Posted on by Jon Voisey

Zooming in on Proto-Planetary Disks

On the road to planetary formation, the first step is an accretion disk around a proto-star. Such disks, known as proplyds, are frequently detected in star forming regions like the Orion nebula providing an understanding of the early life of planetary systems. The telltale hint that they exist is the warm infrared glow of the forming (or perhaps nearly formed) star heating the gas and dust, but although many have been detected this way, few have been observed with resolution that makes out any details on the disk itself. A new study aims to help add to the understanding of these systems with spatially resolved observations of two proplyds, including one already known to be host to a multiple planet system.

The two new systems under study are HD 107146 and HR 8799. The latter of these two systems is notable for having four known planets which have been directly imaged previously. HD 107146 is relatively close to our solar system, being only 28.5 pc away. This young star is similar to the Sun in mass and composition and is estimated to be somewhere between 80 and 200 million years young. Previous studies have examined this system’s disk and revealed that it is composed of nearly as much dust as there is gas, which means that much of the gas has likely been either accreted or stripped. Although not directly detected, the earlier studies have also suggested that the system may be hiding young planets. The evidence for this comes from possible banding in the disk. This is interpreted as similar to the rings and gaps in Saturn’s system, caused by shepherding moons, except in this case, the moon’s role would be fulfilled by planets creating resonances.

The new research, led by Meredith Hughes from the University of California, Berkeley, confirmed the presence of the disk around the star and found its brightness peaked at a distance of about 100 AU from the parent star (more than twice the average orbital distance of Pluto). Overall, their observations match models with a “broad ring extending from 50 to 170 AU”.

When looking at HR 8799’s disk, the team was given four nights, but due to poor weather, only one night’s worth of data from the Submillimeter Array atop Mauna Kea. The reduced amount of data left high uncertainties in the subsequent analysis. While the team attempted to search for banding that could induced by planets, the team was unable to find any. A study published earlier this year by a team at the University of Exeter also examined the HR 8799 disk and reported a slightly brighter clump on one side. The new study finds a similar clump but cautions that, due to the still poor observations of this system, the result may be suspect. A similar case happened when astronomers studied Vega’s dust disk and reported finding clumpy structure when it was, in reality, it was nothing but statistical noise.

These results, as well as the previous ones from the Exeter team and observations from Spitzer have suggested that the dust ring extends out to as far as 250 AU, and as far inwards as 80, but it is likely the inner radius is closer to 150 AU. If the inner radius is the correct value, this places it at roughly the limit that it could be shaped by the outermost planet HR 8799b which lies at just under 70 AU.

Posted on by Jon Voisey

Another Kepler Planet Confirmed

Artist's concept of Kepler in action. NASA/Kepler mission/Wendy Stenzel.

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The Kepler mission, launched in 2009, is looking to greatly improve our understanding of planets. Since beginning operation, the planet hunting spacecraft has made tentative identifications of over 1,200 planets, having spotted them as they transited their parent stars. However, these planets need confirmation from a more robust method, specifically the spectroscopically detected wobbles, before they’re added to the official list of extrasolar planets.

Thus far, confirmations have been slow to come; only 16 of the planets have been detected using other methods. But recently, astronomers using the Hobby-Eberly Telescope (HET), operated by the University of Texas, Austin have confirmed another.

The planet, Kepler-15b, is the first confirmed by this unique telescope. As opposed to most observatories, the mirror at the HET does not track the stars. Instead, the mirror remains stationary and the detecting instruments are moved along the focal plane to track the object in question. While this doesn’t allow for the object to track the entire night, it does let astronomers get continuous observation of the target for up to 2 hours. This unusual configuration was estimated to reduce the construction costs by as much as 80%.

From the Kepler observations, the tentative planet was expected to have an orbital period of just under 5 days and would transit the parent star for 3.5 hours, dimming the star’s light by about 1.2%. Using this information, the expectation was that the planet should have a radius of 1.4 times that of Jupiter, putting it in the class of “hot-Jupiters”.

The observations by the HET were taken from March until November of 2010. The team used the telescope’s spectrometer to search for the signs of variation between 2 and 100 days. When analyzed for periodicity, the team independently confirmed a strong signal with a period of 4.94 days.

Using the new spectroscopic data, the team estimates the new planet has a mass of 0.66 Jupiter masses, and reduces the estimated radius to 0.96 times that of Jupiter, giving a mean density of ~.9 grams per cubic centimeter. The parent star contains high amounts of heavy elements and is tied with Kepler-6 for the most metal rich parent star of the Kepler findings. If the planet, being formed from the same interstellar cloud, has similar metallicity, then it could be expected that the presence of these additional heavy elements could help to shrink the planet.

The team also reports that they have observed other purported Kepler planets and intends to include the findings in an upcoming publication. Additionally, the HET is scheduled for a major upgrade starting later this year. This will include upgrades to the tracking assembly, as well as the fiber optics used in the spectroscope. Currently, this instrument is only capable of performing confirmations for Jovian massed planets, but once upgrades are complete, the team expects to be able to use the system to search for lower mass candidates in the mass range of Neptune and those in the “Super-Earth” category.

Posted on by Jon Voisey

More Images of HR 8799

HR 8799 system
One of the discovery images of the system obtained at the Keck II telescope using adaptive optics system and the NIRC2 Near-Infrared Imager. Image shows all four confirmed planets indicated as b, c, d and e in the labeled image. Planet "b" is a ~5 Jupiter-mass planet orbiting at about ~68 AU, while planets c, d, and e are ~7 Jupiter-mass companions orbiting the star at about 38, 24 and 14.5 AU. Credit: NRC-HIA, C. Marois & Keck Observatory

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Late last year, astronomers using the Keck II telescope released the first direct image of a planetary system including four planets. These planets orbited the star HR 8799 and were taken in the J and L bandpasses which are in the near-infrared portion of the spectrum. Since then the team has collected new data using the same telescope, extending the spectral range into the mid-infrared portion of the spectra.

The new images are important to astronomers because this provides a more complete understanding of the distribution of radiation that the planets are emitting. This can be compared to models of planetary formation, allowing these young planets to act as a test bed. Previous comparison to models have suggested that these planets have cool, dusty atmospheres without the presence of methane or other common absorbing molecules.

The team hopes that the new observations will help distinguish between the various models that explain this deficiency of methane. Unfortunately, getting good observations in this portion of the spectra is challenging. In particular, at the Keck telescope, the design of the telescope itself makes observations especially challenging due to portions of the instrument themselves emitting in the infrared, masking the faint signals from the planet.

To bring out the planets, the team developed a new technique to help clean the images of the unwanted noise. They estimate that their new technique is nine times more efficient than previously used techniques. To do this, they moved the telescope slightly between images, allowing the patterns of interference to change between exposures, thereby making them more apparent and easier to remove.

When the results were analyzed and compared to models, the team found that they were in good agreement with predictions of planetary evolution for planets c and d. However, for planet b, the models predicted a planet with a radius that would be too small to account for the observed luminosity. The observations could be brought into agreement with the models by increasing the metallicity of the model.

With additional future observations, the team hopes to constrain these models and further investigate the atmospheres of these planets.

NOTE: I Emailed the authors of the paper to ask permission to reproduce the new image here, but have not gotten a reply. The one used above is the K and L band images from last year. To see the new ones, feel free to go to the paper directly.

Posted on by Jon Voisey

New Planet Discovered In Trinary Star System

A planet 6 times the mass of Earth orbits around the star Gliese 667 C, which belongs to a triple system. Credit: ESO

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Until recently, astronomers were highly skeptical of whether or not planets should be possible in multiple star systems. It was expected that the constantly varying gravitational force would eventually tug the planet out of orbit. But despite doubts, astronomers have found several planets in just such star systems. Recently, astronomers announced another, this time in the trinary star HD 132563.

The detection of the new planet came as part of a larger study on the trinary star system spanning 10 years. The two main stars that comprise the system are both similar to the Sun in mass, although somewhat less prevalent in metals, and orbit each other at a distance of around 400 AU. The main star, HD 132563A is also itself, a binary. This fact was not previously recognized and also reported by the team, led by Silvano Desidera from the Astronomical Observatory in Padova, Italy.

The newly discovered planet orbits the secondary star in the system, HD 132563B. As with the binary component of the main star, the new planet was discovered spectroscopically. The planet is at least 1.3 times the mass of Jupiter, with an average distance from its parent star of 2.6 AU, and an moderately high eccentricity of 0.22.

The team also attempted to image the planet directly using adaptive optics from the Italian Telescopio Nazionale Galileo. While there was a hint in the glare of the star that may have been the planet in question, the team could not rule out that the detection was not an instrumental effect.

With the discovery of this new planet, the total number of discovered planets in multiple star systems lies at eight. while this is rather small numbers from which to draw firm conclusions, it appears that planets can be commonly found orbiting the more remote members of trinary star systems for good periods of time. On the shorter end, the stellar system is anticipated to be 1-3 billion years in aged, based on the amount of stellar activity and amount of lithium present in the star’s atmosphere (which decreases with time). However, fitting of the mass and luminosity onto isochrones suggest the stars may be as much as 5 billion years in age. In either situation, the planetary system is dynamically stable.

Also based on these eight systems, the team also suggests that planets existing around such far removed members of a multiple star system may be as common as planets around wide binaries, or even single stars.

Posted on by Nancy Atkinson

One Million Observations Now in the Books for Hubble Telescope

Artist's impression of the transiting exoplanet HAT-P-7b. Credit: NASA/ESA

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After 21 years in orbit, the Hubble Space Telescope has reached an historic milestone: the venerable HST has made its millionth observation. The telescope was used to search for the chemical signature of water in the atmosphere of planet HAT-P-7b, a gas giant larger than Jupiter which orbits the star HAT-P-7, about 1,000 light-years away from Earth. The observation was led by Dr. Drake Deming, planetary scientist and astronomer from the University of Maryland and the Goddard Space Flight Center.

With this announcement, however, there is no stunning image or unprecedented view of an exoplanet. The millionth observation will show up as squiggly lines on a graph, since the observation was done with Hubble’s spectrograph.

Spectroscopy is the technique of splitting light into its component colors, and the gases present in a planet’s atmosphere leave a fingerprint in the form of the distinctive color patterns that different gases absorb. Analyzing this data can give precise measurements of which elements are present in the exoplanet’s atmosphere.

“We are looking for the spectral signature of water vapor. This is an extremely precise observation and it will take months of analysis before we have an answer,” said Deming. “Hubble has demonstrated that it is ideally suited for characterizing the atmospheres of exoplanets and we are excited to see what this latest targeted world will reveal.”

“With a million observations and many thousands of scientific papers to its name, Hubble is one of the most productive scientific instruments ever built,” said Alvaro Gimenez, head of science and robotic exploration for the European Space Agency. “As well as changing our view of the Universe with its stunning imagery, Hubble has revolutionized whole areas of science.”

Hubble’s on-orbit history began when it was launched on the space shuttle Discovery on April 24, 1990. The HST has collected over 50 terabytes of data, enough to fill more than 10,000 DVDs. While the the data collected in the one millionth observation is now proprietary for the scientists, within a year, it will be released to the public. The huge and varied library of data Hubble has produced is made freely available to scientists and the public through an online archive at his link:

http://hla.stsci.edu/

Hubble made the millionth observation using its Wide Field Camera 3, a visible- and infrared-light imager with an on-board spectrometer. It was installed by astronauts during the Hubble Servicing Mission 4 in May 2009.

More Hubble info and images can be found at the HubbleSite, and ESA’s Hubble website.

Posted on by Jon Voisey

Rocky, Low-Mass Planet Discovered by Microlensing

A low-mass, rocky planet orbits a distant sun
A low-mass, rocky planet orbits a distant sun

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In planet hunting today, there seems to be one burning question that nearly every new article published touches on: Where did these planets come from?

As astronomers discovered the first extrasolar planets, it quickly became obvious that the formation theories that we’d built on our own solar system were only part of the story. They didn’t predict the vast number of hot Jupiters astronomers found nearly everywhere. Astronomers went back to the drawing board to put more details into the theory, breaking formation down into quick, single collapses and more gradual accretion of gas disks, and worrying about the effects of migration. It’s likely all these effects take place to some extent, but ferreting out just how much is now the big challenge for astronomers. Hampering their efforts is the biased sample from the gravitational-wobble technique which preferentially discovered high mass, tightly orbiting planets. The addition of Kepler to planet hunter’s arsenal has removed some of this bias, readily finding planets to far lower masses, but still prefers planets in short orbits where they are more likely to transit. However, the addition of another technique, gravitational microlensing, promises to find planets down to 10 Earth masses, much further out from their parent stars. Using this technique, a team of astronomers has just announced the detection of a rocky planet just in this range.

According to the Extrasolar Planet Encyclopaedia, astronomers have discovered 13 planets using gravitational microlensing. The newly announced one, MOA-2009-BLG-266Lb, is estimated to be just over 10 times the mass of Earth and orbits at a distance of 3.2 AUs around a parent star with roughly half the mass of the Sun. The new finding is important because it is one of the first planets in this mass range that lies beyond the “snow line”, the distance during formation of a planetary system beyond which ice can form from water, ammonia, and methane. This presence of icy grains is expected to assist in the formation of planets since it creates additional, solid material to form the planetary core. Just beyond the snow line, astronomers would expect that planets would form the most quickly since, as you move further, beyond this line, the density drops. Models have predicted that planets forming here should quickly reach a mass of 10 Earth masses by accumulating most of the solid material in the vicinity. The forming planet then, can slowly accrete gaseous envelopes. If it accumulates this material quickly enough, the gaseous atmosphere may become too massive and collapse, beginning a rapid gas accretion phase forming a gas giant.

The timing of these three phases, as well as their distance dependency, makes testable predictions that can be contrasted with the observations as astronomers discover more planets in this vicinity. In particular, it has suggested that we should see few gas giants around low mass stars because the gas disk is expected to dissipate before the atmosphere collapse leading to the rapid accretion phase. This expectation has been generally supported by the findings of the 500+ confirmed extrasolar planets, as well as the 1,200+ candidates from Kepler, lending credence to this core collapse + slow accretion model. Additionally, Kepler has also reported a large population of relatively low mass planets, interior to the snow line. This too supports the hypothesis since the greater difficulty in forming cores without the presence of ice would hamper the formation of large planets. However, other predictions, such as not expecting massive planets in tight orbits, is still largely contradictory to the hypothesis and greater testing with additional discoveries will be needed.

Assisting with this, several new observing programs will be coming on line in the near future. The Optical Gravitational Lensing Experiment IV (OGLE-IV) has just entered operation and a new program at Wise Observatory in Tel Aviv will begin operation following up on microlensing events next year. Also expected in the near future is the Korean Microlensing Network (KMT-Net) which will operate telescopes in South Africa, Chile, and Australia using 1.6 meter telescopes covering 4 square degrees of the galactic bulge.

Posted on by Jon Voisey

Exoplanet Kepler-7b Unexpectedly Reflective

Artist concept of Kepler in space. Credit: NASA/JPL

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Early on in the hunt for extra solar planets, the main method for discovering planets was the radial velocity method in which astronomers would search for the tug of planets on their parent stars. With the launch of NASA’s Kepler mission, the transit method is moving into the spotlight, the radial velocity technique provided an early bias in the detection of planets since it worked most easily at finding massive planets in tight orbits. Such planets are referred to as hot Jupiters. Currently, more than 30 of this class of exoplanet have had the properties of their emission explored, allowing astronomers to build a picture of the atmospheres of such planets. However, one of the new hot Jupiters discovered by the Kepler mission doesn’t fit the picture.

The consensus on these planets is that they are expected to be rather dark. Infrared observations from Spitzer have shown that these planets emit far more heat than they absorb directly in the infrared forcing astronomers to conclude that visible light and other wavelengths are absorbed and reemitted in the infrared, producing the excess heat and giving rise to equilibrium temperatures over 1,000 K. Since the visible light is so readily absorbed, the planets would be rather dull when compared to their namesake, Jupiter.

The reflectivity of an object is known as its albedo. It is measured as a percentage where 0 would be no reflected light, and 1 would be perfect reflection. Charcoal has an albedo of 0.04 while fresh snow has an albedo of 0.9. The theoretical models of hot Jupiters place the albedo at or below 0.3, which is similar to Earth’s. Jupiter’s albedo is 0.5 due to clouds of ammonia and water ice in the upper atmosphere. So far, astronomers have placed upper limits on their albedo. Eight of them confirm this prediction, but three of them seem to be more reflective.

In 2002, it was reported that the albedo for υAnd b was as high as 0.42. This year, astronomers have placed constraints on two more systems. For HD189733 b, astronomers found that this planet actually reflected more light than it absorbed. For Kepler-7b, an albedo of 0.38 has been reported.

Revisiting this for the latter case, a new paper, slated for publication in an upcoming issue of the Astrophysical Journal, a team of astronomers led by Brice-Olivier Demory of the Massachusetts Institute of Technology confirms that Kepler-7b has an albedo that breaks the expected limit of 0.3 set by theoretical models. However, the new research does not find it to be as high as the earlier study. Instead, they revise the albedo from 0.38 to 0.32.

To explain this additional flux, the team proposes two models. They suggest that Kepler-7b may be similar to Jupiter in that it may contain high altitude clouds of some sort. Due to the proximity to its parent star, it would not be ice crystals and thus, would not reach as high of an albedo as Jupiter, but preventing the incoming light from reaching lower layers where it could be more effectively trapped would help to increase the overall albedo.

Another solution is that the planet may be lacking the molecules most responsible for absorption such as sodium, potassium, titanium monoxide and vanadium monoxide. Given the temperature of the planet, it is unlikely that the molecular components would be present in the first place since they would be broken apart from the heat. This would mean that the planet would have to have 10 to 100 times less sodium and potassium than the Sun, whose chemical composition is the basis for models since our star’s composition is generally representative of stars around which planets have been discovered and presumably, the cloud from which it formed and would also form into planets.

Presently there is no way for astronomers to determine which possibility is correct. Since astronomers are slowly becoming able to retrieve spectra of extrasolar planets, it may be possible in the future for them to test chemical compositions. Failing that, astronomers will need to examine the albedo of more exoplanets and determine just how common such reflective hot Jupiters are. If the number remains low, the plausibility of metal deficient planets remains high. However, if the numbers start creeping up, it will prompt a revision to models of such planets and their atmospheres with greater emphasis on clouds and atmospheric haze.

Posted on by Jon Voisey

Update on Gliese 581d’s Habitability

An artist’s impression of Gliese 581d, an exoplanet about 20.3 light-years away from Earth, in the constellation Libra. Credit: NASA

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When last we checked in on Gliese 581d, a team from the University of Paris had suggested that the popular exoplanet, Gliese 581d may be habitable. This super-Earth found itself just on the edge of the Goldilocks zone which could make liquid water present on the surface under the right atmospheric conditions. However, the team’s work was based on one dimensional simulations of a column of hypothetical atmospheres on the day side of the planet. To have a better understanding of what Gliese 581d might be like, a three dimensional simulation was in order. Fortunately, a new study from the same team has investigated the possibility with just such an investigation.

The new investigation was called for because Gliese 581d is suspected to be tidally locked, much like Mercury is in our own solar system. If so, this would create a permanent night side on the planet. On this side, the temperatures would be significantly lower and gasses such as CO2 and H2O may find themselves in a region where they could no longer remain gaseous, freezing into ice crystals on the surface. Since that surface would never see the light of day, they could not be heated and released back into the atmosphere, thereby depleting the planet of greenhouse gasses necessary to warm the planet, causing what astronomers call an “atmospheric collapse.”

To conduct their simulation the team assumed that the climate was dominated by the greenhouse effects of CO2 and H2O since this is true for all rocky planets with significant atmospheres in our solar system. As with their previous study, they performed several iterations, each with varying atmospheric pressures and compositions. For atmospheres less than 10 bars, the simulations suggested that the atmosphere would collapse, either on the dark side of the planet, or near the poles. Past this, the effects of greenhouse gasses prevented the freezing of the atmosphere and it became stable. Some ice formation still occurred in the stable models where some of the CO2 would freeze in the upper atmosphere, forming clouds in much the same way it does on Mars. However, this had a net warming effect of ~12°C.

In other simulations, the team added in oceans of liquid water which would help to moderate the climate. Another effect of this was that the vaporization of water from these oceans also produced warming as it can serve as a greenhouse gas, but the formation of clouds could decrease the global temperature since water clouds increase the albedo of the planet, especially in the red region of the spectra which is the most prevalent form of light from the parent star, a red dwarf. However, as with models without oceans, the tipping point for stable atmospheres tended to be around 10 bars of pressure. Under that, “cooling effects dominated and runaway glaciation occurred, followed by atmospheric collapse.” Above 20 bars, the additional trapping of heat from the water vapor significantly increased temperatures compared to an entirely rocky planet.

The conclusion is that Gliese 581d is potentially habitable. The potential for surface water exists for a “wide range of plausible cases”. Ultimately, they all depend on the precise thickness and composition of any atmosphere. Since the planet does not transit the star, spectral analysis through transmission of starlight through the atmosphere will not be possible. Yet the team suggests that, since the Gliese 581 system is relatively close to Earth (only 20 lightyears), it may be possible to observe the spectra directly in the infrared portion of the spectra using future generations of instruments. Should the observations match the synthetic spectra predicted for the various habitable planets, this would be taken as strong evidence for the habitability of the planet.

Posted on by Jon Voisey

Transiting Super-Earth Detected Around Naked Eye Star

55 Cancri. Image credit: NASA/JPL

One of the first known stars to host an extrasolar planet, was that of 55 Cancri. The first planet in this system was reported in 1997 and today the system is known to host at least five planets, the inner most of which, 55 Cnc e, was recently discovered to transit the star, giving new information about this planet.

55 Cnc is an interesting system in many respects. Being a mere 41 lightyears from the Earth, the system is composed of a primary, yellow dwarf star in a wide binary orbit (1,000 AU) with a red dwarf. The planetary system lies within this orbit. The primary star is just brighter than 6th magnitude meaning it is visible to the naked eye under good viewing conditions.

One of these planets, 55 Cnc e, was discovered in this system via radial velocity measurements in 2004. At that point, the planet was reported to have a period of 2.8 days, and a minimum mass of 14.2 times the mass of the Earth. However, in 2010, Rebekah Dawson and Daniel Fabrycky from the Harvard-Smithsonian Center for Astrophysics argued that gaps in the observational period skewed the statistics and the true period the planet should be a short 0.7365 days.

One of the results of this was that the planet would have to orbit closer to the parent star. In turn, this increased the likelihood that the planet could transit the star from 13% to 33%. A team led by Joshua Winn from the Massachusetts Institute of Technology went searching for this faint transit and report its detection in a recent paper. But while the star itself is one of the brightest stars in our sky to harbor known extrasolar planets, the eclipse is far from visible without precise observations, changing by only 0.0002%, one of the smallest changes known. The timing of the eclipses confirms that correction by Dawson and Fabrycky and adds new information about the body.

Given the radius determined as well as the mass, the team was able to estimate the structure of the planet and report that the mass is 8.57 ± 0.64 Earth masses. The reported radius is 1.63 ± 0.16 times that of Earth, and the density is 10.9 ± 3.1 g cm-3 (the average density of Earth is 5.515 g cm-3). This places the planet firmly into the categories of a rocky super-Earth.

The team also explores whether or not the planet could retain an atmosphere in such a close orbit (only three times the radius of the star itself). At this close range, the planet would likely be tidally locked and with an albedo typical of rocky planets, the planet would likely have an average temperature of nearly 2970 K (5,000° F). If the planet were able to redistribute the heat, it may be as low as 2100 K (3,300° F). Either way, a planet of such mass would have difficulty retaining any primordial, gaseous atmosphere. However, the team reports that it may be possible for volcanic activity to create a thin atmosphere of high molecular weight components.

While this new report adds precious little in the grand scheme of the rapidly growing body of knowledge of exoplanets, the authors close with the note that, “there is some pleasure in being able to point to a naked-eye star and know the mass and radius of one of its planets.”

Posted on by Nancy Atkinson

Amazing Image: Kepler’s Transiting Exoplanets

Visualization of Kepler's planet candidates shown in transit with their parent stars. Credit: Jason Rowe/Kepler Mission/NASA

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Wow. This remarkable visualization shows every Kepler planetary candidate host star with its transiting companion in silhouette. Jason Rowe from the Kepler science team created the image, and the sizes of the stars and transiting companions are properly scaled. For reference, Rowe has included the Sun with a transiting Earth and Jupiter (below the top row on the right by itself.) The largest star is 6.1 times larger that the Sun and the smallest stars are estimated to be only 0.3 times the radius of the Sun. On his Flickr page, Rowe says the colors of the stars represent how the eye would see the star outside of the Earths atmosphere. “Stars have been properly limb darkened and the companions have been offset relative to one another to match the modeled impact parameter. Some stars will even show more than one planet!” he writes.

For more information and high resolution versions of the image, see Jason Rowe’s Flickr page. This image is featured on today’s (March 29, 2011) Astronomy Picture of the Day.