Evidence for a sub-Jovian planet in the young TWA 7 disk

Abstract

Planets are thought to form from dust and gas in protoplanetary disks, with debris disks being the remnants of planet formation. Aged a few million up to a few billion years, debris disks have lost their primordial gas, and their dust is produced by steady-state collisions between larger, rocky bodies^1,2. Tens of debris disks, with sizes of tens, sometimes hundreds, of astronomical units have been resolved with high-spatial-resolution, high-contrast imagers at optical and near-infrared or (sub)millimetre interferometers^3,4. They commonly show cavities, ring-like structures and gaps, which are often regarded as indirect signatures of the presence of planets that gravitationally interact with unseen planetesimals^2,5. However, no planet responsible for these features has been detected yet, probably because of the limited sensitivity (typically 2-10 M_J) of high-contrast imaging instruments (see, for example, refs. ^6-9) before the James Webb Space Telescope. Here we have used the unprecedented sensitivity of the James Webb Space Telescope's Mid-Infrared Instrument^10,11 in the thermal infrared to search for such planets in the disk of the approximately 6.4-Myr-old star TWA 7. With its pole-on orientation, this three-ring debris disk is indeed ideally suited for such a detection. We unambiguously detected a source 1.5 arcsec from the star, which is best interpreted as a cold, sub-Jupiter-mass planet. Its estimated mass (about 0.3 M_J) and position (about 52 AU, de-projected) can thoroughly account for the main disk structures.

Fig. 1. JWST MIRI image of TWA 7 in the F1140C filter.

North is up, and east is left. The status of three identified sources is indicated. Note that the faint signal north of the background galaxy is an artefact. bgd, background.

Fig. 2. Fitting of the candidate companion’s available data using the HADES model.

Modelled photometry is shown with crosses. The 1–15-μm spectra correspond to representative solutions that fit the observed flux of TWA 7b in the JWST F1140C filter (blue), with respect to the 5σ upper limits from the VLT SPHERE data in the H2 and H3 filters (red), and are consistent with an age of 6.4 ± 1 Myr. The bandwidths of H2 and H3 are 0.052 μm and 0.054 μm, respectively. A zoomed-in view around H2 and H3 highlights their bandwidths and the integrated model spectrum points below the upper limit. met, metallicity; T_eff, effective temperature; f_sed, sedimentation rate.

Fig. 3. Image of the TWA disk and candidate companion and simulations.

a, Polarimetric image (in log scale) of the disk composed of the sum of three epochs (26 April 2016 presented in ref. , 20 March 2017 presented in ref. , and a new epoch, 8 February 2022, reduced as in ref. ) from the SPHERE Infrared Dual-Band Imager and Spectrograph (IRDIS), with the MIRI image (resampled to the SPHERE pixel size) as an overlay with contours. The log of these data is provided in Supplementary Table 2. The peak densities of the rings are also indicated. The central hatched disk is a numerical mask to hide the stellar residuals. b, Disk simulations. Top view of a disk of massless planetesimals perturbed by a 0.34-M_J planet at 52 au, on a circular orbit, after 6 Myr (see details in text). The orbit of the perturbing planet is sketched in green and the location of the planet on its orbit is shown in red.

Extended Data Fig. 1. JWST individual data sets.

Orientation of the 4QPM and its phase transitions in the sky plane for the two telescope rolls. North is up, East is left.

Extended Data Fig. 2. SED of a set of 14 representative starburst galaxies and AGN at various redshifts.

The curves are distinguished by their colors, and the corresponding labels, valid for all panels. All curves are calibrated to have a flux of 22 mJy at 11 μm. The two additional constraints are marked by black symbols (square and triangle): the flux should be lower than 60 mJy at 1.6 μm, and 96 mJy at 870 μm. The SED which are not consistent with the limits are plotted in dashed lines.

Extended Data Fig. 3. Planet characterization.

Corner plot of cloudy forward modeling using SPHERE upper limits and age constraints of 6.4+/− 1 Myr. The associated priors are listed in Extended Data Table 3. The mass found is 0.34+/− 0.06 M_J (considering errors from the MCMC only). Core given in Earth mass, T_int corresponds to the intrinsic temperature and f_sed the sedimentation rate of the considered clouds.

Extended Data Fig. 4. Cooling models.

Thermal evolution curves from ref. , showing the effective temperature evolution of cloudy planets with an [Fe/H] of 0.4 dex. The estimated age and effective temperature of TWA 7b supposing the planet and star are coeval is represented by the blue point. The effective temperature used is 316+19/−23K (derived from the forward modeling) and the age 6.4+/− 1 Myr.

Extended Data Fig. 5. ALMA image of TWA7.

Combined ALMA 0.88 mm image of the TWA 7 system obtained with Briggs 0.5 weighting, centered at the phase center of the April compact configuration observations. The background galaxy is clearly detected East of the expected stellar position, at a position consistent with the East source detected by MIRI (black and white circle). The stellar location at each of the 2016 ALMA epochs is shown by the green star (positions largely overlapping), whereas the stellar location at the 2024 MIRI observation is shown by the orange star. The position of the CC#1 source at the epoch of the 2024 MIRI observation is shown by the cyan circle. The image (not primary beam-corrected) has a resolution of 0.19” x 0.18” (shown as the circle in the bottom left of the image) and an RMS noise level of 23 μJy/beam.

Extended Data Fig. 6. SPHERE detection limits.

Contrast 5-sigma confidence level curves of the SPHERE observation used to compute the upper limits on the candidate companion flux.