A temperate super-Jupiter imaged with JWST in the mid-infrared

Abstract

Of the approximately 25 directly imaged planets to date, all are younger than 500 Myr, and all but six are younger than 100 Myr (ref. ¹). Eps Ind A (HD209100, HIP108870) is a K5V star of roughly solar age (recently derived as 3.7-5.7 Gyr (ref. ²) and ${3.5}_{-1.3}^{+0.8}$ Gyr (ref. ³)). A long-term radial-velocity trend^4,5 and an astrometric acceleration^6,7 led to claims of a giant planet^2,8,9 orbiting the nearby star (3.6384 ± 0.0013 pc; ref. ¹⁰). Here we report JWST coronagraphic images which reveal a giant exoplanet that is consistent with these radial and astrometric measurements but inconsistent with the previously claimed planet properties. The new planet has a temperature of approximately 275 K and is remarkably bright at 10.65 and 15.50 µm. Non-detections between 3.5 and 5.0 µm indicate an unknown opacity source in the atmosphere, possibly suggesting a high-metallicity, high carbon-to-oxygen ratio planet. The best-fitting temperature of the planet is consistent with theoretical thermal evolution models, which were previously untested at this temperature range. The data indicate that this is probably the only giant planet in the system, and therefore we refer to it as b, despite it having significantly different orbital properties than the previously claimed planet b.

Fig. 1. Point source detected in JWST/MIRI coronagraphic images of Eps Ind A.

The target was observed at 10.65 and 15.50 µm. Starlight was removed with RDI. Only the central portion of the field of view is shown. The stellar position is marked with an orange star. A bright point source was detected in the upper left corner of these images at a projected separation 4.11″ (15.0 au at the distance of Eps Ind A). Top scale bar, 2.75″ = 10.0 au; bottom scale bar, 2″ = 7.28 au.

Fig. 2. Point source detected at a consistent location in VISIR/NEAR images of Eps Ind A.

a,b, Co-added images (main panels) and PCA results for a small patch around the expected target location (insets). Panel b shows the images in a after convolution with a top-hat function.

Fig. 3. Eps Ind Ab is consistent with theoretical atmosphere models with suppressed 3.5–5.0 µm flux.

Measured photometry (squares and circles with uncertainties of 1σ) and 5σ upper limits (triangles), compared to out-of-the-box model spectra^, (coloured lines; circles indicate the integrated flux for each observed filter). Normalized filter profiles are overlaid as grey lines. Planet radii are scaled to match the measured 15.50 µm photometry, and labels indicate the temperature T, surface gravity g, log eddy diffusion coefficient (log(zz)), log-metallicity ([M/H]), and carbon-to-oxygen ratio (C/O). The ATMO models include non-equilibrium (NEQ) chemistry. A high metallicity and carbon-to-oxygen ratio are required to suppress the 3.5–5.0 µm flux to below the observed upper limit.

Fig. 4. Comparison of Eps Ind Ab to evolutionary models.

Cooling curves for a 6.3 M_J planet and an 8.6 M_J planet for models with equilibrium and with non-equilibrium chemistry. The mid-infrared companion photometry is consistent with a more massive planet, although these models do not incorporate the high metallicity or carbon-to-oxygen ratio of the planet nor the correspondingly low 3.5–5.0 µm flux.

Extended Data Fig. 1. Full field-of-view JWST/MIRI coronagraphic images of Eps Ind A in the 10.65 µm filter.

Two visual companions to Eps Ind A, and one visual companion to DI Tuc, are identified: (1) is Eps Ind Ab, (2) is the background star Gaia DR3 6412595290591430784 (also identified in the Spitzer 8 µm observations of the background field) and (3) is the background star Gaia DR3 6411654761473726464 in the field of the DI Tuc observations.

Extended Data Fig. 2. Contrast sensitivity of the MIRI observations.

Curves are 5$\sigma$ sensitivities calculated with spaceKLIP for each coronagraphic filter.

Extended Data Fig. 3. Spitzer IRAC images of Eps Ind A.

The three columns show the science-ready Eps Ind A image from the Spitzer archive (left), an RDI processed image with Eps Eri subtracted from Eps Ind A (centre), and the RDI processed image zoomed at the JWST epoch position of Eps Ind A (right). For the RDI processed image, purple (negative) sources are in the field of the reference star, and orange (positive) sources are in the field of Eps Ind A. Blue and green circles have radii 10'', and are centred on the Spitzer and JWST epoch positions of Eps Ind A respectively. If Eps Ind Ab were a background object, it would be ~4'' from the JWST epoch position of Eps Ind A. This is well within the blue circle. One source is identified within this circle at 3.6 µm, 4.5 µm and marginally at 5.8 µm: this is a background star also identified in the JWST/MIRI images (see text for details).

Extended Data Fig. 4. Spitzer MIPS 24µm and 70µm images of Eps Ind A.

Blue and green circles have radii 20'', and are centred on the Spitzer and JWST epoch positions of Eps Ind A respectively; no sources are detected at the background position (the JWST epoch position of Eps Ind A). The 70 µm data cover only a narrow strip around the Eps Ind A location, and white regions at the edge of the box indicate regions outside the telescope field of view.

Extended Data Fig. 5. Spectrum (measured flux and upper limits) of the point source if it were a background object.

These upper limits apply only if the point source were a stationary background at RA = 22:03:33.17 and Dec = −56:48:06.0. Constraints for the planetary case (which require high-contrast facilities to resolve a source that moves with same proper motion as the host star) are given in Fig. 3. Green circles indicate the measured JWST photometry, while pink triangles indicate upper limits from Gaia, 2MASS, Spitzer/IRAC and Spitzer/MIPS. Most stationary background contaminants would not reproduce the 10.65 µm and 15.50 µm flux while evading detection at other wavelengths.

Extended Data Fig. 6. Orbit fits including RV, Hipparcos-Gaia astrometry, and both imaging points (left) or the JWST imaging only (right), assuming Eps Ind Ab is the only massive planet in the system.

Rows represent (1) the on-sky orbit, (2) the RV of the target (3) the proper motion in right ascension of the host star and (4) the proper motion in declination of the host star. Orbits are very similar in both cases, and explain all in-hand data. RVs are from LC (green), VLC (pink), HARPS03 (cyan), UVES (yellow), HARPS15 (blue) and HARPS20 (pink).

Extended Data Fig. 7. Best-fit spectrum for Eps Ind A.

The spectrum is shown in black and integrated to R~100. Measured photometry is shown in green if included in the fit, and pink otherwise, while the model photometry is indicated in blue. The WISE W1, W2, and W3 channels are saturated, and in particular the W1 and W3 magnitudes are several $\sigma$ fainter than the best-fit model.