A Caltech Library Service

Spitzer Reveals Evidence of Molecular Absorption in the Atmosphere of the Hot Neptune LTT 9779b

Dragomir, Diana and Crossfield, Ian J. M. and Benneke, Björn and Wong, Ian and Daylan, Tansu and Díaz, Matías and Deming, Drake and Mollière, Paul and Kreidberg, Laura and Jenkins, James S. and Berardo, David and Christiansen, Jessie L. and Dressing, Courtney D. and Gorjian, Varoujan and Kane, Stephen R. and Mikal-Evans, Thomas and Morales, Farisa Y. and Werner, Michael and Ricker, George R. and Vanderspek, Roland and Seager, S. and Winn, Joshua N. and Jenkins, Jon M. and Colón, Knicole D. and Fong, Willie and Guerrero, Natalia and Hesse, Katharine and Osborn, Hugh P. and Rose, Mark E. and Smith, Jeffrey C. and Ting, Eric B. (2020) Spitzer Reveals Evidence of Molecular Absorption in the Atmosphere of the Hot Neptune LTT 9779b. Astrophysical Journal Letters, 903 (1). Art. No. L6. ISSN 2041-8213.

[img] PDF - Published Version
See Usage Policy.

[img] PDF - Accepted Version
See Usage Policy.


Use this Persistent URL to link to this item:


Non-rocky sub-Jovian exoplanets in high-irradiation environments are rare. LTT 9779b, also known as Transiting Exoplanet Survey Satellite (TESS) object of interest (TOI) 193.01, is one of the few such planets discovered to date, and the first example of an ultrahot Neptune. The planet's bulk density indicates that it has a substantial atmosphere, so to investigate its atmospheric composition and shed further light on its origin, we obtained Spitzer InfraRed Array Camera secondary eclipse observations of LTT 9779b at 3.6 and 4.5 μm. We combined the Spitzer observations with a measurement of the secondary eclipse in the TESS bandpass. The resulting secondary eclipse spectrum strongly prefers a model that includes CO absorption over a blackbody spectrum, incidentally making LTT 9779b the first TESS exoplanet (and the first ultrahot Neptune) with evidence of a spectral feature in its atmosphere. We did not find evidence of a thermal inversion, at odds with expectations based on the atmospheres of similarly irradiated hot Jupiters. We also report a nominal dayside brightness temperature of 2305 ± 141 K (based on the 3.6 μm secondary eclipse measurement), and we constrained the planet's orbital eccentricity to e < 0.01 at the 99.7% confidence level. Together with our analysis of LTT 9779b's thermal phase curves reported in a companion paper, our results set the stage for similar investigations of a larger sample of exoplanets discovered in the hot-Neptune desert, investigations that are key to uncovering the origin of this population.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Dragomir, Diana0000-0003-2313-467X
Crossfield, Ian J. M.0000-0002-1835-1891
Benneke, Björn0000-0001-5578-1498
Wong, Ian0000-0001-9665-8429
Daylan, Tansu0000-0002-6939-9211
Díaz, Matías0000-0002-2100-3257
Deming, Drake0000-0001-5727-4094
Mollière, Paul0000-0003-4096-7067
Kreidberg, Laura0000-0003-0514-1147
Jenkins, James S.0000-0003-2733-8725
Berardo, David0000-0001-6298-412X
Christiansen, Jessie L.0000-0002-8035-4778
Dressing, Courtney D.0000-0001-8189-0233
Gorjian, Varoujan0000-0002-8990-2101
Kane, Stephen R.0000-0002-7084-0529
Mikal-Evans, Thomas0000-0001-5442-1300
Morales, Farisa Y.0000-0001-9414-3851
Ricker, George R.0000-0003-2058-6662
Vanderspek, Roland0000-0001-6763-6562
Seager, S.0000-0002-6892-6948
Winn, Joshua N.0000-0002-4265-047X
Jenkins, Jon M.0000-0002-4715-9460
Colón, Knicole D.0000-0001-8020-7121
Guerrero, Natalia0000-0002-5169-9427
Hesse, Katharine0000-0002-2135-9018
Osborn, Hugh P.0000-0002-4047-4724
Rose, Mark E.0000-0003-4724-745X
Smith, Jeffrey C.0000-0002-6148-7903
Ting, Eric B.0000-0002-8219-9505
Additional Information:© 2020 The American Astronomical Society. Received 2020 July 8; revised 2020 September 7; accepted 2020 September 21; published 2020 October 26. We are grateful to the referee for feedback that has improved the clarity of the Letter and has prompted us to perform additional tests to further verify our results. We thank James Owen for his thoughts on photoevaporation's impact on exoplanet atmospheres. D.D. acknowledges support from NASA through Caltech/JPL grant RSA-1006130 and through the TESS Guest Investigator Program Grant 80NSSC19K1727. I.J.M.C. acknowledges support from the NSF through grant AST-1824644, and from NASA through Caltech/JPL grant RSA-1610091. T.D. acknowledges support from MIT's Kavli Institute as a Kavli postdoctoral fellow. M.R.D acknowledges the support of CONICYT/PFCHA-Doctorado Nacional 21140646, Chile. J.N.W. thanks the Heising-Simons Foundation for support. C.D.D. acknowledges support from the Hellman Faculty Fund, the Alfred P. Sloan Foundation, and the David and Lucile Packard Foundation. J.S.J. acknowledges support through FONDECYT grant 1201371, and partial support from CONICYT project Basal AFB-170002. This work is based [in part] on observations made with the Spitzer Space Telescope, which was operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. It is thanks to Spitzer's unique mid-IR capabilities combined with the overlap between its final year of operations and most of TESS's primary mission, that we have been able to obtain and present in this Letter the first glimpse into a hot Neptune's atmosphere. Funding for the TESS mission is provided by NASA's Science Mission directorate. We acknowledge the use of public TESS Alert data from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center. This research has made use of the Exoplanet Follow-up Observation Program website, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. Software: allesfitter (Günther & Daylan 2019), ellc (Maxted 2016), dynesty (Speagle 2020), emcee (Foreman-Mackey et al. 2013), batman (Kreidberg 2015), matplotlib (Hunter 2007), numpy (van der Walt et al. 2011), scipy (Virtanen et al. 2020). Facilities: Spitzer - Spitzer Space Telescope satellite, TESS. -
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Massachusetts Institute of Technology (MIT)UNSPECIFIED
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)21140646
Heising-Simons FoundationUNSPECIFIED
Hellman FellowshipUNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
David and Lucile Packard FoundationUNSPECIFIED
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1201371
Subject Keywords:Sky surveys ; Eclipses ; Exoplanets ; Hot Neptunes ; Infrared astronomy ; Exoplanet atmospheres
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Sky surveys (1464); Eclipses (442); Exoplanets (498); Hot Neptunes (754); Infrared astronomy (786); Exoplanet atmospheres (487)
Record Number:CaltechAUTHORS:20201027-153053132
Persistent URL:
Official Citation:Diana Dragomir et al 2020 ApJL 903 L6
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106307
Deposited By: Tony Diaz
Deposited On:27 Oct 2020 22:44
Last Modified:27 Oct 2020 22:44

Repository Staff Only: item control page