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TRAPPIST-1: Global results of the Spitzer Exploration Science Program Red Worlds

Ducrot, E. and Gillon, M. and Delrez, L. and Agol, E. and Rimmer, P. and Turbet, M. and Günther, M. N. and Demory, B.-O. and Triaud, A. H. M. J. and Bolmont, E. and Burgasser, A. and Carey, S. J. and Ingalls, J. G. and Jehin, E. and Leconte, J. and Lederer, S. M. and Queloz, D. and Raymond, S. N. and Selsis, F. and Van Grootel, V. and de Wit, J. (2020) TRAPPIST-1: Global results of the Spitzer Exploration Science Program Red Worlds. Astronomy and Astrophysics, 640 . Art. No. A112. ISSN 0004-6361. doi:10.1051/0004-6361/201937392.

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Context. With more than 1000 h of observation from Feb. 2016 to Oct. 2019, the Spitzer Exploration Program Red Worlds (ID: 13067, 13175 and 14223) exclusively targeted TRAPPIST-1, a nearby (12 pc) ultracool dwarf star, finding that it is orbited by seven transiting Earth-sized planets. At least three of these planets orbit within the classical habitable zone of the star, and all of them are well-suited for a detailed atmospheric characterization with the upcoming JWST. Aims. The main goals of the Spitzer Red Worlds program were (1) to explore the system for new transiting planets, (2) to intensively monitor the planets’ transits to yield the strongest possible constraints on their masses, sizes, compositions, and dynamics, and (3) to assess the infrared variability of the host star. In this paper, we present the global results of the project. Methods. We analyzed 88 new transits and combined them with 100 previously analyzed transits, for a total of 188 transits observed at 3.6 or 4.5 μm. For a comprehensive study, we analyzed all light curves both individually and globally. We also analyzed 29 occultations (secondary eclipses) of planet b and eight occultations of planet c observed at 4.5 μm to constrain the brightness temperatures of their daysides. Results. We identify several orphan transit-like structures in our Spitzer photometry, but all of them are of low significance. We do not confirm any new transiting planets. We do not detect any significant variation of the transit depths of the planets throughout the different campaigns. Comparing our individual and global analyses of the transits, we estimate for TRAPPIST-1 transit depth measurements mean noise floors of ~35 and 25 ppm in channels 1 and 2 of Spitzer/IRAC, respectively. We estimate that most of this noise floor is of instrumental origins and due to the large inter-pixel inhomogeneity of IRAC InSb arrays, and that the much better interpixel homogeneity of JWST instruments should result in noise floors as low as 10 ppm, which is low enough to enable the atmospheric characterization of the planets by transit transmission spectroscopy. Our analysis reveals a few outlier transits, but we cannot conclude whether or not they correspond to spot or faculae crossing events. We construct updated broadband transmission spectra for all seven planets which show consistent transit depths between the two Spitzer channels. Although we are limited by instrumental precision, the combined transmission spectrum of planet b to g tells us that their atmospheres seem unlikely to be CH4-dominated. We identify and model five distinct high energy flares in the whole dataset, and discuss our results in the context of habitability. Finally, we fail to detect occultation signals of planets b and c at 4.5 μm, and can only set 3-σ upper limits on their dayside brightness temperatures (611 K for b 586 K for c).

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Ducrot, E.0000-0002-7008-6888
Gillon, M.0000-0003-1462-7739
Delrez, L.0000-0001-6108-4808
Agol, E.0000-0002-0802-9145
Rimmer, P.0000-0002-7180-081X
Günther, M. N.0000-0002-3164-9086
Demory, B.-O.0000-0002-9355-5165
Triaud, A. H. M. J.0000-0002-5510-8751
Bolmont, E.0000-0001-5657-4503
Burgasser, A.0000-0002-6523-9536
Carey, S. J.0000-0002-0221-6871
Ingalls, J. G.0000-0003-4714-1364
Jehin, E.0000-0001-8923-488X
Leconte, J.0000-0002-3555-480X
Lederer, S. M.0000-0003-2805-8653
Queloz, D.0000-0002-3012-0316
Raymond, S. N.0000-0001-8974-0758
Selsis, F.0000-0001-9619-5356
Van Grootel, V.0000-0003-2144-4316
de Wit, J.0000-0003-2415-2191
Additional Information:© ESO 2020. Article published by EDP Sciences. Received 21 December 2019; Accepted 15 June 2020; Published online 24 August 2020. We thank Benjamin Rackham for useful discussions and the anonymous referee for very constructive remarks that improved the paper in a significant way. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. The research leading to these results has received funding from the European Research Council under the FP/2007-2013 ERC Grant Agreement no. 336480, the European Union’s Horizon 2020 research and innovation programme (grant agreement n° 679030/WHIPLASH), and from the ARC grant for Concerted Research Actions, financed by the Wallonia-Brussels Federation. This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant Agreement n° 832738/ESCAPE. M.T. and L.D. acknowledge funding from the Gruber Foundation. M.G., E.J., and V.V.G. are F.R.S.-FNRS senior Research Associates. P.B.R. acknowledges support from the Simons Foundation (SCOL Grant #599634). M.N.G. acknowledges support from MIT’s Kavli Institute as a Juan Carlos Torres Fellow. This work has been carried out within the framework of the National Centre of Competence in Research PlanetS supported by the Swiss National Science Foundation. The authors acknowledge the financial support of the SNSF.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
European Research Council (ERC)336480
European Research Council (ERC)679030
Australian Research CouncilUNSPECIFIED
Wallonia-Brussels FederationUNSPECIFIED
Marie Curie Fellowship832738
Gruber FoundationUNSPECIFIED
Fonds de la Recherche Scientifique (FNRS)UNSPECIFIED
Simons Foundation599634
Massachusetts Institute of Technology (MIT)UNSPECIFIED
Swiss National Science Foundation (SNSF)UNSPECIFIED
Subject Keywords:planets and satellites: terrestrial planets – planets and satellites: atmospheres – techniques: photometric
Record Number:CaltechAUTHORS:20200824-152231639
Persistent URL:
Official Citation:TRAPPIST-1: Global results of the Spitzer Exploration Science Program Red Worlds. E. Ducrot, M. Gillon, L. Delrez, E. Agol, P. Rimmer, M. Turbet, M. N. Günther, B.-O. Demory, A. H. M. J. Triaud, E. Bolmont, A. Burgasser, S. J. Carey, J. G. Ingalls, E. Jehin, J. Leconte, S. M. Lederer, D. Queloz, S. N. Raymond, F. Selsis, V. Van Grootel and J. de Wit. A&A, 640 (2020) A112; DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105089
Deposited By: Tony Diaz
Deposited On:24 Aug 2020 23:02
Last Modified:16 Nov 2021 18:39

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