APOD: Fomalhaut b (2008 Nov 14)

[Chris Peterson]

Thanks. If it's the same thing as lens eye/artifacts Ithink I understand.
I'm trying to put together a decent graphical representation of how it might look close up. For example, if I was floating in the position of Fomalhaut B and facing away from the star, I would see the thin illuminated inside edge of the belt of dust? There looks to be some kind of light diffusion inside and a bit outside the belt. Is this also glare from starlight, or is there still a significant amount of dust inside the belt reflecting light? And the CG image (http://hubblesite.org/newscenter/archiv ... /image/d/) in the press release, Fomalhaut B isn't actually ploughing through illuminated dust like this, is it?

My interpretation would be that the dust cloud is fairly well defined, so the glow on the inside is scattered light from Fomalhaut, and probably the outside as well. I say probably because the suggestion here is that the dynamics of Fomalhaut b are keeping the inner edge of the dust cloud sharp. It might or might not be more diffuse on the outside.

This image has probably been highly enhanced to make the dust ring visible. If, as they suggest, it is somewhat analogous to the Kuiper belt, it isn't going to be intrinsically bright. If you are at the Sun, looking out, you can't see the Kuiper belt. If it's visible at all, I think it would be something like the gegenschein, or maybe Zodiacal light- that is, a faint, barely visible glowing area of the sky.

I doubt the planet is moving through the dust. It is large enough that it would have long since cleared its own orbit of debris (except for material in the L4 and L5 points).

[culwin]

It's the Eye of Sauron...

[dculp]

Do the two (merged) photos of the planet define the rotational sense of the system? Has that already been determined using doppler measurements on the dust ring? Would this be the first system in which sense of rotation is established? Is there a standard definition of "north" using the right hand rule?

[tricera]

My interpretation would be that the dust cloud is fairly well defined, so the glow on the inside is scattered light from Fomalhaut, and probably the outside as well. I say probably because the suggestion here is that the dynamics of Fomalhaut b are keeping the inner edge of the dust cloud sharp. It might or might not be more diffuse on the outside.

This image has probably been highly enhanced to make the dust ring visible. If, as they suggest, it is somewhat analogous to the Kuiper belt, it isn't going to be intrinsically bright. If you are at the Sun, looking out, you can't see the Kuiper belt. If it's visible at all, I think it would be something like the gegenschein, or maybe Zodiacal light- that is, a faint, barely visible glowing area of the sky.

I doubt the planet is moving through the dust. It is large enough that it would have long since cleared its own orbit of debris (except for material in the L4 and L5 points).

Thanks Chris. This is all very helpful.
I think I'll do a toned down version of the artistic impression on HubbleSite.

Mark

[apodman]

Fomalhaut

The brightest star in the constellation Piscis Austrinus (the Southern Fish), 24 light-years from Earth.

[Arabic fam al-ḥūt, mouth of the fish, Fomalhaut : fam, mouth + al-, the + ḥūt, fish.]

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Taxonomological note: Jabba the Hutt was a slug, not a fish.

[iamlucky13]

Heh, somehow astronauts drinking their own "urine" is overshadowing this news. Sigh.

I agree with your sentiment, but it also bothers me when people say they're drinking their own urine. In that case, everyone had better think really long and hard about where the water they drink comes from and how much of it probably passed through the digestive track of other animals before them, from bacteria up through dinosaurs.

The water coming out of the recycling system on the ISS is probably cleaner than what you'd get out of the tap in even the best supplies, and probably even most bottled waters. The solutes and solids that make urine what it is very effectively removed.

Anyway, enough of that. Back to planet-hunting.

How awesome is it that we went thousands of years not knowing of any planets beyond our solar system, and then in the space of 10 years, we've discovered 300 of them.

[neufer]

Fomalhaut
The brightest star in the constellation Piscis Austrinus (the Southern Fish), 24 light-years from Earth.

[Arabic fam al-ḥūt, mouth of the fish, Fomalhaut : fam, mouth + al-, the + ḥūt, fish.]
---
Taxonomological note: Jabba the Hutt was a slug, not a fish.

Matthew 17:27 Go thou to the sea, and cast an hook, and take up the fish that first cometh up; and when thou hast opened his mouth, thou shalt find a piece of money: that take, and give unto them for me and thee.
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http://en.wikipedia.org/wiki/Fomalhaut

<<Fomalhaut (α PsA / α Piscis Austrini / Alpha Piscis Austrini) is the brightest star in the constellation Piscis Austrinus and one of the brightest stars in the sky. Its name means "mouth of the whale", from the Arabic فم الحوت fum al-ḥawt.>>

<<This is a picture of the backside of the shelf cloud of severe thunderstorms near Spiceland, Indiana. The boiling appearance of the clouds (sheared by outflow air meeting air ahead of the storm system) is sometimes called the "whale's mouth".>>
http://www.sky-chaser.com/mwcl2006.htm
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http://antwrp.gsfc.nasa.gov/apod/ap040123.html
http://antwrp.gsfc.nasa.gov/apod/ap071012.html
..............................................
Raven and the Whale
an Inuit (Eskimo) story retold by Laura Simms
http://www.healingstory.org/wwwboard/ra ... Whale.html

<<In the very beginning of time, the Inuit people say, Raven made the world. Raven was both a god and a bird with a man inside. After Raven created everything, he decided to remain on the earth. He loved the people and the animals and he was curious about them all. Even though he had made the world, he did not know everything there was to know.

Raven liked to paddle his kayak out into the sea. One day he saw a large whale.
He said, "I wonder what it looks like inside the belly of a whale."

Raven waited until the whale yawned. When its mouth was wide open, he rowed right in. He tied his kayak to one of the whale's teeth and started walking deeper inside the whale's body. The mouth of the whale closed behind him and it grew dark. Raven heard a sound like a drum or distant thunder. He walked until he came to the belly of the whale. The white bones of the whale's ribs rose up around him like ivory pillars.

In the center of the whale's belly, Raven saw a beautiful girl dancing. She had strings attached to her feet and hands stretching to the heart of the whale. Raven thought, "She is so beautiful. I would like to take her out of this whale and marry her."

So he said to her, "I am Raven. I made the world. Will you come with me into the world and be my wife?"

The maiden replied, "Raven, I cannot leave the whale. I am the heart and the soul of the whale. But if you want to stay here and keep me company, that would make me happy."

Raven threw back his beak, revealing his human face. He tossed back his wings and sat with his hands on his knees. He watched the girl as she danced.

When she danced quickly the whale soared through the water. When she danced slowly the whale floated calmly. Soon, the girl danced so slowly that she stopped moving and her eyes closed. Raven felt a cool wind from the world blow through the spout of the whale. He thought again of taking the girl with him into the world. He felt human desire. And, he forgot what she said.

Raven pulled his beak back down over his face and covered his arms with his wings. He grabbed the girl. He heard the strings snap as he flew with her out of the whale up into the sky.

As he flew, Raven heard the whale thrashing below in the ocean. He watched the whale's body as it was tossed by the waves onto the shore. The whale was dead and the girl in his arms grew smaller and smaller and disappeared.

Raven realized that everything that is alive has a heart and a soul and everything in the world is born and dies. He was overcome with great sorrow. He was so sad that he landed on the sand beside the body of the whale. For weeks he cried and cried. Then Raven began to dance. He danced for weeks. Then Raven began to sing. He sang for weeks and weeks until his heart was soothed. Then he flew back up into the sky.

He promised the humans and the animals that he would always return to this world as long as we cared for one another and understood that everything in this world lives and dies, and everyone human and animal has a heart and a soul. Raven's tears were the first tears. His dance and his song of grief and healing were the first song and the first dance.>>
...............................................
© 2001 Laura Simms reprinted from STORIES THAT NOURISH THE HEARTS OF OUR CHILDREN, Holland-Knight Publication; the Raven stories exist throughout Alaska and the Northwest Coast. This is my retelling combining several sources.
-----------------------------------------------------------------

[geckzilla]

Heh, somehow astronauts drinking their own "urine" is overshadowing this news. Sigh.

I agree with your sentiment, but it also bothers me when people say they're drinking their own urine. In that case, everyone had better think really long and hard about where the water they drink comes from and how much of it probably passed through the digestive track of other animals before them, from bacteria up through dinosaurs.

The water coming out of the recycling system on the ISS is probably cleaner than what you'd get out of the tap in even the best supplies, and probably even most bottled waters. The solutes and solids that make urine what it is very effectively removed.

Anyway, enough of that. Back to planet-hunting.

How awesome is it that we went thousands of years not knowing of any planets beyond our solar system, and then in the space of 10 years, we've discovered 300 of them.

Yeah, that's exactly why I put it in quotation marks because that's what the headlines said. When the facts aren't exciting you gotta spice 'em up somehow. You aren't drinking your own urine if all the urea and salt and whatnot is taken out. Meh! Back to planet hunting indeed. Too bad we can't just fire up Google Earth into space mode and search for them. Heh.

[neufer]

http://apod.nasa.gov/apod/ap081117.html

viewtopic.php?f=31&t=19068
viewtopic.php?f=9&t=15069

Young Exoplanet is Cloudy With a Chance of Heat Waves
Posted in: Extrasolar Planets, Observatories by Nancy Atkinson (Aug 30th 2010)

<<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.

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.

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Although over 500 planets have been discovered around other stars, only six planets have been directly imaged. 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, 67 AU, 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. There's also a new paper out that suggests the these planets around HR 8799 could actually be brown dwarfs.>>

[bystander]

Exoplanet's misstep raises doubts
Nature News | Eric Hand | 2011 Sept 23

Astronomers argue over object's status after it unexpectedly veers off course.

[url=http://apod.nasa.gov/apod/ap081114.html][b][i]APOD: Fomalhaut b (2008 Nov 14)[/i][/b][/url][i] - (Credit: NASA/ESA/P. Kalas et al) Two successive images of Fomalhaut b suggest it is following a conventional planetary orbit (white line). A 2010 image, however, shows the object straying from this course.[/i]

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As astronomers continue to rack up exoplanet discoveries by the dozen, the precise status of just one may not seem like much to fret over. But Fomalhaut b is different.

Unveiled in 2008, the tiny dot spotted circling Fomalhaut, a star just 7.7 parsecs from our own Solar System, was billed as the first exoplanet to be directly imaged at optical wavelengths. Now Fomalhaut b's identity is being questioned after data, presented last week at an exoplanet conference in Grand Teton National Park, Wyoming, showed that it has moved in an unexpected way.

Until now, Fomalhaut b had all the makings of a picture-perfect exoplanet. Two Hubble Space Telescope images, from 2004 and 2006, were used to show how the planet is tracing a textbook orbit just inside a luminous ring of dust encircling Fomalhaut. The implication was that the planet's gravity was helping to sweep away dust that was closer than the ring, giving it a sharp inner edge.

Paul Kalas, an astronomer at the University of California, Berkeley, and lead author on the 2008 study, says the latest image indicates that the planet's orbit crosses into the dust disk. And that has led Ray Jayawardhana, an astronomer at the University of Toronto in Canada, to question the planet's existence. On such a trajectory, the planet's gravitational influence would have previously disrupted the clearly delineated disk. "It's quite clear that the original story cannot stand anymore," Jayawardhana says.

Stirring controversy

Kalas acknowledges that the latest data point is puzzling, but he says he remains confident that Fomalhaut b is a planet. "You have one scientist trying to create a controversy out of nothing," he says. Hundreds of exoplanets have been detected indirectly by measuring their gravitational influence on the stars they orbit or by recording brightness changes as they cross in front of their stars. Only a handful of planets have been imaged directly. For the lucky astronomers who have bagged one of these, bragging rights have accrued — but so has the backbiting.

Fomalhaut b is already known as an oddball among exoplanets. It is far too bright in visible light for something expected to be only a few times the size of Jupiter. And ground-based follow-up observations in the infrared have been fruitless, even though this is the part of spectrum where hot, youthful planets are supposed to be brightest.

Kalas says one explanation may be that the Fomalhaut system is older than previously thought, and therefore cooler and fainter in the infrared. And, he says, the excessive optical brightness can be explained if the planet is surrounded by bright material, just as Saturn is surrounded by a system of rings, which would increase its overall reflectivity.

Jayawardhana says this alone should bump Fomalhaut b from the list of directly imaged planets, because the light would be coming from the dust, not the planet's surface. "They continue to call it a directly imaged planet," he says. "I think it's time to stop doing that."

The new data point, and the potential disk-cutting orbit, adds to the mystery. Kalas says it might just be a problem with the latest image. The pictures in 2004 and 2006 were taken using a high-resolution channel on the Hubble's Advanced Camera for Surveys that failed in 2007 and was not restored when the camera was brought back online in 2009.

For the latest image, Kalas had to resort to another Hubble instrument, the Space Telescope Imaging Spectrograph. He says the switch to a different detector may explain the planet's slight deviation from its expected position. He has been allocated time to take another picture with that same instrument next summer. If the planet's unexpected motion persists, he says it is still possible to explain why the disk around the star is undisturbed: perhaps his team is seeing the planet just as some dynamic instability in the star system is knocking it off course.

Fighting words

Christian Marois, of the Herzberg Institute of Astrophysics in Victoria, Canada, doesn't like arguments that rely on coincidence. With an orbital period of about 800 years, Fomalhaut b would have had to have changed course quite recently.

Marois says it's far more likely that Kalas is adjusting his analysis to the different instrument on Hubble, and that the original orbit will hold. If anything, he says, the fact that Kalas spotted Fomalhuat b at all in 2010 is "another confirmation that this thing is real".

Jean Schneider, an astronomer at the Paris Observatory who maintains the exoplanet.eu database, says that Fomalhaut b will remain on the list. But on 22 September, he added a comment to the planet's entry saying that doubts have been raised (go.nature.com/ojgjjd).

In an e-mail to Schneider today, Kalas said that, to be scrupulously fair, Schneider should also mention that there are doubts associated with 1RXJ1609, a planet imaged directly at infrared wavelengths that Jayawardhana co-discovered and announced in 2008, a few months before the unveiling of Fomalhaut b.

The dispute has all the makings of a celestial grudge match: Jayawardhana suggests that fierce professional competition and the glare of the media spotlight can fuel 'planet mania', leading astronomers to overstate their discoveries. Kalas notes that he coined the term 'planet mania' in a 1998 article in Science, in which he criticized Jayawardhana for making inflated claims about observing planets in the process of forming.

For its part, Fomalhaut b seems to know what it's doing, even if no one else does.

[bystander]

New Research Suggests Fomalhaut b May Not Be a Planet After All
Universe Today | Paul Scott Anderson | 2012 Jan 26

When the Hubble Space Telescope photographed the apparent exoplanet Fomalhaut b in 2008, it was regarded as the first visible light image obtained of a planet orbiting another star. The breakthrough was announced by a research team led by Paul Kalas of the University of California, Berkeley. The planet was estimated to be approximately the size of Saturn, but no more than three times Jupiter’s mass, or perhaps smaller than Saturn according to some other studies, and might even have rings. It resides within a debris ring which encircles the star Fomalhaut, about 25 light-years away.

Another team at Princeton, however, has just announced that they believe the original findings are in error, and that the planet is actually a dust cloud, based on new observations by the Spitzer Space Telescope. Their paper has just been accepted by the Astrophysical Journal.

According to the abstract:

• The nearby A4-type star Fomalhaut hosts a debris belt in the form of an eccentric ring, which is thought to be caused by dynamical influence from a giant planet companion. In 2008, a detection of a point-source inside the inner edge of the ring was reported and was interpreted as a direct image of the planet, named Fomalhaut b. The detection was made at ~600–800 nm, but no corresponding signatures were found in the near-infrared range, where the bulk emission of such a planet should be expected. Here we present deep observations of Fomalhaut with Spitzer/IRAC at 4.5 µm, using a novel PSF subtraction technique based on ADI and LOCI, in order to substantially improve the Spitzer contrast at small separations. The results provide more than an order of magnitude improvement in the upper flux limit of Fomalhaut b and exclude the possibility that any flux from a giant planet surface contributes to the observed flux at visible wavelengths. This renders any direct connection between the observed light source and the dynamically inferred giant planet highly unlikely. We discuss several possible interpretations of the total body of observations of the Fomalhaut system, and find that the interpretation that best matches the available data for the observed source is scattered light from transient or semi-transient dust cloud.

Kalas has responded to the new study, saying that they considered the dust cloud possibility but ruled it out for various reasons. For one thing, Spitzer lacks the light sensitivity to detect a Saturn-sized planet, and bright rings could also explain the optical characteristics observed. He says, “We welcome the new Spitzer data, but we don’t really agree with this interpretation.”

The Princeton team, interestingly, thinks that there may be a real planet orbiting Fomalhaut, but still hiding from detection. From the paper:

• In particular, we find that there is almost certainly no direct flux from a planet contributing to the visible-light signature. This, in combination with the existing body of data for the Fomalhaut system, strongly implies that the dynamically inferred giant planet companion and the visible-light point source are physically unrelated. This in turn implies that the ‘real’ Fomalhaut b still hides in the system. Although we do find a tentative point source in our images that could in principle correspond to this object, its significance is too low to distinguish whether it is real or not at this point.

A resolution to the debate may come from the James Webb Space Telescope, scheduled to launch in 2018.

Of course it will be disappointing if Fomalhaut b does turn out to not be a planet after all, but let’s not forget that thousands of other ones are being discovered and confirmed. There may occasionally be hits-and-misses, but so far the planetary hunt overall has been nothing short of a home run…

Infrared Non-detection of Fomalhaut b -- Implications for the Planet Interpretation - Markus Janson et al

• arXiv.org > astro-ph > arXiv:1201.4388 > 20 Jan 2012

Fomalhaut's giant exoplanet may be small lava world
New Scientist | Lisa Grossman | 2012 Feb 02

[bystander]

Herschel spots comet massacre around nearby star
ESA Space Science | Herschel | 2012 Apr 11

[b][i]Herschel’s image of Fomalhaut[/i][/b] [i]Credits: ESA/Herschel/PACS/Bram Acke, KU Leuven, Belgium[/i]

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ESA’s Herschel Space Observatory has studied the dusty belt around the nearby star Fomalhaut. The dust appears to be coming from collisions that destroy up to thousands of icy comets every day.

Fomalhaut is a young star, just a few hundred million years old, and twice as massive as the Sun. Its dust belt was discovered in the 1980s by the IRAS satellite, but Herschel’s new images of the belt show it in much more detail at far-infrared wavelengths than ever before.

Bram Acke, at the University of Leuven in Belgium, and colleagues analysed the Herschel observations and found the dust temperatures in the belt to be between –230 and –170ºC. However, because Fomalhaut is slightly off-centre and closer to the southern side of the belt, the southern side is warmer and brighter than the northern side.

Both the narrowness and asymmetry of the belt are thought to be due to the gravity of a possible planet in orbit around the star, as suggested by earlier Hubble Space Telescope images.

The Herschel data show that the dust in the belt has the thermal properties of small solid particles, with sizes of only a few millionths of a metre across.

But this created a paradox because the Hubble Space Telescope observations suggested solid grains more than ten times larger.

Those observations collected starlight scattering off the grains in the belt and showed it to be very faint at Hubble’s visible wavelengths, suggesting that the dust particles are relatively large. But that appears to be incompatible with the temperature of the belt as measured by Herschel in the far-infrared.

To resolve the paradox, Dr Acke and colleagues suggest that the dust grains must be large fluffy aggregates, similar to dust particles released from comets in our own Solar System.

These would have both the correct thermal and scattering properties. However, this leads to another problem.

The bright starlight from Fomalhaut should blow small dust particles out of the belt very rapidly, yet such grains appear to remain abundant there.

The only way to overcome this contradiction is to resupply the belt through continuous collisions between larger objects in orbit around Fomalhaut, creating new dust.

To sustain the belt, the rate of collisions must be impressive: each day, the equivalent of either two 10 km-sized comets or 2000 1 km-sized comets must be completely crushed into small fluffy, dust particles.

“I was really surprised,” says Dr Acke, “To me this was an extremely large number.”

To keep the collision rate so high, there must be between 260 billion and 83 trillion comets in the belt, depending on their size. Our own Solar System has a similar number of comets in its Oort Cloud, which formed from objects scattered from a disc surrounding the Sun when it was as young as Fomalhaut.

“These beautiful Herschel images have provided the crucial information needed to model the nature of the dust belt around Fomalhaut,” says Göran Pilbratt, ESA Herschel Project Scientist.

Frantic Comet Massacre Taking Place at Fomalhaut
Universe Today | Nancy Atkinson | 2012 Apr 11

Caution: Comet Crash Zone Ahead
Discovery News | Irene Klotz | 2012 Apr 11

Herschel sees dusty disc of crushed comets
UK Space Agency | 2012 Apr 12

Dusty Disc Created by Crushed Comets
NASA Astrobiology Magazine | 2012 Apr 13

http://asterisk.apod.com/viewtopic.php?f=31&t=25629

[bystander]

ALMA Reveals Workings of Nearby Planetary System
ESO | NRAO | NAOJ | U Florida | 2012 Apr 13

[i]Credit: ALMA (ESO/NAOJ/NRAO). Visible light image: NASA/ESA/Hubble[/i]

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A new observatory still under construction has given astronomers a major breakthrough in understanding a nearby planetary system that can provide valuable clues about how such systems form and evolve. The scientists used the Atacama Large Millimeter/submillimeter Array (ALMA) to discover that planets orbiting the star Fomalhaut must be much smaller than originally thought.

The discovery, which helped resolve a controversy among earlier observers of the system, was made possible by high-resolution images of a disk, or ring, of dust orbiting the star, about 25 light-years from Earth. The ALMA images show that both the inner and outer edges of the thin, dusty disk have very sharp edges. That fact, combined with computer simulations, led the scientists to conclude that the dust particles in the disk are kept within the disk by the gravitational effect of two planets -- one closer to the star than the disk and one more distant.*

Their calculations also indicated the probable size of the planets -- larger than Mars but no larger than a few times the size of the Earth. This is much smaller than astronomers had previously thought. In 2008, a Hubble Space Telescope (HST) image had revealed the inner planet, then thought to be larger than Saturn, the second-largest planet in our Solar System. However, later observations with infrared telescopes failed to detect the planet.

That failure led some astronomers to doubt the existence of the planet in the HST image. Also, the HST visible-light image detected very small dust grains that are pushed outward by the star's radiation, thus blurring the structure of the dusty disk. The ALMA observations, at wavelengths longer than those of visible light, traced larger dust grains -- about 1 millimeter in diameter -- that are not moved by the star's radiation. This clearly revealed the disk's sharp edges, which indicate the gravitational effect of the two planets.

"Combining ALMA observations of the ring's shape with computer models, we can place very tight limits on the mass and orbit of any planet near the ring," said Aaron Boley, a Sagan Fellow at the University of Florida, leader of the study. "The masses of these planets must be small; otherwise the planets would destroy the ring," he added. The small sizes of the planets explain why the earlier infrared observations failed to detect them, the scientists said.

The ALMA research shows that the ring's width is about 16 times the distance from the Sun to the Earth, and is only one-seventh as thick as it is wide. "The ring is even more narrow and thinner than previously thought," said Matthew Payne, also of the University of Florida.

The ring is about 140 times the Sun-Earth distance from the star. In our own Solar System, Pluto is about 40 times more distant from the Sun than the Earth. "Because of the small size of the planets near this ring and their large distance from their host star, they are among the coldest planets yet found orbiting a normal star," Boley said.

The scientists observed the Fomalhaut system in September and October of 2011, when only about a quarter of ALMA's planned 66 antennas were available. When construction is completed next year, the full system will be much more capable. ALMA's new capabilities, however, revealed the telltale structure that had eluded earlier millimeter-wave observers.

"ALMA may still be under construction, but it already has proven to be the world's most powerful telescope for observing the Universe at millimeter and submillimeter wavelengths," said Stuartt Corder, of the National Radio Astronomy Observatory, a member of the observing team. The scientists will report their findings in an upcoming edition of the Astrophysical Journal Letters.

• [*] The effect of planets or moons in keeping a dust ring's edges sharp was first seen when the Voyager 1 spacecraft flew by Saturn in 1980 and made detailed images of that planet's ring system. One ring of the planet Uranus is confined sharply by the moons Cordelia and Ophelia, in exactly the manner the ALMA observers propose for the ring around Fomalhaut. The moons confining those planets' rings are dubbed "shepherding moons."
  
  The moons or planets confining such dust rings do so through gravitational effects. A planet on the inside of the ring is orbiting the star more rapidly than the dust particles in the ring. Its gravity adds energy to the particles, pushing them outward. A planet on the ring's outside is moving more slowly than the dust particles, and its gravity decreases the energy of the particles, making them fall slightly inward.[/i]

Constraining the Planetary System of Fomalhaut Using High-Resolution ALMA Observations - Aaron C. Boley et al

• arXiv.org > astro-ph > arXiv:1204.0007 > 30 Mar 2012

Weird Super-Earths Found Orbiting Neighbor Star
Discovery News | Irene Klotz | 2012 Apr 13

[bystander]

New Study Brings a Doubted Exoplanet 'Back from the Dead'
NASA | GSFC | Hubble | 2012 Oct 25

Click to play embedded YouTube video.

In 2008, Hubble astronomers announced the detection of a giant planet around the
bright star Fomalhaut. Recent studies have questioned this conclusion. Now, a
reanalysis of Hubble data has revived the "deceased" exoplanet as a dust-shrouded
world with less than twice the mass of Jupiter. (Credit: NASA/GSFC)

[i]This visible-light image from the Hubble Space Telescope shows the vicinity of the star Fomalhaut, including the location of its dust ring and disputed planet, Fomalhaut b. A coronagraphic mask helped dim the star's brightness. This view combines two 2006 observations that were taken with masks of different sizes (1.8 and 3 arcseconds). [b](Credit: NASA/ESA/T. Currie, U. Toronto)[/b][/i]

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A second look at data from NASA's Hubble Space Telescope is reanimating the claim that the nearby star Fomalhaut hosts a massive exoplanet. The study suggests that the planet, named Fomalhaut b, is a rare and possibly unique object that is completely shrouded by dust.

Fomalhaut is the brightest star in the constellation Piscis Austrinus and lies 25 light-years away.

In November 2008, Hubble astronomers announced the exoplanet, named Fomalhaut b, as the first one ever directly imaged in visible light around another star. The object was imaged just inside a vast ring of debris surrounding but offset from the host star. The planet's location and mass -- no more than three times Jupiter's -- seemed just right for its gravity to explain the ring's appearance.

Recent studies have claimed that this planetary interpretation is incorrect. Based on the object's apparent motion and the lack of an infrared detection by NASA's Spitzer Space Telescope, they argue that the object is a short-lived dust cloud unrelated to any planet.

A new analysis, however, brings the planet conclusion back to life.

"Although our results seriously challenge the original discovery paper, they do so in a way that actually makes the object's interpretation much cleaner and leaves intact the core conclusion, that Fomalhaut b is indeed a massive planet," said Thayne Currie, an astronomer formerly at NASA's Goddard Space Flight Center in Greenbelt, Md., and now at the University of Toronto.

The discovery study reported that Fomalhaut b's brightness varied by about a factor of two and cited this as evidence that the planet was accreting gas. Follow-up studies then interpreted this variability as evidence that the object actually was a transient dust cloud instead.

In the new study, Currie and his team reanalyzed Hubble observations of the star from 2004 and 2006. They easily recovered the planet in observations taken at visible wavelengths near 600 and 800 nanometers, and made a new detection in violet light near 400 nanometers. In contrast to the earlier research, the team found that the planet remained at constant brightness.

The team attempted to detect Fomalhaut b in the infrared using the Subaru Telescope in Hawaii, but was unable to do so. The non-detections with Subaru and Spitzer imply that Fomalhaut b must have less than twice the mass of Jupiter.

Another contentious issue has been the object's orbit. If Fomalhaut b is responsible for the ring's offset and sharp interior edge, then it must follow an orbit aligned with the ring and must now be moving at its slowest speed. The speed implied by the original study appeared to be too fast. Additionally, some researchers argued that Fomalhaut b follows a tilted orbit that passes through the ring plane.

Using the Hubble data, Currie's team established that Fomalhaut b is moving with a speed and direction consistent with the original idea that the planet's gravity is modifying the ring.

"What we've seen from our analysis is that the object's minimum distance from the disk has hardly changed at all in two years, which is a good sign that it's in a nice ring-sculpting orbit," explained Timothy Rodigas, a graduate student in the University of Arizona and a member of the team.

Currie's team also addressed studies that interpret Fomalhaut b as a compact dust cloud not gravitationally bound to a planet. Near Fomalhaut's ring, orbital dynamics would spread out or completely dissipate such a cloud in as little as 60,000 years. The dust grains experience additional forces, which operate on much faster timescales, as they interact with the star's light.

"Given what we know about the behavior of dust and the environment where the planet is located, we think that we're seeing a planetary object that is completely embedded in dust rather than a free-floating dust cloud," said team member John Debes, an astronomer at the Space Telescope Science Institute in Baltimore, Md.

A paper describing the findings has been accepted for publication in The Astrophysical Journal Letters.

Because astronomers detect Fomalhaut b by the light of surrounding dust and not by light or heat emitted by its atmosphere, it no longer ranks as a "directly imaged exoplanet." But because it's the right mass and in the right place to sculpt the ring, Currie's team thinks it should be considered a "planet identified from direct imaging."

Fomalhaut was targeted with Hubble most recently in May by another team. Those observations are currently under scientific analysis and are expected to be published soon.

Direct Imaging Confirmation and Characterization of a Dust-Enshrouded Candidate Exoplanet Orbiting Fomalhaut - Thayne Currie et al

• arXiv.org > astro-ph > arXiv:1210.6620 > 24 Oct 2012

On Again, Off Again Exoplanet Fomalhaut b is Back from the Dead
Universe Today | Nancy Atkinson | 2012 Oct 26

The return of Sauron’s planet
Discover Blogs | Bad Astronomy | 2012 Oct 27

[bystander]

Hubble Reveals Rogue Planetary Orbit for Fomalhaut b
NASA | STScI | 2013 Jan 08

Rogue Planetary Orbit for Fomalhaut b
(Credit: NASA, ESA, and P. Kalas (UC Berkeley and SETI Institute))

[url=http://hubblesite.org/newscenter/archive/releases/2013/01/image/e/][b][i]Schematic of Fomalhaut System[/i][/b][/url] [b][i]Illustration Credit: NASA, ESA, and A. Feild (STScI) Science Credit: NASA, ESA, and P. Kalas (UC Berkeley)[/i][/b]

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YouTube: Paul Kalas: Fomalhaut b orbit simulations

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Newly released NASA Hubble Space Telescope images of a vast debris disk encircling the nearby star Fomalhaut and a mysterious planet circling it may provide forensic evidence of a titanic planetary disruption in the system.

Astronomers are surprised to find the debris belt is wider than previously known, spanning a section of space from 14 to nearly 20 billion miles from the star. Even more surprisingly, the latest Hubble images have allowed a team of astronomers to calculate the planet follows an unusual elliptical orbit that carries it on a potentially destructive path through the vast dust ring.

The planet, called Fomalhaut b, swings as close to its star as 4.6 billion miles, and the outermost point of its orbit is 27 billion miles away from the star. The orbit was recalculated from the newest Hubble observation made last year.

"We are shocked. This is not what we expected," said Paul Kalas of the University of California at Berkeley and the SETI Institute in Mountain View, Calif.

The Fomalhaut team led by Kalas considers this circumstantial evidence there may be other planet-like bodies in the system that gravitationally disturbed Fomalhaut b to place it in such a highly eccentric orbit. The team presented its finding Tuesday at the 221st meeting of the American Astronomical Society in Long Beach, Calif.

Among several scenarios to explain Fomalhaut b's 2,000-year-long orbit is the hypothesis that an as yet undiscovered planet gravitationally ejected Fomalhaut b from a position closer to the star, and sent it flying in an orbit that extends beyond the dust belt.

"Hot Jupiters get tossed through scattering events, where one planet goes in and one gets thrown out," said co-investigator Mark Clampin of NASA's Goddard Space Flight Center in Greenbelt, Md. "This could be the planet that gets thrown out."

Hubble also found the dust and ice belt encircling the star Fomalhaut has an apparent gap slicing across the belt. This might have been carved by another undetected planet. Hubble's exquisite view of the dust belt shows irregularities that strongly motivate a search for other planets in the system.

If its orbit lies in the same plane with the dust belt, then Fomalhaut b will intersect the belt around 2032 on the outbound leg of its orbit. During the crossing, icy and rocky debris in the belt could crash into the planet's atmosphere and create the type of cosmic fireworks seen when Comet Shoemaker-Levy 9 crashed into Jupiter. Most of the fireworks from collisions will be seen in infrared light. However, if Fomalhaut b is not co-planar with the belt, the only thing to be seen will be a gradual dimming of Fomalhaut b as it travels farther from the star.

Kalas hypothesized that Fomalhaut b's extreme orbit is a major clue in explaining why the planet is unusually bright in visible light, but very dim in infrared light. It is possible the planet's optical brightness originates from a ring or shroud of dust around the planet, which reflects starlight. The dust would be rapidly produced by satellites orbiting the planet, which would suffer extreme erosion by impacts and gravitational stirring when Fomalhaut b enters into the planetary system after a millennium of deep freeze beyond the main belt. An analogy can be found by looking at Saturn, which has a tenuous, but very large dust ring produced when meteoroids hit the outer moon Phoebe.

The team has also considered a different scenario where a hypothetical second dwarf planet suffered a catastrophic collision with Fomalhaut b. The collision scenario would explain why the star Fomalhaut has a narrow outer belt linked to an extreme planet. But in this case the belt is young, less than 10,000 years old, and it is difficult to produce energetic collisions far from the star in such young systems.

Fomalhaut is a special system because it looks like scientists may have a snapshot of what our solar system was doing 4 billion years ago. The planetary architecture is being redrawn, the comet belts are evolving, and planets may be gaining and losing their moons. Astronomers will continue monitoring Fomalhaut b for decades to come because they may have a chance to observe a planet entering an icy debris belt that is like the Kuiper Belt at the fringe of our own solar system.

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Science NOW | Govert Schilling | 2013 Jan 10