Understanding the driving forces behind spiral arms in protoplanetary disks remains a challenge due to the faintness of young giant planets. MWC 758 hosts such a protoplanetary disk with a two-armed spiral pattern that is suggested to be driven by an external giant planet. We present observations in the thermal infrared that are uniquely sensitive to redder (that is, colder, or more attenuated) planets than past observations at shorter wavelengths. We detect a giant protoplanet, MWC 758c, at a projected separation of roughly 100 au from the star. The spectrum of MWC 758c is distinct from the rest of the disk and consistent with emission from a planetary atmosphere with Teff = 500 ± 100 K for a low level of extinction (AV ≤ 30), or a hotter object with a higher level of extinction. Both scenarios are commensurate with the predicted properties of the companion responsible for driving the spiral arms. MWC 758c provides evidence that spiral arms in protoplanetary disks can be caused by cold giant planets or by those whose optical emission is highly attenuated. MWC 758c stands out both as one of the youngest giant planets known, and as one of the coldest and/or most attenuated. Furthermore, MWC 758c is among the first planets to be observed within a system hosting a protoplanetary disk.
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All LBTI data are available online via the LBTO archive (http://archive.lbto.org).
All software, codes and data processing scripts that were developed for this study are available at https://github.com/astrowagner/MWC758_ALES.
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We thank T. Karalidi, J. Szulágyi, T. Currie, R. Fernandes, B. Ren and C. Xie for conversations that were helpful to our analysis. Support for this work was provided by NASA through the NASA Hubble Fellowship grant no. HST-HF2-51472.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract no. NAS5-26555. This paper is based on work funded by NSF Grant no. 1608834. The results reported herein benefited from collaborations and/or information exchange within NASA’s Nexus for Exoplanet System Science research coordination network sponsored by NASA’s Science Mission Directorate. M.L.S., J.W. and K.L. were supported in part by NASA XRP program via grant nos. 80NSSC20K0252 and NNX17AF88G. F.M. acknowledges funding from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 101053020, project Dust2Planets). We acknowledge the expertise of the Large Binocular Telescope Observatory (LBTO) staff, including J. Power and J. Carlson, for their support of these observations, and to LBTO director C. Veillet for enabling these observations through director’s discretionary time.
The authors declare no competing interests.
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Wagner, K., Stone, J., Skemer, A. et al. Direct images and spectroscopy of a giant protoplanet driving spiral arms in MWC 758. Nat Astron 7, 1208–1217 (2023). https://doi.org/10.1038/s41550-023-02028-3