the star together with the planet (first panel), then, as the planet disappears from view, a spectrum of just the star (second panel). By subtracting the star's spectrum from the combined spectrum of the star plus the planet, it is able to get the spectrum for just the planet (third panel).

This ground-breaking technique was used by Spitzer to obtain the first-ever spectra of two planets beyond our solar system, HD 209458b and HD 189733b. The results suggest that the hot planets are socked in with dry clouds high up in the planet's stratospheres. In addition, HD 209458b showed hints of silicates, indicating those high clouds might be made of very fine sand-like particles.

Image credit: NASA/JPL-Caltech

+ High-resolution TIFF (21Mb)

Source: NASA - Spitzer - News

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Cracking the Code of Faraway Worlds

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This infrared data from NASA's Spitzer Space Telescope -- called a spectrum -- tells astronomers that a distant gas planet, a so-called "hot Jupiter" called HD 209458b, might be smothered with high clouds. It is one of the first spectra of an alien world.

A spectrum is created when an instrument called a spectrograph cracks light from an object open into a rainbow of different wavelengths. Patterns or ripples within the spectrum indicate the presence, or absence, of molecules making up the object.

Astronomers using Spitzer's spectrograph were able to obtain infrared spectra for two so-called "transiting" hot-Jupiter planets using the "secondary eclipse" technique. In this method, the spectrograph first collects the combined infrared light from the planet plus its star, then, as the planet is eclipsed by the star, the infrared light of just the star. Subtracting the latter from the former reveals the planet's own rainbow of infrared colors.

When astronomers first saw the infrared spectrum above, they were shocked. It doesn't look anything like what theorists had predicted. For example, theorists thought there'd be signatures of water in the wavelength ranges of 8 to 9 microns. The fact that water is not detected might indicate that it is hidden under a thick blanket of high, dry clouds.

In addition, the spectrum shows signs of silicate dust -- tiny grains of sand -- in the wavelength range of 9 to 10 microns. This suggests that the planet's skies could be filled with high clouds of dust unlike anything seen in our own solar system.

There is also an unidentified molecular signature at 7.78 microns. Future observations using Spitzer's spectrograph should be able to determine the nature of the mysterious feature.

This spectrum was produced by Dr. Jeremy Richardson of NASA's Goddard Space Flight Center, Greenbelt, Md. and his colleagues. The data were taken by Spitzer's infrared spectrograph on July 6 and 13, 2005.

Image credit: NASA/JPL-Caltech/GSFC

+ High-resolution TIFF (1Mb)

Source: NASA - Spitzer - News

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Cracking the Code of Faraway Worlds

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This infrared data from NASA's Spitzer Space Telescope -- called a spectrum -- tells astronomers that a distant gas planet, a so-called "hot Jupiter" called HD 209458b, might be smothered with high clouds. It is one of the first spectra of an alien world.

A spectrum is created when an instrument called a spectrograph spreads light from an object apart into a rainbow of different wavelengths. Patterns or ripples within the spectrum indicate the presence, or absence, of molecules making up the object.

Astronomers using Spitzer's spectrograph were able to obtain infrared spectra for two so-called "transiting" hot-Jupiter planets using the "secondary eclipse" technique. In this method, the spectrograph first collects the combined infrared light from the planet plus its star, then, as the planet is eclipsed by the star, the infrared light of just the star. Subtracting the latter from the former reveals the planet's own rainbow of infrared colors.

When astronomers first saw the infrared spectrum above, they were shocked. It doesn't look anything like what theorists had predicted. Theorists though the spectra for hot, Jupiter-like planets like this one would be filled with the signatures of molecules in the planets' atmospheres. But the spectrum doesn't show any molecules. It is what astronomers call "flat." For example, theorists thought there'd be signatures of water in the wavelength ranges of 8 to 9 microns. The fact that water is not seen there might indicate that the water is hidden under a thick blanket of high, dry clouds.

This spectrum was produced by Dr. Mark R. Swain of NASA's Jet Propulsion Laboratory in Pasadena, Calif., using a complex set of mathematical tools. It was derived using two different methods, both of which led to the same result. The data were taken on July 6 and 13, 2005, by Dr. Jeremy Richardson of NASA's Goddard Space Flight Center and his team using Spitzer's infrared spectrograph.

Image credit: NASA/JPL-Caltech

+ High-resolution TIFF (1Mb)

Source: NASA - Spitzer - News

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Cracking the Code of Faraway Worlds

linked-image

This infrared data from NASA's Spitzer Space Telescope -- called a spectrum -- tells astronomers that a distant gas planet, a so-called "hot Jupiter" called HD 189733b, might be smothered with high clouds. It is one of the first spectra of an alien world.

A spectrum is created when an instrument called a spectrograph cracks light from an object open into a rainbow of different wavelengths. Patterns or ripples within the spectrum indicate the presence, or absence, of molecules making up the object.

Astronomers using Spitzer's spectrograph were able to obtain infrared spectra for two so-called "transiting" hot-Jupiter planets using the "secondary eclipse" technique. In this method, the spectrograph first collects the combined infrared light from the planet plus its star, then, as the planet is eclipsed by the star, the infrared light of just the star. Subtracting the latter from the former reveals the planet's own rainbow of infrared colors.

Astronomers were perplexed when they first saw the infrared spectrum above. It doesn't look anything like what theorists had predicted. Theorists thought the spectra of hot, Jupiter-like planets like this one would be filled with the signatures of molecules in the planets' atmospheres. But the spectrum doesn't show any molecules, and is instead what astronomers call "flat." For example, theorists thought there'd be a strong signature of water in the form of a big drop in the wavelength range between 7 and 10 microns. The fact that water is not detected may indicate that it is hidden underneath a thick blanket of high, dry clouds. The average brightness of the spectrum is also a bit lower than theoretical predictions, suggesting that very high winds are rapidly moving the terrific heat of the noonday sun from the day side of HD 189733b to the night side.

This spectrum was produced by Dr. Carl Grillmair of NASA's Spitzer Science Center at the California Institute of Technology in Pasadena, Calif., and his colleagues. The data were taken by Spitzer's infrared spectrograph on November 22, 2006.

Image credit: NASA/JPL-Caltech

+ High-resolution TIFF (815Kb)

Source: NASA - Spitzer - News

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  • 2 weeks later...

last updated: 22/02/2007

• The exosolar planets - that is, planets which lie beyond our own Solar System - were studied by the Spitzer Space Telescope, an £400 million instrument launched in 2003.

• Neither of the parent stars for HD 209458b or HD 189733b can be seen with the naked eye.

Spitzer revealed that HD 209458b and HD 189733b had no water in the tops of their atmospheres, a finding which surprised astronomers.

• HD 209458b, nicknamed Osiris, is a "hot Jupiter" that orbits a Sun like star in the constellation Pegasus and bakes at 800 deg C

• HD 189733b is another hot, cloudy Jupiter-like planet, having a mass 365 times that of the Earth and a radius 14 times larger. Its density is comparable to that of Saturn.

• HD 209458b is located about 153 light-years away in the constellation Pegasus, while HD 189733b is about 62 light-years away in the constellation Vulpecula.

• One light year - the distance light covers in one year - is equivalent to 5.9 million million miles.

• Both planets zip around their stars in very tight orbits; HD 209458b circles once every 3.5 days, while HD 189733b orbits once every 2.2 days.

• Of the more than 200 known exoplanets, there are 12 besides HD 209458b and HD 189733b whose orbits are inclined in such a way that, from our point of view, they pass in front of their stars.

www.news.yahoo.com

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NASA Telescope Finds Planets Thrive Around Stellar Twins


For Release: March 29, 2007

The double sunset that Luke Skywalker gazed upon in the film Star Wars might not be a fantasy.

Astronomers using NASA's Spitzer Space Telescope have observed that planetary systems -- dusty disks of asteroids, comets, and possibly planets -- are at least as abundant in twin-star systems as they are in those, like our own, with only one star. Since more than half of all stars are twins, or binaries, the finding suggests the universe is packed with planets that have two suns. Sunsets on some of those worlds would resemble the ones on Luke Skywalker's planet, Tatooine, where two fiery balls dip below the horizon one by one.

"There appears to be no bias against having planetary system formation in binary systems," said David Trilling of the University of Arizona, Tucson, lead author of a new paper about the research appearing in the April 1 issue of the Astrophysical Journal. "There could be countless planets out there with two or more suns."

Previously, astronomers knew that planets could form in exceptionally wide binary systems, in which stars are 1,000 times farther apart than the distance between Earth and the sun, or 1,000 astronomical units. Of the approximately 200 planets discovered so far outside our solar system, about 50 orbit one member of a wide stellar duo.

The new Spitzer study focuses on binary stars that are a bit more snug, with separation distances between zero and 500 astronomical units. Until now, not much was known about whether the close proximity of stars like these might affect the growth of planets. Standard planet-hunting techniques generally don't work well with these stars, but, in 2005, a NASA-funded astronomer found evidence for a planet candidate in one such multiple-star system.

Trilling and his colleagues used Spitzer's infrared, heat-seeking eyes to look not for planets, but for dusty disks in double-star systems. These so-called debris disks are made up of asteroid-like bits of leftover rock that never made it into rocky planets. Their presence indicates that the process of building planets has occurred around a star, or stars, possibly resulting in intact, mature planets.

In the most comprehensive survey of its kind, the team looked for disks in 69 binary systems between about 50 and 200 light-years away from Earth. All of the stars are somewhat younger and more massive than our middle-aged sun. The data show that about 40 percent of the systems had disks, which is a bit higher than the frequency for a comparable sample of single stars. This means that planetary systems are at least as common around binary stars as they are around single stars.

In addition, the astronomers were shocked to find that disks were even more frequent (about 60 percent) around the tightest binaries in the study. These coziest of stellar companions are between zero and three astronomical units apart. Spitzer detected disks orbiting both members of the star pairs, rather than just one. Extra-tight star systems like these are where planets, if they are present, would experience Tatooine-like sunsets.

"We were very surprised to find that the tight group had more disks," said Trilling. "This could mean that planet formation favors tight binaries over single stars, but it could also mean tight binaries are just dustier. Future observations should provide a better answer."

The Spitzer data also reveal that not all binary systems are friendly places for planets to form. The telescope detected far fewer disks altogether in intermediately spaced binary systems, between three to 50 astronomical units apart. This implies that stars may have to be either very close to each other, or fairly far apart, for planets to arise.

"For a planet in a binary system, location is everything," said co-author Karl Stapelfeldt of NASA's Jet Propulsion Laboratory in Pasadena, Calif.

"Binary systems were largely ignored before," added Trilling. "They are more difficult to study, but they might be the most common sites for planet formation in our galaxy."

Other authors on the paper include: John Stansberry, George Rieke and Kate Su of the University of Arizona; Richard Gray of the Appalachian State University, Boone, N.C.; Chris Corbally of the Vatican Observatory, Tucson; Geoff Bryden, Andy Boden and Charles Beichman of JPL; and Christine Chen of the National Optical Astronomical Observatory, Tucson.

JPL manages Spitzer for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. The multiband imaging photometer for Spitzer was built by Ball Aerospace Corporation, Boulder, Colo.; the University of Arizona; and Boeing North American, Canoga Park, Calif. Co-author Rieke is the principal investigator.

Whitney Clavin (818) 354-4673
Jet Propulsion Laboratory, Pasadena, Calif.

ssc2007-05


Source: NASA/CalTech - Spitzer- Newsroom
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Where Planets Take Up Residence

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Credit: NASA/JPL-Caltech/T. Pyle (SSC)

This diagram illustrates that mature planetary systems like our own might be more common around twin, or binary, stars that are either really close together, or really far apart.

NASA's Spitzer Space Telescope observed that debris disks, which are signposts of mature planetary systems, are more abundant around the tightest and widest of binary stars it studied. Specifically, the infrared telescope found significantly more debris disks around binary stars that are 0 to 3 astronomical units apart (top panel) and 50 to 500 astronomical units apart (bottom panel) than binary stars that are 3 to 50 astronomical units apart (middle panel). An astronomical unit is the distance between Earth and the sun.

In other words, if two stars are as far apart from each other as the sun is from Jupiter (5 astronomical units) or Pluto (40 astronomical units), they would be unlikely to host a family of planetary bodies.

The Spitzer data also revealed that debris disks circle all the way around both members of a close-knit binary (top panel), but only a single member of a wide duo (bottom panel). This could explain why the intermediately spaced binary systems (middle panel) can be inhospitable to planetary disks: they are too far apart to support one big disk around both stars, and they are too close together to have enough room for a disk around just one star.

Source: NASA/CalTech - Spitzer- Newsroom

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Solar System with Snug Suns

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Credit: NASA/JPL-Caltech/T. Pyle (SSC)

This artist's concept depicts a faraway solar system like our own -- except for one big difference. Planets and asteroids circle around not one, but two suns. NASA's Spitzer Space Telescope found evidence that such solar systems might be common in the universe.

Spitzer did not see any planets directly, but it detected dust that is kicked up from disks of asteroids and comets like the one depicted here. The disks were spotted circling all the way around several double, or binary, stars, some of which were closer together than Earth is to our sun. In fact, Spitzer found more disks in orbit around close-knit binary stars than single stars. This could mean that planets prefer two parent stars to one, but more research is needed to figure out exactly what's going on.

Source: NASA/CalTech - Spitzer- Newsroom

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Alien Sunset

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Credit: NASA/JPL-Caltech/R. Hurt (SSC)

Our solitary sunsets here on Earth might not be all that common in the grand scheme of things. New observations from NASA's Spitzer Space Telescope have revealed that mature planetary systems -- dusty disks of asteroids, comets, and possibly planets -- are more frequent around close-knit twin, or binary, stars than single stars like our sun. That means sunsets like the one portrayed in this artist's photo concept, and more famously in the movie Star Wars, might be quite commonplace in the universe.

Binary and multiple-star systems are about twice as abundant as single-star systems in our galaxy, and, in theory, other galaxies. In a typical binary system, two stars of roughly similar masses twirl around each other like pair-figure skaters. In some systems, the two stars are very far apart and barely interact with each other. In other cases, the stellar twins are intricately linked, whipping around each other quickly due to the force of gravity.

Astronomers have discovered dozens of planets that orbit around a single member of a very wide stellar duo. Sunsets from these worlds would look like our own, and the second sun would just look like a bright star in the night sky.

But do planets exist in the tighter systems, where two suns would dip below a planet's horizon one by one? Unveiling planets in these systems is tricky, so astronomers used Spitzer to look for disks of swirling planetary debris instead. These disks are made of asteroids, comets and possibly planets. The rocky material in them bangs together and kicks up dust that Spitzer's infrared eyes can see. Our own solar system is swaddled in a similar type of disk.

Surprisingly, Spitzer found more debris disks around the tightest binaries it studied (about 20 stars) than in a comparable sample of single stars. About 60 percent of the tight binaries had disks, while the single stars only had about 20 percent. These snug binary systems are as close or closer than just three times the distance between Earth and the sun. And the disks in these systems were found to circumnavigate both members of the star pair, rather than just one.

Though follow-up studies are needed, the results could mean that planet formation is more common around extra-tight binary stars than single stars. Since these types of systems would experience double sunsets, the artistic view portrayed here might not be fiction.

Source: NASA/CalTech - Spitzer- Newsroom

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Alien Sunset

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Credit: NASA/JPL-Caltech/T. Pyle (SSC)

This artist's animation depicts a faraway solar system like our own -- except for one big difference. Planets and asteroids circle around not one, but two suns. NASA's Spitzer Space Telescope found evidence that such solar systems might be common in the universe.

The movie begins by showing two snug, sun-like stars. It then pans out to show an Earth-like planet and a surrounding disk of asteroids and comets.

Spitzer did not see any planets directly, but it detected dust that is kicked up from disks like this one. The disks were spotted circling all the way around several double, or binary, stars, some of which were closer together than Earth is to our sun. In fact, Spitzer found more disks in orbit around close-knit binary stars than single stars. This could mean that planets prefer two parent stars to one, but more research is needed to figure out exactly what's going on.

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Source: NASA/CalTech - Spitzer- Newsroom

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Mar. 29

Astronomers using NASA’s Spitzer Space Telescope have found that twin-star systems are just as likely to be surrounded by dusty debris disks as ones with only a single star. Debris disks are made up of asteroid-sized rock chunks and other material that could be leftovers of planets that have formed in the system.

The majority of stars like our Sun have at least one stellar companion. Astronomers have theorized that planets could form with little trouble in two-star systems, called binaries, despite the more complex gravitational tugging. The new study provides strong observational evidence to support that idea.

“There appears to be no bias against having planetary system formation in binary systems,” said study leader David Trilling of the University of Arizona. “There could be countless planets out there with two or more suns.”

Trilling and his team looked for disks in 69 binary systems between 50 and 200 light-years away from Earth. All the stars are more massive and younger than our middle-aged Sun. The researchers found that about 40 percent of the binary systems they looked at had disks. This frequency is a bit higher than that for a comparable sample of single stars and suggests planets are at least as common around binary stars as they are around single stars.

Deepak Rhagavan, an astronomer at Georgia State University who was not involved in the study, says the new findings are exciting because they are the first evidence of a planetary nursery in a multiple star system. “Until now, we knew planets existed [in multiple star systems], but I think this is the first time that we’ve gotten a comprehensive study that looks at the debris disk where planets are born,” Rhagavan said.

Last year, Rhagavan’s team reported that many star systems known to harbor planets actually contained two, and in some cases, even three, stars.

Surprisingly, most of the debris disks found in the new survey were around so-called tight binary systems, where the stars are separated by 500 AU or less. One AU is equal to the distance between the Earth and the Sun.

Scientists know of about 50 planets that have two Suns, but all of them belong to “wide” binary systems, where the stars are separated by about 1,000 AU.

“The fact that they’ve found some positive evidence of planet-forming disks being around close binaries is really a new step,” Boss said.

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  • 2 weeks later...
Water Identified in Extrasolar Planet Atmosphere


The Lowell Observatory press release is reproduced below:

Flagstaff, Ariz. – For the first time, water has been identified in the atmosphere of an extrasolar planet. Through a combination of previously published Hubble Space Telescope measurements and new theoretical models, Lowell Observatory astronomer Travis Barman has found strong evidence for water absorption in the atmosphere of transiting planet HD209458b. This result was recently accepted for publication in the Astrophysical Journal (http://lanl.arxiv.org/abs/0704.1114).

"We now know that water vapor exists in the atmosphere of one extrasolar planet and there is good reason to believe that other extrasolar planets contain water vapor," said Barman.

Water vapor (or steam) has been expected to be present in the atmospheres of nearly all of the known extrasolar planets, even those that orbit closer to their parent star than Mercury is to our Sun. For the majority of extrasolar planets, their close proximity to their parent star has made detecting water and other compounds difficult. The identification reported here takes advantage of the fact that HD209458b, as seen from Earth, passes directly in front of its star every three and half days. As a planet passes in front of a star, its atmosphere blocks a different amount of the starlight at different wavelengths. In particular, absorption by water in the atmosphere of a giant planet makes the planet appear larger across a specific part of the infrared spectrum compared to wavelengths in the visible spectrum. An analysis of visible and infrared Hubble data carried out last year by Harvard student Heather Knutson made possible a direct comparison to new theoretical models developed by Barman at Lowell Observatory. This ultimately led to the identification of water absorption in a planet 150 light years from Earth.

“It is encouraging that theoretical predictions of water in extrasolar planets seem to agree reasonably well with observations,” said Barman.

This research was supported by NASA’s Origins of Solar System program.

end


About Lowell Observatory

Lowell Observatory is a private, non-profit research institution founded in 1894 by Percival Lowell. The Observatory has been the site of many important findings including the discovery of the large recessional velocities (redshift) of galaxies by Vesto Slipher in 1912-1914 (a result that led ultimately to the realization the universe is expanding), and the discovery of Pluto by Clyde Tombaugh in 1930. Today, Lowell's 19 astronomers use ground-based telescopes around the world, telescopes in space, and NASA planetary spacecraft to conduct research in diverse areas of astronomy and planetary science. Lowell Observatory currently has four research telescopes at its Anderson Mesa dark sky site east of Flagstaff, Arizona, and is building a 4-meter class research telescope, the Discovery Channel Telescope, in partnership with Discovery Communications, Inc.

Source: Lowell Observatory Press Release
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a transiting planet - that's a good find.. -

other planets could be just as visible by timing of orbit..

very cool indeed !!

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NASA Shows Future Space Telescopes Could Detect Earth Twin


For the first time ever, NASA researchers have successfully demonstrated in the laboratory that a space telescope rigged with special masks and mirrors could snap a photo of an Earth-like planet orbiting a nearby star. This accomplishment marks a dramatic step forward for missions like the proposed Terrestrial Planet Finder, designed to hunt for an Earth twin that might harbor life.

Trying to image an exoplanet - a planet orbiting a star other than the sun - is a daunting task, because its relatively dim glow is easily overpowered by the intense glare of its much bigger, brighter parent star. The challenge has been compared to looking for a firefly next to a searchlight.

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Image above: Three simulated planets -- one
as bright as Jupiter, one half as bright as
Jupiter and one as faint as Earth -- stand
out plainly in this image created from a
sequence of 480 images captured by the
High Contrast Imaging Testbed at JPL. A
roll-subtraction technique, borrowed from
space astronomy, was used to distinguish
planets from background light. The asterisk
marks the location of the system's simulated
star.
Image credit: NASA/JPL-Caltech
+ Browse version of image


Now, two researchers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., have shown that a fairly simple coronagraph - an instrument used to "mask" a star's glare - paired with an adjustable mirror, could enable a space telescope to image a distant planet 10 billion times fainter than its central star.

"Our experiment demonstrates the suppression of glare extremely close to a star, clearing a field dark enough to allow us to see an Earth twin. This is at least a thousand times better than anything demonstrated previously," said John Trauger, lead author of a paper appearing in the April 12 issue of Nature. This paper describes the system, called the High Contrast Imaging Testbed, and how the technique could be used with a telescope in space to see exoplanets. The lab experiment used a laser as a simulated star, with fainter copies of the star serving as "planets."

To date, scientists have used various techniques to detect more than 200 exoplanets. Most of these exoplanets are from five to 4,000 times more massive than Earth, and are either too hot, too cold or too much of a giant gas ball to be considered likely habitats for life. So far, no one has managed to capture an image of an exoplanetary system that resembles our own solar system. Scientists are eager to take a closer look at nearby systems, to hunt for and then characterize any Earth-like planets - those with the right size, orbit and other traits considered friendly for life.

In the lab demonstration, the High Contrast and Imaging Testbed overcame two significant hurdles that all telescopes face when trying to image exoplanets - diffracted and scattered light.

When starlight hits the edge of a telescope's primary mirror, it becomes slightly disturbed, producing a pattern of rings or spikes surrounding the major source of light in the focused image. This diffracted light can completely obscure any planets in the field of view.

To address this problem, Trauger and his colleagues at JPL fashioned a pair of masks for their system. The first, which resembles a blurry barcode, directly blocks most of the starlight, while the second clears away the diffracted rings and spikes. The combination creates enough darkness to allow the light of any planets to shine through.

"Mathematically, and sort of magically, this coronagraph blocks both the central star and its rings," said Wesley Traub of JPL, co-author of the new paper and Terrestrial Planet Finder project scientist.

Scattered light presents the additional hurdle. Minor ripples on a telescope's mirror produce "speckles" - faint copies of a star, shifted to the side, which can also hide planets. In the High Contrast Imaging Testbed, a deformable mirror the size of a large coin limits scattered light. With a surface that can be altered ever so slightly by computer-controlled actuators, this mirror compensates for the effects of minor imperfections in the telescope and instrument.

"This result is important because it points the way to building a space telescope with the ability to detect and characterize Earth-like planets around nearby stars," Traub said.

For their next steps, Trauger and Traub plan to improve the suppression of speckles by a factor of 10, and extend the method to accommodate many wavelengths of light simultaneously.

More information on NASA's planet-finding missions, including Terrestrial Planet Finder, is at http://planetquest.jpl.nasa.gov .

JPL manages the Terrestrial Planet Finder mission for NASA's Science Mission Directorate, Washington. JPL is a division of the California Institute of Technology in Pasadena.

Media contact: Jane Platt 818-354-0880
Jet Propulsion Laboratory, Pasadena, Calif.

2007-039


Source: NASA - Exploring the Universe - New Worlds
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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.

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Image above: 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."

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Image above: 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.

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Image above: 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.

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Image above: 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.

This graph shows the intensity of light by color that reaches the surface of Earth like planets orbiting different types of stars.

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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.

Related Link:
+ NAI website

Rob Gutro
Goddard Space Flight Center


Source: NASA/GSFC - News
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Apr. 11

Orange grass, or a real black forest might flourish under the light of stars that produce more of different spectra of light than our sun.

Plants do not have to be green. To be sure, the vast majority of vascular plants on Earth are green because during photosynthesis (the conversion of photons of light into stored chemical energy) they absorb more of the red and blue wavelength light emitted by the sun. But in the murky depths of Earth's waters lurk photosynthetic bacteria that appear purple to the human eye, employing light in the infrared spectrum to store energy; more archaic plants—such as lichens and moss—utilize more of the blue spectrum in visible light. There are even red, shade-dwelling vascular plants. The photon flux spectrum peaks in the red, which is where chlorophyll has peak absorption.

In fact, the photosynthetic organisms of Earth are exquisitely tuned to take full advantage of the specific sunlight that filters down to the surface (and below the sea). By understanding how photosynthesis works on Earth, scientists aim to predict how it might occur in alien atmospheres, potentially enabling scientists to identify planets that support life with future telescopes. Photosynthesis is a very widespread, very successful process. It is the dominant form of life,it is detectable at the global scale and you can see it from really big distances from the planet.

Based on this modeling and analysis, scientists could detect alien photosynthesis simply by measuring the light reflected from suitable alien worlds. So, for example, a cooler, dimmer but far more abundant M-type star emits photons that peak in the infrared range. If scientists detect significant absorption around that particular wavelength on a planet in its orbit, they might reasonably assume that some form of photosynthesis was taking place.Plants on that dark world might predominantly be black to absorb as much of the available light as possible.

Anyone training an advanced telescope on Earth would detect such a signature of life: Earth seems to suck up light in the red wavelength while sending back a large portion of the sun's infrared energy. Plants are a lot less green than they are infrared. When satellites measure vegetative cover they look at the infrared signal of plants, which is a strong reflectance signal. They are not absorbing infrared.

It remains a mystery why most plants do not take advantage of this infrared light by absorbing it (snow algae and lichens seem to make use of it, for unknown reasons), but it does provide a clear signal to anyone watching that there is something going on that is more than what would be expected from its various constituent elements. And when sufficiently specialized telescopes reach Earth orbit in a decade or so, researchers may be able to detect similar signatures of photosynthesis on an Earth-size worlds orbiting an F type star (larger and hotter than our own G-type sun), for example.

Plants on that newly discovered planet would be predominantly orange. But given the conditions here on Earth, plants find it easiest to be green. Life here is very intimately adapted to the qualities of our home planet and the sun.

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  • 2 weeks later...
Astronomers Find First Earth-like Planet in Habitable Zone


The European Southern Observatory (ESO) press release 22-07 is reproduced below:

ESO 22/07 - Science Release

25 April 2007
For Immediate Release

Astronomers Find First Earth-like Planet in Habitable Zone

The Dwarf Carried Other Worlds Too!


Astronomers have discovered the most Earth-like planet outside our Solar System to date, an exoplanet with a radius only 50% larger than the Earth and capable of having liquid water. Using the ESO 3.6-m telescope, a team of Swiss, French and Portuguese scientists discovered a super-Earth about 5 times the mass of the Earth that orbits a red dwarf, already known to harbour a Neptune-mass planet. The astronomers have also strong evidence for the presence of a third planet with a mass about 8 Earth masses.

This exoplanet - as astronomers call planets around a star other than the Sun - is the smallest ever found up to now [1] and it completes a full orbit in 13 days. It is 14 times closer to its star than the Earth is from the Sun. However, given that its host star, the red dwarf Gliese 581 [2], is smaller and colder than the Sun - and thus less luminous - the planet nevertheless lies in the habitable zone, the region around a star where water could be liquid! The planet's name is Gliese 581 c.

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Artist's impression of the planetary system around the red dwarf Gliese 581. Using the instrument HARPS on the ESO 3.6-m telescope, astronomers have uncovered 3 planets, all of relative low-mass: 5, 8 and 15 Earth masses. The five Earth-mass planet (seen in foreground - Gliese 581 c) makes a full orbit around the star in 13 days, the other two in 5 (the blue, Neptunian-like planet - Gliese 581 B) and 84 days (the most remote one, Gliese 581 d). © ESO

linked-image

Artist's impression of the five-Earth mass planet, Gliese 581 c, found in the habitable zone around the red dwarf Gliese 581, with the instrument HARPS on the ESO 3.6-m telescope. © ESO

"We have estimated that the mean temperature of this super-Earth lies between 0 and 40 degrees Celsius, and water would thus be liquid," explains Stéphane Udry, from the Geneva Observatory (Switzerland) and lead-author of the paper reporting the result. "Moreover, its radius should be only 1.5 times the Earth's radius, and models predict that the planet should be either rocky - like our Earth - or fully covered with oceans," he adds.

linked-image

The star Gliese 581. Source: Digital Sky Survey.

"Liquid water is critical to life as we know it," avows Xavier Delfosse, a member of the team from Grenoble University (France). "Because of its temperature and relative proximity, this planet will most probably be a very important target of the future space missions dedicated to the search for extra-terrestrial life. On the treasure map of the Universe, one would be tempted to mark this planet with an X."

The host star, Gliese 581, is among the 100 closest stars to us, located only 20.5 light-years away in the constellation Libra ("the Scales"). It has a mass of only one third the mass of the Sun. Such red dwarfs are intrinsically at least 50 times fainter than the Sun and are the most common stars in our Galaxy: among the 100 closest stars to the Sun, 80 belong to this class.

"Red dwarfs are ideal targets for the search for low-mass planets where water could be liquid. Because such dwarfs emit less light, the habitable zone is much closer to them than it is around the Sun," emphasizes Xavier Bonfils, a co-worker from Lisbon University. Planets lying in this zone are then more easily detected with the radial-velocity method [3], the most successful in detecting exoplanets.

linked-image

Three-planet Keplerian model of the Gliese 581 radial-velocity variations. The panels display the phase-folded curve of each of the planets, with points representing the observed radial velocities, after removing the effect of the other planets. Top panel refers to the 15 Earth-mass planet orbiting close to the star (5-d period), the middle one is the 5 Earth-mass planet in the habitable zone and the lower panel shows evidence for a third, 8 Earth-mass planet with a period of 84 days. The error on one measurement is of the order of 1 m/s.

This press release is also accompanied by video material.


Two years ago, the same team of astronomers already found a planet around Gliese 581 (see ESO 30/05). With a mass of 15 Earth-masses, i.e. similar to that of Neptune, it orbits its host star in 5.4 days. At the time, the astronomers had already seen hints of another planet. They therefore obtained a new set of measurements and found the new super-Earth, but also clear indications for another one, an 8 Earth-mass planet completing an orbit in 84 days. The planetary system surrounding Gliese 581 contains thus no fewer than 3 planets of 15 Earth masses or less, and as such is a quite remarkable system.

The discovery was made thanks to HARPS (High Accuracy Radial Velocity for Planetary Searcher), perhaps the most precise spectrograph in the world. Located on the ESO 3.6-m telescope at La Silla, Chile, HARPS is able to measure velocities with a precision better than one metre per second (or 3.6 km/h)! HARPS is one of the most successful instruments for detecting exoplanets and holds already several recent records, including the discovery of another 'Trio of Neptunes' (ESO 18/06, see also ESO 22/04).

The detected velocity variations are between 2 and 3 metres per second, corresponding to about 9 km/h! That's the speed of a person walking briskly. Such tiny signals could not have been distinguished from 'simple noise' by most of today's available spectrographs.

"HARPS is a unique planet hunting machine," says Michel Mayor, from Geneva Observatory, and HARPS Principal Investigator. "Given the incredible precision of HARPS, we have focused our effort on low-mass planets. And we can say without doubt that HARPS has been very successful: out of the 13 known planets with a mass below 20 Earth masses, 11 were discovered with HARPS!"

HARPS is also very efficient in finding planetary systems, where tiny signals have to be uncovered. The two systems known to have three low mass planets - HD 69830 and Gl 581 - were discovered by HARPS.

"And we are confident that, given the results obtained so far, finding a planet with the mass of the Earth around a red dwarf is within reach," affirms Mayor.

More Information

This research is reported in a paper submitted as a Letter to the Editor of Astronomy and Astrophysics ("The HARPS search for southern extra-solar planets : XI. An habitable super-Earth (5 MEarth) in a 3-planet system", by S. Udry et al.) The paper is available from http://obswww.unige.ch/~udry/udry_preprint.pdf.
The team is composed of Stéphane Udry, Michel Mayor, Christophe Lovis, Francesco Pepe, and Didier Queloz (Geneva Observatory, Switzerland), Xavier Bonfils (Lisbonne Observatory, Portugal), Xavier Delfosse, Thierry Forveille, and C.Perrier (LAOG, Grenoble, France), François Bouchy (Institut d'Astrophysique de Paris, France), and Jean-Luc Bertaux (Service d'Aéronomie du CNRS, France)

Notes

[1]: Using the radial velocity method, astronomers can only obtain a minimum mass (as it is multiplied by the sine of the inclination of the orbital plane to the line of sight, which is unknown). From a statistical point of view, this is however often close to the real mass of the system. Two other systems have a mass close to this. The icy planet around OGLE-2005-BLG-390L, discovered by microlensing with a network of telescopes including one at La Silla (ESO 03/06), has a (real) mass of 5.5 Earth masses. It, however, orbits much farther from its small host star than the present one and is hence much colder. The other is one of the planets surrounding the star Gliese 876. It has a minimum mass of 5.89 Earth masses (and a probable real mass of 7.53 Earth masses) and completes an orbit in less than 2 days, making it too hot for liquid water to be present.

[2]: Gl 581, or Gliese 581, is the 581th entry in the Gliese Catalogue, which lists all known stars within 25 parsecs (81.5 light years) of the Sun. It was originally compiled by Gliese and published in 1969, and later updated by Gliese and Jahreiss in 1991.

[3]: This fundamental observational method is based on the detection of variations in the velocity of the central star, due to the changing direction of the gravitational pull from an (unseen) exoplanet as it orbits the star. The evaluation of the measured velocity variations allows deducing the planet's orbit, in particular the period and the distance from the star, as well as a minimum mass.

Source: ESO Press Release pr-22-07
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I have reproduced this press release, mostly for the sake of completeness... I usually place ESO press releases in this section. However I should point out that there are two discussions already about this subject.

From the Astronomical point of view there is Habitable ExoPlanet Found! in the Space and Astronomy forum.

From the perspective of what this means in terms of extraterrestrial life there is Habitable planet found in the Extraterrestrial Life & The UFO Phenomenon forum.

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Astronomers Find Super-massive Planet


The Harvard-Smithsonian Center for Astrophysics press release is reproduced below:

Release No.: 2007-11
For Release: Wednesday, May 02, 2007



Cambridge, MA - Today, astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) announced that they have found the most massive known transiting extrasolar planet. The gas giant planet, called HAT-P-2b, contains more than eight times the mass of Jupiter, the biggest planet in our solar system. Its powerful gravity squashes it into a ball only slightly larger than Jupiter.

HAT-P-2b shows other unusual characteristics. It has an extremely oval orbit that brings it as close as 3.1 million miles from its star before swinging three times farther out, to a distance of 9.6 million miles. If Earth's orbit were as elliptical, we would loop from almost reaching Mercury out to almost reaching Mars. Because of its orbit, HAT-P-2b gets enormously heated up when it passes close to the star, then cools off as it loops out again. Although it has a very short orbital period of only 5.63 days, this is the longest period planet known that transits, or crosses in front of, its host star.

"This planet is so unusual that at first we thought it was a false alarm - something that appeared to be a planet but wasn't," said CfA astronomer Gaspar Bakos. "But we eliminated every other possibility, so we knew we had a really weird planet."

Bakos is lead author of a paper submitted to the Astrophysical Journal describing the discovery. That paper is available online at http://arxiv.org/abs/0705.0126.

HAT-P-2b orbits an F-type star, which is almost twice as big and somewhat hotter than the Sun, located about 440 light-years away in the constellation Hercules. Once every 5 days and 15 hours, it crosses directly in front of the star as viewed from Earth-a sort of mini-eclipse. Such a transit offers astronomers a unique opportunity to measure a planet's physical size from the amount of dimming.

Brightness measurements during the transit show that HAT-P-2b is about 1.18 times the size of Jupiter. By measuring how the star wobbles as the planet's gravity tugs it, astronomers deduced that the planet contains about 8.2 times Jupiter's mass. A person who weighs 150 pounds on Earth would tip the scale at 2100 pounds, and experience 14 times Earth's gravity, by standing on the visible surface (cloud tops) of HAT-P-2b.

CfA astronomer and co-author Robert Noyes said, "All the other known transiting planets are like 'hot Jupiters.' HAT-P-2b is hot, but it's not a Jupiter. It's much denser than a Jupiter-like planet; in fact, it is as dense as Earth even though it's mostly made of hydrogen."

"This object is close to the boundary between a star and a planet," said Harvard co-author Dimitar Sasselov. "With 50 percent more mass, it could have begun nuclear fusion for a short time."

An intriguing feature of HAT-P-2b is its highly eccentric (e=0.5) orbit. Gravitational forces between star and planet tend to circularize the orbit of a close-in planet. There is no other planet known with such an eccentric, close-in orbit. In addition, all other known transiting planets have circular orbits.

The most likely explanation is the presence of a second, outer world whose gravity pulls on HAT-P-2b and perturbs its orbit. Although existing data cannot confirm a second planet, they cannot rule it out either.

HAT-P-2b orbits the star HD 147506. With visual magnitude 8.7, HD 147506 is the fourth brightest star known to harbor a transiting planet, making the star (but not the planet) visible in a small, 3-inch telescope.

HAT-P-2b was discovered using a network of small, automated telescopes known as HATNet, which was designed and built by Bakos. The HAT network consists of six telescopes, four at the Smithsonian Astrophysical Observatory's Whipple Observatory in Arizona and two at its Submillimeter Array facility in Hawaii. As part of an international campaign, the Wise HAT telescope, located in the Negev desert (Israel) also took part in the discovery. The HAT telescopes conduct robotic observations every clear night, each covering an area of the sky 300 times the size of the full moon with every exposure. About 26,000 individual observations were made to detect the periodic dips of intensity due to the transit.

Major funding for HATnet was provided by NASA. More information about HAT is available online at http://www.hatnet.hu

For more information, contact:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu


Source: CfA Press Release
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