WISPIT 2b: Accreting Planet in Multi-Ring Disk

• WISPIT 2b is an accreting giant planet embedded in a young, multi-ring transitional disk around a solar-analog, identified by its gap-clearing signature.
• Multi-epoch VLT/SPHERE and MagAO-X Hα imaging established its co-moving, low-eccentricity orbit, with a mass estimate near 5 M_Jup and a deprojected separation of ~55 au.
• ALMA observations constrain its circumplanetary dust emission to a CPD radius <0.62 au, highlighting a discrepancy between scattered-light disk features and mm-continuum morphology.

WISPIT 2b is a directly imaged, accreting giant planet embedded in a young, multi-ringed disk around the young ($\sim$5 Myr), nearby ($\sim$133 pc), solar-analog designated as WISPIT 2 $(=$ TYC 5709-354-1). It was identified within the WISPIT survey, “Wide Separation Planets In Time,” as a gap-clearing planet in a structured transitional disk, and subsequent H$\alpha$ and ALMA observations established both its accretion signature and the current limits on circumplanetary dust emission (Capelleveen et al., 26 Aug 2025).

1. System context and host star

WISPIT 2 $(=$ TYC 5709-354-1) is described as a young classical T Tauri star and as a young, roughly solar-mass pre-main-sequence star. The reported stellar parameters include a distance of $133.35^{+0.37}_{-0.38}$ pc, an effective temperature $T_{\rm eff} = 4400 \pm 50$ K, a bolometric luminosity $L_{\rm bol} = 0.699 \pm 0.021\,L_\odot$, a radius $R_\star = 1.418 \pm 0.004\,R_\odot$, a mass $M_\star = 1.08^{+0.06}_{-0.17}\,M_\odot$, and an age of $\sim$0 Myr. The star also shows strong stellar H$\sim$1 emission, with $\sim$2 Å, consistent with active accretion and CTTS status (Close et al., 26 Aug 2025).

The disk was first characterized in high-resolution direct imaging observations with VLT/SPHERE. Those observations reveal for the first time an extended (380 au) disk in scattered light with a multi-ringed sub-structure. In scattered light, the disk contains four rings plus a prominent gap; the gap between the inner bright ring and the next bright outer ring is the structure most directly associated with WISPIT 2b. Disk inclination estimates cluster around $\sim$3, with reported values $\sim$4 in $\sim$5 and $\sim$6 in $\sim$7 from SPHERE, and $\sim$8 in the H$\sim$9 planet analysis (Capelleveen et al., 26 Aug 2025).

The WISPIT survey is motivated by the search for wide-separation ($(=$0 au) planets in young (few Myr) disks, especially accreting protoplanets traced by H$(=$1. Within that framework, WISPIT 2 was singled out because its large multi-ring transitional disk contains a dark annular gap between bright dust rings, making it a prime target for searching for gap-opening planets.

2. Discovery and observational basis

The first direct-imaging characterization of the planet was obtained with VLT/SPHERE in four independent epochs using polarized light and total intensity observations. Multiple SPHERE epochs demonstrate that WISPIT 2b is co-moving with its host star and shows orbital motion consistent with Keplerian motion in the observed disk gap. In those data, the source appears as a compact point source embedded in the gap between ring 3 and ring 2, rather than as an extended disk clump or polarized scattering feature (Capelleveen et al., 26 Aug 2025).

A second line of evidence came from MagAO-X H$(=$2 imaging. Excellent $(=$3 mas) H$(=$4 images of the star TYC 5709-354-1 led to the discovery of a rare H$(=$5 protoplanet. The H$(=$6 source was first detected on 2025 April 13 at $(=$7 in H$(=$8 ASDI and was confirmed on 2025 April 16 at $(=$9, with the latter epoch adopted for the main astrometric and photometric characterization (Close et al., 26 Aug 2025).

The discovery data combine multiple techniques. SPHERE supplied multi-epoch scattered-light and near-infrared total-intensity imaging, MagAO-X provided visible-light extreme-AO H$\alpha$0 ASDI, and LBT/LMIRcam supplied $\alpha$1-band photometry. This combination was central to establishing that WISPIT 2b is simultaneously a thermal near-infrared source, an accreting H$\alpha$2 emitter, and a companion with common proper motion and measurable orbital motion.

3. Astrometry, photometry, and inferred planetary properties

The adopted MagAO-X astrometry for WISPIT 2b is

$\alpha$3

At $\alpha$4, this corresponds to a projected separation of $\alpha$5. Assuming coplanarity with the disk at $\alpha$6, the deprojected separation is quoted as $\alpha$7–$\alpha$8 (Close et al., 26 Aug 2025).

Near-infrared photometry from SPHERE and LMIRcam yields the currently used mass scale. SPHERE $\alpha$9 and $(=$0-band photometric data are consistent with thermal emission from a young planet. By comparison with planet evolutionary models, the SPHERE analysis finds a mass of $(=$1 Jupiter masses. Independent $(=$2 photometry from LBT/LMIRcam gives $(=$3 mag and $(=$4 mag, which, when coupled with an age of $(=$5 Myr, yields a planet mass estimate of $(=$6 from the DUSTY evolutionary models (Capelleveen et al., 26 Aug 2025).

Property	Value	Measurement context
Angular separation	$(=$7 mas	MagAO-X H$(=$8
Position angle	$(=$9	MagAO-X H$133.35^{+0.37}_{-0.38}$0
Deprojected separation	$133.35^{+0.37}_{-0.38}$1–$133.35^{+0.37}_{-0.38}$2 au	Disk-coplanar interpretation
$133.35^{+0.37}_{-0.38}$3 magnitude	$133.35^{+0.37}_{-0.38}$4 mag	LMIRcam
Mass estimate	$133.35^{+0.37}_{-0.38}$5	DUSTY from $133.35^{+0.37}_{-0.38}$6
Mass estimate	$133.35^{+0.37}_{-0.38}$7	SPHERE $133.35^{+0.37}_{-0.38}$8

The orbital analysis from SPHERE astrometry uses orbitize! with OFTI sampling. The resulting posterior peaks around a semi-major axis of $133.35^{+0.37}_{-0.38}$9 au, and the eccentricity distribution is strongly weighted to low values: $T_{\rm eff} = 4400 \pm 50$0 of solutions have $T_{\rm eff} = 4400 \pm 50$1, and $T_{\rm eff} = 4400 \pm 50$2 have $T_{\rm eff} = 4400 \pm 50$3. This is consistent with a low-eccentricity, co-planar orbit embedded in the observed gap.

4. Accretion diagnostics and H$T_{\rm eff} = 4400 \pm 50$4 interpretation

WISPIT 2b is one of a small number of directly imaged protoplanets detected in H$T_{\rm eff} = 4400 \pm 50$5. The adopted April 16 H$T_{\rm eff} = 4400 \pm 50$6 ASDI measurements are an H$T_{\rm eff} = 4400 \pm 50$7 contrast of $T_{\rm eff} = 4400 \pm 50$8, an H$T_{\rm eff} = 4400 \pm 50$9 line flux of $L_{\rm bol} = 0.699 \pm 0.021\,L_\odot$0, and an H$L_{\rm bol} = 0.699 \pm 0.021\,L_\odot$1 luminosity

$L_{\rm bol} = 0.699 \pm 0.021\,L_\odot$2

under the assumption of negligible extinction in the line of sight to the planet, $L_{\rm bol} = 0.699 \pm 0.021\,L_\odot$3 (Close et al., 26 Aug 2025).

The accretion rate is derived with a semi-empirical magnetospheric accretion framework. The chain of inference is: convert $L_{\rm bol} = 0.699 \pm 0.021\,L_\odot$4 to $L_{\rm bol} = 0.699 \pm 0.021\,L_\odot$5 using empirical $L_{\rm bol} = 0.699 \pm 0.021\,L_\odot$6–$L_{\rm bol} = 0.699 \pm 0.021\,L_\odot$7 relations, then relate $L_{\rm bol} = 0.699 \pm 0.021\,L_\odot$8 to $L_{\rm bol} = 0.699 \pm 0.021\,L_\odot$9 through

$R_\star = 1.418 \pm 0.004\,R_\odot$0

Using the adopted $R_\star = 1.418 \pm 0.004\,R_\odot$1–$R_\star = 1.418 \pm 0.004\,R_\odot$2 and $R_\star = 1.418 \pm 0.004\,R_\odot$3, the reported result is

$R_\star = 1.418 \pm 0.004\,R_\odot$4

In comparative terms, WISPIT 2b is described as very similar to the other H$R_\star = 1.418 \pm 0.004\,R_\odot$5 protoplanets in terms of mass, age, flux, and accretion rate. The comparison sample discussed in the H$R_\star = 1.418 \pm 0.004\,R_\odot$6 paper includes PDS 70 b/c, MaXProtoPlanetS 1b, and the LkCa 15b candidate. WISPIT 2b is distinctive not because its H$R_\star = 1.418 \pm 0.004\,R_\odot$7 flux or $R_\star = 1.418 \pm 0.004\,R_\odot$8 is anomalous, but because it is the first H$R_\star = 1.418 \pm 0.004\,R_\odot$9-detected protoplanet in an annular ring-gap between two bright rings.

The same paper emphasizes an inclination clustering: PDS 70 b/c at $M_\star = 1.08^{+0.06}_{-0.17}\,M_\odot$0, LkCa 15b at $M_\star = 1.08^{+0.06}_{-0.17}\,M_\odot$1, MaXProtoPlanetS 1b at $M_\star = 1.08^{+0.06}_{-0.17}\,M_\odot$2, and WISPIT 2b at $M_\star = 1.08^{+0.06}_{-0.17}\,M_\odot$3, all within

$M_\star = 1.08^{+0.06}_{-0.17}\,M_\odot$4

Monte Carlo tests yield a probability of $M_\star = 1.08^{+0.06}_{-0.17}\,M_\odot$5 $M_\star = 1.08^{+0.06}_{-0.17}\,M_\odot$6 for the observed clustering under the stated detectability assumptions. The authors therefore speculate that magnetospherical accretion might have a preferred inclination range $M_\star = 1.08^{+0.06}_{-0.17}\,M_\odot$7–$M_\star = 1.08^{+0.06}_{-0.17}\,M_\odot$8 degrees) for the direct line of sight to the H-alpha line formation/shock region. This is presented explicitly as a speculative interpretation rather than as an established mechanism.

5. Disk architecture and the gap-clearing interpretation

The key structural claim associated with WISPIT 2b is that it is embedded in a gap and likely clearing a dust-free gap between the two brightest dust rings in the transitional disk. In the SPHERE analysis, the gap center is at $M_\star = 1.08^{+0.06}_{-0.17}\,M_\odot$9 au in scattered light, and the planet’s preferred semi-major axis is $\sim$00 au. In the H$\sim$01 paper, the relevant disk geometry is summarized as an inner bright ring at $\sim$02–$\sim$03, an outer bright ring at $\sim$04–$\sim$05, and a dark annular gap centered at $\sim$06 (Capelleveen et al., 26 Aug 2025).

The dynamical interpretation relies on standard gap-opening arguments. The Hill radius is

$\sim$07

For $\sim$08, $\sim$09, and $\sim$10, the estimate given in the H$\sim$11 analysis is $\sim$12. The discovery paper additionally compares the observed gap width with hydrodynamical gap-width prescriptions. It states that the mass of the planet is also consistent with the width of the observed disk gap, retrieved from hydrodynamic models.

At the same time, the dust morphology depends on wavelength. Scattered-light imaging traces small grains in multiple rings, whereas the 0.88 mm continuum observed by ALMA is much simpler: it reveals a single, narrow ring with a deprojected radius of $\sim$13 au and width of $\sim$14 au, together with an enormous inner cavity (Facchini et al., 22 Jan 2026). This difference in morphology is central to the later reassessment of WISPIT 2b’s dynamical role.

6. ALMA constraints on circumplanetary material and on the mm dust structure

The 2026 ALMA study was designed to detect circumplanetary emission in the vicinity of the newly discovered WISPIT 2b planet. Observations with the most extended baseline configuration offered by ALMA, achieving an angular resolution of $\sim$15 mas $\sim$16 au), revealed a single, narrow ring with a deprojected radius of $\sim$17 au and width of $\sim$18 au, and no evidence of circumplanetary emission within the cavity (Facchini et al., 22 Jan 2026).

Injection and recovery tests demonstrate that these observations can rule out point-like emission at the location of WISPIT 2b brighter than $\sim$19 at the $\sim$20 level. The corresponding $\sim$21 upper limit is $\sim$22. Under the optically thin assumption,

$\sim$23

these limits imply

$\sim$24

for mm-sized grains and

$\sim$25

for $\sim$26m-sized grains, adopting $\sim$27 K and the stated Band 7 opacities.

Under the optically thick assumption,

$\sim$28

the study derives

$\sim$29

This is contrasted with the expected gas circumplanetary disk radius

$\sim$30

The conclusion is that the ALMA data exclude an optically thick CPD whose mm continuum extends out to one-third of the Hill radius. At the same time, the upper limit is consistent with empirical mass-flux relationships extrapolated from the stellar regime, and the paper explicitly notes that these data can rule out PDS 70c-like circumplanetary emission.

The same ALMA study sharpens the main dynamical controversy. Visibility modeling of the continuum ring confirms that WISPIT 2b lies significantly interior to the mm dust ring, raising doubts about the ability of WISPIT 2b to be the only driver of the dust structure. The proposed solutions are limited to three scenarios already stated in the paper: either another lower mass companion, residing between WISPIT 2b and the cavity edge, likely in the gap seen by SPHERE at $\sim$31 au; or that WISPIT 2b is either substantially more massive than IR-photometry based estimates $\sim$32 or on a moderately eccentric orbit.

7. Comparative significance and open problems

WISPIT 2b occupies a distinctive position in the small sample of directly imaged protoplanets. It is reported as the first unambiguous planet detection in a multi-ringed disk and as the first H$\sim$33-detected protoplanet in an annular ring-gap between two bright rings (Capelleveen et al., 26 Aug 2025). These two formulations describe different aspects of the same significance: the source is both a robustly identified young planet and a planet embedded in a disk morphology more structured than the large common cavities of systems such as PDS 70.

Its similarity to other H$\sim$34 protoplanets in mass, age, flux, and accretion rate suggests that WISPIT 2b does not define a new class of accreting object. Instead, its importance lies in the geometry of its environment and in the tension between scattered-light and millimeter-continuum interpretations. The SPHERE and MagAO-X data support the view that WISPIT 2b is the planet responsible for the annular gap between the bright rings at tens of au. The ALMA data, by contrast, indicate that the large-grain dust ring at $\sim$35 au is too far from a $\sim$36 planet at $\sim$37 au to be straightforwardly attributed to that planet alone.

This suggests a system in which a directly imaged accreting planet is securely established, but the full disk architecture may require additional dynamical agents or a revised planetary mass-orbit solution. The papers explicitly identify the relevant next steps: multi-epoch astrometry of WISPIT 2b, spectroscopic follow-up, higher-resolution ALMA imaging of gas and dust, deeper optical/NIR imaging for additional planets, and detailed MHD plus radiative transfer and hydrodynamical modeling. A plausible implication is that WISPIT 2 may become, for annular-gap systems, what PDS 70 became for cavity-hosting disks: a benchmark laboratory for linking direct planet detections to disk substructure, accretion physics, and circumplanetary environments.