First Extra-Galactic Planet May Have Been Detected

Panel on the right shows The upper panel shows the simulated light curve (black dots) of a planetary event in M31. Credit: Ingrosso, et al.

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Using a technique called Pixel-lensing, a group of astronomers in Italy may have detected a planet orbiting another star. But this planet is unique among the 300-plus exoplanets discovered so far, as it and its parent star are in another galaxy. The Andromeda Galaxy, to be exact. Technically, the star in M31 was found to have a companion about 6 times the mass of Jupiter, so it could be either a brown dwarf or a planet. But either way, this is a remarkable feat, to find an object of that size in another galaxy.

Pixel-lensing, or gravitational microlensing was developed to look for MAssive Compact Halo Objects MACHOs in the galactic halo of the Milky Way. Because light rays are bent when they pass close to a massive object, the gravity of a nearby star focuses the light from a distant star towards Earth. This method is sensitive to finding planets in our own galaxy, ranging is sizes from Jupiter-like planets to Earth-sized ones. And recently, astronomers used gravitational microlensing to be able to see about a dozen or so stars in M31, an extraordinary accomplishment in itself.

The advantage of microlensing is that it works best for more distant objects, therefore in theory it would seem to be ideal for planet hunting in other galaxies. So, the researchers from the National Institute of Nuclear Physics in Italy, led by Gabriele Ingrosso decided to see if this method would work to detect planets orbiting the stars seen in Andromeda. They used a Monte Carlo approach, where they selected the physical parameters of the binary lens system –a star hosting a planet– and calculated the pixel-lensing light curve, taking into account the finite source effects. The team thought they should be able to detect a planet with about 2 Jupiter masses.

The light from one of the stars they studied in Andromeda showed a distinct variability, most likely from a companion, which could be an orbiting planet based on the object’s mass.

One disadvantage to microlensing is that exposures are available for a few days at most, so the team is hoping for another chance to follow up on their discovery.

The team notes in their paper that perhaps an extrasolar planet in M31 might have already been detected since an anomaly in a pixel-lensing light curve was previously reported by another research team in 2004, who claimed that a possible binary system in M31 was responsible for an observed anomaly in an observed light curve.

Read the team’s paper here.

Source: arXiv, Technology Review Blog

Astrometry Finally Finds an Exoplanet

This artist's concept shows the smallest star known to host a planet. Image credit: NASA/JPL-Caltech

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Using the method of astrometry to find planets orbiting other stars has been around for 50 years, and until now it hasn’t bagged a single exoplanet. But finally, astronomers found a Jupiter-sized planet , called VB 10b, using this method. Astrometry is difficult and requires very precise measurements over long periods of time. So why did they keep trying for so long? “This method is optimal for finding solar-system configurations like ours that might harbor other Earths,” said astronomer Steven Pravdo of JPL. “We found a Jupiter-like planet at around the same relative place as our Jupiter, only around a much smaller star. It’s possible this star also has inner rocky planets. And since more than seven out of 10 stars are small like this one, this could mean planets are more common than we thought.”

The finding confirms that astrometry could be a powerful planet-hunting technique for both ground- and space-based telescopes. For example, a similar technique would be used by SIM Lite, a NASA concept for a space-based mission that is currently being explored.

The newfound exoplanet is about 20 light-years away in the constellation Aquila. It is a gas giant, with a mass six times that of Jupiter’s, and an orbit far enough away from its star to be labeled a “cold Jupiter” similar to our own. In reality, the planet’s own internal heat would give it an Earth-like temperature.

The planet’s star, called VB 10, is tiny. It is what’s known as an M-dwarf and is only one-twelfth the mass of our sun, just barely big enough to fuse atoms at its core and shine with starlight. For years, VB 10 was the smallest star known — now it has a new title: the smallest star known to host a planet. In fact, though the star is more massive than the newfound planet, the two bodies would have a similar girth.

Because the star is so small, its planetary system would be a miniature, scaled-down version of our own. For example, VB 10b, though considered a cold Jupiter, is located about as far from its star as Mercury is from the sun. Any rocky Earth-size planets that might happen to be in the neighborhood would lie even closer in.

“Some other exoplanets around larger M-dwarf stars are also similar to our Jupiter, making the stars fertile ground for future Earth searches,” said Stuart Shaklan, Pravdo’s co-author and the SIM Lite instrument scientist at JPL. “Astrometry is best suited to find cold Jupiters around all kinds of stars, and thus to find more planetary systems arranged like our home.”

Two to six times a year, for the past 12 years, Pravdo and Shaklan have bolted their Stellar Planet Survey instrument onto Palomar’s five-meter Hale telescope to search for planets. The instrument, which has a 16-megapixel charge-coupled device, or CCD, can detect very minute changes in the positions of stars. The VB 10b planet, for instance, causes its star to wobble a small fraction of a degree. Detecting this wobble is equivalent to measuring the width of a human hair from about three kilometers away.

Other ground-based planet-hunting techniques in wide use include radial velocity and the transit method. Like astrometry, radial velocity detects the wobble of a star, but it measures Doppler shifts in the star’s light caused by motion toward and away from us. The transit method looks for dips in a star’s brightness as orbiting planets pass by and block the light. NASA’s space-based Kepler mission, which began searching for planets on May 12, will use the transit method to look for Earth-like worlds around stars similar to the sun.

“This is an exciting discovery because it shows that planets can be found around extremely light-weight stars,” said Wesley Traub, the chief scientist for NASA’s Exoplanet Exploration Program at JPL. “This is a hint that nature likes to form planets, even around stars very different from the sun.”

Source: JPL

New Technique Could Find Another “Pale Blue Dot”

EPOXI image of the Moon transiting Earth from 31 million miles. Credit: NASA/JPL

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By looking back at Earth from alien’s point of view, scientists have developed a new technique to look for other worlds that might harbor oceans, and therefore life. Using the old Deep Impact spacecraft, which is now being used for the EPOXI mission, scientists are able to look at the spectrum of an extrasolar planet’s light which would reveal the presence of water. “We used the High Resolution Imager telescope on Deep Impact to look at Earth from tens of millions of miles away,” said Nicolas B. Cowan, of the University of Washington, ” and developed a method to indicate the presence of oceans by analyzing how Earth’s light changes as the planet rotates. This method can be used to identify extrasolar ocean-bearing Earths.”

Last year, the EPOXI science team was able to take videos of the Moon transiting Earth, (see our article from July 2008). The team has now practiced the technique by looking back at Earth, and have determined that they should be able to detect oceans on other worlds by looking at the changing spectrum of light the planet gives off as it rotates.

Cowan is lead author of a paper on this research appearing in the August 2009 issue of the Astrophysical Journal. Our planet looks blue all the time because of Rayleigh scattering of sunlight by the atmosphere, the same reason that the sky appears blue to us down on the surface, points out Cowan. “What we studied in this paper was how that blue color changes in time: oceans are bluer than continents, which appear red or orange because land is most reflective at red and near-infrared wavelengths of light. Oceans only reflect much at blue (short) wavelengths,” said Cowan.

“A ‘pale blue dot‘ is the best picture we will get of an Earth-like extrasolar world using even the most advanced telescopes planned for the next couple decades,” Cowan continued. “So how do we find out if it is capable of supporting life? If we can determine that the planet has oceans of liquid water, it greatly increases the likelihood that it supports life.”

palebluedot_jpg This narrow-angle color image of the Earth, dubbed ‘Pale Blue Dot‘, is a part of the first ever ‘portrait’ of the solar system taken by Voyager 1, and made famous by astronomer Carl Sagan. The spacecraft acquired a total of 60 frames for a mosaic of the solar system from a distance of more than 4 billion miles from Earth and about 32 degrees above the ecliptic. From Voyager’s great distance Earth is a mere point of light, less than the size of a picture element even in the narrow-angle camera. Earth was a crescent only 0.12 pixel in size. Coincidentally, Earth lies right in the center of one of the scattered light rays resulting from taking the image so close to the sun. This blown-up image of the Earth was taken through three color filters — violet, blue and green — and recombined to produce the color image. The background features in the image are artifacts resulting from the magnification. Credit: NASA JPL

The maps that the team created are only sensitive to the longitudinal (East – West) positions of oceans and continents. Furthermore, the observations only pick out what is going on near the equator of Earth: the equator gets more sunlight than higher latitudes, and the EPOXI spacecraft was above the equator when the observations were taken. These limitations of viewing geometry could plague observations of extrasolar planets as well: “We could erroneously see the planet as a desert world if it had a nearly solid band of continents around its equator and oceans at its poles,” said Cowan.

Other things besides water can make a planet appear blue; for example, in our solar system the planet Neptune is blue due in part to the presence of methane in its upper atmosphere. “However, a Neptune-like world would appear as an unchanging blue using this technique, and again it’s the changes in the blue color that reveal oceans to us,” said Cowan. “There are some weird scenarios you can dream up that don’t involve oceans but would lead to varying patches of blue on a planet, but these are not very plausible.”

“A spectrum of the planet’s light that reveals the presence of water is necessary to confirm the existence of oceans,” said Drake Deming, a co-author of the paper at NASA’s Goddard Space Flight Center in Greenbelt, Md. Instruments that produce a spectrum are attached to telescopes and spread out light into its component colors, like a prism separates white light into a rainbow. Every element and molecule emits and absorbs light at specific colors. These colors can be used like a fingerprint to identify them.

“Finding the water molecule in the spectrum of an extrasolar planet would indicate that there is water vapor in its atmosphere, making it likely that the blue patches we were seeing as it rotates were indeed oceans of liquid water. However, it will take future large space telescopes to get a precise spectrum of such distant planets, while our technique can be used now as an indication that they could have oceans,” said Deming. The technique only requires relatively crude spectra to get the intensity of light over broad color ranges, according to the team.

EPOXI is a combination of the names for the two extended mission components: a search for extrasolar planets during the cruise to Hartley 2, called Extrasolar Planet Observations and Characterization (EPOCh), and the flyby of comet Hartley 2, called the Deep Impact eXtended Investigation (DIXI).

Source: NASA

On Your Mark, Get Set, Let’s Find Planets!

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

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The checkout and calibration phase for the Kepler spacecraft has been completed, and now the telescope will begin one of the longest and most important stare-downs ever attempted. Kepler will spend the next three-and-a-half years staring at more than 100,000 stars searching for telltale signs of planets. Kepler should have the ability to find planets as small as Earth that orbit sun-like stars at distances where temperatures are right for possible lakes and oceans. “Now the fun begins,” said William Borucki, Kepler science principal investigator for the mission. “We are all really excited to start sorting through the data and discovering the planets.”

During the checkout phase scientists have collected data to characterize the imaging performance as well as the noise level in the measurement electronics. The scientists have constructed the list of targets for the start of the planet search, and this information has been loaded onto the spacecraft.

“If Kepler got into a staring contest, it would win,” said James Fanson, Kepler project manager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “The spacecraft is ready to stare intently at the same stars for several years so that it can precisely measure the slightest changes in their brightness caused by planets.” Kepler will hunt for planets by looking for periodic dips in the brightness of stars — events that occur when orbiting planets cross in front of their stars and partially block the light.

The mission’s first finds are expected to be large, gas planets situated close to their stars. Such discoveries could be announced as early as next year.

We’ll be eagerly awaiting!

The Case of the Missing Planets: Are Stars Eating Their Young?

COROT-exo-7b, bottom left dot shadows in front of his central star (artist's impression). Because of its proximity to the star, researcher believe it will be pulled into the star and destroyed. Image: Klaudia Einhorn.

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A new era on astronomy began in 1995 when the first extrasolar planet was detected. To date, 346 planets have been found orbiting stars other than our sun. But new research indicates astronomers might have found even more extrasolar planets except for one thing: some planets have either been pulled into their parent star and devoured or gravitationally torn apart. .And astronomers say the most Earth-like planet detected so far, CoRoT-7 B will inevitably be destroyed by the star it orbits.

The idea that gravitational forces might pull a planet into its parent star have recently been predicted by computer models and Barnes and his team now have evidence that such planet destruction has already occurred.

“When we look at the observed properties of extrasolar planets, we can see that this has already happened – some extrasolar planet have already fallen into their stars,” said Rory Barnes from the University of Washington.

The computer models can show where planets should line up in a particular star system, but direct observations show that some systems are missing planets close to the stars where models say they should be.

But because the planet is so close to the star, the two bodies begin pulling on each other with increasingly strong gravitational force, misshaping the star’s surface with rising tides from its gaseous surface.

“Tides distort the shape of a star. The bigger the tidal distortion, the more quickly the tide will pull the planet in,” said lead author Brian Jackson from the Lunar and Planetary Institute.
Most of the planets discovered outside of our solar system are gas giants like Jupiter except that they are much more massive. However, earlier this year astronomers detected an extrasolar planet called CoRoT-7 B that, while significantly larger than our planet, is more like Earth than any other extrasolar planet found so far.

However, that planet orbits only about 1.5 million miles from its star, much closer than Mercury is to our sun, a distance that puts it in the category of a planet that will fall into its star. Its surface temperature is around 2,500 degrees Fahrenheit “so it’s not a pleasant environment,” Barnes said, and in a short time cosmically – a billion years or so – CoRoT-7 B will be consumed.

The destruction is slow but inevitable, Jackson said.

“The orbits of these tidally evolving planets change very slowly, over timescales of tens of millions of years,” Jackson said. “Eventually the planet’s orbit brings it close enough to the star that the star’s gravity begins tearing the planet apart.

“So either the planet will be torn apart before it ever reaches the surface of the star, or in the process of being torn apart its orbit eventually will intersect the star’s atmosphere and the heat from the star will obliterate the planet.”

The researchers hope the work leads to better understanding of how stars destroy planets and how that process might affect a planet’s orbit, Jackson said.

The scientists also say their research will have to be updated as more extrasolar planets are discovered, and the researchers are looking forward to investigating new planets found by the Kepler telescope, which is designed specifically to look for extrasolar planets that are closer in size to Earth.

Jackson hopes new observations will provide new lines of evidence to investigate how a star’s tides can destroy planets.

“For example, the rotation rates of stars tend to drop, so older stars tend to spin more slowly than younger stars,” he said. “However, if a star has recently consumed a planet, the addition of the planet’s orbital angular momentum will cause the star to rapidly increase its spin rate. So we would like to look for stars that are spinning too fast for their age.”

Read the paper on this topic.

Source: EurekAlert

Nearly Earth-sized Planet, Possible Watery World Spotted Near Another Star

Astronomers are announcing a newly discovered exoplanet in the habitable zone of its star, and another one — in the same system — that’s just twice the size of Earth.

The Gliese 581 planetary system now has four known planets, with masses of about 1.9 (planet e, left in the foreground), 16 (planet b, nearest to the star), 5 (planet c, center), and 7 Earth-masses (planet d, with the bluish colour).

gliese-581-chart1

This diagram shows the distances of the planets in the Solar System (upper row) and in the Gliese 581 system (lower row), from their respective stars (left). The habitable zone is indicated as the blue area, showing that Gliese 581 d is located inside the habitable zone around its low-mass red star. Based on a diagram by Franck Selsis, Univ. of Bordeaux.

Michel Mayor, a well-known exoplanet researcher from the Geneva Observatory, announced the find today. The planet, “e,” in the famous system Gliese 581, is only about twice the mass of our Earth. The team also refined the orbit of the planet Gliese 581 d, first discovered in 2007, placing it well within the habitable zone, where liquid water oceans could exist. 

Both planets were discovered by the so-called “wobble method,” using the HARPS spectrograph attached to the 3.6-meter (11.8-foot) ESO telescope at La Silla, Chile.

The gentle pull of an exoplanet as it orbits the host star introduces a tiny wobble in the star’s motion that can just be detected on Earth with today’s most sophisticated technology. Low-mass red dwarf stars such as Gliese 581 are potentially fruitful hunting grounds for low-mass exoplanets in the habitable zone. Such cool stars are relatively faint and their habitable zones lie close in, where the gravitational tug of any orbiting planet found there would be stronger, making the telltale wobble more pronounced.

Many more exoplanets have been discovered using the transit method being employed by NASA’s Kepler mission: as planets pass between their host stars and Earth, they cause an observable, periodic dimming.

Planet Gliese 581 e orbits its host star – located only 20.5 light-years away in the constellation Libra (“the Scales”) — in just 3.15 days.

“With only 1.9 Earth-masses, it is the least massive exoplanet ever detected and is, very likely, a rocky planet,” says co-author Xavier Bonfils from Grenoble Observatory. Being so close to its host star, the planet e is not in the habitable zone. But another planet in this system appears to be.

“Gliese 581 d is probably too massive to be made only of rocky material, but we can speculate that it is an icy planet that has migrated closer to the star,” added team member Stephane Udry. The new observations have revealed that this planet is in the habitable zone, where liquid water could exist. “‘d’ could even be covered by a large and deep ocean — it is the first serious ‘water world’ candidate,” he said.

Mayor said it’s “amazing to see how far we have come since we discovered the first exoplanet around a normal star in 1995 — the one around 51 Pegasi. The mass of Gliese 581 e is 80 times less than that of 51 Pegasi b. This is tremendous progress in just 14 years.”

But the astronomers aren’t finished yet. “With similar observing conditions an Earth-like planet located in the middle of the habitable zone of a red dwarf star could be detectable,” says Bonfils. “The hunt continues.”

The findings were presented this week at the European Week of Astronomy & Space Science, which is taking place at the University of Hertfordshire in the UK. The results have also been submitted for publication in the research journal Astronomy & Astrophysics. A preprint is available here.

Source: ESO. (The site also offers numerous videos about the find.)

Ancient Solar Systems Found Around Dead Stars

Asteroids Around Dead Stars. Credit: NASA/JPL

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Were there once habitable planets long ago around stars that are now dead? A team of astronomers have found evidence that between 1-3 percent of white dwarf stars are orbited by rocky planets and asteroids, suggesting these objects once hosted solar systems similar to our own. White dwarf stars are the compact, hot remnants left behind when stars like our Sun reach the end of their lives. Using data from the Spitzer Space Telescope, an international team of astronomers have determined that asteroids are found in orbit around a large number of white dwarfs, perhaps as many as 5 million in our own Milky Way Galaxy.

The atmospheres of these white dwarf stars should consist entirely of hydrogen and helium but are sometimes found to be contaminated with heavier elements like calcium and magnesium. The new observations suggest that these Earth-sized stars are often polluted by a gradual rain of closely orbiting dust that emits infrared radiation picked up by Spitzer.

Presenting his team’s findings at the European Week of Astronomy and Space Science conference at the University of Hertfordshire, Dr. Jay Farihi of the University of Leicester said that the data from Spitzer suggest that at least 1 in 100 of white dwarf stars are contaminated in this way and that the dust originates from rocky bodies like asteroids (also known as minor planets). In our Solar System, minor planets are the left over building blocks of the rocky terrestrial planets like the Earth.

“In the quest for Earth-like planets, we have now identified numerous systems which are excellent candidates to harbour them,” said Farihi. “Where they persist at white dwarfs, any terrestrial planets will likely not be habitable, but may have been sites where life developed during a previous epoch. “

The new findings indicate the dust is completely contained within the Roche limit of the star — close enough that any object larger than a few kilometers would be ripped apart by gravitational tides (the same phenomenon which led to the creation of Saturn’s rings). This backs up the team’s hypothesis that the dust disks around white dwarfs are produced by tidally disrupted minor planets. In order to pass this close to the white dwarf, an asteroid must be perturbed from its regular orbit further out – and this can occur during a close encounter with as yet unseen planets.

Because white dwarfs descend from main sequence stars like the Sun, the team’s work implies that at least 1% to 3% of main sequence stars have terrestrial planets around them.

Emissions from the White Dwarf System GD 16. Credit: NASA, JPL -Caltech, University of Leicester
Emissions from the White Dwarf System GD 16. Credit: NASA, JPL -Caltech, University of Leicester

Perhaps the most exciting and important aspect of this research is that the composition of these crushed asteroids can be measured using the heavy elements seen in the white dwarf.

Farihi sees this as a crucial step forward. “With high quality optical and ultraviolet observations (e.g. the Hubble Space Telescope), we should be able to measure up to two dozen different elements in debris-polluted white dwarfs. We can then address the question, “Are the rocky extrasolar planets we find similar to the terrestrial planets of our Solar System?”

Source: RAS

Kepler’s “First Light” Images

This image zooms into a small portion of Kepler's full field of view -- an expansive, 100-square-degree patch of sky in our Milky Way galaxy. Credit: NASA/JPL -Caltech

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W00t! Kepler has seen first light! The spacecraft has taken its first images of the star-rich sky where it will soon begin hunting for planets like Earth. These first images show the mission’s target patch of sky, a vast starry field in the Cygnus-Lyra region of our Milky Way galaxy. One image shows millions of stars in Kepler’s full field of view, while two others zoom in on portions of the larger region. “Kepler’s first glimpse of the sky is awe-inspiring,” said Lia LaPiana, Kepler’s program executive at NASA Headquarters in Washington. “To be able to see millions of stars in a single snapshot is simply breathtaking.”

The image above zooms into a small portion — just 0.2 percent –of Kepler’s full field of view, and shows an an expansive, 100-square-degree patch of sky in our Milky Way galaxy, and a cluster of stars located about 13,000 light-years from Earth, called NGC 6791, can be seen in the upper right corner. These images were taken on April 8, 2009, one day after Kepler’s dust cover was jettisoned. See more below.

Kepler main field of view.  Credit: NASA/JPL - Caltech
Kepler main field of view. Credit: NASA/JPL - Caltech



This image shows Kepler’s entire field of view — a 100-square-degree portion of the sky, equivalent to two side-by-side dips of the Big Dipper. The regions contain an estimated 14 million stars, more than 100,000 of which were selected as ideal candidates for planet hunting. “It’s thrilling to see this treasure trove of stars,” said William Borucki, science principal investigator for Kepler at NASA’s Ames Research Center at Moffett Field, Calif. “We expect to find hundreds of planets circling those stars, and for the first time, we can look for Earth-size planets in the habitable zones around other stars like the sun.”

Kepler will spend the next three-and-a-half years searching more than 100,000 pre-selected stars for signs of planets. It is expected to find a variety of worlds, from large, gaseous ones, to rocky ones as small as Earth. The mission is the first with the ability to find planets like ours — small, rocky planets orbiting sun-like stars in the habitable zone, where temperatures are right for possible lakes and oceans of water.
Kepler's view of a star with a known "Hot Jupiter."  Credit: NASA/JPL


This image zooms in on a region containing a star, called Tres-2, with a known Jupiter-like planet orbiting every 2.5 days.

To find the planets, Kepler will stare at one large expanse of sky for the duration of its lifetime, looking for periodic dips in starlight that occur as planets circle in front of their stars and partially block the light. Its 95-megapixel camera, the largest ever launched into space, can detect tiny changes in a star’s brightness of only 20 parts per million. Images from the camera are intentionally blurred to minimize the number of bright stars that saturate the detectors. While some of the slightly saturated stars are candidates for planet searches, heavily saturated stars are not.

“Everything about Kepler has been optimized to find Earth-size planets,” said James Fanson, Kepler’s project manager at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Our images are road maps that will allow us, in a few years, to point to a star and say a world like ours is there.”

Scientists and engineers will spend the next few weeks calibrating Kepler’s science instrument, the photometer, and adjusting the telescope’s alignment to achieve the best focus. Once these steps are complete, the planet hunt will begin.

“We’ve spent years designing this mission, so actually being able to see through its eyes is tremendously exciting,” said Eric Bachtell, the lead Kepler systems engineer at Ball Aerospace & Technology Corp. in Boulder, Colo. Bachtell has been working on the design, development and testing of Kepler for nine years.

Source: NASA

Kepler Will Be Used to Measure the Size of the Universe

Artist's rendering of the Kepler Mission (NASA)

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On April 7th, commands were sent to NASA’s exoplanet-hunting Kepler telescope to eject the 1.3×1.7 metre lens cap so the unprecedented mission could begin its hunt for Earth-like alien worlds orbiting distant stars. However, one UK astronomer won’t be using the Kepler data to detect the faint transits of rocky exoplanets in front of their host stars. He’ll be using it to monitor the light from a special class of variable star, and through the extreme precision of Kepler’s optics he will be joining an international team of collaborators to redefine the size of the Universe…

Kepler is carrying the largest camera ever launched into space. The camera has 42 charge-coupled devices (CCDs) to monitor the very slight changes in star brightness as an exoplanet passes in front of its host star. Considering the fact that it is hoped Kepler will detect exoplanets a little larger than our planet (known as super-Earths), the instrument is extremely sensitive. It is for this reason that not only exoplanet hunters are interested in using Kepler’s sensitive eye.

Using Kepler data, Dr Alan Penny, a researcher at the University of St Andrews will be joining a 200-strong team of astronomers to analyse the light not emitted from exoplanet-harbouring stars, but from a smaller group of variable stars that fluctuate in brightness with striking regularity and precision. These stars are Cepheid variables, also known as “standard candles” as they can be relied upon for their strong correlation between period of variability and absolute luminosity. This means that no matter where Cepheids are observed in galaxies or clusters, astronomers can always deduce the distance from the Earth to the Cepheid with great precision. The only thing limiting astronomers is the precision that can be attained by instrumentation, so when Kepler left Earth, carrying the most advanced and sensitive camera ever to be taken into space, Penny and his collaborators jumped at the chance to use Kepler to refine the measurement of the Universe.

While Kepler is doing its exciting planet-hunting, we will be using its extreme precision to resolve a possible problem with our measurement of the size of the Universe,” said Penny. “These variable stars known as ‘Cepheids’ form the base of a series of steps by which we measure the distance to distant galaxies and, through them, we can measure the size of the Universe.”

Current estimates place the size of the Universe at 93 billion light years across, but Penny believes Kepler observations of a small selection of Cepheids may change this value by a few percent. When precision observations of a very precise stellar period-brightness relationship, it’s nice to be able to use the most precise instrument you can lay your hands on. However, our understanding of the “standard candles” themselves is very poor, and small-scale, dynamic changes on the star itself can go unnoticed on the ground. Kepler should shed some light on gaps in our knowledge of Cepheids as well as give us the best-yet measurement of the scale of our Universe.

These Cepheid stars which get brighter and fainter by some tens of percent every ten to a hundred days are mostly understood. But recently it has become clear that our theories of what happens in the outer layers of these stars which cause the variations in brightness do not totally agree with what we see. The exquisite accuracy of Kepler in measuring star brightness, one hundred times better than we can do from the ground, means we can get such good measurements that we should be able to match theory with observation. Resolving the issue may only change estimates of the size of the Universe by a small amount, but we won’t rest easy until the problem is solved.” — Dr Alan Penny

Source: Physorg.com

Kepler Flips Its Lid; Soon Ready for Planet Hunt

Artist concept of the Kepler spacecraft's dust cover coming off. Image credit: NASA/JPL

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Engineers successfully ejected the dust cover from NASA’s Kepler telescope last night and the space observatory will soon begin searching for Earth-like planets. “The cover released and flew away exactly as we designed it to do,” said Kepler Project Manager James Fanson from JPL. “This is a critical step toward answering a question that has come down to us across 100 generations of human history — are there other planets like Earth, or are we alone in the galaxy?”

Click here for an animation of the event.

Kepler launched on March 6, 2009 and will spend at least three-and-a-half years staring at more than 100,000 stars in our Milky Way galaxy for signs of Earth-size planets. Some of the planets are expected to orbit in a star’s “habitable zone,” a warm region where water could pool on the surface. The mission’s science instrument, called a photometer, contains the largest camera ever flown in space — its 42 charge-coupled devices (CCDs) will detect slight dips in starlight, which occur when planets passing in front of their stars partially block the light from Kepler’s view.

The telescope’s oval-shaped dust cover, measuring 1.7 meters by 1.3 meters (67 inches by 52 inches), protected the photometer from contamination before and after launch. The dust cover also blocked stray light from entering the telescope during launch — light that could have damaged its sensitive detectors. In addition, the cover was important for calibrating the photometer. Images taken in the dark helped characterize noise coming from the instrument’s electronics, and this noise will later be removed from the actual science data.

“Now the photometer can see the stars and will soon start the task of detecting the planets,” said Kepler’s Science Principal Investigator William Borucki at NASA’s Ames Research Center, Moffett Field, Calif. “We have thoroughly measured the background noise so that our photometer can detect minute changes in a star’s brightness caused by planets.”

At 7:13 p.m. PDT on April 7, engineers at Kepler’s mission operations center at the Laboratory for Atmospheric and Space Physics, Boulder, Colo., sent commands to pass an electrical current through a “burn wire” to break the wire and release a latch holding the cover closed. The spring-loaded cover swung open on a fly-away hinge, before drifting away from the spacecraft. The cover is now in its own orbit around the sun, similar to Kepler’s sun-centric orbit.