A Possible Planet around Fomalhaut

Watching the motion of the stars they orbit has been how most of the planets beyond our Sun have thus far been discovered. Such radial-velocity methods are getting more precise all the time, but a likely planet around the nearby star Fomalhaut comes out of an entirely different line of research. Alice Quillen (University of Rochester) is an expert on stellar disks and the planets that help to shape them. And she has learned to predict a planet’s size and position from her studies.

In the case of Fomalhaut, Quillen worked with Hubble Space Telescope imagery showing the star’s surroundings in greater detail than ever before. The Hubble images took advantage of a coronagraph to mask the light of the star to bring out detail in the dimmer ring, confirming what astronomers had previously noted — Fomalhaut is off-center within its ring.

Image: Hubble’s view of Fomalhaut’s dust ring. Credit: University of Rochester/STScI.

Quillen’s models examine ring/planet interactions for young stars, around which the dust is fine enough to act much like a fluid, and older stars where larger bodies have begun to form. The Fomalhaut offset, more than 15 times the distance between Earth and the Sun, suggests a hidden planet in a highly eccentric orbit. Quillen has this to say:

“Something had to skew that planet, and that’s what we’re working on now. There may have been fantastic planetary collisions early on that changed their orbits. We’re working on figuring out how many more planets of what size you’d need to account for that elliptical orbit, and to account for why there is no other dust inside that ring.”

We won’t know for sure whether Quillen and team are right until we’ve got the tools to make an actual detection. At 25 light years from Earth, Fomalhaut is likely to receive detailed study by coronagraph or starshade technologies on future planet-hunter missions. But don’t be surprised if a Neptune-class world fitting Quillen’s increasingly fine-tuned model turns up in the system there. Up tight against the inner side of the ring, its presence would explain nicely how ring dust is being so clearly displaced.

The paper is Hosseinbor, Quillen et al., “The formation of an eccentric gap in a gas disc by a planet in an eccentric orbit,” Monthly Notices of the Royal Astronomical Society (OnlineEarly Articles), with abstract available.

Comments on this entry are closed.

• djlactin June 16, 2007, 22:25

Whoa! Wait a minute!

1) When we look at an ellipse from an angle, the true focus is displaced from where we would expect it to be: it’s not at a focus of the projected ellipse that we ‘see’. (Classic example is position of Sirius A relative to the orbit of Sirius B).

Have the authors corrected for viewing angle? (And how could they?)

2) Why expect Fomalhaut to be at the centre of an elliptical ring? It is at one of 2 (off-centre) foci. If the ellipse has high eccentricity, the off-centre location is no surprise.

• djlactin June 16, 2007, 23:09

Having done some internet searching…

I also note that Fomalhaut has a fainter companion star TW Pisces Austrini, which is separated by a distance of less than 1 light year and has the same proper motion. What effects could this critter have on the shape and location of F’s disk?

• Adam June 17, 2007, 0:59

Hi djlactin

Give the researchers some credit – they would’ve thought of all your objections. And the thing about “rings” is that any eccentricity is quickly erased by the natural processes of dispersion that govern dust in all systems – perturbation, the Yarkovsky effcct and the Poynting-Robertson effect. A circular ring is a natural end state for a system of dust – anything else has to be actively maintained by something more substantial, like a planet’s gravity. The appearance of dust-rings and Kuiper Belts have been extensively modelled, so the researchers have a pretty good idea of what they’re looking at.

• djlactin June 17, 2007, 2:31

Admin: the quote that you give in the entry does not occur in the paper. What is the true source?

The authors barely mention Fomalhaut (a single glancing reference in the Discussion) and do not make any explicit claim about the presence of a planet.

“…the thing about “rings” is that any eccentricity is quickly erased…”

Therefore, I suggest that we are observing a circular disk from a skewed angle. (I know my earlier post spoke of an ellipse, but I am allowed to modify my hypotheses! )

Call me a skeptic (and I am), but models are hypotheses: they still need to be tested by observation.

• Juan June 17, 2007, 4:29

Unrelated to this post: SF writer Charles Stross wrote an interesting essay on the futility of interstellar colonization.
http://www.antipope.org/charlie/blog-static/2007/06/the_high_frontier_redux.html
Would love to see a response here…

• Adam June 17, 2007, 8:17

Hi djlactin

Science would be dull if our hypotheses were always right! ;-)

Just making sure your scepticism was reasonable – I see too much knee-jerk scepticism around the fora.

• djlactin June 17, 2007, 10:43

(you may notice that i post in clusters.)

Can we be sure that the faint dot near the centre is Fomalhaut? After all, the image used a coronagraph.

It seems awfully dim for a first-magnitude star.

• Administrator June 17, 2007, 13:23

djlactin asks the source of the Quillen quote. It’s from this University of Rochester news release:

http://www.rochester.edu/news/show.php?id=2928

Be aware also of Quillen, “Predictions for a planet just inside Fomalhaut’s eccentric ring,” also in MNRAS Volume 372, Issue 1, pp. L14-L18. From the abstract: “We propose that the eccentricity and sharpness of the edge of Fomalhaut’s disc are due to a planet just interior to the ring edge.”

• Administrator June 17, 2007, 14:01

Good idea, Juan. Stross is always worth looking at, and I’ll see if we can’t get to this essay soon.

• Edg Duveyoung June 17, 2007, 14:44

Stross sure is a party pooper. Makes clear just how far tech has to advance before we can even begin to think we’re masters of space.

Sudden idea though from this reading: The moon might be our escape vehicle! It seems to me that the moon is close enough to terriform in the next 100 years, or so. Then, a million years from now when the sun starts swelling up, we’ll have the tech to make the moon into our hollowed out space ship, and we’ll fit all the earthlings inside it and off we’ll go watching the earth burn to a crisp.

Sure, a million years from now, we’ll have “had at” mars and beyond, but when the sun finally does go nova, we’d have a tough time even on a terriformed sub-planet 50 AUs out. And with our moon being so close, the cost of getting everyone to it and nice and comfy seems much more doable.

Hollowed out, haven’t done the math, but it seems the moon would be a nice BIG place for all of us to fit.

As for what kind of propulsion we’d have for the moonship, well, maybe by then Bussard’s engine will be perfected.

Edg

• Athena June 17, 2007, 19:43

Juan, Paul — I read the Stross essay, and its 200+ responses (I even posted one). There can be no quarrel with his numbers, but they are all based on current technology.

I have been thinking about the issue of human (crewed) exploration of space for a long time, both as a biologist and a space exploration aficionado. You can see some of my views in my Making Aliens essay (written in 6 parts, starting here: Making Aliens 1

Perhaps we can craft an essay that tackles this question from several angles (engineering, biology, culture…) What do you think, people?

• Edg Duveyoung June 17, 2007, 21:02

http://tinyurl.com/2s2l3q

Edg

• ljk June 18, 2007, 9:34

A revised paper on the possible exoplanet around Fomalhaut
may be found online here:

http://arxiv.org/abs/astro-ph/0605372

• ljk June 18, 2007, 9:41

This really needs to be in its own topic, but regarding Mr. Stross’
argument that we will never colonize the galaxy – he’s right. We
will never colonize the Milky Way or beyond in our current human
form. It is absurd to think that we will remain as we are in the
biological sense by the time such undertakings are truly possible.

The first true interstellar voyagers will be what we now call artificial,
though what makes them any more “fake” than we? Even the first
probes to head out for the stars, even though they will take ages to
get anywhere in the galaxy, were robots, not crewed vessels.

We will either become/create our next stage in evolution and it will
not be humans with bigger bald heads. It will be radical. We cannot
continue as we are and think/hope that Earth is going to accomodate
our wanton need for resources and our endless need to be a bunch
of territorial animals. We will change or create something very
different that will become the next true intelligence on this planet,
or we will go extinct.

• Administrator June 18, 2007, 13:12

I think Freeman Dyson would agree with much of this, Larry. And you’re right — we do need a separate topic on it. I can’t get to the Stross story until tomorrow afternoon, but I’ll post a short filler topic right now where comments can collect until the larger post goes online.

• ljk June 23, 2007, 8:54

Vortex generation in protoplanetary disks with an embedded giant planet

Authors: M. de Val-Borro, P. Artymowicz, G. D’Angelo, A. Peplinski

(Submitted on 21 Jun 2007)

Abstract: Vortices in protoplanetary disks can capture solid particles and form planetary cores within shorter timescales than those involved in the standard core-accretion model. We investigate vortex generation in thin unmagnetized protoplanetary disks with an embedded giant planet with planet to star mass ratio $10^{-4}$ and $10^{-3}$. Two-dimensional hydrodynamical simulations of a protoplanetary disk with a planet are performed using two different numerical methods. The results of the non-linear simulations are compared with a time-resolved modal analysis of the azimuthally averaged surface density profiles using linear perturbation theory. Finite-difference methods implemented in polar coordinates generate vortices moving along the gap created by Neptune-mass to Jupiter-mass planets. The modal analysis shows that unstable modes are generated with growth rate of order $0.3 \Omega_K$ for azimuthal numbers m=4,5,6, where $\Omega_K$ is the local Keplerian frequency. Shock-capturing Cartesian-grid codes do not generate very much vorticity around a giant planet in a standard protoplanetary disk. Modal calculations confirm that the obtained radial profiles of density are less susceptible to the growth of linear modes on timescales of several hundreds of orbital periods. Navier-Stokes viscosity of the order $\nu=10^{-5}$ (in units of $a^2 \Omega_p$) is found to have a stabilizing effect and prevents the formation of vortices. This result holds at high resolution runs and using different types of boundary conditions. Giant protoplanets of Neptune-mass to Jupiter-mass can excite the Rossby wave instability and generate vortices in thin disks. The presence of vortices in protoplanetary disks has implications for planet formation, orbital migration, and angular momentum transport in disks.

Comments: 14 pages, 15 figures, accepted for publication in A&A

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0706.3200v1 [astro-ph]

Submission history

From: Miguel de Val-Borro [view email]

[v1] Thu, 21 Jun 2007 19:00:55 GMT (573kb,D)

http://arxiv.org/abs/0706.3200

• ljk June 28, 2007, 23:47

Telescope limitation could reveal exoplanets (Jun 22)

Astronomers in the UK, the US and Germany are the first to use a new
data-analysis technique that could boost a telescope’s ability to search
for “exoplanets” — planets outside our solar system. Surprisingly, the
technique makes clever use of the diffraction of light, an effect that
had previously prevented telescopes from resolving many exoplanets from
their parent stars. The astronomers used the technique to get a combined
image and spectrum of a faint star 48 light-years away (Astrophys. J. in
press).

• ljk June 29, 2007, 12:35

Gap Formation in the Dust Layer of 3D Protoplanetary Disks

Authors: S. T. Maddison (1), L. Fouchet (2 and 3), J.-F. Gonzalez (2) ((1) Swinburne, Australia, (2) CRAL, Lyon, France, (3) ETH, Zurich, Switzerland)

(Submitted on 28 Jun 2007)

Abstract: We numerically model the evolution of dust in a protoplanetary disk using a two-phase (gas+dust) Smoothed Particle Hydrodynamics (SPH) code, which is non-self-gravitating and locally isothermal. The code follows the three dimensional distribution of dust in a protoplanetary disk as it interacts with the gas via aerodynamic drag. In this work, we present the evolution of a disk comprising 1% dust by mass in the presence of an embedded planet for two different disk configurations: a small, minimum mass solar nebular (MMSN) disk and a larger, more massive Classical T Tauri star (CTTS) disk. We then vary the grain size and planetary mass to see how they effect the resulting disk structure. We find that gap formation is much more rapid and striking in the dust layer than in the gaseous disk and that a system with a given stellar, disk and planetary mass will have a different appearance depending on the grain size and that such differences will be detectable in the millimetre domain with ALMA. For low mass planets in our MMSN models, a gap can open in the dust disk while not in the gas disk. We also note that dust accumulates at the external edge of the planetary gap and speculate that the presence of a planet in the disk may facilitate the growth of planetesimals in this high density region.

Comments: 5 page, 4 figures. Accepted for publication in Astrophysics & Space Science

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0706.4248v1 [astro-ph]

Submission history

[v1] Thu, 28 Jun 2007 15:45:06 GMT (2000kb,D)

http://arxiv.org/abs/0706.4248

• ljk April 12, 2009, 23:37

The spin-orbit alignment of the Fomalhaut planetary system probed by optical long baseline interferometry

Authors: Jean-Baptiste Le Bouquin (ESO), Olivier Absil, Myriam Benisty, Fabrizio Massi, Antoine Merand (ESO), Stan Stefl (ESO)

(Submitted on 10 Apr 2009)

Abstract: We discuss the spin-orbit orientation of the Fomalhaut planetary system composed of a central A4V star, a debris disk, and a recently discovered planetary companion. We use spectrally resolved, near-IR long baseline interferometry to obtain precise spectro-astrometric measurements across the brG absorption line. The achieved astrometric accuracy of 3 nu-as and the spectral resolution R=1500 from the AMBER/VLTI instrument allow us to spatially and spectrally resolve the rotating photosphere.

We find a position angle PAstar=65deg pm 3deg for the stellar rotation axis, perfectly perpendicular with the literature measurement for the disk position angle (PAdisk=156deg pm 0.3deg). This is the first time such test can be performed for a debris disk, and in a non-eclipsing system. Additionally, our measurements suggest unexpected backward-scattering properties for the circumstellar dust grains.

Our observations validate the standard scenario for star and planet formation, in which the angular momentum of the planetary systems are expected to be collinear with the stellar spins.

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Cite as: arXiv:0904.1688v1 [astro-ph.SR]

Submission history

From: Jean-Baptiste Le Bouquin [view email] [via CCSD proxy]

[v1] Fri, 10 Apr 2009 13:44:46 GMT (289kb)

http://arxiv.org/abs/0904.1688

• ljk October 26, 2012, 9:36

25 October 2012

** Contact information appears below. **

Text, images, and video:

http://www.nasa.gov/mission_pages/hubble/science/fomalhaut-exo.html

NEW STUDY BRINGS A DOUBTED EXOPLANET ‘BACK FROM THE DEAD’

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.

Contact:

Francis Reddy
+1 301-286-4453
francis.j.reddy@nasa.gov

“Direct Imaging Confirmation and Characterization of a Dust-Enshrouded Candidate Exoplanet Orbiting Fomalhaut,” by Thayne Currie et al.:

http://arxiv.org/abs/1210.6620

“The Case of the Missing Planet” (05.29.12):

http://www.spitzer.caltech.edu/explore/blog/245-The-Case-of-the-Missing-Planet

“Hubble Directly Observes a Planet Orbiting Another Star” (11.13.08):

http://www.nasa.gov/mission_pages/hubble/science/fomalhaut.html