Posted on by Jon Voisey

The Origin of Exoplanets

Artist's impression of the planet OGLE-TR-L9b. Credit: ESO/H. Zodet

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We truly live in an amazing time for exoplanet research. It was only 18 years ago the first planet outside our solar system was discovered. Fifteen since the first confirmation of one around a main sequence star. Even more recently, direct images have begun to sprout up, as well as the first spectra of the atmospheres of such planets. So much data is becoming available, astronomers have even begun to be able to make inferences as to how these extra solar planets could have formed.

In general, there are two methods by which planets can form. The first is via coaccretion in which the star and the planet would form from gravitational collapse independently of one another, but in close enough proximity that their mutual gravity binds them together in orbit. The second, the method through which our solar system formed, is the disk method. In this, material from a thin disk around a proto-star collapses to form a planet. Each of these processes has a different set of parameters that may leave traces which could allow astronomers to uncover which method is dominant. A new paper from Helmut Abt of Kitt Peak National Observatory, looks at these characteristics and determines that, from our current sampling of exoplanets, our solar system may be an oddity.

The first parameter that distinguishes the two formation methods is that of eccentricity. To establish a baseline for comparison, Abt first plotted the distribution of eccentricities for 188 main-sequence binary stars and compared that to the same type of plot for the only known system to have formed via the disk method (our Solar System). This revealed that, while the majority of stars have orbits with low eccentricity, this percentage falls off slowly as the eccentricity increases. In our solar system, in which only one planet (Mercury) has an eccentricity greater than 0.2, the distribution falls off much more steeply. When Abt constructed the distribution for the 379 planets with known eccentricity, it was nearly identical to that for binary stars.

A similar plot was created for the semi major axis of binary stars and our solar system. Again, when this was plotted for the known extra solar planets the distribution was similar to that of binary star systems.

Abt also inspected the configuration of the systems. Star systems containing three stars generally contained a pair of stars in a tight binary orbit with a third in a much larger orbit. By comparing the ratios of such orbits, Abt quantified the orbital spacing. However, instead of simply comparing to the solar system, he considered the analogous situation of formation of stars around the central mass of the galaxy and built a similar distribution in this manner. In this case, the results were ambiguous; Both modes of formation produced similar results.

Lastly, Abt considered the amount of heavy elements in the more massive body. It is widely known that most extra-solar planets are found around metal-rich stars. While there’s no reason planets forming in a disk couldn’t be formed around high mass stars, having a metal-rich cloud from which to form stars and planets is a requirement for the coaccretion model because it tends to accelerate the collapse process, allowing giant planets to fully form before the cloud was dissipated as the star became active. Thus, the fact that the vast majority of extra-solar planets exist around metal-rich stars favors the coaccretion hypothesis.

Taken together, this provides four tests for formation models. In every case, current observations suggest that the majority of planets discovered thus far formed from coaccretion and not in a disc. However, Abt notes that this is most likely due to statistical biases imposed by the sensitivity limits of current instruments. As he notes, astronomers “do not yet have the radial velocity sensitivity to detect disk systems like the solar system, except for single large planets, like Jupiter at 5 AU.” As such, this view will likely change as new generations of instruments become available. Indeed, as instruments improve to the point that three dimensional mapping becomes available, and orbital inclinations can be directly observed, astronomers will be able to add another test to determine the modes of formation.

EDIT: Following some confusion and discussion in the comments, I wanted to add one further note. Keep in mind this is only the average of all systems currently known that looks like coaccreted systems. While there are undoubtedly some in there that did form from disks, their rarity in the current data makes them not stand out. Certainly, we know of at least one system that fits a strong test for the disk method. This recent discovery by Kepler, in which three planets have been observed transiting their host star demonstrates that all of these planets must lie in a disk which does not conform to expectations of independent condensation. As more systems like this are discovered, we expect that the distributions of the tests described above will become bimodal, having components that match each formation hypothesis.

Posted on by Nancy Atkinson

Young Exoplanet is Cloudy With a Chance of Heat Waves

Keck II image of the young extrasolar planet HR 8799 b, seen as the point source in center of image.Credit: Brendan Bowler and Michael Liu, IfA/Hawaii

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Back in 2008, the first multi-planet system of extrasolar planets was imaged, and further study of the planets in this very young system is yielding some puzzling results. Astronomers using the Keck Observatory have been able to obtain the spectrum of one planet, HR 8799 b, revealing the temperature, chemical composition, and atmospheric properties of the planet. The planet’s atmosphere is unlike that of any previously studied extrasolar planet, and it appears the planet is extremely cloudy, and also quite hot, even though it is very far from its host star.


“We are at a point where not only can we directly image planets around other stars, but we can begin to study the properties of their atmospheres in detail. Direct spectroscopy of exoplanets is the future of this field,” said Brendan Bowler, a graduate student at the University of Hawaii and the lead author of the study.

Although over 500 planets have been discovered around other stars, only six planets have been directly imaged.

Three exoplanets orbiting a young star 140 light years away are captured using Keck Observatory near-infrared adaptive optics. The planets are labeled and the two outer ones have arrows showing the size of their motion over a 4 year period.

HR 8799 b, is one of those imaged, and is one of three gas-giant planets orbiting the star HR 8799, located 130 light-years away from Earth in the constellation Pegasus. Bowler and his team said the properties of the planet’s atmosphere can’t be explained by current theoretical models of gas giant exoplanets, even those with what is considered a normal amount of thick or dusty atmospheres. From the new data on this planet, the astronomers believe that this exoplanet is extremely cloudy, and perhaps, all young gas-giant planets exhibit the same type of cloud cover in their atmospheres.

The technique the team used to determine the planet’s temperature relies on the chemistry of the planet’s atmosphere. Specifically, the presence or absence of gaseous methane can be used as a thermometer. The team found that HR 8799 b shows little or no methane in its atmosphere. Based on their spectrum and previously obtained images of the planet, and by comparing the observations to theoretical models of low-temperature atmospheres, they estimate the coolest possible temperature for the planet is about 1200 Kelvin (about 1,700 degrees Fahrenheit).

This planet is quite far from the star, 67 times the Earth-sun separation from the host star.

Current theoretical models predict HR 8799 b should be about 400 Kelvin cooler than they measured, based on the age of the planet and the amount of energy it is currently emitting. The team suspects the discrepancy arises because the planet is much more dusty and cloudy than expected by current models.

“Direct studies of extrasolar planets are just in their infancy. But even at this early stage, we are learning they are a different beast than objects we have known about previously,” said University of Hawaii astronomy professor Michael Liu, coauthor of the study.

The planets around HR 8799 are incredibly faint, about 100,000 times dimmer than their parent star. To obtain the spectrum of HR 8799 b, the team relied on the adaptive optics system of the Keck II Telescope, and focused on the star for several hours. Then they used the Keck facility instrument called OSIRIS, a special kind of spectrograph, to precisely separate the spectrum of the planet from the light of its parent star.

A paper describing the study will be published in the Astrophysical Journal later this year, but you can read the team’s abstract here.

There’s also a new paper out that suggests the these planets around HR 8799 could actually be brown dwarfs.

Source: Keck Observatory

Posted on by Nancy Atkinson

Kepler Discovers Multi-Planet System

Relative sizes and orbital periods of the newly discovered planets and the super-Earth candidate as they cross their host star, Kepler-9. Image courtesy of NASA/Kepler/Darin Ragozzine

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The Kepler mission has discovered a system of two Saturn size planets with perhaps a third planet that is only 1.5 times the radius of Earth. While the news of this discovery is tempered somewhat with the announcement by a team from the European Southern Observatory of a system with five confirmed Neptune-sized planets and perhaps two additional smaller planets, both discoveries highlight that the spacecraft and techniques astronomers are using to find exoplanets are getting the desired results, and excitingly exoplanet reseach now includes the study of multiplanet systems. This discovery is the first time multiple planets were found by looking at transit time variations, which can provide more information about planets, such as their masses.

“What is particularly special about this system, is that the variations in transit times are large enough, that we can use these transit timing to detect the masses of these bodies” said Matthew Holman, Kepler team lead for the study of star Kepler-9, speaking on the AAAS Science podcast. Additionally, these findings should provide the tools astronomers need to determine even more physical conditions of these planets — and others — in the future.

The inner world weighs in at 0.25 Jupiter mass (80 Earths) while the outer world is a slimmer 0.17 Jupiter mass (54 Earths).

The team analyzed seven months of data from the orbiting Kepler telescope, and the two large confirmed planets—Kepler-9b and Kepler-9c— are transiting the parent star at unstable rates. The planets’ 19.2- and 38.9-day transition periods are increasing and decreasing at average, respective rates of four and 39 minutes per orbit.

“One thing that caught our attention right off, is when we do preliminary estimates at the time of the transit, we saw large variations in this particular system. Not only did we see more than one planet transiting, but one planet seemed to be speeding up and one slowing down,” Holman said.

Because period one is roughly twice the other, they have a signature of what is called a 2:1 orbital resonance, where astronomers expect to see large timing variation, due to the orbital gravitational push and pull the systems has on all the objects.

“The variation in transit times depend upon the masses of the planets,” Holman told reporters in a news conference announcing the findings. “The larger the mass the larger the variations. These variations allows us to determine the mass of the objects and we can confirm that they are planets.”

The team also confirmed the objects were planets with radial velocity observations with the Keck I telescope.

The third planet, with a mass several times that of the Earth, is transiting the star in a more interior orbit, but further analysis will be necessary to confirm that this signature is actually a planet.

“We are being very careful at this point to only call it a planet candidate, rather than a confirmed planet,” Holman said. “If it is confirmed it would only have a radius of about 1.5 that of Earth’s. It has a much shorter orbital period of 1.6 days, so it is very close to its host star, so we should be able to see evidence of many transits.”

Holman added that this discovery — regardless of whether they are able to confirm that this is a planet or not — highlights the sensitivity of Kepler to very small signatures.

Holman said the planets have probably migrated to be closer to the star from where they started out when they formed. “Likely they formed with the star, but likely they formed farther out at the “snow line” several times farther away from the star than the Earth is, and by a dynamical process move in closer,” he said in the Science podcast.

The resonance is a signature that some kind of migration had occurred, called convergent migration, where planets are moving towards the star and also coming closer to each other.

From all the transit timing information that has been gathered so far, astronomers are piecing together the migration history of this planetary system. “The whole history of that system may be encoded in the information we have,” said Alycia Weinberger, from the Department of Terrestrial Magnetism at the Carnegie Institution. “Isn’t it cool that what the planetary system looks like today has much to tell us about its history?”.

Kepler looks for the signatures of planets by measuring tiny decreases in the brightness of stars when planets cross in front of, or transit them. The size of the planet can be derived from the change in the star’s brightness. In June, mission scientists announced the mission has identified more than 700 planet candidates, including five systems with more than one planet candidate. This is the first of those systems to be confirmed.

Kepler principal investigator William Borucki said the team is working hard to get these candidates “turned into confirmed planets.”

Asked about why the public seems to be so interested in the Kepler mission, Borucki said, “We addressing a very important question, which is, are there other earths out there and are they frequent? Any answer is important. If we get zero that might mean there is very little life out there in the universe.”

Sources: Science, AAAS Science podcast, NASA,

Posted on by Nancy Atkinson

Updated Exoplanet iPhone App

Screenshot of a new exoplanet app for iPhone and iPad.

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Just in time for the announcement yesterday of the multi-planet solar system discovery, and an upcoming exoplanet announcement by the Kepler team comes a new version of a free exoplanet app for iPhone and iPad. We got a note from Hanno Rein, who developed “Exoplanet,” and who just finished his PhD in astrophysics at the University of Cambridge. “It lists all discovered extrasolar planets with a lot of background information, many visualizations and animations,” he said. Other highlights include an easy search and filter for the database, real telescope images of the host star, visualizations of the orbits and the habitable zone, interactive 3D size comparison to our own solar system and much more.

With all the exoplanet news lately, “Exoplanet” is updated daily and push notifications are sent out whenever a new planet is discovered (although they can be turned off if you don’t want to get notifications). Pretty much everything known about any exoplanet is included, such as physical parameters, along with various visualizations and background information, which make this exciting subject accessible for a wider audience.
New for version 3.9 are direct links to planets and planetary systems, links to other planets of the same multi-planetary system have been added, and you can now link from any e-mail or website directly to this application by using a URL form of the exoplanet, for example, ://Fomalhaut

Rein developed this app while a student, and wanted to keep it free (knowing how hard it is to be a poor student!) so there are ads on the app. But a non-ad version is available for only $.99 USD.

I don’t have an iPhone or iPad (yet!) but Fraser does, and he said the Exoplanet app is very cool!

For more information, or to download, find Exoplanet at the iTunes Store.

Posted on by Nancy Atkinson

Another Solar System Like our Own?

Artists impression shows the planetary system around the Sun-like star HD 10180. Credit: ESO/L. Calçada

There is another Sun-like star out there with an intriguing family of planets orbiting about and it could be the closest parallel to our own solar system that astronomers have found yet. European astronomers discovered a planetary system containing at least five planets, orbiting the star HD 10180, with evidence that two other planets may be present. If confirmed, one of those would have the lowest mass ever found.

“We have found what is most likely the system with the most planets yet discovered,” says Christophe Lovis, who led the team. “This remarkable discovery also highlights the fact that we are now entering a new era in exoplanet research: the study of complex planetary systems and not just of individual planets. Studies of planetary motions in the new system reveal complex gravitational interactions between the planets and give us insights into the long-term evolution of the system.”

To make this system even more intriguing, the team also found evidence that the distances of the planets from their star follow a regular pattern, as also seen in our Solar System. “This could be a signature of the formation process of these planetary systems,” said team member Michel Mayor.

HD 10180, is located 127 light years away in the southern constellation of Hydrus. The five confirmed planets are large, about the size of Neptune — between 13 and 25 Earth masses —with orbital periods ranging from between six and 600 days. The planets’ distances from the star ranges from 0.06 and 1.4 times the Earth–Sun distance.

A close-up of the sky around the star HD 10180. Credit: ESO and Digitized Sky Survey 2. Acknowledgment: Davide De Martin

“We also have good reasons to believe that two other planets are present,” said Lovis. One would be a Saturn-like planet (with a minimum mass of 65 Earth masses) orbiting in 2200 days. The other would be the least massive exoplanet ever discovered, with a mass of about 1.4 times that of the Earth. It is very close to its host star, at just 2 percent of the Earth–Sun distance. One “year” on this planet would last only 1.18 Earth-days.

“This object causes a wobble of its star of only about 3 km/hour— slower than walking speed — and this motion is very hard to measure,” says team member Damien Ségransan. If confirmed, this object would be another example of a hot rocky planet, similar to Corot-7b.

The team used the planet-finding HARPS spectrograph, attached to ESO’s 3.6-metre telescope at La Silla, Chile, and made observations of HD 10180 for six years.

The newly discovered system of planets around HD 10180 is unique in several respects. First of all, with at least five Neptune-like planets lying within a distance equivalent to the orbit of Mars, this system is more populated than our Solar System in its inner region, and has many more massive planets there. Furthermore, the system probably has no Jupiter-like gas giant. In addition, all the planets seem to have almost circular orbits.

With this new announcement, the total number of exoplanets found is 472.

The team’s paper was submitted to Astronomy and Astrophysics (“The HARPS search for southern extra-solar planets. XXVII. Up to seven planets orbiting HD 10180: probing the architecture of low-mass planetary systems” by C. Lovis et al.).

Source: ESO

Posted on by Nancy Atkinson

Tight Binaries are ‘Death Stars’ for Planets

This plot of data from NASA's Spitzer Space Telescope tells astronomers that a dusty planetary smashup probably occurred around a pair of tight twin, or binary, stars. Image credit: NASA/JPL-Caltech/Harvard-Smithsonian CfA

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Astronomers studying double star systems where the two stars are extremely close have found a pattern of destruction. While there probably isn’t a Star Wars-like Death Star roaming the Universe, tight binary systems might provide the equivalent of Darth Vader’s favorite weapon. “This is real-life science fiction,” said Jeremy Drake of the Harvard-Smithsonian Center for Astrophysics. “Our data tell us that planets in these systems might not be so lucky — collisions could be common. It’s theoretically possible that habitable planets could exist around these types of stars, so if there happened to be any life there, it could be doomed.”

Using the Spitzer Space Telescope, Drake and his team spotted a surprisingly large amount of dust around three mature, close-orbiting star pairs, that might be the aftermath of tremendous planetary collisions.

Drake is the principal investigator of the research, published in the Aug.19 issue of the Astrophysical Journal Letters.

The particular class of binary stars in the study are extremely close together. Named RS Canum Venaticorums, or RS CVns for short, they are separated by only about 3.2-million kilometers (two-million miles ), or two percent of the distance between Earth and our sun. The binaries orbit around each other every few days, with one face on each star perpetually locked and pointed toward the other.

These stars are familiarly like our own Sun – about the same size and probably about a billion to a few billion years old — roughly the age of our sun when life first evolved on Earth. But these stars spin much faster, and, as a result, have powerful magnetic fields, and giant, dark spots. The magnetic activity drives strong stellar winds — gale-force versions of the solar wind — that slow the stars down, pulling the twirling duos closer over time.

This is not a good scenario for planetary survival.

As the stars cozy up to each other, their gravitational influences change, and this could cause disturbances to planetary bodies orbiting around both stars. Comets and any planets that may exist in the systems would start jostling about and banging into each other, sometimes in powerful collisions. This includes planets that could theoretically be circling in the double stars’ habitable zone, a region where temperatures would allow liquid water to exist. Though no habitable planets have been discovered around any stars beyond our sun at this point in time, tight double-star systems are known to host planets; for example, one system not in the study, called HW Vir, has two gas-giant planets.

“These kinds of systems paint a picture of the late stages in the lives of planetary systems,” said Marc Kuchner, a co-author from NASA Goddard Space Flight Center. “And it’s a future that’s messy and violent.”

The temperatures around these systems measured by Spitzer are about the same as molten lava. The astronomers says that dust normally would have dissipated and blown away from the stars by this mature stage in their lives. They conclude that something — most likely planetary collisions — must therefore be kicking up the fresh dust. In addition, because dusty disks have now been found around four, older binary systems, the scientists know that the observations are not a fluke. Something chaotic is very likely going on.

If any life forms did exist in these star systems, and they could look up at the sky, they would have quite a view. Marco Matranga, lead author of the paper, also from Harvard-Smithsonian said, “The skies there would have two huge suns, like the ones above the planet Tatooine in ‘Star Wars.'”

The research was published in the Aug.19 issue of the Astrophysical Journal Letters.

Source: JPL

Posted on by Nancy Atkinson

Did Kepler Scientist Leak Data? Um, Not Really

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. (NASA/Ames/JPL-Caltech)

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Mainstream media (MSM) is funny. Well, maybe funny isn’t the right word, especially when they hose things up and create a story when there really isn’t one. Or when they miss the real story. MSM recently succeeded in spades on both accounts in regards to the Kepler mission. Just last month, the Kepler team announced they had found over 750 candidates for extrasolar planets, and 706 of these candidates potentially are planets from as small as Earth to around the size of Jupiter, with the majority having radii less than half that of Jupiter. This is such incredible news, especially when you factor in that the data was from just 43 days of observations! But MSM seemed to miss all this and instead focused on the fact that the Kepler team got approval from NASA to keep over half of their data for an additional six months to verify and confirm their findings, rather than releasing all of it, as per NASA’s standard policy which requires astronomers to release their data from publicly funded instruments in one year. Then over this past weekend, from a TED talk by Kepler co-investigator Dimitar Sasselov, MSM finally realized that Kepler has found a boat-load of potential Earth-sized exoplanets. Well, yes. That’s what they said in June.

But then MSM took things out of context and exaggerated just a tad.

Even though in his talk, Sasselov used the words “potential” and “candidates” and said the planets are “like Earth, that is, having a radius smaller than twice Earth’s radius,” MSM reported news that NASA has found rocky planets with land and water.

And now some people are saying that Sasselov “leaked” the proprietary Kepler data, and some say he is in trouble for doing so. Today, the Kepler team said via Twitter that they are “working hard to thoughtfully respond to the media flurry surrounding the TEDGlobal talk.”

Let me use one of my mother’s favorite admonitions: For Pete’s sakes!

Watch the TED talk. In my opinion, Sasselov does a good job of getting people excited about exoplanets and he doesn’t say we have actually found another Earth. He also does a good job of presenting what the Kepler team has found without revealing any really huge proprietary data, even though he used this graph:

Screenshot from Sasselov's TED talk.

But really, this is pretty much what the Kepler team said in June, that they expected half of the 750 planet candidates would turn out not to be planets, and a fair number of those might be Earth-sized. The graph takes into account the amount of potential planets that Kepler found, plus the planets found previously by other telescopes and missions.

While it is exciting to think about the potential of finding Earth-sized and maybe even Earth-like planets, we’re likely a long way off from actually finding and then actually confirming another Earth. Additionally, right now, we’re only capable of finding planets that orbit relatively close to their parent star, which most likely wouldn’t put them in the “Goldilocks Zone” of being habitable.

You can read our original article from June here, where the Kepler team announced their findings. There’s also an explanation there of why the team requested to keep part of their data for an extra six months.

UPDATE: 10 pm Tuesday: Sasselov has written an blog post at the Kepler website, bascially saying that there is a big difference between Earth-sized and Earth-like. You can read it here.

Posted on by Steve Nerlich

Astronomy Without A Telescope – Brown Dwarfs Are Magnetic Too

Brown dwarf TWA 5B compared to Jupiter and the Sun. Although brown dwarfs are similar in size to Jupiter, they are much more dense and massive - between 13 and 80 Jupiter masses. Credit: chandra.harvard.edu

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I feel a certain empathy for brown dwarfs. The first confirmed finding of one was only fifteen years ago and they remain frequently overlooked in most significant astronomical surveys. I mean OK, they can only (stifles laughter) burn deuterium but that’s something, isn’t it?

It has been suggested that a clever way of finding more brown dwarfs is in the radio spectrum. A brown dwarf with a strong magnetic field and a modicum of stellar wind should produce an electron cyclotron maser. Roughly speaking (something you can always depend on from this writer), electrons caught in a magnetic field are spun energetically in a tight circle, stimulating the emission of microwaves in a particular plane from the star’s polar regions. So you get a maser, essentially the microwave version of a laser, that would be visible on Earth – if we are in line of sight of it.

While the maser effect can probably be weakly generated by isolated brown dwarfs, it’s more likely we will detect one in binary association with a less mass-challenged star that is capable of generating a more vigorous stellar wind to interact with the brown dwarf’s magnetic field.

This maser effect is also proposed to offer a clever way of finding exoplanets. An exoplanet could easily outshine its host star in the radio spectrum if its magnetic field is powerful enough.

So far, searches for confirmed radio emissions from brown dwarfs or orbiting bodies around other stars have been unsuccessful, but this may become achievable in the near future with the steadily growing resolution of the European LOw Frequency ARray (LOFAR), which will be the best such instrument around until the Square Kilometer Array (SKA) is built – which won’t be seeing first light before at least 2017.

Geometrically-challenged aliens struggling to make a crop circle? Nope, it's a component of the LOFAR low frequency radio telescope array. Credit: www.lofar.org

But even if we can’t see brown dwarfs and exoplanets in radio yet, we can start developing profiles of likely candidates. Christensen and others have derived a magnetic scaling relationship for small scale celestial objects, which delivers predictions that fit well with observations of solar system planets and low mass main sequence stars in the K and M spectral classes (remembering the spectral class mantra Old Backyard Astronomers Feel Good Knowing Mnemonics).

Using the Christensen model, it’s thought that brown dwarfs of about 70 Jupiter masses may have magnetic fields in the order of several kilo-Gauss in their first hundred million years of life, as they burn deuterium and spin fast. However, as they age, their magnetic field is likely to weaken as deuterium burning and spin rate declines.

Brown dwarfs with declining deuterium burning (due to age or smaller starting mass) may have magnetic fields similar to giant exoplanets, anywhere from 100 Gauss up to 1 kilo-Gauss. Mind you, that’s just for young exoplanets – the magnetic fields of exoplanets also evolve over time, such that their magnetic field strength may decrease by a factor of ten over 10 billion years.

In any case, Reiners and Christensen estimate that radio light from known exoplanets within 65 light years will emit at wavelengths that can make it through Earth’s ionosphere – so with the right ground-based equipment (i.e. a completed LOFAR or a SKA) we should be able to start spotting brown dwarfs and exoplanets aplenty.

Further reading: Reiners, A. and Christensen, U.R. (2010) A magnetic field evolution scenario for brown dwarfs and giant planets.

Posted on by Ryan Anderson

Hubble Confirms Comet-like Tail on Vaporizing Planet

Next time you hear someone complaining that it’s too hot outside, you can make them feel better by pointing out that at least their planet isn’t so hot it is vaporizing into space. Unless of course you happen to be speaking to someone from the gaseous extrasolar planet HD 209458b.

New observations from the Hubble Cosmic Origins Spectrograph (COS) confirm suspicions from 2003 that the planet HD 209458b is behaving like a Jupiter-sized comet, losing its atmosphere in a huge plume due to the powerful solar wind of its too-close star.

HD 209458b is a “hot Jupiter”: a gas giant that orbits extremely close to its star. It whips around its star in 3.5 days, making even speedy little Mercury with its 88 day orbit around the sun look like a slacker.

Astronomers have managed to learn a lot about HD 209458b because it is a transiting planet. That means that its orbit is aligned just right, so from our point of view it blocks some of the light from its star. When that happens, it gives hints at the planet’s size, and gives a much better constraint on the mass. HD 209458b is a little more than two thirds the mass of Jupiter, but heat from its star has puffed it up to two and a half times Jupiter’s diameter.

In the case of HD 209458b, during transits some of the star’s light passes through the planet’s escaping, 2,000-degree-Fahrenheit atmosphere, allowing scientists to tell what it is made of and how fast it is being lost to space.

“We found gas escaping at high velocities, with a large amount of this gas flowing toward us at 22,000 miles per hour,” said astronomer Jeffrey Linsky of the University of Colorado in Boulder, leader of the COS study. “This large gas flow is likely gas swept up by the stellar wind to form the comet-like tail trailing the planet.”

The escaping planetary gases absorbed starlight at wavelengths characteristic of heavier elements like carbon and silicon, suggesting that the star’s intense heat is driving circulation deep in HD 209458b’s atmosphere, dredging up material that would otherwise remain far beneath lighter elements like hydrogen.

Even though its atmosphere is constantly streaming away into space, HD 209458b won’t be disappearing anytime soon. At the measured rate of loss, the planet would last about a trillion years, far longer than the lifetime of its host star.

So, be thankful that even on hot summer days, your planet is in no danger of being vaporized by its star. And if you do happen to be speaking to someone from HD 209458b, you can reassure them that their planet will still be there when they return home. Well, most of it, anyway.

Oh, and remind them to stock up on sunscreen.

Posted on by Nancy Atkinson

Astronomers Watch Superstorm Raging on Distant Exoplanet

Artists impression of the 'hot Jupiter' HD209458b, which has incredible storms. Credit: ESO.

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Likely, future interstellar flights will not include the exoplanet HD209458b as a featured get-away destination. Not only is this extrasolar planet a scorchingly hot world where the poisonous carbon monoxide atmosphere is being evaporated, but new observations show this gas giant also has superstorms with winds of 5,000 to 10,000 km per hour. “It’s definitely not a place for the faint-hearted,” said Ignas Snellen, from Leiden University in the Netherlands who led a team of astronomers using the Very Large Telescope (VLT) to observe HD209458b, one of the most-studied planets orbiting around other stars. But Snellen told Universe Today that being able to detect this superstorm is extremely exciting and bodes well for finding possible life on other, more Earth-like planets.

“Astronomers have tried to do this for more than a decade,” Snellen said in an email, “basically since the first exoplanets were discovered. We now learn a lot about this gas-giant’s atmosphere, like what kind of gases are there, how hot is it, about its circulation. But we really would like to do this for Earth-like planets. This will be interesting, because using the same techniques we could find out whether there could be life on these planets.”

HD209458b (unofficially called Osiris) is an exoplanet with about 60% the mass of Jupiter orbiting a sun-like star located 150 light-years from Earth towards the constellation of Pegasus.

It orbits at a distance of only one twentieth of the Earth’s orbit around the Sun, and is heated intensely by its parent star, a yellow dwarf with 1.1 solar masses, and a surface temperature of 6000 K. The planet has a surface temperature of about 1000 degrees Celsius on the hot side. But as the planet always has the same side to its star, one side is very hot, while the other is much cooler.

Just as big temperature differences on Earth cause high winds, the same processes cause high winds on HD209458b. But even Earth’s hurricanes are nothing compared to this exoplanet’s superstorms.

Using the powerful CRIRES spectrograph on the VLT the team from Leiden University’s Institute for Space Research (SRON), and MIT in the United States were able to detect and analyze faint fingerprints which showed the high winds. They observed the planet for about five hours, as it passed in front of its star. “CRIRES is the only instrument in the world that can deliver spectra that are sharp enough to determine the position of the carbon monoxide lines at a precision of 1 part in 100,000,” said team member Remco de Kok. “This high precision allows us to measure the velocity of the carbon monoxide gas for the first time using the Doppler effect.”

The astronomers were also able to directly measured the velocity of the exoplanet as it orbits its home star, a first for exoplanet study. “The planet moves with 140 km/sec, and the star moves at 84 meters/second,” said Snellen, “so more than a thousand times slower. Both star and planet orbit the common center of gravity of the system. Having both velocities, using Newton’s laws of gravity we can simply solve for the masses of the two objects.”

The reason this planet is so well studied is that it is the brightest known transiting system in the sky. “The planet moves, as seen from the Earth, in front of its star once per three-and-a-half days,” said Snellen. “This takes about 3 hours. During these three hours, a tiny little bit of starlight filters through the atmosphere of the planet, leaving an imprint of the molecular absorption lines which we have now measured.”

Also for the first time, the astronomers measured how much carbon is present in the atmosphere of this planet. “It seems that H209458b is actually as carbon-rich as Jupiter and Saturn. This could indicate that it was formed in the same way,” said Snellen.

Snellen hopes that by refining these techniques, astronomers may one day be able to study the atmospheres of Earth-like planets, and determine whether life also exists elsewhere in the Universe.

“However, this will be about one hundred times more difficult than what we do now,” he said. “In particular oxygen and ozone are very interesting. On Earth we only have oxygen in the atmosphere because it is constantly produced by living organism, with photosynthesis of plants. If there would be some kind of global disaster and all the life on Earth would go extinct, including plant life and that in the oceans, all the oxygen in the earth atmosphere would quickly disappear. Hence finding oxygen in the atmosphere of an earth-like planet would be extremely exciting! Something to dream about for the future!”

Read the team’s paper.

Sources: ESO, email interview with Ignas Snellen