Characterizing 51 Eri b from 1 to 5 μm: a partly cloudy exoplanet

Abhijith Rajan*, Julien Rameau, Robert J. De Rosa, Mark S. Marley, James R. Graham, Bruce Macintosh, Christian Marois, Caroline Morley, Jennifer Patience, Laurent Pueyo, Didier Saumon, Kimberly Ward-Duong, S. Mark Ammons, Pauline Arriaga, Vanessa P. Bailey, Travis Barman, Joanna Bulger, Adam S. Burrows, Jeffrey Chilcote, Tara CottenIan Czekala, Rene Doyon, Gaspard Duchêne, Thomas M. Esposito, Michael P. Fitzgerald, Katherine B. Follette, Jonathan J. Fortney, Stephen J. Goodsell, Alexandra Z. Greenbaum, Pascale Hibon, Li-Wei Hung, Patrick Ingraham, Mara Johnson-Groh, Paul Kalas, Quinn Konopacky, David Lafrenière, James E. Larkin, Jérôme Maire, Franck Marchis, Stanimir Metchev, Maxwell A. Millar-Blanchaer, Katie M. Morzinski, Eric L. Nielsen, Rebecca Oppenheimer, David Palmer, Rahul I. Patel, Marshall Perrin, Lisa Poyneer, Fredrik T. Rantakyrö, Jean-Baptiste Ruffio, Dmitry Savransky, Adam C. Schneider, Anand Sivaramakrishnan, Inseok Song, Rémi Soummer, Sandrine Thomas, Gautam Vasisht, J. Kent Wallace, Jason J. Wang, Sloane Wiktorowicz, Schuyler Wolff

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We present spectrophotometry spanning 1–5 μm of 51 Eridani b, a 2–10 MJup planet discovered by the Gemini Planet Imager Exoplanet Survey. In this study, we present new K1 (1.90–2.19 μm) and K2 (2.10–2.40 μm) spectra taken with the Gemini Planet Imager as well as an updated LP (3.76 μm) and new MS (4.67 μm) photometry from the NIRC2 Narrow camera. The new data were combined with J (1.13–1.35 μm) and H (1.50–1.80 μm) spectra from the discovery epoch with the goal of better characterizing the planet properties. The 51 Eri b photometry is redder than field brown dwarfs as well as known young T-dwarfs with similar spectral type (between T4 and T8), and we propose that 51 Eri b might be in the process of undergoing the transition from L-type to T-type. We used two complementary atmosphere model grids including either deep iron/silicate clouds or sulfide/salt clouds in the photosphere, spanning a range of cloud properties, including fully cloudy, cloud-free, and patchy/intermediate-opacity clouds. The model fits suggest that 51 Eri b has an effective temperature ranging between 605 and 737 K, a solar metallicity, and a surface gravity of log(g) = 3.5–4.0 dex, and the atmosphere requires a patchy cloud atmosphere to model the spectral energy distribution (SED). From the model atmospheres, we infer a luminosity for the planet of −5.83 to −5.93 (log L/L⊙), leaving 51 Eri b in the unique position of being one of the only directly imaged planets consistent with having formed via a cold-start scenario. Comparisons of the planet SED against warm-start models indicate that the planet luminosity is best reproduced by a planet formed via core accretion with a core mass between 15 and 127 M⊕.
Original languageEnglish
Article number10
Number of pages20
JournalAstronomical Journal
Issue number1
Early online date16 Jun 2017
Publication statusPublished - 1 Jul 2017


  • Instrumentation: adaptive optics
  • Planets and satellites: atmospheres
  • Planets and satellites: composition
  • Planets and satellites: gaseous planets
  • Stars: individual: 51 Eridani


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