Shedding Some Light on a Dark Discovery

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Earlier this month astronomers released news of the darkest exoplanet ever seen: discovered in 2006, the gas giant TrES-2b reflects less than 1% of the visible light from its parent star… it’s literally darker than coal! Universe Today posted an article about this intriguing announcement on August 11, and now Dr. David Kipping of the Harvard-Smithsonian Center for Astrophysics is featuring a podcast on 365 Days of Astronomy in which he gives more detail about the dark nature of this discovery.

Listen to the podcast here.

The 365 Days of Astronomy Podcast is a project that will publish one podcast per day, for all 365 days of 2011. The podcast episodes are written, recorded and produced by people around the world.

“TrES-2b is similar in mass and radius to Jupiter but Jupiter reflects some 50% of the incident light. TrES-2b has a reflectivity less than that of any other planet or moon in the Solar System or beyond. The reflectivity is significantly less than even black acrylic paint, which makes the mind boggle as to what a clump of this planet would look like in your hand. Perhaps an appropriate nickname for the world would be Erebus, the Greek God of Darkness and Shadow. But what really is causing this planet to be so dark?”

– Dr. David Kipping

David Kipping obtained a PhD in Astrophysics from University College London earlier this year. His thesis was entitled ‘The Transits of Extrasolar Planets with Moons’ and David’s main research interest revolves around exomoons. He is just starting a Carl Sagan Fellowship at the Harvard-Smithsonian Center for Astrophysics.

The paper on which the the podcast is based can be found here.

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Jason Major is a graphic designer, photo enthusiast and space blogger. Visit his website Lights in the Dark and follow him on Twitter @JPMajor and on Facebook for more astronomy news and images!

Astronomers Discover a Dark Alien World

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An exoplanet has been discovered by astronomers that reflects less than one percent of the light it receives from its parent star. Less reflective than black acrylic paint, this planet is literally darker than coal!

TrES-2b is a Jupiter-sized gas giant orbiting the star GSC 03549-02811, about 750 light-years away in the direction of the constellation Draco. First discovered in 2006 by the Trans-Atlantic Exoplanet Survey (TrES), its unusual darkness has been identified by researchers led by David Kipping from the Harvard-Smithsonian Center for Astrophysics (CfA) and David Spiegel from Princeton University, using data from NASA’s Kepler spacecraft.

Kepler has located more than 1,200 planetary candidates in its field of view. Additional analysis will reveal whether any other unusually dark planets lurk in that data. (Image: NASA/Kepler mission/Wendy Stenzel)

The team monitored the brightness of the TrES-2 system as the planet orbited its star and detected a subtle dimming and brightening due to the planet’s changing phase. A more reflective planet would have shown larger brightness variations as its phase changed.

The dark exoplanet is tidally locked with its star and orbits it at a distance of only 5 million kilometers (3.1 million miles), keeping it heated to a scorching 1000º C (1,832º F). Too hot for the kinds of reflective ammonia clouds seen on Jupiter, TrES-2b is wrapped in an atmosphere containing light-absorbing chemicals like vaporized sodium and potassium, or gaseous titanium oxide. Still, this does not completely explain its extremely dark appearance.

“It’s not clear what is responsible for making this planet so extraordinarily dark,” stated co-author David Spiegel of Princeton University. “However, it’s not completely pitch black. It’s so hot that it emits a faint red glow, much like a burning ember or the coils on an electric stove.”

Regardless of its faint glow TrES-2b is still much darker than any planet or moon in our solar system.

The new work appears in a paper in the journal Monthly Notices of the Royal Astronomical Society. Read the news release here.

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Jason Major is a graphic designer, photo enthusiast and space blogger. Visit his website Lights in the Dark and follow him on Twitter @JPMajor and on Facebook for more astronomy news and images!

Kepler Drops In On Planetary Nebula

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Discovered by amateur Austrian astronomer, Matthias Kronberger, planetary nebula Kn 61 just happens to be in a relatively small piece of celestial real estate being monitored by NASA’s Kepler planet finding mission. Lucky for us, we’re able to take a look at the photographic results of the new nebula obtained with the Gemini Observatory.

“Kn 61 is among a rather small collection of planetary nebulae that are strategically placed within Kepler’s gaze,” said Orsola De Marco of Macquarie University in Sydney, Australia who is the author of a 2009 paper speculating on how companion stars or even planets may influence and shape the intricate structure seen in many planetary nebulae. “Explaining the puffs left behind when medium sized stars like our Sun expel their last-breaths is a source of heated debate among astronomers, especially the part that companions might play,” says De Marco, “it literally keeps us up at night!”

And visions like this keeps the Kepler Mission continually monitoring a 105 square degree area of sky located in Cygnus looking for changes in stellar brightness which could spell a planetary transit, companion star – or something else. “It is a gamble that possible companions, or even planets, can be found due to these usually small light variations,” says George Jacoby of the Giant Magellan Telescope Organization and the Carnegie Observatories (Pasadena). “However, with enough objects it becomes statistically very likely that we will uncover several where the geometries are favorable – we are playing an odds game and it isn’t yet known if Kn 61 will prove to have a companion.” Jacoby also serves as the Principal Investigator for a program to obtain follow-up observations of Kn 61’s central star with Kepler.

To help sift through the huge amount of data provided by Kepler, professional and amateur astronomers are working as partners to help locate objects such as planetary nebula. So far, six have been found in the digital sky survey – including Kn 61. “Without this close collaboration with amateurs, this discovery would probably not have been made before the end of the Kepler mission. Professionals, using precious telescope time, aren’t as flexible as amateurs who did this using existing data and in their spare time. This was a fantastic pro-am collaboration of discovery,” says Jacoby, who serves as the liaison with the Deep Sky Hunters (DSH) and requested their help to survey the Kepler field. Jacoby published a paper with DSH members in 2010 that describes the techniques used.

“Planetary nebulae present a profound mystery,” says De Marco. “Some recent theories suggest that planetary nebulae form only in close binary or even planetary systems – on the other hand, the conventional textbook explanation is that most stars, even solo stars like our sun, will meet this fate. That might just be too simple.” Jacoby also elucidates that terrestrial observations are unable to detect such phenomena with a high rate of regularity “This is quite likely due to our inability to detect these binaries from the ground and if so then Kepler is likely to push the debate strongly in one direction or the other.”

As for our own galaxy, over 3,000 planetary nebulae have been identified and cataloged. We know they are the end product of a dying star, but not what role companions stars (or even planets) may take in their structure. Of these, only 20% have binary central stars – but this low number may be our inability to resolve them. Hopefully the space-based Kepler telescope can one day reveal their mysteries us!

Original News Source: Gemini Observatory Image Release.

June 21 ATV Re-Entry: A Man-Made Fireball In The Sky

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The Johannes Kepler ATV (Automated Transfer Vehicle) has undocked from the International Space station and will re- enter Earth’s atmosphere on June 21st ending its mission in fiery destruction.

The ATV has been docked with the ISS since February, where it delivered supplies, acted as a giant waste disposal and boosted the orbit of the International Space Station with its engines.

The X-wing ATV delivered approximately 7 tonnes of supplies to the station and will be leaving with 1,200kg of waste bags, including unwanted hardware.

The Johannes Kepler ATV-2 approaches the International Space Station. Docking of the two spacecraft occurred on Feb. 24, 2011. Credit: NASA

On June 21st at 17:07 GMT the craft will fire its engines and begin its suicide mission, tumbling and burning up as a bright manmade fireball over the Pacific Ocean. Any leftover debris will strike the surface of the Pacific ocean at 20:50 GMT.

During the ATV’s re-entry and destruction there will be a prototype onboard flight recorder (Black Box) transmitting data to Iridium satellites, as some aspects of a controlled destructive entry are still not well known.

ESA says that this area is used for controlled reentries of spacecraft because it is uninhabited and outside shipping lanes and airplane routes. Extensive analysis by ESA specialists will ensure that the trajectory stays within safe limits.

There still are some chances to see the ISS and Johannes Kepler ATV passing over tonight, but if you in a location where you can see the south Pacific skies starting at about 20:00 GMT, keep an eye out for a glorious manmade fireball.

A shower of debris results as the ATV continues its plunge through the atmosphere. Credit: ESA

Read more about the re-entry at ESA.

Multi-Planet Systems Common in Kepler Findings

 

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Of the 1235 planetary candidates that NASA’s Kepler space telescope has found so far, 408 reside in multiple-planet systems – a growing trend that indicates planets do, in fact,  like company.

The systems observed also seem to behave quite differently than our own solar system. In particular many are flatter than ours; that is, the planets orbit their stars in more or less the same exact plane. This, of course, is what allows Kepler to see them in the first place… the planets have to transit their stars perpendicular to Kepler’s point of view in order for it to detect the oh-so-subtle change in brightness that indicates the likely presence of a planet. In our solar system there’s a variation in the orbital plane of some planets up to 7º – enough of a difference that an alien Kepler-esque telescope might very well not be able to spot all eight planets.

The reason for this relative placidity in exoplanet orbits may be due to the lack of gas giants like Jupiter in these systems. So far, all the multiple-planet systems found have planets smaller than Neptune. Without the massive gravitational influence of a Jupiter-sized world to shake things up, these exosystems likely experience a much calmer environment – gravitationally speaking, of course.

“Most likely, if our solar system didn’t have large planets like Jupiter and Saturn to have stirred things up with their gravitational disturbances, it would be just as flat. Systems with smaller planets probably had a much more sedate history.”

– David Latham, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA

Slide showing Kepler multi-planet systems (blue dots). Credit: David Latham.

Systems containing large gas giants have also been found but they are not as flat as those without, and many smaller worlds are indeed out there… “probably including a lot of them comparable in size to Earth,” said planet-hunter Geoff Marcy of the University of California, Berkeley.

While multiple-planet systems were expected, the scientists on the Kepler team were surprised by the amount that have been discovered.

“We didn’t anticipate that we would find so many multiple-transit systems. We thought we might see two or three. Instead, we found more than 100,” said Latham.

A total of 171 multiple-planet systems have been found so far… with many more to come, no doubt!

Announced yesterday at the American Astronomical Society conference in Boston, these findings are the result of only the first four months of Kepler’s observations. There will be another news release next summer but in the meantime the team wants time to extensively research the data.

“We don’t want to get premature information out. There’s still a lot of analysis that needs to be done.”

– Kepler principal investigator William Borucki

Read more on the Kepler mission site, or on Science NOW.

Kepler Team Announces New Rocky Planet

 

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Today at the American Astronomical Society conference in Boston, the Kepler team announced the confirmation of a new rocky planet in orbit around Kepler-10. Dubbed Kepler-10c, this planet is described as a “scorched, molten Earth.”

2.2 times the radius of Earth, Kepler-10c orbits its star every 45 days. Both it and its smaller, previously-discovered sibling 10b are located too close to their star for liquid water to exist.

Kepler-10c was validated using a new computer simulation technique called “Blender” as well as additional infrared data from NASA’s Spitzer Space Telescope. This method can be used to locate Earth-sized planets within Kepler’s field of view and could also potentially help find Earth-sized planets within other stars’ habitable zones.

This is the first time the team feels sure that it has exhaustively ruled out alternative explanations for dips in the brightness of a star… basically, they are 99.998% sure that Kepler-10c exists.

The Kepler-10 star system is located about 560 light-years away near the Cygnus and Lyra constellations.

Read the release on the Nature.com blog.

Image credit: NASA/Ames/JPL-Caltech

The Flip Side of Exoplanet Orbits

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It was once thought that our planet was part of a “typical” solar system. Inner rocky worlds, outlying gas giants, some asteroids and comets sprinkled in for good measure. All rotating around a central star in more or less the same direction. Typical.

But after seeing what’s actually out there, it turns out ours may not be so typical after all…

Astronomers researching exoplanetary systems – many discovered with NASA’s Kepler Observatory – have found quite a few containing “hot Jupiters” that orbit their parent star very closely. (A hot Jupiter is the term used for a gas giant – like Jupiter – that resides in an orbit very close to its star, is usually tidally locked, and thus gets very, very hot.) These worlds are like nothing seen in our own solar system…and it’s now known that some actually have retrograde orbits – that is, orbiting their star in the opposite direction.

“That’s really weird, and it’s even weirder because the planet is so close to the star. How can one be spinning one way and the other orbiting exactly the other way? It’s crazy. It so obviously violates our most basic picture of planet and star formation.”

– Frederic A. Rasio, theoretical astrophysicist, Northwestern University

Now retrograde movement does exist in our solar system. Venus rotates in a retrograde direction, so the Sun rises in the west and sets in the east, and a few moons of the outer planets orbit “backwards” relative to the other moons. But none of the planets in our system have retrograde orbits; they all move around the Sun in the same direction that the Sun rotates. This is due to the principle of conservation of angular momentum, whereby the initial motion of the disk of gas that condensed to form our Sun and afterwards the planets is reflected in the current direction of orbital motions. Bottom line: the direction they moved when they were formed is (generally) the direction they move today, 4.6 billion years later. Newtonian physics is okay with this, and so are we. So why are we now finding planets that blatantly flaunt these rules?

The answer may be: peer pressure.

Or, more accurately, powerful tidal forces created by neighboring massive planets and the star itself.

By fine-tuning existing orbital mechanics calculations and creating computer simulations out of them, researchers have been able to show that large gas planets can be affected by a neighboring massive planet in such a way as to have their orbits drastically elongated, sending them spiraling closer in toward their star, making them very hot and, eventually, even flip them around. It’s just basic physics where energy is transferred between objects over time.

It just so happens that the objects in question are huge planets and the time scale is billions of years. Eventually something has to give. In this case it’s orbital direction.

“We had thought our solar system was typical in the universe, but from day one everything has looked weird in the extrasolar planetary systems. That makes us the oddball really. Learning about these other systems provides a context for how special our system is. We certainly seem to live in a special place.”

– Frederic A. Rasio

Yes, it certainly does seem that way.

The research was funded by the National Science Foundation. Details of the discovery are published in the May 12th issue of the journal Nature.

Read the press release here.

Main image credit: Jason Major. Created from SDO (AIA 304) image of the Sun from October 17, 2010 (NASA/SDO and the AIA science team) and an image of Jupiter taken by the Cassini-Huygens spacecraft on October 23, 2000 (NASA/JPL/SSI).

Kepler Discovers a Rare Triple Gem

 

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It may be visible to the naked eye, but it took the unblinking gaze of NASA’s Kepler space telescope to reveal the true triple nature of this star system.

Animation of HD 181068 (click to play)

Unofficially dubbed “Trinity”, object HD 181068 is a multiple star system comprised of three stars: a red giant more than twelve times the diameter of the Sun and two red dwarf stars each slightly smaller than the Sun. The red dwarfs orbit each other in tight rotation around a central point, which in turn orbits the red giant. The smaller stars complete a full orbit around the giant every 45.5 days and, from our point of view, pass directly in front of and behind the huge star.

The orbital eclipse events of HD 181068 last about 2 days. What’s surprising is that during these eclipses the brightness of the system is not affected very much. This is because the surface brightnesses of the three stars are very similar. The current metaphor is a “white rabbit in a snowfall”, wherein the two red dwarfs effectively become invisible when they pass in front of the red giant. It wasn’t until the Kepler mission that we had an observational tool precise enough to detect the structure of this intriguing star system, located 800 light-years away from our own.

“The intriguing nature of this unique system remained unnoticed until now despite the fact that it is nearly bright enough to be visible to the naked eye. We really needed Kepler with its unprecedentedly precise and uninterrupted photometric monitoring to uncover such a rare gem.”

– Aliz Derekas, Eotvos University and Konkoly Observatory, Budapest, Hungary

Another unexpected feature of Trinity is its “quiet” nature. Astronomers have known that red giant stars exhibit seismic oscillations, as does our own Sun. But these oscillations are not present in Trinity’s red giant. Scientists speculate that the two red dwarfs may be creating some sort of gravitational offset, effectively negating the red giant’s vibrations. More research will be needed to determine if this is in fact the case.

Find out more about HD 181068 and other recent Kepler discoveries on NASA’s mission site or in the press release issued by the Ames Research Center, or read the published report on Science.

Image credit: NASA/KASC

 

 

New Technique Separates the Modest Red Giants From the … Giant Red Giants

Based on results from the first year of the Kepler mission, researchers have learned a way to distinguish two different groups of red giant stars: the giants, and the truly giant giants. The findings appear this week in Nature.

Red giants, having exhausted the supply of hydrogen in their cores, burn hydrogen in a surrounding shell. Once a red giant is sufficiently evolved, the helium in the core also undergoes fusion. Until now, the very different stages looked roughly the same.

Lead author Timothy Bedding, from the University of Sydney in Australia, and his colleagues used high-precision photometry obtained by the Kepler spacecraft over
more than a year to measure oscillations in several hundred red giants.

Using a technique called asteroseismology, the researchers were able to place the stars into two clear groups, “allowing us to distinguish unambiguously between hydrogen-shell-burning stars (period spacing mostly 50 seconds) and those that are also burning helium (period spacing 100 to 300 seconds),” they write. The latter population lend to the star an oscillation pattern dominated by gravity-mode period spacings.

In a related News and Views article, Travis Metcalfe of the Boulder, Colo.-based National Center for Atmospheric Research explains that like the sun, “the surface of a red giant seems to boil as convection brings heat up from the interior and radiates it into the coldness of outer space. These turbulent motions act like continuous starquakes, creating sound waves that travel down through the interior and back to the surface.” Some of the sounds, he writes, have just the right tone — a million times lower than what people can hear — to set up standing waves known as oscillations that cause the entire star to change its brightness regularly over hours and days, depending on its size. Asteroseismology is a method to measure those oscillations.

Metcalfe goes on to explain that a red giant’s life story depends not only on its age but also on its mass, with stars smaller than about twice the mass of the sun undergoing a sudden ignition called a helium flash.

“In more massive stars, the transition to helium core burning is gradual, so the stars exhibit a wider range of core sizes and never experience a helium flash. Bedding and colleagues show how these two populations can be distinguished observationally using their oscillation modes, providing new data to validate a previously untested prediction of stellar evolution theory,” he writes.

The study authors conclude that their new measurement of gravity-mode period spacings “is an extremely reliable parameter for distinguishing between stars in these two evolutionary stages, which are known to have very different core densities but are otherwise very similar in their fundamental properties (mass, luminosity and radius). We note that other asteroseismic observables, such as the small p-mode separations, are not able to do this.”

Source: Nature

Amazing Image: Kepler’s Transiting Exoplanets

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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.