Hubble sees asteroids colliding at nearby star for first time

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Fomalhaut cs1 and cs2 (annotated)

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Fomalhaut cs1 and cs2 (clean image)

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Fomalhaut cs2 (artist’s concept)

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Fomalhaut cs2 (artist’s concept animation)


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Space Sparks episode 21: Hubble sees asteroids colliding at nearby star for first time

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In a historical milestone, catastrophic collisions in a nearby planetary system were witnessed for the first time by astronomers using the NASA/ESA Hubble Space Telescope. As they observed the bright star Fomalhaut, the scientists saw the impact of massive objects around the star. The Fomalhaut system appears to be in a dynamical upheaval, similar to what our solar system experienced in its first few hundred million years after formation.

“This is certainly the first time I’ve ever seen a point of light appear out of nowhere in an exoplanetary system,” said principal investigator Paul Kalas of the University of California, Berkeley. “It’s absent in all of our previous Hubble images, which means that we just witnessed a violent collision between two massive objects and a huge debris cloud unlike anything in our own solar system today. Amazing!"

Just 25 light-years from Earth, Fomalhaut is one of the brightest stars in the night sky. Located in the constellation Piscis Austrinus, also known as the Southern Fish, it is more massive and brighter than the Sun and is encircled by several belts of dusty debris.

In 2008, scientists used Hubble to discover a candidate planet around Fomalhaut, making it the first stellar system with a possible planet found using visible light. That object, called Fomalhaut b, now appears to be a dust cloud masquerading as a planet – the result of colliding planetesimals. While searching for Fomalhaut b in recent Hubble observations, scientists were surprised to find a second point of light at a similar location around the star. They call this object “circumstellar source 2” or “cs2” while the first object is now known as “cs1.”

Tackling mysteries of colliding planetesimals

Why astronomers are seeing both of these debris clouds so physically close to each other is a mystery. If the collisions between asteroids and planetesimals were random, cs1 and cs2 should appear by chance at unrelated locations. Yet, they are positioned intriguingly near each other along the inner portion of Fomalhaut’s outer debris disk.

Another mystery is why scientists have witnessed these two events within such a short timeframe. “Previous theory suggested that there should be one collision every 100,000 years, or longer. Here, in 20 years, we've seen two,” explained Kalas. “If you had a movie of the last 3,000 years, and it was sped up so that every year was a fraction of a second, imagine how many flashes you'd see over that time. Fomalhaut’s planetary system would be sparkling with these collisions.”

Collisions are fundamental to the evolution of planetary systems, but they are rare and difficult to study.

“The exciting aspect of this observation is that it allows researchers to estimate both the size of the colliding bodies and how many of them there are in the disk, information which is almost impossible to get by any other means,” said co-author Mark Wyatt at the University of Cambridge in England. “Our estimates put the planetesimals that were destroyed to create cs1 and cs2 at just 30 kilometres in size, and we infer that there are 300 million such objects orbiting in the Fomalhaut system.”

“The system is a natural laboratory to probe how planetesimals behave when undergoing collisions, which in turn tells us about what they are made of and how they formed,” explained Wyatt.

Cautionary tale

The transient nature of Fomalhaut cs1 and cs2 poses challenges for future space missions aiming to directly image exoplanets. Such telescopes may mistake dust clouds like cs1 and cs2 for actual planets.

“Fomalhaut cs2 looks exactly like an extrasolar planet reflecting starlight,” said Kalas. “What we learned from studying cs1 is that a large dust cloud can masquerade as a planet for many years. This is a cautionary note for future missions that aim to detect extrasolar planets in reflected light."

Looking to the future

Kalas and his team have been granted Hubble time to monitor cs2 over the next three years. They want to see how it evolves -- does it fade, or does it get brighter? Being closer to the dust belt than cs1, the expanding cs2 cloud is more likely to start encountering other material in the belt. This could lead to a sudden avalanche of more dust in the system, which could cause the whole surrounding area to get brighter.

“We will be tracing cs2 for any changes in its shape, brightness, and orbit over time,” said Kalas, “It’s possible that cs2 will start becoming more oval or cometary in shape as the dust grains are pushed outward by the pressure of starlight.” The team also will use the NIRCam (Near-Infrared Camera) instrument on the NASA/ESA/CSA James Webb Space Telescope to observe cs2. Webb’s NIRCam has the ability to provide color information that can reveal the size of the cloud’s dust grains and their composition. It can even determine if the cloud contains water ice.

Hubble and Webb are the only observatories capable of this kind of imaging. While Hubble primarily sees in visible wavelengths, Webb could view cs2 in the infrared. These different, complementary wavelengths are needed to provide a broad multi-spectral investigation and a more complete picture of the mysterious Fomalhaut system and its rapid evolution.

This research appears today in the December 18 issue of Science.

Source: ESA/Hubble/News

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More information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

Image Credit: NASA, ESA, P. Kalas (UC Berkeley), J. DePasquale (STScI)

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Links

• Release on ESA website
• Release on NASA website
• Science paper

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Contacts:

Bethany Downer
ESA/Hubble Chief Science Communications Officer
Email: Bethany.Downer@esahubble.org

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Neighboring Star’s Warped Ring Shaped by Evolving Planets

The bright star in the center, Fomalhaut, is surrounded by an ancient debris disk of uneven brightness. The disk is closer to the star in the south, where the disk is wider and fainter, and further from the star in the north, where the disk is narrower and brighter. The dotted ring shows the possible orbit of a planet implied by Lovell et al. Credit: NSF/AUI/NSF NRAO/B.Saxton. Hi-Res File

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Unusual shape of Fomalhaut’s debris ring shows evidence of sculpting by ancient planets, rewriting story of planetary system evolution

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have made the highest resolution image to date, revealing new insights into the unusual and mysterious architecture of the debris disk encircling Fomalhaut, one of the brightest and most well-studied stars in our cosmic neighborhood. Debris disks are vast belts of dust and rocky bodies, similar to our Solar System’s asteroid belt—but much larger. The lopsidedness (or eccentricity) of Fomalhaut’s disk has fascinated astronomers for nearly two decades.

An international research team, led by astronomers at the Center for Astrophysics | Harvard & Smithsonian and Johns Hopkins University, published two papers analyzing these new observations in the Astrophysical Journal/Astrophysical Journal Letters. They have now found that Fomalhaut’s disk is not just eccentric—its eccentricity changes with distance from the star. Unlike previous models assuming a uniform or “fixed” eccentricity, their new data-driven model shows that the disk’s shape grows less stretched (or less eccentric) the farther a segment is from Fomalhaut. This morphology is known as a negative eccentricity gradient. You can imagine the offsets between the star and the ring’s center, much like Saturn’s rings, if Saturn wasn’t sitting neatly in the middle.

“Our observations show, for the first time, that the disk’s eccentricity isn’t constant,” said lead author of one of the papers, Joshua Bennett Lovell, a Submillimeter Array Fellow with the Harvard-Smithsonian Center for Astrophysics. “It steadily drops off with distance, a finding that has never before been conclusively demonstrated in any debris disk.” Lovell is also an ALMA Ambassador with the U.S. National Science Foundation National Radio Astronomy Observatory’s North American ALMA Science Center.

Using high-resolution ALMA images at 1.3mm wavelengths, the team fitted a new model setup to the data, one that accounts for the disk’s radius, width, and asymmetries, with an eccentric ring model that can alter its eccentricity with distance from the star. The best-fitting model pointed to a steep decline in eccentricity with distance, as predicted by dynamical theories of how planets can shape debris disks, but as-yet seen anywhere in the universe.

This negative gradient offers clues about hidden planets, currently unseen by astronomers, orbiting Fomalhaut. The new model suggests a massive planet orbiting inside of Fomalhaut’s disk may have sculpted its eccentricity profile early in the extrasolar system’s history. The unusual shape of the debris disk may have formed in the system’s youth, during the protoplanetary disk phase, and has remained this way for more than 400 million years, thanks to the continued push, and pull of this planet.

In the second paper, led by Graduate Student Jay Chittidi at Johns Hopkins University, the team exhausted the possibility that the ring’s eccentricity is fixed with the distance from the star. “Although the shift in brightness from the pericenter side of the disk, nearest to the star, to the apocenter side, furthest from the star, between the JWST and ALMA data was expected, the precise shifts that we measured in the disk brightness and the ring’s width could not be explained by the old models,” said Jay. “Simply put: we couldn’t find a model with a fixed eccentricity that could explain these peculiar features in Fomalhaut’s disk. Comparing the old and new models, we are now able to better interpret this disk, and reconstruct the history and present state of this dynamic system.”

Researchers hope this new model will be further tested with more ALMA observations, which were recently approved, “And hopefully we’ll find new clues that will help us uncover that planet!” adds Lovell. The team has shared the eccentricity model code developed for this newly published research to enable other astronomers to apply it to similar systems.

Source: National Radio Astronomy Observatory (NRAO)/News

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About NRAO

The National Radio Astronomy Observatory (NRAO) is a facility of the U.S. National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

About ALMA

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

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Hubble Observes Aftermath of Massive Collision

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Visualisation of Fomalhaut and Fomalhaut b (Artist’s Impression)

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Illustration of Hubble’s Observation of Fomalhaut b’s Expanding Dust Cloud

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DSS image of Fomalhaut (ground-based image)

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Fomalhaut and Piscis Austrinus (ground-based image)

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Hubblecast 127 Light: The Mysteries of Fomalhaut b

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The Hubble Space Telescope offers insight into the nature of exoplanet Fomalhaut b

What astronomers thought was a planet beyond our solar system, has now seemingly vanished from sight. Astronomers now suggest that a full-grown planet never existed in the first place. The NASA/ESA Hubble Space Telescope had instead observed an expanding cloud of very fine dust particles caused by a titanic collision between two icy asteroid-sized bodies orbiting the bright star Fomalhaut, about 25 light-years from Earth.

“The Fomalhaut system is the ultimate test lab for all of our ideas about how exoplanets and star systems evolve,” said George Rieke of the University of Arizona’s Steward Observatory. “We do have evidence of such collisions in other systems, but none of this magnitude has ever been observed. This is a blueprint for how planets destroy each other.”

The object was previously believed to be a planet, called Fomalhaut b, and was first announced in 2008 based on data taken in 2004 and 2006. It was clearly visible in several years of Hubble observations that revealed it as a moving dot. Unlike other directly imaged exoplanets, nagging puzzles with Fomalhaut b arose early on. The object was unusually bright in visible light, but did not have any detectable infrared heat signature. Astronomers proposed that the added brightness came from a huge shell or ring of dust encircling the object that may have been collision-related. Also, early Hubble observations suggested the object might not be following an elliptical orbit, as planets usually do.

“These collisions are exceedingly rare and so this is a big deal that we actually get to see one,” said András Gáspár of the University of Arizona. “We believe that we were at the right place at the right time to have witnessed such an unlikely event with the Hubble Space Telescope.”

“Our study, which analysed all available archival Hubble data on Fomalhaut b, including the most recent images taken by Hubble, revealed several characteristics that together paint a picture that the planet-sized object may never have existed in the first place,” [1] said Gáspár.

Hubble images from 2014 showed the object had vanished, to the disbelief of the astronomers. Adding to the mystery, earlier images showed the object to continuously fade over time. “Clearly, Fomalhaut b was doing things a bona fide planet should not be doing,” said Gáspár.

The resulting interpretation is that Fomalhaut b is not a planet, but a slowly expanding cloud blasted into space as a result of a collision between two large bodies. Researchers believe the collision occurred not too long prior to the first observations taken in 2004. By now the debris cloud, consisting of dust particles around 1 micron (1/50th the diameter of a human hair), is below Hubble’s detection limit. The dust cloud is estimated to have expanded by now to a size larger than the orbit of Earth around our Sun.

Equally confounding is that the object is not on an elliptical orbit, as expected for planets, but on an escape trajectory, or hyperbolic path. “A recently created massive dust cloud, experiencing considerable radiative forces from the central star Fomalhaut, would be placed on such a trajectory” Gáspár said, “Our model is naturally able to explain all independant observable paramters of the system: its expansion rate, its fading and its trajectory.”

Because Fomalhaut b is presently inside a vast ring of icy debris encircling the star, the colliding bodies were likely a mixture of ice and dust, like the cometary bodies that exist in the Kuiper belt on the outer fringe of our solar system. Gáspár and Rieke estimate that each of these comet-like bodies measured about 200 kilometers across. The also suggest that the Fomalhaut system may experience one of these collision events only every 200 000 years.

Gáspár, Rieke, and other astronomers will also be observing the Fomalhaut system with the upcoming NASA/ESA/CSA James Webb Space Telescope, which is scheduled to launch in 2021.

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Notes

[1] The team’s paper “New HST data and modeling reveal a massive planetesimal collision around Fomalhaut” is being published in the Proceedings of the National Academy of Sciences on 20 April 2020.

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More information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

The team of astronomers in this study consists of A. Gáspár and G. Rieke of the University of Arizona, USA.

Image credit: ESA/NASA, M. Kornmesser

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Links

• Images of Hubble 
• Hubblesite release
• Science paper
• Link to Space Scoop

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Contact

András Gáspár

University of Arizona

Tucson, Arizona, USA

Email: agaspar@arizona.edu

Bethany Downer

ESA/Hubble, Public Information Officer

Garching, Germany

Email: Bethany.Downer@partner.eso.org

Source: ESA/Hubble/News

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Orbit Flips in Exoplanet Systems

An artist's rendition of the Fomalhaut exoplanetary system. The planet Fomalhaut_b has a highly elliptical orbit, with an eccentricity about ten times that of the Earth's orbit. CfA astronomers have shown that multiplanet systems with highly eccentric orbits can suddenly flip the orbital direction of one of its planets (video link of orbit flip).

The orbits of the planets in our solar system are almost circular (Kepler made the case for their actually being ellipses). This nearly circular, concentric property helps keep the solar system stable, since highly elliptical orbits could occasionally bring planets close enough together for their gravitational interactions to disrupt their paths. Orbital shapes are quantified by their eccentricity, a measure of the closest distance of a planet from the Sun compared to its largest distance (thus helping determine the annual variations in stellar illumination); the Earth’s eccentricity is small, 0.0167, and in December the Earth is only about 3% closer to the Sun than in June.

The northern hemisphere is cooler in December (not June) because the Earth's axis of rotation is tilted with respect to its orbital motion, and in December the north pole is pointed slightly away from the Sun. The size of this tilt (called the obliquity) is 23.4 degrees, and it was likely produced in a cataclysmic impact between the Earth and another large body about 4.5 billion years ago. The impact is also thought to have formed the moon, whose presence plays the important role of stabilizing the value of the tilt which otherwise might wobble. Mars, for example, has no large moon, and its obliquity – currently 25 degrees – wobbles by up to tens of degrees on time scales of only hundreds of thousands of years, driving profound climate changes on the planet as detected in the structure of its polar ice caps. Eccentricity and obliquity are thus key planetary parameters, and they are not necessarily constant but can evolve in time.

There are currently about 1783 confirmed exoplanets and of this group, forty-one are estimated to have eccentricities like the Earth’s or smaller. The others have larger values – sometimes much larger, with a few known exoplanets varying their distances from their star periodically by ten or more times. CfA astronomers Gongjie Li, Smadar Naoz, Bence Kocsis, and Avi Loeb have examined what happens to a system of three or more bodies (for example a star with two planets), when the orbits are elliptical (and/or when some other conditions pertain). They were prompted in part by the fact that in some unusual exoplanetary systems a planet orbits in a sense opposite to the star’s spin (a counter-orbit); in other systems the orbit is in the same direction, but the planet’s spin (its obliquity) is 180 degrees so that its north pole points “down.”

The astronomers show that the gravitational perturbations that can result from close encounters in systems with elliptical orbits can induce complex processes that result in such odd behaviors. They present a previously unidentified mechanism whereby such interactions can, in a relatively short time period (just a few thousand years!), completely flip the planet from normal to counter-rotating. The new paper not only helps to explain why some exoplanet systems are weird, it provides new insights into the planet-making processes while helping us appreciate our own planetary system.

Reference(s): 

“Eccentricity Growth and Orbit Flip in Near-Coplanar Hierarchical Three-Body Systems,” Gongjie Li, Smadar Naoz, Bence Kocsis, and Abraham Loeb, ApJ 785, 116, 2014.

Source: Smithsonian Astrophysical Observatory

NASA, ESA Telescopes Find Evidence for Asteroid Belt Around Vega

This artist's concept illustrates an asteroid belt around the bright star Vega. Image credit: NASA/JPL-Caltech. › Full image and caption

 

Astronomers have discovered what appears to be a large asteroid belt around the bright star Vega, as illustrated here at left in brown. Image credit: NASA/JPL-Caltech . › Full image and caption -  enlarge image

PASADENA, Calif. - Astronomers have discovered what appears to be a large asteroid belt around the star Vega, the second brightest star in northern night skies. The scientists used data from NASA's Spitzer Space Telescope and the European Space Agency's Herschel Space Observatory, in which NASA plays an important role.

 The discovery of an asteroid belt-like band of debris around Vega makes the star similar to another observed star called Fomalhaut. The data are consistent with both stars having inner, warm belts and outer, cool belts separated by a gap. This architecture is similar to the asteroid and Kuiper belts in our own solar system.

What is maintaining the gap between the warm and cool belts around Vega and Fomalhaut? The results strongly suggest the answer is multiple planets. Our solar system's asteroid belt, which lies between Mars and Jupiter, is maintained by the gravity of the terrestrial planets and the giant planets, and the outer Kuiper belt is sculpted by the giant planets.

"Our findings echo recent results showing multiple-planet systems are common beyond our sun," said Kate Su, an astronomer at the Steward Observatory at the University of Arizona, Tucson. Su presented the results Tuesday at the American Astronomical Society meeting in Long Beach, Calif., and is lead author of a paper on the findings accepted for publication in the Astrophysical Journal.

Vega and Fomalhaut are similar in other ways. Both are about twice the mass of our sun and burn a hotter, bluer color in visible light. Both stars are relatively nearby, at about 25 light-years away. The stars are thought to be around 400 million years old, but Vega could be closer to its 600 millionth birthday. Fomalhaut has a single candidate planet orbiting it, Fomalhaut b, which orbits at the inner edge of its cometary belt.

The Herschel and Spitzer telescopes detected infrared light emitted by warm and cold dust in discrete bands around Vega and Fomalhaut, discovering the new asteroid belt around Vega and confirming the existence of the other belts around both stars. Comets and the collisions of rocky chunks replenish the dust in these bands. The inner belts in these systems cannot be seen in visible light because the glare of their stars outshines them.

Both the inner and outer belts contain far more material than our own asteroid and Kuiper belts. The reason is twofold: the star systems are far younger than our own, which has had hundreds of millions more years to clean house, and the systems likely formed from an initially more massive cloud of gas and dust than our solar system.

The gap between the inner and outer debris belts for Vega and Fomalhaut also proportionally corresponds to the distance between our sun's asteroid and Kuiper belts. This distance works out to a ratio of about 1:10, with the outer belt 10 times farther from its host star than the inner belt. As for the large gap between the two belts, it is likely there are several undetected planets, Jupiter-size or smaller, creating a dust-free zone between the two belts. A good comparison star system is HR 8799, which has four known planets that sweep up the space between two similar disks of debris.

"Overall, the large gap between the warm and the cold belts is a signpost that points to multiple planets likely orbiting around Vega and Fomalhaut," said Su.

If unseen planets do, in fact, orbit Vega and Fomalhaut, these bodies will not likely stay hidden.

"Upcoming new facilities such as NASA's James Webb Space Telescope should be able to find the planets," said paper co-author Karl Stapelfeldt, chief of the Exoplanets and Stellar Astrophysics Laboratory at NASA's Goddard Space Flight Center in Greenbelt, Md.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA. For more information about Spitzer, visit: http://spitzer.caltech.edu and http://www.nasa.gov/spitzer .

Herschel is a European Space Agency cornerstone mission, with science instruments provided by consortia of European institutes and with important participation by NASA. NASA's Herschel Project Office is based at JPL, which contributed mission-enabling technology for two of Herschel's three science instruments. The NASA Herschel Science Center, part of the Infrared Processing and Analysis Center at Caltech, supports the United States astronomical community. 

More information is online at: http://www.herschel.caltech.edu , http://www.nasa.gov/herschel , and http://www.esa.int/SPECIALS/Herschel/index.html .

You can follow JPL News on Facebook at: http://www.facebook.com/nasajpl and on Twitter at: http://www.twitter.com/nasajpl .

Whitney Clavin 818-354-4673

Jet Propulsion Laboratory, Pasadena, Calif.
Whitney.clavin@jpl.nasa.gov

 J.D. Harrington 202-358-5241
 NASA Headquarters, Washington
 j.d.harrington@nasa.gov

Hubble Reveals Rogue Planetary Orbit for Fomalhaut b

 

 Fomalhaut System

Credit: NASA, ESA, 

and P. Kalas (University of California, Berkeley and SETI Institute)

Release Images

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

Astronomers are surprised to find that the debris belt is wider than previously known, spanning a gulf of space from 14 billion miles to nearly 20 billion miles from the star. Even more surprisingly, the latest Hubble images have allowed a team of astronomers to calculate that 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 re-calculated from the newest Hubble observation made in 2012. "We are shocked — Fomalhaut b probably passed three times closer to the star than we previously thought, and now it is zipping outward," 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 that there may be other planet-like bodies in the system that gravitationally disturbed Fomalhaut b to place it in such a highly eccentric orbit.

His team is presenting their finding on January 8 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 into 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. This could be the planet that gets thrown out," according to co-investigator Mark Clampin of NASA's Goddard Space Flight Center in Greenbelt, Md.

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

"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," Kalas said. "But if Fomalhaut b is not co-planar with the belt, we may not see anything at all except for a gradual dimming of Fomalhaut b as it travels farther and farther from the star," he explained.

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. The planet could be between the mass of Pluto and Jupiter, but the optical brightness possibly originates from a ring or shroud of dust around the planet, reflecting starlight. The dust is rapidly produced by satellites orbiting the planet, which 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 called Phoebe," Kalas said.

The team has also considered a different scenario where a hypothetical second dwarf planet suffered a catastrophic collision with Fomalhaut b. Kalas explained, "The collision scenario would provide a solution as to why Fomalhaut (the star) 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."

Two previous papers have confirmed Fomalhaut b's existence as derived in the previous Hubble observations.

"Fomalhaut is a rather special system because it looks like we have a snapshot of what our solar system was doing 4 billion years ago," Kalas said. "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.

CONTACT

Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4514
villard@stsci.edu

Paul Kalas
University of California, Berkeley, Calif.
510-642-8285
kalas@astron.berkeley.edu

Dust Models Paint Alien's View of Solar System

These images, produced by computer models that track the movement of icy grains, represent infrared snapshots of Kuiper Belt dust as seen by a distant observer. For the first time, the models include the effects of collisions among grains. By ramping up the collision rate, the simulations show how the distant view of the solar system might have changed over its history. Credit: NASA/Goddard/Marc Kuchner and Christopher Stark. View larger - View unlabeled version

Simulated images of the ancient Kuiper Belt bear a striking resemblance to this Hubble Space Telescope view of the dusty ring around Fomalhaut, a young star located 25 light-years away in the constellation Piscis Austrinus. In 2008, Hubble spotted a planet orbiting inside the ring. The bright central star is masked out so that the faint ring can be seen. Credit: NASA/ESA/P. Kalas (Univ. of California, Berkeley) et al. View larger

New simulations of icy grains moving through the solar system reveal how the ancient Kuiper Belt once appeared strikingly similar to the dusty rings found around some stars today. Credit: NASA's Goddard Space Flight Center. Video formats

New supercomputer simulations tracking the interactions of thousands of dust grains show what the solar system might look like to alien astronomers searching for planets. The models also provide a glimpse of how this view might have changed as our planetary system matured.

"The planets may be too dim to detect directly, but aliens studying the solar system could easily determine the presence of Neptune -- its gravity carves a little gap in the dust," said Marc Kuchner, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md. who led the study. "We're hoping our models will help us spot Neptune-sized worlds around other stars."

fragile grains. A paper on the new models, which are the first to include collisions among grains, appeared in the Sept. 7 edition of The Astronomical Journal.

"People felt that the collision calculation couldn't be done because there are just too many of these tiny grains too keep track of," Kuchner said. "We found a way to do it, and that has opened up a whole new landscape."

With the help of NASA's Discover supercomputer, the researchers kept tabs on 75,000 dust particles as they interacted with the outer planets, sunlight, the solar wind -- and each other.

The size of the model dust ranged from about the width of a needle's eye (0.05 inch or 1.2 millimeters) to more than a thousand times smaller, similar in size to the particles in smoke. During the simulation, the grains were placed into one of three types of orbits found in today's Kuiper Belt at a rate based on current ideas of how quickly dust is produced.

From the resulting data, the researchers created synthetic images representing infrared views of the solar system seen from afar.

Through gravitational effects called resonances, Neptune wrangles nearby particles into preferred orbits. This is what creates the clear zone near the planet as well as dust enhancements that precede and follow it around the sun.

"One thing we've learned is that, even in the present-day solar system, collisions play an important role in the Kuiper Belt's structure," Stark explained. That's because collisions tend to destroy large particles before they can drift too far from where they're made. This results in a relatively dense dust ring that straddles Neptune's orbit.

To get a sense of what younger, heftier versions of the Kuiper Belt might have looked like, the team sped up the dust production rate. In the past, the Kuiper Belt contained many more objects that crashed together more frequently, generating dust at a faster pace. With more dust particles came more frequent grain collisions.

Using separate models that employed progressively higher collision rates, the team produced images roughly corresponding to dust generation that was 10, 100 and 1,000 times more intense than in the original model. The scientists estimate the increased dust reflects conditions when the Kuiper Belt was, respectively, 700 million, 100 million and 15 million years old.

"We were just astounded by what we saw," Kuchner said.

As collisions become increasingly important, the likelihood that large dust grains will survive to drift out of the Kuiper Belt drops sharply. Stepping back through time, today's broad dusty disk collapses into a dense, bright ring that bears more than a passing resemblance to rings seen around other stars, especially Fomalhaut.

"The amazing thing is that we've already seen these narrow rings around other stars," Stark said. "One of our next steps will be to simulate the debris disks around Fomalhaut and other stars to see what the dust distribution tells us about the presence of planets."

The researchers also plan to develop a more complete picture of the solar system's dusty disk by modeling additional sources closer to the sun, including the main asteroid belt and the thousands of so-called Trojan asteroids corralled by Jupiter's gravity.

Related Links:

Geeked on Goddard: Bodies in motion
NASA Supercomputer Shows How Dust Rings Point to Exo-Earths
Twin Keck Telescopes Probe Dual Dust Disks
Warped Debris Disks around Stars are Blowin’ in the Wind

Goddard Release No. 10-085

Francis Reddy
NASA's Goddard Space Flight Center
301-286-4453
francis.j.reddy@nasa.gov