Posts Tagged ‘exoplanets

The Mystery of Tatooine Planet Formation

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How not to build Tatooine: the difficulty of in situ formation of circumbinary planets Kepler 16b, Kepler 34b and Kepler 35b

Histogram of collision velocities for Kepler 16 scenario without dust accretion, t = 250,000 binary orbits. Colours indicate different radii, with r in units of ab

Sijme-Jan Paardekooper, Zoe M. Leinhardt, Philippe Thebault, Clement Baruteau
We study planetesimal evolution in circumbinary disks, focusing on the three systems Kepler 16, 34 and 35 where planets have been discovered recently. We show that for circumbinary planetesimals, in addition to secular forcing, eccentricities evolve on a dynamical timescale, which leads to orbital crossings even in the presence of gas drag. This makes the current locations of the circumbinary Kepler planets hostile to planetesimal accretion. We then present results from simulations including planetesimal formation and dust accretion, and show that even in the most favourable case of 100% efficient dust accretion, in situ growth starting from planetesimals smaller than ~10 km is difficult for Kepler 16b, Kepler 34b and Kepler 35b. These planets were likely assembled further out in the disk, and migrated inward to their current location….
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Written by physicsgg

June 19, 2012 at 10:01 am


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NASA’s Spitzer Sees the Light of Alien ‘Super Earth’

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Seen here in this artist’s concept, the planet is called 55 Cancri e. It’s a toasty world that rushes around its star every 18 hours. Image credit: NASA/JPL-Caltech

NASA’s Spitzer Space Telescope has detected light emanating from a “super-Earth” planet beyond our solar system for the first time. While the planet is not habitable, the detection is a historic step toward the eventual search for signs of life on other planets.

“Spitzer has amazed us yet again,” said Bill Danchi, Spitzer program scientist at NASA Headquarters in Washington. “The spacecraft is pioneering the study of atmospheres of distant planets and paving the way for NASA’s upcoming James Webb Space Telescope to apply a similar technique on potentially habitable planets.”

This artist’s animation depicts 55 Cancri e as it orbits its star. The planet whips around the star closely and quickly: It is 25 times closer to the star than Mercury is to our sun and completes one orbit — its year — in a mere 18 hours.

The planet, called 55 Cancri e, falls into a class of planets termed super Earths, which are more massive than our home world but lighter than giant planets like Neptune. The planet is about twice as big and eight times as massive as Earth. It orbits a bright star, called 55 Cancri, in a mere 18 hours.

Previously, Spitzer and other telescopes were able to study the planet by analyzing how the light from 55 Cancri changed as the planet passed in front of the star. In the new study, Spitzer measured how much infrared light comes from the planet itself. The results reveal the planet is likely dark, and its sun-facing side is more than 2,000 Kelvin (3,140 degrees Fahrenheit), hot enough to melt metal.

The new information is consistent with a prior theory that 55 Cancri e is a water world: a rocky core surrounded by a layer of water in a “supercritical” state where it is both liquid and gas, and topped by a blanket of steam. “It could be very similar to Neptune, if you pulled Neptune in toward our sun and watched its atmosphere boil away,” said Michaël Gillon of Université de Liège in Belgium, principal investigator of the research, which appears in the Astrophysical Journal. The lead author is Brice-Olivier Demory of the Massachusetts Institute of Technology in Cambridge.

The plot shows how the infrared light from the 55 Cancri system, both the star and planet, changed as the planet passed behind its star in what is called an occultation. When the planet disappeared, the total light dropped, and then increased back to normal levels as the planet circled back into view. The drop indicated how much light came directly from the planet itself. This type of information is important for studying the temperatures and compositions of planetary atmospheres beyond our own

The 55 Cancri system is relatively close to Earth, at 41 light-years away. It has five planets, with 55 Cancri e the closest to the star and tidally locked, so one side always faces the star. Spitzer discovered the sun-facing side is extremely hot, indicating the planet probably does not have a substantial atmosphere to carry the sun’s heat to the unlit side.

NASA’s James Webb Space Telescope, scheduled to launch in 2018, likely will be able to learn even more about the planet’s composition. The telescope might be able to use a similar infrared method to Spitzer to search other potentially habitable planets for signs of molecules possibly related to life.

“When we conceived of Spitzer more than 40 years ago, exoplanets hadn’t even been discovered,” said Michael Werner, Spitzer project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Because Spitzer was built very well, it’s been able to adapt to this new field and make historic advances such as this.”

In 2005, Spitzer became the first telescope to detect light from a planet beyond our solar system. To the surprise of many, the observatory saw the infrared light of a “hot Jupiter,” a gaseous planet much larger than the solid 55 Cancri e. Since then, other telescopes, including NASA’s Hubble and Kepler space telescopes, have performed similar feats with gas giants using the same method.

In this method, a telescope gazes at a star as a planet circles behind it. When the planet disappears from view, the light from the star system dips ever so slightly, but enough that astronomers can determine how much light came from the planet itself. This information reveals the temperature of a planet, and, in some cases, its atmospheric components. Most other current planet-hunting methods obtain indirect measurements of a planet by observing its effects on the star….
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Written by physicsgg

May 8, 2012 at 10:59 pm


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The Milky Way’s 100 Billion Planets

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This artist’s illustration gives an impression of how common planets are around the stars in the Milky Way. The planets, their orbits and their host stars are all vastly magnified compared to their real separations. A six-year search that surveyed millions of stars using the microlensing technique concluded that planets around stars are the rule rather than the exception. The average number of planets per star is greater than one. This means that there is likely to be a minimum of 1,500 planets within just 50 light-years of Earth.

The results are based on observations taken over six years by the PLANET (Probing Lensing Anomalies NETwork) collaboration, which was founded in 1995. The study concludes that there are far more Earth-sized planets than bloated Jupiter-sized worlds. This is based on calibrating a planetary mass function that shows the number of planets increases for lower mass worlds. A rough estimate from this survey would point to the existence of more than 10 billion terrestrial planets across our galaxy.

The results were published in the Jan. 12, 2012, issue of the British science journal Nature.
Image Credit: NASA, ESA, and M. Kornmesser (ESO)

Written by physicsgg

April 26, 2012 at 12:21 pm


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New look at HD 10180 shows it might have nine planets

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HD 10180 planetary system (Artist's Impression). Image: ESO/L. Calçada

Astronomer Mikko Tuomi of the University of Hertfordshire, has found after looking at data regarding the solar system surrounding the star HD 10180, that it likely has nine planets making it the most highly populated solar system known to man (ours has just eight after the demotion of Pluto). He details his findings in a paper pre-published on arXiv (and set for publication in Astronomy and Astrophysics) describing how after studying slight wobbles by the star as it’s tugged by planetary gravitation, he found what he believes is confirmation of a seventh planet, and evidence for two more.

HD 10180 is about 130 light years away from us, in the Hydrus constellation and was first noted by astronomers in 2010. At the time it was thought the solar system consisted of just five planets, though there was speculation that it might have as many as seven. Since that time, other work has shown that there are likely six planets, five of which are believed to have a mass close to that of Neptune. The other appears closer in mass to Saturn. Researchers come to these conclusions by studying the way a star appears to wobble (a Doppler shift) as it responds to the gravitational pull of planets orbiting around it. By studying these light shifts, astronomers can deduce not only the size of the planet that causes it, but its period as well. Those originally noted had periods ranging from 5 to 2000 days.

Tuomi didn’t make any new observations, instead he went back and looked at the original data using different kinds of statistical analysis techniques. In so doing, he found evidence for three more planets, all much smaller than the original six. These new planets, which he estimates to be 1.3, 1.9, and 5.1 times the size of Earth, have much shorter periods (1.2, 10 and 68 days) than the other planets indicating that they are very close to their star, closer even than Mercury is to our sun, which would mean they are far too hot to support water retention or life, at least as we know it.

It’s important to note that such work doesn’t actually prove that any of the planets suspected of revolving around HD 10180 actually exist, it merely offers strong evidence. Adding even more is statistical evidence offered by Tuomi suggesting that if there are truly planets there, they all appear to have stable orbits…..

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More information: Evidence for 9 planets in the HD 10180 system, … 4.1254v1.pdf

Written by physicsgg

April 9, 2012 at 4:44 pm


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Kepler Catalog Adds More Planet Candidates

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The histogram summarizes the findings in the Feb. 27, 2012 Kepler Planet Candidate catalog release. The catalog contains 2,321 planet candidates identified during the first 16 months of observation conducted May 2009 to September 2010. Of the 46 planet candidates found in the habitable zone, the region in the planetary system where liquid water could exist, ten of these candidates are near-Earth-size. Credit: NASA Ames/Wendy Stenzel

Since science operations began in May 2009, the Kepler team has released two catalogs of transiting planet candidates. The first catalog (Borucki et al, 2010), released in June 2010, contains 312 candidates identified in the first 43 days of Kepler data. The second catalog (Borucki et al, 2011), released in February 2011, is a cumulative catalog containing 1,235 candidates identified in the first 13 months of data.

Now the team presents the third catalog containing 1,091 new planet candidates identified in the first 16 months of observation conducted May 2009 to September 2010. These are the same candidates that the team discussed at the Kepler Science Conference held at NASA Ames Research Center in December 2011.

Here are the highlights of the new catalog:

  •  Planet candidates smaller than twice the size of Earth increased by 197 percent, compared to 52 percent for candidates larger than twice the size of Earth.
  • Planet candidates with orbital periods longer than 50 days increased by 123 percent, compared to 85 percent for candidates with orbital periods shorter than 50 days.

Since the last catalog was released in February 2011, the number of planet candidates identified by Kepler has increased by 88 percent and now totals 2,321 transiting 1,790 stars.

The cumulative catalog now contains well over 200 Earth-size planet candidates and more than 900 that are smaller than twice Earth-size. Of the 46 planet candidates found in the habitable zone, the region in the planetary system where liquid water could exist, ten of these candidates are near-Earth-size.

The number of planetary systems found with more than one planet candidate also has increased. Last year, 17 percent, or 170 stars, had more than one transiting planet candidate. Today, 20 percent, or 365, stars have more than one.

“With each new catalog release a clear progression toward smaller planets at longer orbital periods is emerging, ” said Natalie Batalha, Kepler deputy science team lead at San Jose State University in California. “This suggests that Earth-size planets in the habitable zone are forthcoming if, indeed, such planets are abundant.”

Nearly 5,000 periodic transit-like signals were analyzed with known spacecraft instrumentation and astrophysical phenomena that could masquerade as transits, which can produce false positives. The most common false positive signatures are associated with eclipsing binary stars- a pair of orbiting stars that eclipse each other from the vantage point of the spacecraft.

The Kepler space telescope identifies planet candidates by repeatedly measuring the change in brightness of more than 150,000 stars in search of planets that pass in front, or “transit,” their host star. Kepler must record at least three transits to verify a signal as a planet.

The findings are published in the “Planetary Candidates Observed by Kepler III: Analysis of the First 16 Months of Data”. The catalog is available at the Kepler data archive at the Space Telescope Science Institute and can be downloaded from the NASA Exoplanet Archive.………
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Written by physicsgg

March 11, 2012 at 12:53 pm

Distant ‘waterworld’ is confirmed

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GJ 1214b orbits close to its host star, as this artist's impression shows

Astronomers have confirmed the existence of a new class of planet: a waterworld with a thick, steamy atmosphere.

The exoplanet GJ 1214b is a so-called “Super Earth” – bigger than our planet, but smaller than gas giants such as Jupiter.

Observations using the Hubble telescope now seem to confirm that a large fraction of its mass is water.

The planet’s high temperatures suggest exotic materials might exist there.

“GJ 1214b is like no planet we know of,” said lead author Zachory Berta, from the Harvard Smithsonian Center for Astrophysics.

The planet was discovered in 2009 by ground-based telescopes. It is about 2.7 times the Earth’s diameter, but weighs almost seven times as much. It orbits its red-dwarf star at a distance of just two million km, meaning temperatures on GJ 1214b probably reach above 200C.

In 2010, astronomers released measurements of its atmosphere. These suggested that GJ 1214b’s atmosphere was probably made up of water, but there was another possibility – that the planet was covered in a haze, of the type that envelopes Saturn’s moon Titan.

Hot ice

Mr Berta and his colleagues used the Hubble Space Telescope’s wide-field camera to study the planet as it crossed in front of its star – a transit. During these transits, the star’s light is filtered through the planet’s atmosphere, giving clues to the mixture of gases present.

The researchers said their results are more consistent with a dense atmosphere of water vapour, than one with a haze.

Calculations of the planet’s density also suggest that GJ 1214b has more water than Earth. This means the internal structure of this world would be very different to that of our own.

“The high temperatures and pressures would form exotic materials like ‘hot ice’ or ‘superfluid water’, substances that are completely alien to our everyday experience,” said Dr Berta.

The planet’s short distance from Earth makes it a likely candidate for follow-up observations with the James Webb Space Telescope, which may launch by the end of this decade.

The study has been accepted for publication by the Astrophysical Journal….

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Written by physicsgg

February 21, 2012 at 7:47 pm


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Scattered Light Could Reveal Alien Atmospheres

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The light scattered off distant worlds could help reveal details about their atmospheres that no other method could uncover, scientists find.

Nearly all the information astronomers have of the atmospheres of alien planets or exoplanets comes from worlds whose orbits happen to be precisely aligned from our vantage point. Once per orbit, these exoplanets go in front of (transit) their host stars from our point of view, and the light from these stars passes through the atmospheres of these planets on its way to Earth. The molecules in these alien atmospheres absorb some of this starlight, resulting in patterns known as spectra that allow scientists to identify what they are.

However, “we know of many other planets that do not transit their host stars, and we therefore know almost nothing about those atmospheres,” said astronomer Sloane Wiktorowicz at University of California, Santa Cruz. Indeed, “less than 10 percent of the known exoplanets have had their atmospheres detected. This is because planets are at least a thousand times fainter than their host stars.”

Instead of looking at starlight that has passed through alien atmospheres on its way to Earth, Wiktorowicz and his colleagues aim to look for light that has scattered off alien atmospheres. This strategy should work equally well for exoplanets in both transiting and non-transiting orbits, “which will open up many previously unstudied planets for exploration,” he explained.

Tripping the Light Fantastic

To understand how this strategy works, one can think of all light waves as electric fields rippling either up and down, left and right, or at any angle in between, a property known as polarization. When starlight gets scattered off a planet’s atmosphere, its polarization changes in a way that makes it distinct from both the direct light from a star and the light bouncing off the surface of a planet. Analyzing this polarization, a technique known as polarimetry, could yield details not only concerning the existence of an alien atmosphere, but also its composition and how it might be structured into different layers.

As a planet passes in front of its parent star, the brightness of the star decreases. Credit: Hans Deeg

“Polarimetry provides extra information over photometry — measuring planet brightness at different colors — because there is extra information encoded in the polarization of scattered light,” said astrophysicist Sara Seager at the Massachusetts Institute of Technology, who was the first to propose polarimetry studies for exoplanets. “This extra information can tell us whether or not clouds or hazes are present, and something about the properties of the clouds or hazes. It’s information that is difficult to get any other way.”

The canonical example are the clouds of Venus, Seager explained. “Very early in planetary atmosphere studies, people thought Venus could potentially have water clouds,” she said. Although photometry measurements of Venus could not uniquely identify the droplets in these clouds, polarimetry studies from ground-based measurements reported in the early 1970s discovered the Venusian clouds were sulfuric acid droplets, findings confirmed via spacecraft sent to the the planet.

With polarimetry, “we can tell if clouds are present on exoplanets and potentially what clouds are made of,” Seager said.

“It’s a completely new way to look at extrasolar planets, a completely novel technique for getting information,” said astronomer Greg Laughlin at the University of California, Santa Cruz, who did not take part in this research. “It’s very hard to get any information about what extrasolar planets are like — we can detect they exist, but anything that can tell you about their physical properties other than that is extraordinarily valuable. Also, it doesn’t require a billion-dollar build-up — we can do it with existing resources. I think Sloane’s on the ground floor of something that’s going to be a big deal.”

A major advantage of this strategy “is that we may be able to study the composition of exoplanet atmospheres with comparatively small, ground-based telescopes,” Wiktorowicz explained. This is crucial for future exoplanet research, given the difficulty in funding space-based observatories such as the James Webb Space Telescope.

One disadvantage of this method is that the farther the planet orbits from its star, the fainter it will be. This means only the closest-in planets can be studied with this technique, which means it won’t be of much help finding new exoplanets — existing planet-hunting strategies are already quite good at discovering worlds that are near their stars, Wiktorowicz said. Still, he noted this method is not meant to find new planets — “rather, it’s meant to study planets we already know about.”

POLISH2 See the Light

To see how starlight is polarized, Wiktorowicz and his colleagues developed a polarimeter based on bars of glass that vibrate tens of thousands of times per second. These “photoelastic modulators” will each very subtly alter a select polarization of light while leaving others unchanged. The latest version of his instrument, POLISH2, has two of these vibrating glass bars, which allows it to simultaneously detect all the key polarizations of light.

The search for exoplanet atmospheres using polarimetry has taken place for nearly two years with POLISH2, which is attached to the Lick Observatory’s 3-meter telescope.

“It’s amazing to think that we might be able to see light scattered from the surface of a planet tens of light years away,” Wiktorowicz said.

Bright yellow lines in the absorption-line spectrum are produced by the sodium content in the planet's atmosphere

Although POLISH2 should already be precise enough to detect exoplanets, “the issue is whether my system, and the stars themselves, are stable enough to allow such detections,” Wiktorowicz said. Many factors might affect what the instrument observes on a nightly basis. “Any changes to the telescope or the atmosphere or anything else might cause a change in measurements — the amount of dust that settles on a telescope mirror from one night to the next can actually affect what you see,” he explained.

To overcome this challenge, the researchers have to account for all the minute disturbances the polarimeter may experience nightly — to set the scale to zero, essentially. They do this by looking at nearby stars. The light from these stars tends to have almost no polarization, and thus helps calibrate every other measurement the instrument makes. In contrast, light from more distant stars has encountered more interstellar dust grains, which can reflect away some polarizations of light but not others, making the light from them that does reach Earth polarized.

Such calibration observations are very time-consuming — “about a third of every night is spent on them,” Wiktorowicz said.

To increase his chances of finding planets, “I’m currently working on improving my data-processing software, because squeezing out every last drop of information from 500 gigabytes of data per night can be difficult,” Wiktorowicz said. “Once this is done, I will re-analyze my old data, while gathering new data as well, and hopefully detect some planets.”

This strategy involves monitoring exoplanet systems at different times in that world’s orbit. “I’m spending most of my effort on two stars known to have one planet each,” Wiktorowicz said. “But I have recently added three more stars, and the list will increase with time.” In the end, “I hope to be able to study a few tens of exoplanets,” he added.
Bringing polarimetry to a 10-meter telescope would enable analysis of still more exoplanets. “A larger telescope should allow smaller, Neptune-sized planets to be detected, which are thought to be much different from larger, Jupiter-sized planets,” Wiktorowicz said. There has even been interest in bringing instruments similar to POLISH2 to the 30-meter telescopes that groups in Europe the United States and elsewhere are contemplating building. “Of course, we have to prove that it works on the smaller telescopes first,” he added.

Spectrum of planet around HR 8799. Credit: ESO/M. Janson

Seager , who did not participate on this work, noted, “research with exoplanets is pushed forward only when people like Sloane are brave enough and bold enough to push a technology most people don’t think is viable.”

Wiktorowicz and his colleagues detailed their findings Jan. 11 at the annual meeting of the American Astronomical Society in Austin, Texas.

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February 20, 2012 at 7:14 pm


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NASA’s Kepler Announces 11 Planetary Systems Hosting 26 Planets

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(click image to enlarge) Kepler's Planetary Systems, Jan. 2012

NASA’s Kepler mission has discovered 11 new planetary systems hosting 26 confirmed planets. These discoveries nearly double the number of verified Kepler planets and triple the number of stars known to have more than one planet that transits, or passes in front of, its host star. Such systems will help astronomers better understand how planets form.

The planets orbit close to their host stars and range in size from 1.5 times the radius of Earth to larger than Jupiter. Fifteen of them are between Earth and Neptune in size, and further observations will be required to determine which are rocky like Earth and which have thick gaseous atmospheres like Neptune. The planets orbit their host star once every six to 143 days. All are closer to their host star than Venus is to our sun.

“Prior to the Kepler mission, we knew of perhaps 500 exoplanets across the whole sky,” said Doug Hudgins, Kepler program scientist at NASA Headquarters in Washington. “Now, in just two years staring at a patch of sky not much bigger than your fist, Kepler has discovered more than 60 planets and more than 2,300 planet candidates. This tells us that our galaxy is positively loaded with planets of all sizes and orbits.”

Kepler identifies planet candidates by repeatedly measuring the change in brightness of more than 150,000 stars to detect when a planet passes in front of the star. That passage casts a small shadow toward Earth and the Kepler spacecraft.

“Confirming that the small decrease in the star’s brightness is due to a planet requires additional observations and time-consuming analysis,” said Eric Ford, associate professor of astronomy at the University of Florida and lead author of the paper confirming Kepler-23 and Kepler-24. “We verified these planets using new techniques that dramatically accelerated their discovery.”

Each of the new confirmed planetary systems contains two to five closely spaced transiting planets. In tightly packed planetary systems, the gravitational pull of the planets among themselves causes one planet to accelerate and another planet to decelerate along its orbit. The acceleration causes the orbital period of each planet to change. Kepler detects this effect by measuring the changes, or so-called Transit Timing Variations (TTVs).

Planetary systems with TTVs can be verified without requiring extensive ground-based observations, accelerating confirmation of planet candidates. The TTV detection technique also increases Kepler’s ability to confirm planetary systems around fainter and more distant stars.

“By precisely timing when each planet transits its star, Kepler detected the gravitational tug of the planets on each other, clinching the case for ten of the newly announced planetary systems,” said Dan Fabrycky, Hubble Fellow at the University of California, Santa Cruz and lead author for a paper confirming Kepler-29, 30, 31 and 32.”

Five of the systems (Kepler-25, Kepler-27, Kepler-30, Kepler-31 and Kepler-33) contain a pair of planets where the inner planet orbits the star twice during each orbit of the outer planet. Four of the systems (Kepler-23, Kepler-24, Kepler-28 and Kepler-32) contain a pairing where the outer planet circles the star twice for every three times the inner planet orbits its star.

“These configurations help to amplify the gravitational interactions between the planets, similar to how my sons kick their legs on a swing at the right time to go higher,” said Jason Steffen, the Brinson postdoctoral fellow at Fermilab Center for Particle Astrophysics in Batavia, Ill., and lead author of a paper confirming Kepler-25, 26, 27 and 28.

The system with the most planets among these discoveries is Kepler-33, a star that is older and more massive than our sun. Kepler-33 hosts five planets, ranging in size from 1.5 to 5 times that of Earth and all located closer to their star than any planet is to the sun……
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Written by physicsgg

January 26, 2012 at 9:05 pm


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