A 2 au resolution view by ALMA of the planet-hosting WISPIT 2 disk

TL;DR

This study uses high-resolution ALMA Band 7 imaging to map the mm continuum emission in the WISPIT 2 system and to search for circumplanetary emission around the newly discovered protoplanet WISPIT 2b. The observations reveal a single, narrow ring peaking at $R_{\rm ring}\approx144.4$ au, well outside the planet’s location at ~57 au, with no detectable CPD down to a $3\sigma$ limit of $45\,\mu$Jy for a point source. CPD-injection tests further constrain potential CPD emission, linking the non-detection to optically thin/thick regimes and placing tight mass and size limits that are broadly consistent with, but sometimes in tension with, empirical CPD trends extrapolated from stellar-mass systems. The results, together with SPHERE scattered-light data showing multiple outer rings, imply either an additional outer companion or alternative dynamical scenarios (e.g., a more massive or eccentric WISPIT 2b) to explain the observed gap and ring morphology. The work demonstrates the value of combining high-resolution mm-continuum imaging with multi-wavelength data and motivates future gas-dynamics modeling to disentangle planet–disk interactions and CPD formation in this system.

Abstract

We present deep, high spatial resolution interferometric observations of 0.88 mm continuum emission from the TYC 5709-354-1 system, hereafter WISPIT 2, obtained with the goal of detecting 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 $25 \times 17$ mas ($3.3 \times 2.2$ au), revealed a single, narrow ring with a deprojected radius of 144.4 au and width of 7.2 au, and no evidence of circumplanetary emission within the cavity. Injection and recovery tests demonstrate that these observations can rule out point-like emission at the location of WISPIT 2b brighter than $\approx 45$ $μ$Jy at the $3σ$ level. While these data can rule out PDS 70c like circumplanetary emission, the upper limit is consistent with empirical mass-flux relationships extrapolated from the stellar regime. 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. Possible solutions include either another lower mass companion, residing between WISPIT 2b and the cavity edge, likely in the gap seen by SPHERE at $\sim130$ au, or that WISPIT 2b is either substantially more massive than IR-photometry based estimates ($\sim15$ $M_{\rm Jup}$) or on a moderately eccentric orbit. The combination of observations sensitive to the gas and dust distributions on larger spatial scales and dedicated hydrodynamical modeling will help differentiate between scenarios.

Figures (10)

• Figure 1: 0.88 mm continuum intensity of the WISPIT 2 system, showing a thin ring at $1\farcs086$ ($144.4\,$au deprojected distance). The right panel shows the same image, with white dashed lines indicating the radial peaks observed in IR scattered light by van_Capelleveen2025, projected onto the disk midplane. The numbering ($R_{N,{\rm S}}$) follows the one by van_Capelleveen2025. The location of the WISPIT 2b planet van_Capelleveen2025Close2025 is highlighted in the right panel. The ALMA resolution element is shown in the bottom left of each panel.
• Figure 2: Data, best fit galario model, and residuals of WISPIT 2. Both the model and the residuals intensity maps have been reconstructed with the same CLEANing parameters as the original data. The rms ($\sigma=16.6\,\mu$Jy) used in the residuals colorbar is the one estimated within the mm-cavity on the data (see Section \ref{['sec:data']}).
• Figure 3: Injected ($F_{\rm CPD,inj}$) vs recovered ($F_{\rm CPD,rec}$) flux density of a point-source at the location of WISPIT 2b. The recovered flux density is estimated as the peak intensity within 1.5 beams at that location. The ribbon indicates the $1\sigma$ uncertainty on the peak intensity estimate.
• Figure 4: Circumstellar and circumplanetary flux density (rescaled to $240\,{\rm GHz}$ and $150\,{\rm pc}$) distribution as function of their host mass. Most planetary mass objects closely follow the trend (best-fit linear correlation, black dashed line) expected for circumstellar disks.
• Figure 5: Gap width (in units of the gap radius) as a function of the planet-to-star mass ratio. For systems hosting detected protoplanets, $R_{\rm gap} = a_{\rm p}$, where $a_{\rm p}$ is the orbital radius of the planet. The candidate protoplanets in (some of) the gaps in the DSHARP sample Andrews_ea_2018Huang2018 and the Taurus survey of Long2018 are displayed as gray dots, with putative planet masses estimated by Ruzza2025 and stellar masses by Andrews_ea_2018Long2019. PDS 70b and c are over-plotted in blue and WISPIT 2b in yellow. The dashed and dashed dotted black lines are the expected gap width to planet mass trends predicted by Rosotti2016 and Facchini2018, their extrapolation to the whole planet mass range we considered is shown in gray.