Searching for Circumplanetary Dust in the Cavity of the AB Aurigae Disk with ALMA

Lillian Jiang; Brendan P. Bowler; Ya-lin Wu; Yifan Zhou

AI summary · arXiv: 2610.37792v1 · astro-ph.EP

Searching for Circumplanetary Dust in the Cavity of the AB Aurigae Disk with ALMA

Lillian Jiang, Brendan P. Bowler, Ya-lin Wu, Yifan Zhou

Original paper Submitted to arXiv on 27 Oct. 2026 Accepted for publication in The Astrophysical Journal Letters License: NONEXCLUSIVE-DISTRIB 1.0

How to read this summary? Illustrated guide

The essentials

Deep ALMA observations detect no circumplanetary dust or localized CO signature around AB Aurigae’s proposed protoplanets, constraining dust mass or emitting size without ruling out planets.

Question

Do AB Aur b and other proposed protoplanets in the AB Aurigae disk have detectable circumplanetary dust or localized molecular-gas signatures?

Method

The authors obtained ALMA Band 7 observations at 0.88 mm over three execution blocks in 2023, totaling 106 minutes on source. Continuum imaging achieved a 32.1 by 18.9 milliarcsecond beam and approximately 20 microJy per beam rms; continuum-subtracted CO J=3–2 imaging used 0.42 km/s channels. They converted continuum upper limits into dust-mass constraints under optically thin assumptions and emitting-area constraints under an optically thick blackbody assumption.

Findings

Result No significant continuum point source was detected at AB Aur b or the other proposed candidate locations, with a 3-sigma upper limit of 60 microJy.
See the passage in the paper
We detect no significant point source at the location of AB Aur b, at any of the other proposed candidates, or elsewhere interior to the ring (Figure 1).
Result Assuming optically thin emission and a dust temperature of 40 K, the continuum limit corresponds to a circumplanetary dust mass no greater than approximately 0.0059 Earth masses.
See the passage in the paper
For optically thin emission, this corresponds to a dust mass of $\lesssim 0.0059\,M_{\oplus}$ (for a dust temperature of 40 K), comparable to the circumplanetary disk around PDS 70 c.
Result CO emission at AB Aur b connects smoothly to the surrounding disk, with no obvious localized excess or coherent velocity deviation.
See the passage in the paper
We find no obvious localized compact excess or coherent velocity deviation associated with AB Aur b: the emission at its position is smoothly connected to the ambient disk in both intensity and velocity.
Result The sensitivity excludes an SR 12 c-like disk at the 3-sigma level around the proposed candidates but only approaches the flux of the PDS 70 c circumplanetary disk.
See the passage in the paper
Our observations therefore reach a depth comparable to the known CPDs: they exclude an SR 12 c-like disk at the $3\sigma$ level around AB Aur b and the other proposed candidates, and approach the flux of the PDS 70 c CPD.
Authors’ interpretation The non-detections do not themselves disfavor a planetary interpretation because compact, optically thick, or millimeter-grain-depleted circumplanetary disks could remain undetected.
See the passage in the paper
Our non-detections do not, by themselves, disfavor a planetary interpretation for AB Aur b. A circumplanetary disk could remain undetected if it is sufficiently compact, optically thick, or depleted in millimeter-sized grains.

Limitations

Optically thin dust-mass limits depend on the assumed dust opacity and temperature.
See the passage in the paper
In this regime, the inferred dust-mass limit also depends on the assumed opacity and temperature.
For optically thick emission, the observations constrain emitting area rather than dust mass, leaving compact reservoirs essentially unconstrained in mass.
See the passage in the paper
This disfavors an extended optically thick emitting region under the blackbody assumption, but allows a more compact dust reservoir whose mass is essentially unconstrained.
The reported absence of candidate-associated velocity deviations is limited to a channel width of 0.42 km/s.
See the passage in the paper
No velocity deviations are seen at the candidate locations at our channel width of 0.42 km s-1.

Why it matters

These observations bring circumplanetary-disk searches in AB Aurigae to sensitivities comparable to known examples and constrain the dust content or emitting size of any such structures. They provide no additional evidence for a circumplanetary structure at AB Aur b, while leaving its planetary interpretation unresolved.

Written by AI from the paper. Passages are checked word for word against the text we analysed; the rest may contain errors.

AI-generated keywords: AB Aurigae circumplanetary dust ALMA observations protoplanetary disks planet formation

Read further

Comprehensive Summary
Layman's Summary
Blog article
Original abstract

This paper searches for circumplanetary dust around proposed young planets in the disk surrounding AB Aurigae, focusing on the debated candidate AB Aur b. AB Aurigae is a roughly 2–4-million-year-old star located 155.9 parsecs away. Its disk contains a broad central cavity, an asymmetric dust ring, and spiral structures. AB Aur b lies approximately 93 astronomical units (au) from the star, but previous optical and infrared observations have not established whether it is a forming planet or a feature of the surrounding disk. The authors investigate whether compact millimeter emission could provide independent evidence of material surrounding this candidate or other proposed planets. The team used ALMA observations at a wavelength of 0.88 millimeters, collected during three observing sessions in 2023 with a total on-source integration time of approximately 106 minutes. They analyzed thermal continuum emission, which traces dust, and the carbon monoxide CO J = 3–2 spectral line, which traces gas structure and motion. Their main continuum image has a resolution of approximately 32 by 19 milliarcseconds, equivalent to about 5 by 3 au, and a noise level of 20 microjanskys per beam. According to the authors, these are the most sensitive and highest-resolution observations of AB Aurigae at this wavelength, offering a tenfold improvement in point-source sensitivity over earlier observations. The continuum images reveal the asymmetric dust ring, whose emission peaks approximately 140 au from the star and is strongest on its western and southwestern sides. They also show a compact central source with an integrated flux density of 3.12 ± 0.45 millijanskys and a marginally resolved size of approximately 3.5 by 1.7 au. This central emission likely combines thermal dust emission with free–free emission from ionized gas. However, no significant compact continuum source is detected at AB Aur b, at the other proposed candidate locations, or elsewhere inside the ring apart from the stellar position. The resulting three-standard-deviation point-source upper limit is 60 microjanskys. Assuming optically thin dust emission, a temperature of 40 kelvin, and a dust opacity of 3.4 square centimeters per gram, this corresponds to a dust-mass upper limit of 0.0059 Earth masses, or approximately half the Moon’s mass. At 15 kelvin, the limit rises to 0.023 Earth masses. Accounting for estimated heating from the proposed planet and its accretion modestly reduces the limit to approximately 0.0045–0.0057 Earth masses. The observations approach the sensitivity needed to detect circumplanetary emission comparable to that around PDS 70 c, although such a source would remain below the reported detection threshold. Unlike the dust continuum, CO emission fills the cavity, revealing inner spirals and an organized rotation pattern. At AB Aur b, the gas emission connects smoothly to the surrounding disk, with no obvious compact brightness enhancement or localized velocity anomaly. None of the candidate locations shows a significant CO brightness excess. The authors conclude that these observations provide no additional evidence for circumplanetary structures, but they do not rule out planets. The dust-mass limits depend on temperature, opacity, and especially optical depth. For optically thick emission, the observations constrain the emitting area rather than the total dust mass: a face-on blackbody at 40 kelvin would need an effective radius smaller than approximately 0.41 au. Compact dust reservoirs, a depletion of millimeter-sized grains, or low dust masses could therefore explain the non-detections. Spatial filtering affects extended gas emission, while the 0.42-kilometer-per-second spectral channels limit sensitivity to subtle velocity disturbances. Multiwavelength observations and tighter size constraints would help distinguish among these possibilities.

A Sharper Look at AB Aurigae Finds No Dust Signal Around Its Proposed Planets

How do astronomers distinguish a planet taking shape from a bright patch in the disk around a young star? That question lies at the heart of the debate over AB Aur b, a proposed planet embedded in the sprawling disk surrounding AB Aurigae. New observations have searched for an independent clue: a compact reservoir of dust around the candidate itself.

In “Searching for Circumplanetary Dust in the Cavity of the AB Aurigae Disk with ALMA,” Lillian Jiang, Brendan P. Bowler, Ya-lin Wu, and Yifan Zhou report the most sensitive, highest-resolution observations of this system at a wavelength of 0.88 millimeters. They find no significant compact dust emission at AB Aur b or the other proposed planet locations. The result narrows the possibilities, but it does not settle whether planets are present.

A Young System With an Unresolved Mystery

AB Aurigae is approximately 2–4 million years old and lies 155.9 parsecs from Earth. Its disk has a broad central cavity, an asymmetric ring of dust, and spiral structures—features that make it a compelling place to investigate planet formation.

AB Aur b sits about 93 astronomical units from the star, with one astronomical unit, or au, equal to the average Earth–Sun distance. Previous optical and infrared observations have not established whether the candidate is a forming planet or a feature of the surrounding disk.

A detection of circumplanetary dust could provide a separate line of evidence. Such material would occupy a compact region around a planet rather than simply belong to the larger circumstellar disk. Millimeter observations offer a way to search for that dust through its thermal emission.

ALMA’s Close-Up View

The team used the Atacama Large Millimeter/submillimeter Array, or ALMA, during three observing sessions in 2023, accumulating approximately 106 minutes on target. They studied both dust continuum emission and the carbon monoxide CO J = 3–2 spectral line, which reveals gas structure and motion.

The main continuum image resolves scales of roughly 5 by 3 au, corresponding to 32 by 19 milliarcseconds. Its noise level is 20 microjanskys per beam. According to the authors, the observations improve point-source sensitivity tenfold over earlier measurements at this wavelength.

The images clearly reveal the asymmetric dust ring. Its emission peaks approximately 140 au from the star and is strongest toward the west and southwest. They also reveal a compact central source with an integrated flux density of 3.12 ± 0.45 millijanskys and a marginally resolved size of about 3.5 by 1.7 au. That central signal likely combines thermal dust emission with free–free emission from ionized gas.

What the Missing Dust Signal Means

Away from the stellar position, the researchers detected no significant compact continuum source inside the ring—not at AB Aur b, at other proposed candidate locations, or elsewhere. Their three-standard-deviation upper limit for a point source is 60 microjanskys.

Converting that brightness limit into a dust mass requires assumptions. If the emission is optically thin, meaning it can escape without being substantially absorbed by the dust itself, the inferred limits are:

At 40 kelvin, using a dust opacity of 3.4 square centimeters per gram, less than 0.0059 Earth masses of dust—approximately half the Moon’s mass.
At 15 kelvin, a higher limit of 0.023 Earth masses, because colder dust emits less strongly.
With estimated heating from the proposed planet and its accretion included, approximately 0.0045–0.0057 Earth masses.

These observations approach the sensitivity needed to detect circumplanetary emission comparable to that associated with PDS 70 c. However, a comparable source would still fall below the reported detection threshold. The non-detection therefore does not establish that AB Aur b lacks a dust reservoir.

Gas Fills the Cavity, but Offers No Clear Planet Signature

The gas presents a different picture from the dust. Carbon monoxide emission fills the cavity, tracing inner spirals and an organized rotation pattern. At AB Aur b, this emission connects smoothly with the surrounding disk rather than standing out as a compact brightness enhancement.

The researchers also find no obvious localized velocity anomaly there, and no significant CO brightness excess at any candidate location. These results provide no additional evidence for circumplanetary structures. However, spatial filtering affects extended gas emission, while the 0.42-kilometer-per-second spectral channels limit sensitivity to subtle disturbances.

A Constraint, Not a Verdict

The largest caveat is optical depth. If a dust reservoir is optically thick, its brightness constrains its emitting area rather than its total mass. For a face-on blackbody at 40 kelvin, the observations require an effective radius smaller than approximately 0.41 au.

A compact reservoir, a shortage of millimeter-sized grains, or a low dust mass could therefore explain the missing signal. Multiwavelength observations and tighter constraints on source size will help distinguish these possibilities. For now, ALMA has sharpened the limits around AB Aurigae’s proposed planets without closing the case on their existence.

Created on 02 Nov. 2026

Was this synthesis useful?

Score: 0

Ask questions about this paper to our AI assistant

How to chat with this paper? Illustrated guide

Compare with the PDF

You can also chat with multiple papers at once here.

AI assistant instructions?

Tools for this paper

Explain it differently 1 free rewrite left today

Save to a collection Group papers in collections to compare them, chat with them and export them. Continue with Google Create a free account Log in

Export BibTeX · RIS (Zotero, Mendeley, EndNote) · Obsidian (Markdown) · Notion (Markdown)

Advanced tools Premium

For researchers who follow a field closely: citation alerts, journal-club slides, version comparison and Zotero export. Discover Premium

Zotero

Citation alerts Citation alerts guide

Who works on it? The people and institutions who publish on its topic

Journal club Premium+ Slides to present it Propose for the journal club

Versions What changed between versions

Talk about it in public Premium+ Press kit: release, questions, hype check Press kit guide

Papers around this one

See them on a map

Ranked by how close their title and abstract are to this paper’s. Select some to read them together.

Closest papers

Very close Same question
Molecules with ALMA at Planet-forming Scales (MAPS). A Circumplanetary Disk Candidate in Molecular Line Emission in the AS 209 Disk
Jaehan Bae, Richard Teague, Sean M. Andrews et al. · 2022 · Earth and Planetary Astrophysics · cited 46 times · AI summary available

The AS 209 study searches for circumplanetary material in a protoplanetary disk, detecting a candidate through localized 13CO emission rather than finding no localized signature.

Abstract
We report the discovery of a circumplanetary disk (CPD) candidate embedded in the circumstellar disk of the T Tauri star AS 209 at a radial distance of about 200 au (on-sky separation of 1."4 from the star at a position angle of $161^\circ$), isolated via $^{13}$CO $J=2-1$ emission. This is the first instance of CPD detection via gaseous emission capable of tracing the overall CPD mass. The CPD is spatially unresolved with a $117\times82$ mas beam and manifests as a point source in $^{13}$CO, indicating that its diameter is $\lesssim14$ au. The CPD is embedded within an annular gap in the circumstellar disk previously identified using $^{12}$CO and near-infrared scattered light observations,…
Close Same question
Mid-infrared Imaging of SR 12 c with JWST/MIRI: Grain Growth in an Evolved Circumplanetary Disk
Ya-Lin Wu, Claire O. Finley, Brendan P. Bowler et al. · 2026 · Earth and Planetary Astrophysics · AI summary available

The SR 12 c study characterizes dust in a directly detected circumplanetary disk using JWST mid-infrared imaging and its infrared-to-submillimeter spectrum.

Abstract
The physical properties of circumplanetary disks offer insights into the formation of giant planets and their satellites. The circumbinary planetary-mass companion SR 12 c (1200 au from SR 12 AB) hosts an isolated dust disk directly detected with ALMA. We present JWST/MIRI imaging of SR 12 c from 5.6 to 21 $μ$m and analyze its spectral energy distribution from infrared to submillimeter wavelengths. Phenomenologically, the dust disk can be described by a two-component blackbody with large contrasts in characteristic temperatures and radii. Physically motivated models with varied geometries and heating mechanisms suggest a predominantly flat, irradiation-heated disk with a smaller contribution…
Close Same question
JWST-TST High Contrast: Medium-resolution spectroscopy reveals a carbon-rich circumplanetary disk around the young accreting exoplanet Delorme 1 AB b
Mathilde Mâlin, Kimberly Ward-Duong, Sierra L. Grant et al. · 2025 · Earth and Planetary Astrophysics · cited 6 times · AI summary available

The Delorme 1 AB b study uses JWST spectroscopy to investigate circumplanetary gas and dust around a young accreting planetary-mass companion.

Abstract
Young accreting planetary-mass objects are thought to draw material from a circumplanetary disk (CPD) composed of gas and dust. While the gas within the disk is expected to disperse within the first million years, strong accretion has nonetheless been detected in older systems, including the 30--45 Myr-old planetary-mass companion Delorme 1 AB b. We conducted spectroscopic observations with JWST/MIRI to investigate the presence of circumplanetary material around this young, accreting planet, and to characterize the planet's atmospheric properties and composition. We perform forward modeling using atmospheric models to characterize the planet's atmosphere. Beyond 10 microns, the SED becomes d…
Close Broader context
The ALMA view of MP Mus (PDS 66): a protoplanetary disk with no visible gaps down to 4 au scales
Á. Ribas, E. Macías, P. Weber et al. · 2023 · Earth and Planetary Astrophysics · cited 15 times · AI summary available

The MP Mus study uses ALMA continuum observations to characterize a protoplanetary disk's dust structure, rather than searching for circumplanetary material.

Abstract
We present ALMA multiwavelength observations of the protoplanetary disk around the nearby (d$\sim$100 pc) young solar analog MP Mus (PDS 66). These observations at 0.89 mm, 1.3 mm, and 2.2 mm have angular resolutions of $\sim$ 1", 0.05", and 0.25", respectively, and probe the dust and gas in the system with unprecedented detail and sensitivity. The disk appears smooth down to the 4 au resolution of the 1.3 mm observations, in contrast with most disks observed at comparable spatial scales. The dust disk has a radius of 60$\pm$5 au, a dust mass of $0.14_{-0.06}^{+0.11} M_{\rm Jup}$, and a mm spectral index $<2$ in the inner 30 au, suggesting optically thick emission from grains with high albed…
Close Broader context
ALMA Observations of the HD~110058 debris disk
Antonio S. Hales, SebastiÁn Marino, Patrick D. Sheehan et al. · 2022 · Solar and Stellar Astrophysics · cited 16 times · AI summary available

The HD 110058 study uses ALMA continuum and CO observations to characterize dust and gas in a debris disk.

Abstract
We present Atacama Large Millimeter Array (ALMA) observations of the young, gas-rich debris disk around HD110058 at 0.3-0.6\arcsec resolution. The disk is detected in the 0.85 and 1.3~mm continuum, as well as in the J=2-1 and J=3-2 transitions of $^{12}$CO and $^{13}$CO. The observations resolve the dust and gas distributions and reveal that this is the smallest debris disk around stars of similar luminosity observed by ALMA. The new ALMA data confirm the disk is very close to edge-on, as shown previously in scattered light images. We use radiative transfer modeling to constrain the physical properties of dust and gas disks. The dust density peaks at around 31~au and has a smooth outer edge …
Close Broader context
Resolved structure and orbital motion of a localized 1 au-scale dust accumulation in the protoplanetary disk around TW Hydrae
T. Tsukagoshi, T. Muto, H. Nomura et al. · 2026 · Nippon Tenmon Gakkai obun kenkyu hokoku · Not summarized yet

The TW Hya study combines high-resolution dust and molecular-line observations to examine a localized disk feature and its gas environment.

Abstract
We present the results of high-resolution (${\sim }1$ au) Atacama Large Millimeter/submillimeter Array (ALMA) observations of the TW Hya protoplanetary disk in the Band 6 dust continuum, as well as the $^{13}{\rm CO}$ and ${\rm C}\, {}^{18}{\rm O}$ J = 2–1 emission lines. The primary focus of this study is to investigate the kinematics, internal morphology, and local gas environment of the prominent dust blob at a radius of 52 au. By comparing our 2021 data with archival observations from 2017, we detect the proper motion of the blob. The measured azimuthal velocity of 3.3 $\pm$0.9 km s$^{-1}$ is fully consistent with local Keplerian rotation. Combined with the lack of significant radial mig…
Close Broader context
Testing planet formation from the ultraviolet to the millimeter
Nick Choksi, Eugene Chiang · 2021 · Earth and Planetary Astrophysics · cited 3 times · AI summary available

The planet-formation study estimates accretion rates for hypothesized gap-embedded planets using gas surface densities and simulated planet masses.

Abstract
Gaps imaged in protoplanetary discs are suspected to be opened by planets. We compute the present-day mass accretion rates $\dot{M}_{\rm p}$ of seven hypothesized gap-embedded planets, plus the two confirmed planets in PDS 70, by combining disc gas surface densities $\Sigma_{\rm gas}$ from C$^{18}$O observations with planet masses $M_{\rm p}$ from simulations fitted to observed gaps. Assuming accretion is Bondi-like, we find in eight out of nine cases that $\dot{M}_{\rm p}$ is consistent with the time-averaged value given by the current planet mass and system age, $M_{\rm p}/t_{\rm age}$. As system ages are comparable to circumstellar disc lifetimes, these gap-opening planets may be undergoi…
Close Broader context
Digging into the Interior of Hot Cores with ALMA (DIHCA). VII. Disk candidates around high-mass stars and evidence of anisotropic infall
Fernando A. Olguin, Patricio Sanhueza, Yoko Oya et al. · 2026 · Solar and Stellar Astrophysics · cited 2 times · AI summary available

The DIHCA study identifies candidate disks around high-mass stars from molecular-gas velocity gradients.

Abstract
We study the kinematics of condensations in 30 fields forming high-mass stars with ALMA at a high-resolution of ~0.08'' on average (~230 au). The presence of disks is important for feeding high-mass stars without feedback halting growth as their masses increase. In the search for velocity gradients resembling rotation that can reveal the presence of disks, we analyze the emission of gas tracers in 49 objects using CH$_3$OH, CH$_3$CN, and tentative detections of HNCO and cis-HCOOH. Most of the velocity distributions show velocity gradients indicative of rotation. We reveal a total of 32 disk candidates, the largest sample to date that has been uniformly analyzed at a few hundred au scales in …

Go further

How are these papers found?

We compare the title and abstract of this paper with those of every paper summarized on this site, and with the papers Semantic Scholar recommends, those it cites and those citing it (for a much-cited paper, its most recent citations and, from OpenAlex, the most cited ones). Among the prior work and the follow-ups, the papers that use each other in depth, a method it uses and the much-cited follow-ups come a little higher. The levels (very close, close, related) come from the similarity of the texts, not from a judgment of quality; * marks a paper without an abstract, compared by its title. The sentence under a paper is written by an AI from the two abstracts: check it in the papers. A paper marked not relevant by three readers leaves the list.

Updated on 2 November 2026.

Disclaimer: The AI-based summarization tool and virtual assistant provided on this website may not always provide accurate and complete summaries or responses. We encourage you to carefully review and evaluate the generated content to ensure its quality and relevance to your needs.

Searching for Circumplanetary Dust in the Cavity of the AB Aurigae Disk with ALMA

The essentials

Question

Method

Findings

Limitations

Why it matters

Read further

Definitions

A Sharper Look at AB Aurigae Finds No Dust Signal Around Its Proposed Planets

A Young System With an Unresolved Mystery

ALMA’s Close-Up View

What the Missing Dust Signal Means

Gas Fills the Cavity, but Offers No Clear Planet Signature

A Constraint, Not a Verdict

Ask questions about this paper to our AI assistant

Tools for this paper

Advanced tools Premium

Papers around this one

Closest papers

Go further

Cite this paper (BibTeX)