OK, this looks nice - but let's think it through. You've got two binary stars with angular diameters and spectral properties roughly analogous to our Sun - shining through an atmosphere containing semi-precipitous water vapor (also known as clouds). Plausible? Credit: NASA.
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So we all know this story. Uncle Owen has just emotionally blackmailed you into putting off your application to the academy for another year – and even after you just got those two new droids, darn it. So you stare mournfully at the setting binary suns and…
Hang on, they look a lot like G type stars – and if so, their roughly 0.5 degree angular diameters in the sky suggest they are both only around 1 astronomical unit away. I mean OK, you could plausibly have a close red dwarf and a distant blue giant having identical apparent diameters, but surely they would look substantially different, both in color and brightness.
So if those two suns are about the same size and at about the same distance away, then you must be standing on a circumbinary planet that encompasses both stars in one orbit.
To allow a stable circumbinary orbit – either a planet has to be very distant from the binary stars – so that they essentially act as a single center of mass – or the two stars have to be really close together – so that they essentially act as a single center of mass. It’s unlikely a planet could maintain a stable orbit around a binary system where it is exposed to pulses of gravitational force, as first one star passes close by, then the other passes close by.
Anyhow, if you can stand on a planet and watch a binary sunset – and you are a water-solvent based life form – then your planet is within the star system’s habitable zone where H2O can exist in a fluid state. Given this – and their apparent size and proximity to each other, it’s most likely that you orbit two stars that are really close together.
To get a planet in a habitable zone around a binary system - your choices are probably limited to circumbinary planets around two close binaries - or circumstellar planets around one star in a widely spread binary. Credit: NASA/JPL.
But, taking this further – if we accept that there are two G type stars in the sky, then it’s unlikely that your planet is exactly one astronomical unit from them – since the presence of two equivalent stars in the sky should roughly double the stellar flux you would get from one. And it’s not a simple matter of doubling the distance to halve the stellar flux. Doubling the distance will halve the apparent diameters of the stars in the sky, but an inverse square relation applies to their brightness and their solar flux, so at double the distance you would only get a quarter of their stellar flux. So, something like the square root of two, that is about 1.4 astronomical units away from the stars, might be about right.
However, this means the stars now need a larger than solar diameter to create the same apparent size that they have in the sky – which means they must have more mass – which will put them into a more intense spectral class. For example, Sirius A has 1.7 times the diameter of the Sun, roughly twice its mass – and consequently about 25 times its absolute luminosity. So even at 2 astronomical units distance, Sirius A would be nearly five times as bright and deliver five times as much stellar flux as the Sun does to Earth (or ten times if there are two such stars in the sky).
So, to sum up…
It’s a struggle to come up with a scenario where you could have two stars in the sky, with the same apparent diameter, color and brightness – unless you are in a circumbinary orbit around two equivalent stars. There’s no reason to doubt that a planet could maintain a stable circumbinary orbit around two equivalent stars, that might be G type Sun analogues or whatever. However, it’s a struggle to come up with a plausible scenario where those stars could have the angular diameter in the sky that they appear to have, while still having your planet in the system’s habitable zone.
I mean OK you’re on a desert world, but two stars of a more intense spectral class than G would probably blow away the atmosphere – and even two G type stars would give you a Venus scenario (which receives roughly double the solar flux that Earth does, being 28% closer to the Sun). They could be smaller K or M class stars, but then they should be redder than they appear to be – and your planet would need to be closer in, towards that range where it’s unlikely your planet could retain a stable orbit.
This is really nifty: a visualization of the 1,235 exoplanet candidates observed by Kepler in the recently released data, created by Jer Thorp. In the video, all the candidates are shown as if orbiting a single star – just for the purposes of comparisons. The size of the colored dot is proportional to the size of the planet, and two of the most promising candidates for habitability are highlighted (KOI 326.01 and KOI 314.02).
Keplers 1200 Planet candidates by size. Finding exoplanets is getting easier, LUVOIR will helps us find signs of life, if any, on them. Credit: NASA/Wendy Stenzel
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With the startling new finding of dozens of Earth-sized extrasolar planets, NASA’s Kepler planet hunting space telescope has just revolutionized our understanding of Earths place in the Universe and the search for Extraterrestrial Life. And the historic science discovery is based on data collected in just the first few months of operation of the powerful telescope as it scans only a tiny portion of the sky.
The discovery of 1235 new extrasolar planet candidates was announced today (Feb.2) by NASA and Kepler scientists at a media briefing. 68 of these planet candidates are Earth-sized. Another 288 are Super-Earth-size, 662 are Neptune-size and 165 are Jupiter-size. Most of these candidates orbit stars like our sun.
Even more significant is that 54 of the planet candidates are located within the ‘habitable zone’ of their host stars and 5 of those are Earth-sized. Before today we knew of exactly ZERO Earth-sized planets within the habitable zone. Now there are 5.
Finding a ‘Pale Blue Dot’ or ‘Second Earth’ inside a habitable zone that harbors water and environmental conditions that can support life is the ‘Holy Grail’ of science.
Are We Alone ?
“We went from zero to 68 Earth-sized planet candidates and zero to 54 candidates in the habitable zone – a region where liquid water could exist on a planet’s surface. Some candidates could even have moons with liquid water,” said William Borucki of NASA’s Ames Research Center, Moffett Field, Calif.. Borucki is the science principal investigator for NASA’s Kepler mission.
“Five of the planetary candidates are both near Earth-size and orbit in the habitable zone of their parent stars.”
Earth-sized water worlds are the most conducive to the formation and evolution of alien life forms. Water is an essential prerequisite for life as we know it.
“Kepler’s blown the lid off everything we know about extrasolar planets,” said Debra Fischer, professor of Astronomy at Yale University, New Haven, Conn
Kepler's over 1200 planet candidates as of Feb. 1, 2011. Credit: NASA/Wendy Stenzel
Kepler is the first NASA mission capable of finding Earth-size planets in or near the habitable zones around their parent stars. The mission uses the transit method to detect the tell tale signatures of planets. The goal is to determine how common are planets the size of Earth orbiting inside the habitable zone of stars like our sun.
Kepler measures the miniscule decreases in the brightness of stars caused by planets crossing in front of them and blocking the starlight. Imagine calculating the difference in light transmission caused by a flea sitting on a cars headlight.
Follow up observations over a period of several years will be required to confirm these results, the scientists explained. Astronomers expect that over 80% of the candidate planets will be positively confirmed as real planets by utilizing ground based observatories and the Spitzer Space Telescope.
For an Earth-sized planet orbiting a sun-like star inside the habitable zone, transits occur about once per year. Since three transits are required to verify a planets status, it will therefore take about three years to reach a definitive conclusion.
These remarkable new planet discoveries are based on observations from only the first four months of Kepler’s telescopic operations – May 12, 2009 to Sept. 17, 2009. The space based observatory continuously monitors more than 156,000 stars using 42 CCD detectors with a field of view that covers only 1/400 of the sky.
“Kepler is making good progress towards its goals,” said Borucki
“We have found over twelve hundred candidate planets – that’s more than all the people have found so far in history.”
“Imagine if we could look wider. Kepler looks at one 400th of the sky. If we had 400 of these fields of view, we’d see 400 times that number of candidates. We would see 400,000 candidate planets.”
Keplers over 1200 Planet candidates sorted by size
“The fact that we’ve found so many planet candidates in such a tiny fraction of the sky suggests there are countless planets orbiting stars like our sun in our galaxy,” Borucki amplified. “Our results indicate there must be millions of planets orbiting the stars that surround our sun.”
“If we find that Earth’s are common in the habitable zones of stars, very likely that means life is common around these stars.”
“Kepler has shown that planetary systems like our own are common,” said Debra Fischer.
Planets in Keplers Field of View.
Before and after the discovery of over 1200 planet candidates by NASA’s Kepler Space Telescope.
“The search for planets is motivated by the search for life,” Fischer added.
“We have allowed the public to participate though the website Planethunters.org,” she added. “And now we have over 16,000 dedicated users. The public is excited to be a part of research and history.”
“Thanks to Kepler for this treasure chest of data!” Fisher concluded.
Kepler is just the first step in finding Earth sized and Earth like planets. “We are building the foundation for future generations of explorers,” said Borucki.
“Future missions will be developed to study the composition of planetary atmospheres to determine if they are compatible with the presence of life. The design for these missions depends on Kepler finding whether Earth-size planets in the habitable zone are common or rare.”
The first planets beyond our solar system were discovered in 1995. Up to today there were just over 500 known extrasolar planets.
Kepler now has 15 confirmed extrasolar planet discoveries and over 1200 possible candidates.
NASA’s Kepler spacecraft was launched on March 6, 2009 from Launch Complex 17-B atop a Delta II rocket at Cape Canaveral Air Force Station in Florida. See spacecraft and launch photos below
Kepler’s science operations are currently funded for three and one half years of operations until November 2012. The mission’s lifetime – and its goal of discovering multitudes of new planets as small as Earth – can be extended if NASA funding is approved by Congress and the President.
William Borucki – Explains Keplers Discovery of Earth Sized Planets
Science principal investigator for NASA’s Kepler mission, NASA’s Ames Research Center
Video Caption: NASA’s Kepler mission has discovered its first Earth-size planet candidates and its first candidates in the habitable zone, a region where liquid water could exist on a planet’s surface. Five of the potential planets are near Earth-size and orbit in the habitable zone of smaller, cooler stars than our sun.
Kepler also found six confirmed planets orbiting a sun-like star, Kepler-11. This is the largest group of transiting planets orbiting a single star yet discovered outside our solar system. Located approximately 2,000 light years from Earth, Kepler-11 is the most tightly packed planetary system yet discovered. All six of its confirmed planets have orbits smaller than Venus, and five of the six have orbits smaller than Mercury’s.
What is an Earth like planet ? Explantion here
David Charbonneau, an exoplanet researcher at Harvard University, explains what scientists mean when they say “earthlike planet” and “super Earth.” This interview was recorded at NASA’s Goddard Space Flight Center on December 10, 2010, by NASA science writer Daniel Pendick.
Kepler Mission Star Field
An image by Carter Roberts of the Eastbay Astronomical Society in Oakland, CA, showing the Milky Way region of the sky where the Kepler spacecraft/photometer will be pointing. Each rectangle indicates the specific region of the sky covered by each CCD element of the Kepler photometer. There are a total of 42 CCD elements in pairs, each pair comprising a square.
Credit: Carter Roberts / Eastbay Astronomical Society.Kepler's target region in the Milky Way. Credit: Jon LombergKepler being prepared in the clean room at Astrotech
prior to launch on March 6, 2009. Credit: nasatech.net
More Kepler photos courtesy of nasatech.net here
Delta 2 rocket streaks to the heavens.
Launch of NASA’s Kepler planet hunting space telescope from Cape Canaveral Air Force Station, FL, Complex 17, on March 6, 2009 at 10:49 p.m. Credit: Ben CooperBen Cooper Featured on Astronomy Picture of the Day (APOD); March 9, 2009
Launch Pad 17 B and a Delta II rocket
from my perch on the 8th floor of Launch Pad 17 A as rocket is encased in launch tower. Credit: Ken KremerView of Launch Complex 17 B and cryogenic storage tanks by Ken Kremer
Using data from the Kepler space telescope, scientists have discovered a horde of six planets orbiting a sun-like star, approximately 2,000 light years from Earth. This is the largest group of planets detected so far around another star. The planets in this newly found solar system are relatively small – they range from 2.3 to 13.5 times the mass of the Earth – and are amazing mix of rock and gases. All six planets are crowded within an orbit the size of Venus’ orbit around our Sun; however, the inner five are closer to their star than any planet in our solar system.
“This is a surprisingly flat and compact system of six transiting planets,” said Jack Lissauer, co-investigator on the Kepler mission, speaking at a press conference on February 2, 2011. “The five inner planets are especially close together, something we didn’t think would happen for worlds of this size. This discovery forces us to go back and look at formation models of planets.”
Lissauer added that the close proximity of the six worlds around the star — now called Kepler 11 — also means that the planets are perturbing each others’ orbits. While having a multi-planet system makes it difficult to untangle the signals from each planet, it has the added benefit of providing more information about each of the worlds.
“In a system where the planets are tugging on one another, that means we can weigh the planets,” Lissauer said. “We have found they are low density planets; some are fluffy, sort of like marshmallows. But they are not all gas, so maybe like a marshmallow with a little hard candy at the core.”
Lissauer was incredibly enthusiastic about the discovery.
“We really were just amazed at his gift that nature has given us,” he said. “With six transiting planets, and five so close and getting the sizes and masses of five of these worlds, there is only one word that adequately describes the new finding: Supercalifragilisticexpialidocious.”
Kepler finds planets by using the transit method. The planets’ orbits are edge-on as seen from Earth, so when they pass in front of their star they block a small portion of its light. That dip in brightness is what Kepler detects.
Lissauer explained the animation (seen at the top of this article): “This is the view of Kepler, and it looks like a very special clock, one with six hands moving at six different rates, and we interpret this as six planets orbiting near the same plane. Then, you can see how it might look face on. This is the most compact system of planets every discovered by any technique anywhere.”
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The time between transits provides the orbital period. To determine the planets’ masses, the scinetists analyzed slight variations in the orbital periods caused by gravitational interactions among the planets.
Lissauer said the five close inner bodies tug on one another’s orbit, and sometimes the pull can retard the transit time by 10-20 minutes.
“The timing of the transits is not perfectly periodic, and that is the signature of the planets gravitationally interacting,” said Daniel Fabrycky, a Hubble postdoctoral fellow at UC Santa Cruz, who led the orbital dynamics analysis. “By developing a model of the orbital dynamics, we worked out the masses of the planets and verified that the system can be stable on long time scales of millions of years.”
Five of the planets’ orbital periods are all less than 50 days, and the sixth planet is larger and farther out, with an orbital period of 118 days and an undetermined mass.
Kepler-11 is a sun-like star around which six planets orbit. At times, two or more planets pass in front of the star at once, as shown in this artist's conception of a simultaneous transit of three planets observed by NASA's Kepler spacecraft on Aug. 26, 2010. Image credit: NASA/Tim Pyle
Finding a large multiplanet system has many people wondering when Kepler will discover an Earth-like world. The scientists on the panel today estimated it will take three years of Kepler data to find another Earth.
“No one is more eager to get to the point of an Earth-like planet than the Kepler team,” said Douglas Hudgins, Kepler program scientist. That will require at least 3 years of Kepler data and painstaking follow-up observations from ground-based before those types of discoveries will emerge from the data.”
Hudgins reminded everyone that the first 15 years of exoplanet searches from ground-based observing produced about 500 planets, and that last year the Kepler team announced 750 exoplanet candidates from just the first three months of Kepler observations. With the release of more Kepler data today, there are now more than 1,200 planet candidates.
“The key thing to remember about every planet candidate,”Hudgins said, “ is that every time we see in data evidence of a signal, there is required analysis and follow-up data and observations to determine it is actually planet and not something masquerading as a planet.”
Translation: this takes time and won’t happen overnight.
But with the release of more data, the Kepler team said they wants to harness the horsepower of the whole planetary community, as well as citizen scientists to scour through the data. The Planet Hunters program from Galaxy Zoo has been a successful project that allows anyone to contribute the science of finding extrasolar planets.
The public has made over 1.3 million classification using just the first 30 days of publicly released Kepler data,” said Debra Fischer, professor of Astronomy at Yale University who heads up the Planet Hunters project. “We are really excited and appreciative that NASA and the Kepler mission has essentially quadrupled the amount of public data with the early release of their latest data.”
A research team led by astronomers from the University of Tokyo and the National Astronomical Observatory of Japan (NAOJ) has discovered that inclined orbits may be typical rather than rare for exoplanetary systems — those outside of our solar system. Their measurements of the angles between the axes of the star’s rotation (stellar rotational axis) and the planet’s orbit (planetary orbital axis) of exoplanets HAT-P-11b and XO-4b demonstrate that these exoplanets’ orbits are highly tilted. This is the first time that scientists have measured the angle for a small planet like HAT-P-11 b. The new findings provide important observational indicators for testing different theoretical models of how the orbits of planetary systems have evolved.
Since the discovery of the first exoplanet in 1995, scientists have identified more than 500 exoplanets, planets outside of our solar system, nearly all of which are giant planets. Most of these giant exoplanets closely orbit their host stars, unlike our solar system’s giant planets, like Jupiter, that orbit the Sun from a distance. Accepted theories propose that these giant planets originally formed from abundant planet-forming materials far from their host stars and then migrated to their current close locations. Different migration processes have been suggested to explain close-in giant exoplanets.
Disk-planet interaction models of migration focus on interactions between the planet and its protoplanetary disk, the disk from which it originally formed. Sometimes these interactions between the protoplanetary disk and the forming planet result in forces that make the planet fall toward the central star. This model predicts that the spin axis of the star and the orbital axis of the planet will be in alignment with each other.
Planet-planet interaction models of migration have focused on mutual scatterings among giant planets. Migration can occur from planet scattering, when multiple planets scatter during the creation of two or more giant planets within the protoplanetary disk. While some of the planets scatter from the system, the innermost one may establish a final orbit very close to the central star. Another planet-planet interaction scenario, Kozai migration, postulates that the long-term gravitational interaction between an inner giant planet and another celestial object such as a companion star or an outer giant planet over time may alter the planet’s orbit, moving an inner planet closer to the central star. Planet-planet migration interactions, including planet-planet scattering and Kozai migration, could produce an inclined orbit between the planet and the stellar axis.
Overall, the inclination of the orbital axes of close-in planets relative to the host stars’ spin axes emerges as a very important observational basis for supporting or refuting migration models upon which theories of orbital evolution center. A research group led by astronomers from the University of Tokyo and NAOJ concentrated their observations with the Subaru Telescope on investigating these inclinations for two systems known to have planets: HAT-P-11 and XO-4. The group measured the Rossiter-McLaughlin (hereafter, RM) effect of the systems and found evidence that their orbital axes incline relative to the spin axes of their host stars.
The RM effect refers to apparent irregularities in the radial velocity or speed of a celestial object in the observer’s line of sight during planetary transits. Unlike the spectral lines that are generally symmetrical in measures of radial velocity, those with the RM effect deviate into an asymmetrical pattern (see Figure 1). Such apparent variation in radial velocity during a transit reveals the sky-projected angle between the stellar spin axis and planetary orbital axis. Subaru Telescope has participated in previous discoveries of the RM effect, which scientists have investigated for approximately thirty-five exoplanetary systems thus far.
In January 2010, a research team led by the current team’s astronomers from the University of Tokyo and the National Astronomical Observatory of Japan used the Subaru Telescope to observe the planetary system XO-4, which lies 960 light years away from Earth in the Lynx region. The system’s planet is about 1.3 times as massive as Jupiter and has a circular orbit of 4.13 days. Their detection of the RM effect showed that the orbital axis of the planet XO-4 b tilts to the spin axis of the host star. Only the Subaru Telescope has measured the RM effect for this system so far.
In May and July 2010, the current research team conducted targeted observations of the HAT-P-11 exoplanetary system, which lies 130 light years away from the Earth toward the constellation Cygnus. The Neptune-sized planet HAT-P-11 b orbits its host star in a non-circular (eccentric) orbit of 4.89 days and is among the smallest exoplanets ever discovered. Until this research, scientists had only detected the RM effect for giant planets. The detection of the RM effect for smaller-sized planets is challenging because the signal of the RM effect is proportional to the size of the planet; the smaller the transiting planet, the fainter the signal.
;The team took advantage of the enormous light-collecting power of the Subaru Telescope’s 8.2m mirror as well as the precision of its High Dispersion Spectrograph. Their observations not only resulted it the first detection of the RM effect for a smaller Neptune-sized exoplanet but also provided evidence that the orbital axis of the planet inclines to the stellar spin axis by approximately 103 degrees in the sky. A research group in the U.S. used the Keck Telescope and made independent observations of the RM effect of the same system in May and August 2010; their results were similar to those from the University of Tokyo/NAOJ team’s May and July 2010 observations.
The current team’s observations of the RM effect for the planetary systems HAT-P-11 and XO-4 have shown that they have planetary orbits highly tilted to the spin axes of their host stars. The latest observational results about these systems, including those obtained independently of the findings reported here, suggest that such highly inclined planetary orbits may commonly exist in the universe. The planet-planet scenario of migration, whether caused by planet-planet scattering or Kozai migration, rather than the planet-disk scenario could account for their migration to the present locations.
However, measurements of the RM effect for individual systems cannot decisively discriminate between the migration scenarios. Statistical analysis can help scientists determine which, if any, process of migration is responsible for the highly inclined orbits of giant planets. Since different migration models predict different distributions of the angle between the stellar axis and planetary orbit, developing a large sample of the RM effect enables scientists to support the most plausible migration process. Inclusion of the measurements of the RM effect for such a small-sized planet as HAT-P-11 b in the sample will play an important role in discussions of planetary migration scenarios.
Many research groups are planning to make observations of the RM effect with telescopes around the world. The current team and the Subaru Telescope will play an integral role in investigations to come. Continuous observations of transiting exoplanetary systems will contribute to an understanding of the formation and migration history of planetary systems in the near future.
NASA's Kepler mission confirmed the discovery of its first rocky planet, named Kepler-10b. Measuring 1.4 times the size of Earth, it is the smallest planet ever discovered outside our solar system.
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NASA’s Kepler planet hunting space telescope has made an historic discovery by finding its first rocky planet – and it’s simultaneously the smallest planet ever found beyond our solar system. The exoplanet, dubbed Kepler-10b, measures barely 1.4 times the diameter of Earth and orbits its star in less than one earth day. Therefore the planet is located well outside the habitable zone and is far too close to the star for liquid water to exist. It is Earth-sized but not Earth-like with respect to the search for life. The finding of such a small and rocky world marks a major milestone for Keplers scientific capabilities in finding another world like our own.
Indeed the scorching hot planet orbits so close to its parent star – once every 0.84 days – that the surface is molten and temperatures exceed 2,500 degrees Fahrenheit, hotter than lava flows here on Earth. Kepler-10b is 20 times closer to its star than Mercury is to our sun. Its density is similar to that of an iron dumbbell.
Check out the amazing video below narrated by Natalie Batalha, Kepler’s deputy science team lead from NASA’s Ames Research Center which describes Kepler’s exciting discovery of the smallest exoplanet known to date – some 560 light years from Erath.
The discovery is based on data that was collected from May 2009 to early January 2010 and was independently confirmed with the W.M. Keck Observatory in Hawaii. A peer reviewed paper has been accepted for publication in the Astrophysical Journal. The spacecraft was launched in March 2009 by a Delta II rocket.
Over 500 exoplanets have been discovered up to now. Kepler uses the transit method to detect exoplanets and monitors 150,000 stars by aiming 42 detectors between the constellations of Cygnus and Lyra.
Kepler Mission Star Field.
An image by Carter Roberts of the Eastbay Astronomical Society in Oakland, CA, showing the Milky Way region of the sky where the Kepler spacecraft/photometer will be pointing. Each rectangle indicates the specific region of the sky covered by each CCD element of the Kepler photometer. There are a total of 42 CCD elements in pairs, each pair comprising a square. Credit: Carter Roberts / Eastbay Astronomical Society.
NASA’s Kepler mission confirmed the discovery of its first rocky planet, named Kepler-10b. Measuring 1.4 times the size of Earth, it is the smallest planet ever discovered outside our solar system.
The discovery of this so-called exoplanet is based on more than eight months of data collected by the spacecraft from May 2009 to early January 2010.
“All of Kepler’s best capabilities have converged to yield the first solid evidence of a rocky planet orbiting a star other than our sun,” said Natalie Batalha, Kepler’s deputy science team lead at NASA’s Ames Research Center in Moffett Field, Calif., and primary author of a paper on the discovery accepted by the Astrophysical Journal. “The Kepler team made a commitment in 2010 about finding the telltale signatures of small planets in the data, and it’s beginning to pay off.”
Kepler’s ultra-precise photometer measures the tiny decrease in a star’s brightness that occurs when a planet crosses in front of it. The size of the planet can be derived from these periodic dips in brightness. The distance between the planet and the star is calculated by measuring the time between successive dips as the planet orbits the star.
Kepler is the first NASA mission capable of finding Earth-size planets in or near the habitable zone, the region in a planetary system where liquid water can exist on the planet’s surface. However, since it orbits once every 0.84 days, Kepler-10b is more than 20 times closer to its star than Mercury is to our sun and not in the habitable zone.
Kepler-10b orbits one of the 150,000 stars that the spacecraft is monitoring between the constellations of Cygnus and Lyra.
We aim our mosaic of 42 detectors there, under the swan’s wing, just above the plane of the Milky Way galaxy. The star itself is very similar to our own sun in temperature, mass and size, but older with an age of over 8 billion years, compared to the 4-and-1/2 billion years of our own sun. It’s a quiet star, slowly spinning with a weak magnetic field and few of the sun spots that characterize our own sun. The star’s about 560 light years from our solar system and one of the brighter stars that Kepler is monitoring. It was the first we identified as potentially harboring a very small transiting planet. The transits of the planet were first seen in July of 2009.
The diameter of Kepler-10b is only about 1.4 times the diameter of Earth and it's mass is about 4.5 times that of Earth. It is the best example of a rocky planet to date.
Kepler-10 was the first star identified that could potentially harbor a small transiting planet, placing it at the top of the list for ground-based observations with the W.M. Keck Observatory 10-meter telescope in Hawaii.
Scientists waiting for a signal to confirm Kepler-10b as a planet were not disappointed. Keck was able to measure tiny changes in the star’s spectrum, called Doppler shifts, caused by the telltale tug exerted by the orbiting planet on the star.
“The discovery of Kepler-10b, a bone-fide rocky world, is a significant milestone in the search for planets similar to our own,” said Douglas Hudgins, Kepler program scientist at NASA Headquarters in Washington. “Although this planet is not in the habitable zone, the exciting find showcases the kinds of discoveries made possible by the mission and the promise of many more to come,” he said.
“Our knowledge of the planet is only as good as the knowledge of the star it orbits,” said Batalha. Because Kepler-10 is one of the brighter stars being targeted by Kepler, scientists were able to detect high frequency variations in the star’s brightness generated by stellar oscillations, or starquakes. “This is the analysis that really allowed us to pin down Kepler-10b’s properties.,” she added.
“We have a clear signal in the data arising from light waves that travel within the interior of the star,” said Hans Keldsen, an astronomer at the Kepler Asteroseismic Science Consortium at Aarhus University in Denmark. Kepler Asteroseismic Science Consortium scientists use the information to better understand the star, just as earthquakes are used to learn about Earth’s interior structure. “As a result of this analysis, Kepler-10 is one of the most well characterized planet-hosting stars in the universe next to our sun,” Kjeldsen said.
Kepler from the high-gain antenna side in the clean room at Astrotech. Credit: nasatech.net
That’s good news for the team studying Kepler-10b. Accurate stellar properties yield accurate planet properties. In the case of Kepler-10b, the picture that emerges is of a rocky planet with a mass 4.6 times that of Earth and with an average density of 8.8 grams per cubic centimeter — similar to that of an iron dumbbell.
“This planet is unequivocally rocky, with a surface you could stand on,” commented team member Dimitar Sasselov, of the Harvard-Smithsonian Center for Astrophysics in Cambridge and a Kepler co-investigator.
“All of Kepler’s best capabilities have converged for this discovery,” Batalha said, “yielding the first solid evidence of a rocky planet orbiting a star other than our sun.”
Ames manages Kepler’s ground system development, mission operations and science data analysis. NASA’s Jet Propulsion Laboratory in Pasadena, Calif., managed Kepler mission development.
Ball Aerospace and Technologies Corp. in Boulder, Colo., developed the Kepler flight system and supports mission operations with the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder. The Space Telescope Science Institute in Baltimore archives, hosts and distributes the Kepler science data.
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Click here to view a hi res 360 degree panorama of Kepler inside the cleanroom. Credit: nasatech.net
Colors are important in astronomy. They can be used to get a quick feel for the temperature of stars, map out hydrogen alpha, or even find oxygen when it gives off a distinctive green glow from the forbidden transistion. Yet thus far, all images of exoplanets have only been taken in a single color filter leaving astronomers with a flat picture and no understanding of the color of a planet. A new paper corrects this oversight while analyzing the polarization of reflected starlight to develop an understanding of the characteristics of the planet’s atmosphere.
One of the properties of light is that it often becomes polarized upon reflection. This allows for polarized sunglasses to effectively reduce glare from road surfaces because the reflection tends to polarize the light in a preferred direction. Similarly, light striking a planet’s atmosphere will have a preferred axis of polarization. The degree of polarization will depend on many factors including, the angle of incidence (corresponding to the planetary phase), the types of molecules in the atmosphere, and the color, or wavelength, of light through which the planet is observed.
The object of interest was HD189733b and observations were taken in using the UBV filters system which uses filters in the ultra-violet, blue, and green (or “visible”) portions of the spectra. They were conduced at the Nordic Optical Telescope in Spain.
To control for the variations, astronomers would need to observe the planet at several wavelengths to understand how the color was affecting the results, as well as to watch the planet for several orbits to trace how the phase impacted the observations. Presently, the authors have not gone so far as to compare various composition models against these observations as this study was largely intended to be a feasibility study at multi-wavelength polarization detection.
Results have shown that the planet is brightest in the blue portion of the spectra, a result that confirms earlier, theoretical predictions for hot Jupiters as well as tentative observational findings based on single color studies done last year. This supports the notion that the dominant mechanism of polarization is Rayleigh scattering in the atmosphere. The result of this is that the planet would likely appear to be a deep blue to the naked eye, much the same way our sky appears blue, but a much more vivid color due to the increased depth to which we would look. The observations also confirmed that polarization was greatest when the planet was near greatest elongation (as far to either side of the star as possible instead of near in front or behind when viewed from Earth) which supports that the polarization is due to scattering in the atmosphere as opposed to the starlight being initially polarized from large starspots.
Certainly, this study has demonstrated the potential for astronomers to begin exploring planetary characteristics with polarization. However, it may be some time before it becomes accepted in general use. While the findings were certainly above the background noise, there existed a significant degree of uncertainty in the measurements resulting from the faint nature of planets. Being a large, hot Jupiter, HD189733b is a strong candidate since it is close to its parent star and thus, receives a large amount of light. Using such methods for other exoplanets, more distant from their parent stars will likely prove an even more daunting task, requiring careful preparation and observations.
The vast majority of the known exoplanets have been discovered by the radial velocity method. This method employs the effects of a planet’s gentle tug on its parent star which is perceived as a “wobble” in the star’s motion. A new study, conducted by Morais and Correia, looks at whether this effect can be mimicked by another, distinctly non-planetary, source: Binary stars.
Conceptually, the idea is rather straightforward. A star of interest lies in a triple star system. It is the third member and in a larger orbit around a tight binary system. As the tight binary system orbits, there will be periods in which they line up with the star of interest giving a minutely greater pull before relaxing the pull later in their orbit. This remote tug would show a distinctly periodic effect very similar to the effects expected from an inferred planet.
The obvious question was how astronomers could miss the presence of binary stars, close enough to have a notable effect. The authors of the paper suggest that if the binary pair orbited sufficiently close, it would be unlikely that they could be resolved as a binary. Additionally, if one member were sufficiently faint (an M dwarf), it may not appear readily either. Both of these instances are plausible given that some three fourths of nearby main sequence stars are M class, and about half of all stars are in binary system.
Next, the team asked how important these effects may be. They considered the case of HD 18875, a binary system in which a distant star (A) has a 25.7 year period around a tight binary (Ba + Bb) that orbit each other with a period of 155 days. This system was noteworthy because a hot Jupiter planet was announced around the A star in 2005, but challenged in 2007 when another team could not repeat the observations.
The new study attempted to use their understanding and modeling of three body systems to see if the binary interaction could have produced the spurious signal. Using their model, they determined that the effects of the system itself would have produced effects similar to those of a planet of 4 Earth masses located at 0.38 AU. A planet of such mass is well below the limit of a hot Jupiter and the distance is somewhat larger than usual as well. Thus, the nearby B-binary could not have been responsible. Furthermore, such minute effects of this type are generally interpreted as “super-Earths” and have only become prevalent in observations in the past few years.
Thus, while the unconfirmed planet around HD 18875 A might not have been caused by the nearby binary, the work in this new paper has shown that effects of nearby binaries will become increasingly important as we start detecting radial velocities indicative of less and less massive planets.
Artist's impression of an extrasolar planet. Image credit: CfA
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You knew it was only a matter of time until the hunt for extrasolar planets joined the Zooniverse family of Citizen Science projects. And the time has now arrived for your chance to make one of the biggest discoveries of the 21st century by finding other planets out there in the Universe.
Planet Hunters is the latest addition to the Zooniverse, and users will help scientists analyze data taken by NASA’s Kepler mission, the biggest, badest exoplanet hunting telescope in space. The project goes live on December 16 at http://www.planethunters.org.
“The Kepler mission has given us another mountain of data to sort through,” said Kevin Schawinski, a Yale University astronomer and Planet Hunters co-founder. Schawinski was one of the original forces behind Galaxy Zoo, the citizen science project that started it all back in 2007, which enlisted hundreds of thousands of Web users round the world to help sort through and classify a million images of galaxies taken by a robotic telescope.
The Kepler telescope has been in space since 2009, continually monitoring nearly 150,000 stars in the constellations Cygnus and Lyra, recording their brightness over time. In June of this year, the Kepler team announced they had found over 750 exoplanet candidates in just the first 43 days of the spacecraft’s observations.
They also just announced they will make an early release of a complete 3 months of observations early in 2011, which will contain light curves for approximately 165,000 stars, most of which are late-type Main Sequence stars.
“The Kepler mission will likely quadruple the number of planets that have been found in the last 15 years, and it’s terrific that NASA is releasing this amazing data into the public domain,” said Debra Fischer, a Yale astronomer and leading exoplanet hunter.
Although Planet Hunters is not tied directly to the Kepler mission, the website will serve as a complement to the work being done by the Kepler team to analyze the data, the team said.
Granted, the Citizen Scientists looking for extrasolar planets will be doing a search akin to looking for a needle in a haystack. But its one of the most exciting needles to be searching for.
Because of the huge amount of data being made available by Kepler, astronomers rely on computers to help them sort through the data and search for possible planet candidates. “But computers are only good at finding what they’ve been taught to look for,” said Meg Schwamb, another Yale astronomer and Planet Hunters co-founder, “whereas the human brain has the uncanny ability to recognize patterns and immediately pick out what is strange or unique, far beyond what we can teach machines to do.”
Galaxy Zoo project has shown how successful this concept of using a network of global volunteers can be, as the Citizen Scientists has helped the Galaxy Zoo team publish over 20 papers about galaxy shapes and distributions, as well as making some unusual discoveries, like Hanny’s Voorwerp.
To participate, you don’t need to have any astronomical or exoplanet expertise. When users log on to the Planet Hunters website, they’ll be asked to answer a series of simple questions about one of the stars’ light curves — a graph displaying the amount of light emitted by the star over time — to help the Yale astronomers determine whether it displays a repetitive dimming of light, identifying it as an exoplanet candidate.
And exoplanet research is one of the hottest topics in astronomy today. Over 500 planets have been found orbiting other stars since 1995. Most of these are large, Jupiter-like planets, but astronomers are refining their searches to try and find smaller planets more the size of Earth.
“The search for planets is the search for life,” Fischer said. “And at least for life as we know it, that means finding a planet similar to Earth.” Scientists believe Earth-like planets are the best place to look for life because they are the right size and orbit their host stars at the right distance to support liquid water, an essential ingredient for every form of life found on Earth.
The point of citizen science is to actively involve people in real research,” Schawinski said. “When you join Planet Hunters, you’re contributing to actual science — and you might just make a real discovery.”
