Beta Pictoris

Sky & Telescope, IAU, ESO






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Beta Pictoris can be found near
the center of Constellation Pictor,
the Painter's Easel, as its
second brightest star (more).

The star is the title member of the Beta Pictoris Moving Group of at least 17 star systems (plus possibly 20 or more additional members discovered since 2001), that are all around 12 million years old and include a ~35 Jupiter-mass brown dwarf "and a wide assortment of dusty circumstellar disks ... [which Zuckerman et al found constitutes] "the comoving, youthful group closest to Earth" (Kiss et al, 2010; Lépine and Simon, 2009; Kaisler et al, 2004; Kastner et al, 2003; and Zuckerman et al, 2001).

Luis Calçada, Nick Risinger, ESO




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Beta Pictoris has circumstellar
dust disks and at least one
giant planet more).

In 1983, astronomers using the Infrared Astronomical Satellite (IRAS) discovered a circumstellar dust disk around this star which was photographed from the ground by the following year (Smith and Terrile, 1984). Subsequent observations suggested the presence of at least two giant planets in outer orbits (details below). On May 7, 2007, astronomers modelling the vertical thickness and dust production in the star's circumstellar "debris" disk based on Hubble observations submitted a paper arguing that its disk likely contains planetary embryos as large as Pluto that are undergoing runaway growth into larger bodies (Quillen et al, 2007 -- more below). On June 10, 2010, astronomers announced that they have been able to directly image and follow the orbital motion of Jupiter-class planet "b," as it moves from one side of its Beta Pictoris to the other. (ESO new release; Lagrange et al, 2010; and Quanz et al, 2010 -- more below).

---------------------------------------------- [Guide] -- [Larger] ----------------------------------------------

	Orbital Distance (a=AUs)	Orbital Period (P=years)	Orbital Eccentricity (e)	Orbital Inclination (i=degrees)	Mass (Earths)	Diameter (Earths)	Density (Earths)	Surface Gravity (Earths)	Metallicity (Solar)
Beta Pictoris	0.0	...	...	...	530,000	150	...	...	~1
Inner H.Z. Edge?	1.908	2.0	0.0	...	...	...	...	...	...
Outer H.Z. Edge?	3.944	5.92	0.0	...	...	...	...	...	...
Innermost Silicate Belt	6.4	...	...	~10?	...	...	...	...	...
Planet "b"	8-15	17-44	<0.05?	3	2-3,500	...	...	...	...
Middle Silicate Belt	~16	...	...	~10?	...	...	...	...	...
Outermost Silicate Belt	~30	...	...	~10?	...	...	...	...	...
Inner Cometary Belt	52 +/- 2	...	...	10-14?	...	...	...	...	...
Planet "c?"	~70	<450	...	~11.5	3,200?	...	...	...	...
Outer Cometary Belt	82 +/- 2	...	...	10-14?	...	...	...	...	...
Outer Dust Disk Edge	>725	...	...	14 +/- 4	...	...	...	...	...

The Star

Beta Pictoris is a bluish white main sequence dwarf star of spectral and luminosity type A5 V, but has been previously classified as A3. It is also classified as a "shell star" because it is surrounded by a shell of mostly hydrogen gas. The star may have about 1.75 times Sol's mass (Lagrange et al, 2010), 1.4 times its diameter, and 8.7 times its luminosity. The star may be as enriched than Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron (Heap et al, 1995). It appears to only be around 12 million years old, as it is part of a stellar moving group that includes 16 other star systems (Zuckerman et al, 2001; ESO new release; and Lagrange et al, 2010). Useful catalogue numbers and designations for the star include: Bet Pic, HR 2020*, Gl 219, Hip 27321, HD 39060, CD-51 1620, CP(D)-51 774, and SAO 234134.

DSS 2, ESO



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Beta Pictoris is a young
bluish white star lying
around 63 light-years
away (more).

Habitable Zone

According to one type of model used in calculations for the NASA Star and Exoplanet Database, the habitable zone orbits of an Earth-like planet (with liquid water) around Beta Pictoris may range between 1.908 to 3.944 AUs -- between the orbital distances of Mars and the Main Asteroid Belt in the Solar System. Assuming that the mass of Beta Pictoris is 1.75 Solar-masses, then such orbital periods could range from around 2.0 years (728 days) to 5.9 years (2,162 days). Astronomers are hoping that they will eventually be able to use NASA's Terrestrial Planet Finder (TPF) and the ESA's Darwin planned groups of observatories to search for a rocky inner planet in the so-called "habitable zone" (HZ) around Upsilon Andromedae A. Now indefinitely postponed, the TPF would include two complementary observatory groups, a visible-light coronagraph and and a "formation-flying" infrared interferometer, while Darwin would launch a flotilla of three mid-infrared telescopes and a fourth communications hub.

The orbit of an Earth-like planet (with liquid water) around the star may be centered around 2.9 AU -- around the central orbital distance of the Main Asteroid Belt in the Solar System -- with an orbital period just under 3.8 years. Even if an Earth-sized planet has already formed around young Beta Pictoris, it is unlikely to have cooled off sufficiently to have formed crustal rock. After it cools off enough for life to develop, only primitive single-cell, anaerobic bacteria is likely survive under constant bombardment by meteorites and comets as Earth was for the first billion years of existence. Since there is unlikely to be free oxygen in the atmosphere of such a planet, it probably would not have an ozone layer (O₃) although Beta Pictoris puts out a lot more hard radiation (especially ultraviolet) than Sol. Astronomers would find it very difficult to detect an Earth-sized planet of this star using present methods.

Dust Disk

A circumstellar disk of dust and gas was first detected around Beta Pictoris in 1983 (Lagrange et al, 1996). Rather than a remnant from the original protoplanetary disk, the structure is now thought to be a "debris" disk of relatively cold dust from the collision of planetesimals and cometary bodies (Okamoto et al, 2004). Initially estimated to around 1,100 AUs in width, some 10 times the size of the known Solar System, the disk is now thought to be even larger at more than 1,450 AUs across (Lagrange et al, 2010) and is probably also much more massive than the disk that the Solar System formed out of. Oddly enough, the outer disk has elliptical rings, and one side of the disk is 20 percent longer and thinner than the other, which may have been caused by the close passage of a red dwarf star (2000 press release).

Submillimetre Common-User Bolometer Array, James Clerk Maxwell Telescope, JAC
(The smaller blob at lower right may be a dusty companion planet or brown dwarf.)

This disk around Beta Pictoris is probably connected with a planetary system. The disk does not start at the star. Rather, its inner edge begins around 25 AUs away, farther than the average orbital distance of Uranus in the Solar System. Its outer edge appears to extend as far out as 725 AUs (rather than the initial estimate of 550 AUs) away from the star.

Interestingly, most dust grains in the disk are not agglomerating to form larger bodies; instead, they are eroding and being moved away from the star by radiation pressure when their size goes below about 2-10 microns. Theoretically, this disk should have lasted for only around 10 million years. That it has persisted for the 20 to 200 million year lifetime of Beta Pictoris may be due to the presence of large disk bodies (i.e., planets) that collide with icy Edgeworth-Kuiper Belt type objects (dormant comets) to replenish the dust (Pawel Artymowicz, 1989). Indeed the variability in the star's brightness has been tentatively attributed to its occultation (partial eclipse) by at least one orbiting planet. Indeed, years of monitoring of transient spectral absorption events have been interpreted as resulting from the transit across the line of sight from Earth of kilometer-sized (0.6 mile-sized) bodies that are evaporating as they graze Beta Pictoris. These numerous star-grazers are thought to originate from 4:1, and possibly 3:1, mean-motion resonances with a massive, Jupiter-sized planet moving between 10 and 20 AUs away from the Star in a mildly eccentric orbit (e~ 0.1) (Thébault and Beust, 2001).

Keck Observatory, S.R. HEAP/STScI, NASA -- larger image



TOP - Three disk features are labelled in this infrared image of the dust disk at 18 microns. Misalignment of dust emission intensity contours (at "A") with respect to the outer disk suggests that the inner disk is "warped."


BOTTOM - Vertically exaggeration of an image using reflected light from Beta Pictoris by the Hubble Space Telescope shows a warp in the outer disk in the opposite direction from the inner disk.


Thus, the star seems to have an inner disk with a radius of five to 30 AUs and an orbital inclination that is tilted 14 +/- 4 degrees with respect to the larger outer disk and warped in the opposite direction. "B" is the center of one of two disk lobes equidistant from the star that is consistent with a 40-AU-radius, dusk ring at the bright inner edge of the outer disk. "C" is a dust peak that may be associated with a dust ring that is even farther out, but whose counterpart on the other side of the star is not very bright in the Keck image.

In April 2002, two teams of astronomers announced that dust confined to a Solar-System sized region close to the star orbits in a plane that is tilted by about 14 degrees relative to the outer disk. The inner "warp" in the disk is in the opposite direction from that of a larger warp previously detected in the outer disk. This double warp may be be due to the presence of one or more unseen planets.

Keck Observatory -- larger simulated image


TOP - Computer illustration shows the infrared
emission from the dust around Beta Pictoris
when viewed at 10 degrees above the disk plane.


BOTTOM - View along the actual line of sight
from Earth to the star (more discussion).

Spectroscopy was used to spread infrared emission from the dust into component wavelengths (like the way that a prism reveals the colors in visible light). Analysis of the inner disk suggests that it is composed of small particles of silicates that are hotter than expected. If a planet is warping the inner disk, it may be causing more collisions of rocks in its neighborhood that result in very small grains and tend to be hotter at the same distance from the star than larger dust grains. In contrast, dust emission from the outer part of the disk appears to come either from larger grains or from dust that is composed of something other than silicates.

D. Golimowski, D. Ardila , J. Krist, M. Clampin , H. Ford, and G. Illingworth,
ACS Science Team, ESA, NASA -- larger image.

Beta Pictoris appears to have another fainter disk that has been created
by the gravitational tug of a Jupiter-class planet (hubblesite.org).

On June 27, 2006, astronomers using the Hubble Space Telescope announced that an odd warp in the young star's known dust disk may actually be another fainter, inclined disk. They have imaged a distinct secondary disk that is tilted by about four degrees from the main disk, which is visible out to 260 AUs from Beta Pictoris but probably extends even farther. Their best explanation for the presence of the second disk is that an unseen planet with as much as 20 times the mass of Jupiter in an orbit within the secondary disk is gravitationally sweeping up dust and icy planetesimals from the primary disk (more from hubblesite.org).

Lynette Cook (Artwork from Extrasolar Planets), FUSE, NASA


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High amounts of carbon dioxide have been found around Beta Pictoris,
which suggests that carbon-rich planets may be forming in the outer
region of the disk that is cold enough to prevent oxygen from "burning
up" vaporized carbon dust, while water-rich planets develop closer to
the star (more).

On June 7, 2006, scientists using NASA's Far Ultraviolet Spectroscopic Explorer (FUSE) announced the discovery of "abundant amounts of carbon gas" in the dusty disk surrounding Beta Pictoris. The abundance of carbon gas in the disk suggests that any planets forming around the star "could be carbon-rich worlds of graphite and methane ....", On the other hand, young Beta Pictoris may simply resemble the Solar System in its early years. Although today's asteroids and comets do not appear particularly carbon-rich, some researchers believe that certain meteorites called enstatite chondrite meteorites formed in a carbon-rich environment, while other scientists believe that Jupiter developed a carbon core in the carbon-rich outer region of Sol's primeval dust disk (NASA news release; Kuchner and Seager, 2005; and Katherina Lodders, 2004).

Silicate and Cometary Belts

On October 7, 2004, a team of Japanese astronomers (led by Yoshiko Okamoto) announced the discovery of an innermost ring of silicate dust around Beta Pictoris. Their spectrographic data of relatively warm dust indicated that a belt of planetesimals or asteroids is located around 6.4 AUs from the star, within two already known outer belts at 16 and 30 AUs out, and even more distant, icier belts at 52 and 82 AUs out discovered in 2003. The inner belts of warm silicate dust are tilted about 4.6 degrees to the exterior, main disk. Moreover, the lack of similar dust between 6.4 and 16 AUs suggested that a planet may be orbiting Beta Pictoris at around 12 AUs out. (More discussion from: Telesco et al, 2005; Robert Burnham, Astronomy.com, October 7, 2004; Okamoto et al, 2004; and Wahhaj et al, 2003).

ISAS / JAXA




Larger illustration.




An innermost belt of silicate dust
has been found around 6.4 AUs from
Beta Pictoris, within two outer belts
at 16 and 30 AUs (more).

A Planetary System?

© Estate of John Whatmough -- larger image
(Artwork from Extrasolar Visions, used with permission from Whatmough)

A massive planet or brown dwarf "b" is warping the inner
dusk disk around Beta Pictoris, as imagined by Whatmough.

Planet "b" - On June, 10, 2010, astronomers finally announced visual confirmation that the warp in the inner dust disk is caused by the presence of a Jupiter-class planet ("b"), which had been predicted to be moving along a slightly inclined orbit (3°) within 20 AU of the star (Krist et al, 1996) that should take less than 67 years to complete. Indeed, the inner edge of the dust disk is apparently being cleared by this planet. As of June 10, 2010, the mass of planet b was estimated from photographic images to have a more precise mass of around 9 +/- 3 Jupiter-masses with a semi-axis of orbit distance between eight to 15 AUs of Beta Pictoris ("assuming a moderate eccentricity" of e < 0.05) (ESO new release; Lagrange et al, 2010; and Quanz et al, 2010) -- which can be calculated to have an orbital period of 17 to 44 years .

Lagrange et al, 2008, NACO, VLT, ESO





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infrared images.





A giant planet "b" (with around nine Jupiter-masses)
was initially imaged about eight AUs from Beta
Pictoris, within its circumstellar disk (more.)

On November 21, 2008, a team of astronomers (including Anne-Marie Lagrange, Gael Chauvin, David Ehrenreich, David Mouillet, Damien Gratadour, Gérard Rousset, Daniel Rouan, Eric Gendron, Thierry Fusco, Laurent Mugnier, Nicole Allard, and the NAOS Consortium) announced that they may have imaged a giant planet "b" in orbit around Beta Pictoris using the European Southern Observatory's Very Large Telescope (ESO press release, and Lagrange et al, 2008). Although intensely radiating infrared light with the heat of formation at around 1,500 degrees Kelvin, the planetary candidate is still roughly a thousand times dimmer than its hypothesized parent star. If the object is a true planetary companion, then it may have around eight Jupiter-masses.

Unknown artist, ESO



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Beta Pictoris "b" was still the
closest orbiting extra-Solar planet
to be imaged directly as of June
10, 2010 (more.)

According to a paper submitted for publication in March 2009, planetary candidate b may have been observed to transit Beta Pictoris on November 10, 1981, which was recorded by the Geneva Observatory in Switzerland as having produced "strong and rapid photometric variations." By the mid-1990s, astronomers had published papers suggesting that the dimming of Beta Pictoris in 1981 was due either to the transit of a giant comet (Lamers et al, 1997) or of a planet in front of the star (Lecavelier des Etangs, 1997; Lecavelier des Etangs, 1995; and Lecavelier des Etangs, 1994). If planet b did transit the star in 1981, then it should have an average orbital distance from Beta Pic of 7.6 to 8.7 AUs and a period of 15.9 to 19.5 years, assuming a mild orbital eccentricity of e= 0.1 (Lecavelier des Etangs and Vidal-Madjar, 2009; and New Scientist, March 30, 2009).

The object was initially found around eight AUs from Beta Pictoris within the relative central void (which has a diameter around 50 AUs) of the star's circumstellar dust disk. Supporting the possibility that the object is an orbiting planet, it is also located along the plane of the disk and is "consistent with the morphological and dynamical percularities" of the disk (Lagrange et al, 2008). New observations are planned to rule out the possibility that the object is instead a foreground or background object, which has already been rejected by archival images taken with the Hubble Space Telescope (ESO press release; Lagrange et al, 2008; and Astronomy Picture of the Day).

Luis Calçada, ESO




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Planet b has around nine
Jupiter-masses and
orbits within eight to 15 AUs
of Beta Pictoris more).

On June 10, 2010, astronomers working with the European Southern Observatory (ESO) announced that they have been able to directly follow the orbital motion of Jupiter-class planet "b," as it moves from one side of its Beta Pictoris to the other. Beta Pictoris b has been confirmed as having the smallest orbit so far of all directly imaged extra-Solar planets ("exoplanets") thus far. Orbiting its host star almost as close as Saturn does around our Sun, Sol, planet b may have formed in a similar way to the giant planets in the Solar System. As Beta Pictoris has been estimated to be only around 12 million years old, the discovery of planet b proves that gas giant planets can form within a star's circumstellar dust ("debris") disk within only a few million years, which is a short time in astronomical terms (ESO new release; and Lagrange et al, 2010).

Anne-Marie Lagrange, NACO, VLT, ESO




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Planet "b" has been imaged in orbit
on both sides of Beta Pictoris (more).