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Beta Pictoris b
The motion of Beta Pictoris b. The orbital plane is viewed side-on; the planet is not moving towards the star.
Discovery
Discovered byLagrange et al.
Discovery siteVery Large Telescope
Discovery dateNovember 18, 2008
Direct imaging
Orbital characteristics[1]
10.03+0.11
−0.10 AU
Eccentricity0.1094±0.0077
23.593+0.248
−0.209[2] years
Inclination88.991°±0.014°
31.773°±0.015°
2448022.339+15.635
−24.710[2]
212.5°+7.2°
−6.4°
Semi-amplitude79+16
−14 m/s[2]
StarBeta Pictoris
Physical characteristics
1.43±0.07[1][note 1] RJ
Mass10.02±0.29[3] MJ
4.46+0.02
−0.04[1][note 1] cgs
8.7±0.8[4] hours
Equatorial rotation velocity
19.9±1.0 km/s[4]
Temperature1607.45+4.85
−6.20 K (1,334 °C; 2,433 °F)[1][note 1]

Beta Pictoris b (abbreviated as β Pic b) is an exoplanet orbiting the young debris disk, A-type main sequence star, Beta Pictoris located approximately 63 light-years (19.4 parsecs, or 6×1014 km) away from Earth in the constellation of Pictor. It has a mass of around 13 Jupiter masses and a radius that's around 46% larger than Jupiter's. It orbits at 9 AU from Beta Pictoris, which is about 3.5 times farther than the orbit of Beta Pictoris c.[5] It orbits close to the plane of the debris disk orbiting the star, with a low eccentricity and a period of 20–21 years.

Physical characteristics

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Mass, radius and temperature

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Beta Pictoris b is a super-Jupiter, an exoplanet that has a radius and mass greater than that of the planet Jupiter. It has a temperature of 1,724 K (1,451 °C; 2,644 °F), most likely due to its dusty atmosphere and mass (normally it would be much colder). It has a mass between 9 and 13 Jupiter masses (MJ),[6] and a radius of 1.46 RJ.[7] In 2018, a study directly measured the astrometric perturbation of Beta Pictoris by Beta Pictoris b, one of the first examples of an exoplanet being measured directly by its astrometric perturbation. Its mass was directly measured as 11±2 MJ.[6]

Host star

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Main article: Beta Pictoris

The planet orbits an (A-type) star named Beta Pictoris. The star has a mass of 1.75 solar masses (M☉) and a radius of 1.8 solar radii (R☉). It has a surface temperature of 8056 K and is 12 million years old. In comparison, the Sun is about 4.6 billion years old[8] and has a surface temperature of 5778 K.[9] It is slightly metal-rich, with a metallicity ([Fe/H]) of 0.06, or 112% of that found in the Sun.[10] Its luminosity (L☉) is 8.7 times that of the Sun.

The star's apparent magnitude, or how bright it appears from Earth's perspective, is 3. Therefore, it can be seen with the naked eye.

Orbit

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Beta Pictoris b orbits its host star every 21 years at a distance of 9.2 AU (about the same as Saturn's distance, which is about 9.55 AU). It receives 11% of the amount of sunlight that Earth does from the Sun.[11]

The orbit of the planet is well aligned to the rotation of the parent star and debris disk, with misalignment measured to be 3±5 degrees in 2020.[12]

Planetary rotation

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In 2014, the rotation period of Beta Pictoris b was calculated from the broadening of its carbon monoxide infrared absorption line. This makes it the first extrasolar planet to have its rotation rate measured.[13]

With a rotation period of 8.1 hours, it was the fastest-spinning exoplanet known as of 2014.[13][14][15] Its rotation period is faster than that of Jupiter, which has a rotation period of around 10 hours. The rotation period was later refined to 8.7±0.8 hours.[4]

Discovery

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The planet was discovered on November 18, 2008, by Anne-Marie Lagrange et al., using the NACO instrument on the Very Large Telescope at Cerro Paranal in northern Chile.[16] This planet was discovered using the direct imaging technique, using reference star differential imaging. The discovery image was taken in 2003, but the planet was not detected when the data were first reduced. A re-reduction of the data in 2008 using modern image processing tools revealed the faint point source now known to be a planet.

Further studies

[edit]

Follow-up observations performed in late 2009 and early 2010 using the same instrument recovered and confirmed the planet, but on the opposite side of the star. These findings were published in the journal Science[17] and represented the closest orbiting planet to its star ever imaged. Observations performed in late 2010 and early 2011 allowed scientists to establish an inclination angle of the planet's orbit of 88.5 degrees, nearly edge-on. The location of the planet was found to be approximately 3.5 to 4 degrees tilted from the main disk in this system, indicating that the planet is aligned with the warped inner disk in the Beta Pictoris system.[18]

The first study of the spectral energy distribution of the planet was published in July 2013.[19] This study shows detections at 1.265, 1.66, 2.18, 3.80, 4.05 and 4.78 μm demonstrating that the planet has a very dusty and/or cloudy atmosphere. The SED is consistent with that of an early L dwarf, but with a lower surface gravity. The effective temperature is constrained to 1700±100 K and the surface gravity to log g = 4.0±0.5. A second study, published in September 2013,[20] provided a new detection at 3.1 μm obtained at the Gemini Observatory along with a reanalysis of previous data. They found the planet to be overluminous in the mid-infrared 3.1 μm band compared to models of early L dwarfs. Models incorporating small dust particles and thick clouds provided the best fit to the SED. The effective temperature is constrained to 1600+50
−25 K and the surface gravity to log g = 3.8±0.02. This fit corresponds to a planet radius of 1.65 times that of Jupiter, arguing that Beta Pictoris b may be younger than its host star (finished forming at 5 Ma).

In 2015, a short video was made from direct images of Beta Pictoris b taken by the Gemini Planet Imager over the course of about two years showing a time-lapse of the planet orbiting around its parent star.[21] It may have been responsible for a transit-like event observed in 1981.[22]

In 2018, the PicSat cubesat was launched in a mission to image the planet Beta Pictoris b transiting its host star Beta Pictoris.

As of 2025, the orbital parameters and mass of Beta Pictoris b have been measured using a combination of data from astrometry and imaging, showing that it has about 10.0 times the mass of Jupiter with a semi-major axis of about 10.0 AU.[3] The orbital period is measured to be 23.59 years based on radial velocity, astrometry and direct imaging.[2]

Potential exomoon

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See also: List of exomoon candidates

Beta Pictoris b has been found to have an obliquity likely misaligned by a 2024 study, based on a wide range of simulations together with published measurements. They find that the planet's obliquity must be misaligned if it spins fast, and might be if it spins slow. This misaligment could be caused by collisions with other planets, an unlikely scenario, or secular spin-orbit resonances modified by the presence of an exomoon. An exomoon with a mass similar to that of Neptune, an orbital separation of 0.02–0.05 AU (20–50 planetary radii) and an orbital period ranging from three to seven weeks (20 to 50 days) would induce the largest obliquities, up to 60°.[23]

Future observations by the James Webb Space Telescope will measure the planet's obliquity, something never done before in an extrasolar multiplanetary system. A detection of nonzero obliquity could be evidence of an exomoon. Currently the possibility of zero obliquity is unlikely.[23]

The use of astrometry does not rule out the exomoon candidate, but has set limits on the presence of exomoons. For short orbital periods (around 50 days), objects with masses over 0.6 MJ are ruled out, while at periods of roughly 200 days, this limit is 0.3 MJ. At orbital periods of 700 and 1,100 days, exomoons with masses over 0.15 MJ and 0.10 MJ, respectively, are ruled out.[3]

The Beta Pictoris b exomoon system
Companion
(in order from planet)
 Mass Semimajor axis
(AU) 		Orbital period Eccentricity Inclination Radius
Candidate 1 (unconfirmed) ≳15 M🜨 0.03–0.05 20–50 d – – –
[edit]
  • Beta Pictoris b time-lapse.[24]
    Beta Pictoris b time-lapse.[24]
  • An annotated view of the Beta Pictoris system.
    An annotated view of the Beta Pictoris system.
  • Equatorial spin velocity vs mass for planets comparing Beta Pictoris b to the Solar System planets.
    Equatorial spin velocity vs mass for planets comparing Beta Pictoris b to the Solar System planets.
  • Artistic rendering of the Beta Pictoris system, showing the accretion disk, and the two planets.
    Artistic rendering of the Beta Pictoris system, showing the accretion disk, and the two planets.
  • Artist's impression of Beta Pictoris b. The debris disk around the parent star can be seen.
    Artist's impression of Beta Pictoris b. The debris disk around the parent star can be seen.

See also

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Notes

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References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Beta Pictoris b

View on Grokipedia
from Grokipedia
Beta Pictoris b is a , one of the first to be directly imaged, orbiting the young A-type star approximately 63 light-years from . Discovered in 2008 using infrared imaging with the , it has a mass of about 11 masses, a radius of 1.65 times that of , and an of roughly 24 years at a semi-major axis of 10 AU. The system, estimated at 21 million years old, is a key laboratory for studying early planetary formation due to its prominent edge-on , which the planet likely influences through gravitational interactions. b's is around 1700 K, indicating a hot, young atmosphere containing and , with observations revealing thick clouds and low consistent with "" formation models for massive planets. Its slightly eccentric orbit (e ≈ 0.11) places it within the inner regions of the , where it may shepherd dust and planetesimals, contributing to the system's dynamic structure. As a benchmark directly imaged , Beta Pictoris b has been extensively observed with instruments like and GPI, enabling detailed that probes its and evolution. Recent studies, including astrometric measurements of the host star's wobble, have refined its mass and orbital parameters, while the confirmed inner companion Beta Pictoris c highlights the system's multi-planet architecture. These observations underscore Beta Pictoris b's role in understanding the formation and migration of giant planets in young stellar environments.

Discovery and observational history

Initial detection

The Beta Pictoris system has been a focal point for exoplanet research since the mid-1980s, following the detection of its circumstellar in observations by the Infrared Astronomical Satellite (IRAS) in 1983, with the first resolved images confirming the disk's edge-on structure obtained in 1984 using optical coronagraphy. These early findings revealed a vast disk of dust and gas extending inward to about 30 AU from the star, prompting theoretical predictions of unseen planets sculpting its asymmetries, warps, and inner clearing—motivating targeted deep imaging searches for companions within 10 AU. On November 18, 2008, a team led by Anne-Marie Lagrange announced the discovery of a faint companion, designated Beta Pictoris b, through re-analysis of archival data from the NACO adaptive optics instrument on the European Southern Observatory's Very Large Telescope (VLT). The detection utilized deep L'-band (3.8 μm) imaging acquired between November 10 and 17, 2003, where the object appeared as a point source with a measured flux of 1.1 ± 0.3 mJy, consistent with a self-luminous giant planet rather than reflected starlight. The initial astrometric measurements placed Beta Pictoris b at a projected separation of 411 ± 8 milliarcseconds (mas) from the host star, corresponding to approximately 8 AU at the system's distance of about 19.4 parsecs, with a position angle of 31.8 ± 1.3 degrees southeast of the star. To confirm its nature, the team cross-referenced against Hubble Space Telescope archival images from 1997 and galactic models, estimating the probability of a contaminating background or foreground object (such as an L or T dwarf) at less than 10^{-5}, far below the detection threshold. Additionally, the companion's position did not align with known disk features, which exhibit faint, symmetric emission in L'-band without significant point-like asymmetries at that location, ruling out scattered light from disk grains as the source. Direct imaging in the thermal infrared, as employed here, proved crucial for detecting young, hot exoplanets like Beta Pictoris b by suppressing the host star's overwhelming brightness through adaptive optics and coronagraphy.

Direct imaging campaigns

Following the initial detection in 2008, sustained direct imaging campaigns targeting Beta Pictoris b have utilized advanced high-contrast instruments on ground-based telescopes to track its position and orbital motion over extended periods. These efforts, spanning from 2010 to 2024, primarily employed the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument on the European Southern Observatory's Very Large Telescope (VLT), the Gemini Planet Imager (GPI) on the Gemini South telescope, and complementary observations from the Hubble Space Telescope (HST). SPHERE, operational since 2014, has been instrumental in capturing multiple epochs of the planet's position using infrared dual-band imaging and integral field spectroscopy in modes like IRDIFS, combined with angular differential imaging for stellar light suppression. Similarly, GPI has provided high-resolution near-infrared images since its first light in 2014, enabling precise astrometric measurements through its integral field spectrograph and coronagraphic capabilities. HST contributions, particularly in visible and near-infrared wavelengths, have supported multi-wavelength datasets for system-wide monitoring, including the debris disk context. A landmark dataset from these campaigns is a 17-year timelapse compiled in 2023 by researchers at , analyzing images from 2003 to 2020 across VLT (including NACO and ), Gemini/GPI, and HST archives. This sequence demonstrates the planet's orbital motion, covering approximately 70% of its ~24-year orbit and revealing its progression from a position southeast of the star in 2003 to the northeast by 2020. The analysis highlights the planet's consistent separation of about 8-9 AU, confirming its dynamical stability within the system. Such long-baseline observations have been crucial for refining astrometric positions with uncertainties as low as 1-2 milliarcseconds, allowing robust orbital fitting. These astrometric measurements have constrained the planet's to a nearly edge-on inclination of approximately 88° relative to the sky plane, aligning with the system's orientation and enabling predictions of future conjunctions. For instance, data from 2014-2016 tracked the planet approaching inferior conjunction, with redetection post-conjunction in September 2018 at a separation of 139 mas and position angle of 30°. GPI observations in 2018 further refined these positions, contributing to combined fits that yield a semi-major axis of approximately 10 AU with eccentricity ~0.11. These multi-epoch datasets from and GPI have collectively provided over a precise position measurements, essential for distinguishing the planet's signal from instrumental artifacts. Imaging Beta Pictoris b presents significant challenges due to the host star's brightness (magnitude ~3.8 in V-band) and the forward-scattered from the edge-on , which can overwhelm the planet's faint thermal emission at 8-12 μm wavelengths. systems, such as SPHERE's SAXO and GPI's high-order deformable mirror with over 1,000 actuators, correct atmospheric turbulence in real-time to achieve Strehl ratios exceeding 0.8 in the near-infrared, sharpening the point-spread function to ~50 mas. Coronagraphs, including apodized phase masks, block the central by factors of 10^6-10^8, creating a dark inner region for companion detection, though residual speckles from imperfect suppression require post-processing techniques like . The disk's scattering further complicates observations near conjunction, as seen in the 2017-2018 period when the planet passed behind the star, necessitating deep integrations of several hours per epoch.

Refinements and recent observations

In 2022, Feng et al. utilized Data Release 3 combined with data to refine the position and orbital constraints of Beta Pictoris b, achieving a more precise dynamical mass estimate of approximately 11 masses by detecting the host star's astrometric wobble. This analysis integrated relative astrometry from direct imaging with absolute astrometric measurements, reducing uncertainties in the planet's semi-major axis to approximately 10 AU and confirming its alignment with the plane. Subsequent observations in 2024 with the upgraded CRIRES+ spectrograph on the VLT provided high-resolution mid-infrared spectra of Beta Pictoris b, revealing rotational broadening in molecular features such as CO absorption. Landman et al. measured a projected rotational velocity of vsin⁡i=22±2v \sin i = 22 \pm 2 km/s, indicating a fast-spinning atmosphere consistent with prior estimates but with improved precision. These data also hinted at potential obliquity misalignment between the planet's spin axis and , suggesting dynamical interactions within the system that could influence . A 2025 dynamical study by Lacquement et al. explored the long-term stability of the system, incorporating updated for planets b and c to model N-body interactions over gigayears. The analysis indicated that the current two-planet configuration is stable for at least 100 Myr, but suggested the possible existence of an undetected outer planet beyond Beta Pictoris b to explain disk asymmetries and maintain configurations. Such a companion, with a mass of 0.15–1 masses at 30–40 AU, would enhance system stability without disrupting the inner . Parallel efforts integrated 17 years of HARPS data to contextualize exocomet activity in the system, revealing periodic sodium absorption lines linked to infalling bodies perturbed by b's gravity, though no direct RV signal from the planet itself was isolated due to stellar activity. This work, by Hoeijmakers et al. in 2025, underscored the planet's role in sculpting the circumstellar environment without yielding new positional refinements for b.

The Beta Pictoris system

Host star properties

Beta Pictoris, the central star of the system hosting the exoplanet Beta Pictoris b, is classified as an A6V spectral type main-sequence star with an effective temperature of 8052 K. This places it among the hotter, more massive A-type stars, characterized by strong hydrogen lines in its spectrum and a blue-white appearance. The star's mass is 1.75 M⊙, and its radius measures 1.81 R⊙, resulting in a bolometric luminosity approximately 8.5 times that of the Sun. These parameters position Beta Pictoris on the main sequence in an early evolutionary phase, where hydrogen fusion in its core dominates its energy output. Located at a distance of 63.4 light-years (19.5 parsecs) from , is one of the nearest A-type stars to the Solar System, enabling detailed observations of its properties and surroundings. Its age is constrained to 23–25 million years (as of 2025), derived from lithium depletion boundary technique using DR3 data and isochrone fitting, complemented by gyrochronology. This youth aligns with the star's membership in the nearby moving group, a loose association of co-moving stars formed from the same . Beta Pictoris exhibits slightly subsolar , with [Fe/H] ≈ -0.21 dex, indicating a lower abundance of heavy elements relative to compared to the Sun. As a young main-sequence star, it displays typical characteristics of early A-type , including rapid and potential δ Scuti pulsations, though these are modulated by its age and activity levels. The star's youth contributes to the formation of its prominent circumstellar , a signature of ongoing collisions.

Circumstellar debris disk

The circumstellar surrounding is a prominent feature of the system, with the primary planetesimal belt located around 80–100 AU, extending radially to over 1000 AU including the outer halo, though recent observations detect inner hot dust within ~7 AU. This structure includes a denser "birth ring" of near 80–100 AU and an extended outer halo of scattered dust, with evidence of inner dust grains possibly produced close to the star or transported inward. The disk's edge-on orientation, viewed nearly perpendicular to its plane, facilitates detailed of its vertical and radial profiles. High-resolution observations reveal a complex inner structure, including a warp in the disk's midplane and variations in inclination between the inner and outer regions. imaging in scattered light has resolved this warp, showing the inner disk (within ~50 AU) inclined by about 4–5° relative to the outer disk, creating a bowed appearance. Complementary Atacama Large Millimeter/submillimeter Array (ALMA) observations at millimeter wavelengths confirm these features, detecting a CO gas belt at ~85 AU with asymmetries and inclination shifts that align with the scattered-light data, indicating ongoing dynamical evolution. Recent JWST/MIRI observations (as of 2024) detect excess from 5–7.5 μm, revealing submicron-sized hot dust grains within ~6.5 AU, suggesting active dust production or radial transport in the innermost regions, potentially influenced by planetary companions. The disk's composition is dominated by micron-sized dust grains, primarily silicates such as and , with evidence for carbonaceous materials and potential ices in the outer regions. Spectroscopic analysis of thermal emission and scattered light indicates a mix of crystalline and amorphous silicates, with grain properties varying radially—smaller, more porous grains closer in and larger, compact ones farther out. Variable absorption lines in the spectrum, observed via high-resolution spectroscopy, provide evidence for exocomets: transient blueshifted features in Ca II and Na I lines, attributed to infalling evaporating bodies, have been detected in HARPS data spanning 2003–2020 and analyzed through 2025, showing events with depths up to 2% and durations from hours to months. The total mass of the disk is estimated at 0.1–1 M⊕, primarily in unseen parent bodies, with the observable dust component around 0.02–0.2 M⊕ derived from submillimeter flux measurements. Dust temperatures decrease radially, from ~100 in the inner birth ring to ~30 in the outer halo, reflecting the stellar irradiation gradient and blackbody equilibrium, though inner hot dust reaches ~500 . The youth of the host star, at approximately 23 Myr, supports the disk's active collisional and dynamical state, sustaining dust replenishment over gigayear timescales.

Orbital characteristics

Key orbital parameters

Beta Pictoris b orbits its host star at a semi-major axis of 10.018^{+0.082}_{-0.076} , corresponding to an of 23.593 \pm 0.248 years (or 8617.5^{+0.251}_{-0.206} days). These values are derived from orbital fits to relative obtained via direct imaging, incorporating data from multiple instruments including VLT/NACO, Gemini/GPI, and . The orbit exhibits a low eccentricity of 0.106^{+0.007}_{-0.006}, indicating a nearly circular path, and an inclination of 89.009^\circ \pm 0.012^\circ relative to the sky plane, consistent with near-edge-on alignment. The argument of periapsis is measured at \omega = 21.835^{+4.099}_{-4.044}^\circ, while the is \Omega \approx 31.77^\circ. The following table summarizes these key orbital parameters from the 2022 analysis:
ParameterSymbolValueUnit
Semi-major axisa10.018^{+0.082}_{-0.076}
Orbital period23.593 \pm 0.248years
Eccentricitye0.106^{+0.007}_{-0.006}-
Inclinationi89.009 \pm 0.012degrees
Argument of periapsis\omega21.835^{+4.099}_{-4.044}degrees
Longitude of ascending node\Omega31.77degrees
These fits are based on astrometric observations spanning over 17 years (from 2003 to 2020), capturing the of the planet's projected separation, which has decreased from approximately 0.45 arcseconds in early data to around 0.3 arcseconds in recent measurements, reflecting its orbital motion toward periapsis.

System dynamics and stability

The system exhibits complex gravitational interactions between its known giant planets, β Pictoris b and the inner β Pictoris c, as well as with the surrounding particles. Numerical models indicate that the two planets can temporarily enter a 7:1 mean-motion (MMR), with capture events lasting approximately 20,000 years and recurring every 40,000 years due to secular eccentricity oscillations. Additionally, high-order MMRs with β Pictoris c, such as 7:1 and 8:1 located at around 4–5 AU, perturb inner disk planetesimals, exciting their eccentricities and driving the production of falling evaporating bodies from regions between 0.6 and 1.5 AU, while β Pictoris b acts as a distant perturber sustaining these dynamics. Secular perturbations from β Pictoris b and c induce long-term oscillations in the eccentricities and inclinations of disk particles, contributing to the observed warp in the inner at approximately 85 AU. These perturbations cause planetesimals to align with the planet's in the inner regions while the outer disk remains relatively flat, with the warp amplitude extending to roughly twice the planet's inclination of about 3.6°. β Pictoris b, orbiting near the disk midplane, is the primary driver of this inner disk morphology, as its inclined excites vertical oscillations that propagate outward. A 2025 study using N-body simulations suggests the presence of an additional outer , tentatively designated β Pictoris d, to explain the sharp truncation of the at around 50 AU, as the known planets alone cannot clear material to this distance. This hypothetical planet has an estimated of 0.15–1 M_Jup and a semi-major axis of 30–40 AU with low eccentricity (≤0.4), enabling it to sculpt the disk's outer edge through gravitational clearing without destabilizing the inner system. Symplectic N-body simulations of the system, incorporating β Pictoris b, c, and test particles in the disk, demonstrate long-term dynamical stability over timescales of 100 million years, with stable regions beyond 25 AU and depletion inside due to planetary perturbations. These models confirm that the planetary orbits remain bounded under secular evolution, supporting the overall architecture despite occasional temporary resonances.

Physical properties

Mass, radius, and density

The of Beta Pictoris b is estimated at 11.729^{+2.337}{-2.135} M\mathrm{Jup}, derived from a joint analysis of astrometric data from and DR2 combined with relative of the planet and measurements of the host star. This dynamical determination resolves previous tensions between spectroscopic and evolutionary model estimates, confirming Beta Pictoris b as a massive . Due to the system's edge-on geometry, signals are detectable but incomplete over the planet's long , contributing to the asymmetry in the uncertainty bounds. The radius of Beta Pictoris b is inferred to be 1.46 \pm 0.01 R_\mathrm{Jup} through fits of atmospheric models to its near-infrared spectrum obtained with the Gemini Planet Imager, assuming a hot-start formation scenario and accounting for thermal emission from its young, hot atmosphere. This measurement relies on synthetic spectra from PHOENIX and other grids to match observed photometry and line profiles, providing constraints on effective temperature and surface gravity as well.
PropertyValueMethodSource
Mass11.729^{+2.337}{-2.135} M\mathrm{Jup} + RVBrandt et al. (2021)
Radius1.46 \pm 0.01 R_\mathrm{Jup} emission modelsChilcote et al. (2017)
Density\sim 5 \ \mathrm{g/cm^3}Derived from mass and radiusDerived from above
The implied mean density of approximately 5 g/cm³ suggests a bloated structure, consistent with a young retaining significant internal heat from formation, leading to an inflated envelope compared to older planets of similar mass. This density exceeds that of Jupiter (1.33 g/cm³) but is lower than expected for a fully contracted massive planet, highlighting the role of youth in its physical state. Uncertainties in both mass and radius propagate to the density estimate, with additional ambiguity from formation models (e.g., hot-start vs. cold-start) that affect evolutionary tracks and the lack of transit data for direct radius confirmation.

Temperature and atmospheric composition

The of Beta Pictoris b is measured at 1724 ± 15 , derived from its bolometric using Gemini Planet Imager and evolutionary track comparisons. This value highlights the planet's substantial internal , driven by residual heat from its formation approximately 20–25 million years ago. In contrast, the equilibrium temperature, based on its orbital separation of roughly 9.8 AU from the host star, is only about 120 , underscoring that re-radiation of stellar plays a negligible role in the planet's thermal emission. The L'-band brightness, observed at magnitudes around 11, further supports this internal heating, as models predict minimal stellar contribution at these wavelengths. Recent JWST/NIRCam observations in 2024 confirmed the detection of Beta Pictoris b and provided new near-infrared photometry, consistent with previous spectra but enhancing constraints on its thermal emission. A September 2025 study incorporating high-resolution continuum spectra from VLTI/, alongside CRIRES+ and other data, refined forward models of the atmosphere, supporting an around 1700 K and confirming thick clouds with supersolar metallicities. Spectroscopic analyses reveal an atmosphere dominated by a cloudy hydrogen-helium , with key molecular absorbers including and . Atmospheric retrievals and forward models, such as those incorporating Drift-Phoenix or Exo-REM frameworks, indicate the presence of thick clouds composed of small grains (∼1 μm), which scatter and absorb light to match the near- and mid-infrared spectrum. These models also suggest possible contributions from iron and (Mg₂SiO₄) condensates in the upper atmosphere. To reconcile observed photometry and spectra, particularly in the H and bands, models invoke supersolar metallicities ranging from 10 to 100 times solar values, enhancing opacity from metal-bearing and cloud formation. High-resolution spectra obtained between 2020 and 2024 provide evidence for atmospheric or through forward-scattered continuum and marginal features, while showing no clear detection of (CO) absorption. This hazy structure aligns with low (log g ≈ 3.5–4.0) and young-age effects, distinguishing Beta Pictoris b from field .

Rotational period and obliquity

The rotational period of Beta Pictoris b has been precisely measured through high-resolution , revealing a value of 8.7 ± 0.8 hours based on the planet's projected rotational velocity of 19.9 ± 1.0 km/s, a of 1.4 ± 0.1 radii (consistent with 1.46 ± 0.01 R_\mathrm{Jup} from atmospheric models within uncertainties), and an assumed spin inclination near 90° relative to the . An independent 2024 M-band study reports v sin i = 22 ± 2 km/s, suggesting a similar period of approximately 7.5–9.5 hours assuming comparable and inclination. This short period indicates rapid rotation for a , comparable to 's approximately 10-hour day but adjusted for Beta Pictoris b's larger size, greater mass (around 11 Jupiter masses), and young age of about 23 million years, which allows for faster spin due to ongoing contraction and limited tidal . The planet's equatorial velocity, derived from these measurements, is approximately 20 km/s, assuming minimal obliquity in the spin axis orientation. This velocity influences models, promoting zonal jets and banded cloud structures similar to those on , though enhanced by the planet's high of around 1724 , which drives stronger winds and potential hotspots at mid-latitudes. Recent spectroscopic data, informed by the planet's atmospheric composition of and , further support interpretations of rotational broadening in emission lines. Beta Pictoris b's obliquity, the tilt of its spin axis relative to its , is predicted to be misaligned by 10–20° under scenarios of rapid (period ≤9.9 hours) consistent with observations, potentially arising from dynamical instabilities during formation such as planet-planet scattering or disk warping. This moderate misalignment contrasts with the system's overall spin-orbit alignment, where the planet's orbit is coplanar with the stellar equator to within 3° ± 5°, but suggests a violent early history that could have excited the planet's spin. Such obliquity levels would imply rotational modulation in future light curves, aiding constraints on spin axis via time-resolved .

Potential companions

Inner planet Beta Pictoris c

Beta Pictoris c is a orbiting the young A-type star at an inner separation, serving as the second confirmed planetary companion in the system after Beta Pictoris b. It was discovered in 2019 through (RV) observations spanning over a decade with the HARPS spectrograph, which revealed a periodic signal after accounting for the star's δ Scuti pulsations that had previously masked it. The planet's existence was directly confirmed in 2020 via infrared using the instrument on the Very Large Telescope Interferometer (VLTI), marking the first such confirmation of an RV-detected planet and providing constraints on its position and temperature of approximately 1250 K. As of 2025, orbital parameters indicate a mass of approximately 9–10 MJup, a semi-major axis of 2.7 AU, and an orbital period of about 3.3 years (1221 days), with an eccentricity of around 0.3. The planet's orbit is nearly coplanar with that of Beta Pictoris b, exhibiting a mutual inclination of less than 5°, consistent with the overall alignment of the planetary system and the outer debris disk. High-contrast imaging with instruments like SPHERE on the VLT has been used to monitor the system and constrain Beta Pictoris c's location indirectly, though direct detection via imaging remains challenging due to its proximity to the star. Beta Pictoris c contributes to the dynamics of the inner system by potentially clearing dust and small bodies in the inner debris disk through gravitational perturbations on falling evaporating bodies (FEBs) and their progenitors, which helps explain the observed inner disk edge at around 2–3 AU. Orbital analyses suggest a possible high-order mean-motion resonance with Beta Pictoris b, such as 7:1, which could influence long-term stability and disk interactions, though further observations are needed to confirm this configuration. Recent 2025 dynamical studies continue to explore the stability of the system, including possibilities for additional inner planets.

Candidate exomoons

In 2024, a study by et al. analyzed the potential for around Beta Pictoris b by modeling the planet's obliquity, suggesting the presence of a large candidate to explain nonzero obliquity values predicted from upcoming observations. This candidate arises from dynamical simulations indicating that a Neptune-mass (approximately 17 masses) could excite the planet's spin axis through gravitational interactions, consistent with the planet's estimated mass of approximately 12 masses, which sets upper limits on stable moon masses from several masses to tens of masses. The proposed would orbit b at a semimajor axis of 0.03–0.05 AU, corresponding to an of 20–50 days, placing it within a zone where and stellar irradiation could potentially allow liquid if the possesses a suitable atmosphere, raising speculative prospects for pending confirmation. Detection efforts for such moons rely on transient photometric signals from eclipses or transits of the moon across the planet's disk, as well as astrometric wobbles in b's path induced by the moon's gravitational pull, which could be measurable with high-precision instruments. Although an excess in mid-infrared emission observed in JWST/ data of the system has been noted, its attribution to a remains tentative and unconfirmed, as it could stem from circumplanetary or other sources. The candidate status is provisional, with no direct detection yet; upcoming JWST observations aim to measure b's obliquity more precisely and search for transit signatures to validate or refute the exomoon's existence, as discussed in 2025 presentations.

Formation and evolution

Theoretical formation scenarios

The formation of Beta Pictoris b, a massive orbiting at approximately 10 AU in a young system, has been modeled through two primary mechanisms: core accretion and gravitational instability. In the core accretion scenario, a solid core of roughly 10-20 masses forms first from planetesimals and pebbles in the , followed by rapid gas accretion once the core reaches a threshold, enabling runaway growth to the planet's estimated 10-13 masses. This process is consistent with the planet's subsolar atmospheric carbon-to-oxygen (C/O) ratio of 0.43 ± 0.05, which can be achieved by accreting approximately 80 masses of solids—primarily ices depleted in carbon—between the (H₂O) and (CO₂) ice lines in the disk. Gravitational instability, in contrast, involves the rapid collapse of a massive, gravitationally unstable region in the outer disk to directly form a , bypassing a distinct core-building phase and typically yielding higher initial luminosities due to less efficient heat retention. However, this mechanism struggles to reproduce the observed low C/O ratio for Beta Pictoris b, as the short formation timescale (on the order of orbital periods) limits the incorporation of carbon-poor solids, requiring an unusually massive disk or extended pre-collapse accretion to match observations. Recent analyses favor core accretion for Beta Pictoris b due to its combination of high , young system age (around 20-25 million years), and atmospheric composition, which align with models incorporating and accretion in a disk with radially varying C/O ratios. Gravitational instability remains plausible if the formed early in a metal-enriched disk, but it is less consistent with the planet's indicators and the disk's observed stability constraints. The core accretion preference is further supported by the planet's evolution, which matches hot-start models where formation shocks retain significant heat, unlike the cooler outcomes expected from pure disk instability. Theoretical models suggest that Beta Pictoris b likely underwent significant inward migration from an initial formation site beyond 20 AU to its current orbit, driven by gravitational interactions with the material. This migration, potentially type II in nature, would have occurred over a few million years, allowing the to accrete gas and solids while torquing the disk and clearing a gap, consistent with the observed inner edge of the at around 30 AU. The plays a crucial role in this process, serving as a of planetesimals and that supplied building materials during growth and later influenced the 's eccentricity through resonant interactions and . These dynamics explain features like the disk's warp and inner clearing, where Beta Pictoris b's mass (>10 masses) enables efficient stirring of debris over timescales of 10-12 million years. Beta Pictoris b shares formation challenges with other directly imaged wide-orbit giants, such as the planets, which also require substantial solid accretion (100-1000 masses) under core accretion to match their near-solar C/O ratios (0.62-0.83 for ) despite forming in outer disk regions. Unlike the more tightly packed system, Beta Pictoris b's isolated orbit and interaction with an extended highlight a scenario where migration and disk-planet torques dominate the architecture, yet both systems underscore the need for rapid, efficient metal enrichment in young disks to form such massive companions.

Evolutionary models and age constraints

The high bolometric luminosity of Beta Pictoris b, estimated at log⁡(L/L⊙)=−4.01−0.05+0.04\log(L/L_\odot) = -4.01^{+0.04}_{-0.05}, aligns with cooling models for young giant s formed via hot-start scenarios, where initial high leads to elevated emission shortly after formation. These models, such as those based on the and Exo-REM atmospheric grids, reproduce the planet's observed of approximately 1500–1600 K and of log⁡g≈4.0\log g \approx 4.0–4.5 dex when assuming a system age of 23 ± 3 Myr. The is consistent with a dynamical mass of around 11–12 MJup_{\rm Jup}, indicating that Beta Pictoris b has not yet undergone significant , as expected for a only tens of millions of years old. Atmospheric evolution models predict that Beta Pictoris b will gradually lose internal heat through , leading to contraction and a decline in over the next 100 Myr. This process is driven by the planet's contraction under its own gravity as ceases and the atmosphere cools, potentially reducing its radius from current estimates of about 1.3–1.6 Jup_{\rm Jup} toward values more akin to mature gas giants. The planet's super-solar ([M/H] ≈ +0.50 dex) and heavy-element enrichment (up to 5% or 20–80 M⊕_\oplus) suggest enhanced opacity in its envelope, which may slow cooling compared to lower- analogs. Recent studies highlight challenges in spin-orbit synchronization for Beta Pictoris b, with predictions of significant obliquity misalignment (up to ~60°) relative to its , potentially induced by secular resonances with an undetected . This misalignment contrasts with aligned systems like those in the Solar System and raises questions about tidal evolution in wide-orbit giants. When benchmarked against Solar System gas giants like and Saturn, Beta Pictoris b's higher and require adjusted evolutionary tracks, showing faster initial cooling but prolonged high due to its youth and formation history.

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