skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: FORWARD AND INVERSE MODELING OF THE EMISSION AND TRANSMISSION SPECTRUM OF GJ 436B: INVESTIGATING METAL ENRICHMENT, TIDAL HEATING, AND CLOUDS

Abstract

The Neptune-mass GJ 436b is one of the most studied transiting exoplanets with repeated measurements of its thermal emission and transmission spectra. We build on previous studies to answer outstanding questions about this planet, including its potentially high metallicity and tidal heating of its interior. We present new observations of GJ 436b’s thermal emission at 3.6 and 4.5 μ m, which reduce uncertainties in estimates of GJ 436b’s flux at those wavelengths and demonstrate consistency between Spitzer observations spanning more than 7 yr. We analyze the Spitzer thermal emission photometry and Hubble WFC3 transmission spectrum. We use a dual-pronged modeling approach of both self-consistent and retrieval models. We vary the metallicity, intrinsic luminosity from tidal heating, disequilibrium chemistry, and heat redistribution. We also study clouds and photochemical hazes, but do not find strong evidence for either. The self-consistent and retrieval models combine to suggest that GJ 436b has a high atmospheric metallicity, with best fits at or above several hundred times solar metallicity, tidal heating warming its interior with best-fit intrinsic effective temperatures around 300–350 K, and disequilibrium chemistry. High metal enrichments (>600× solar) occur from the accretion of rocky, rather than icy, material. Assuming the interior temperature T {submore » int} ∼ 300–350 K, we find a dissipation factor Q ′ ∼ 2 × 10{sup 5}–10{sup 6}, larger than Neptune’s Q ′, implying a long tidal circularization timescale for the orbit. We suggest that Neptune-mass planets may be more diverse than imagined, with metal enhancements spanning several orders of magnitude, to perhaps over 1000× solar metallicity. High-fidelity observations with instruments like the James Webb Space Telescope will be critical for characterizing this diversity.« less

Authors:
 [1];  [2];  [3]; ;  [4];  [5]; ;  [6]
  1. Department of Astronomy, Harvard University, 60 Garden Street, Cambridge, MA 02138 (United States)
  2. Division of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States)
  3. School of Earth and Space Exploration, Arizona State University, 781 South Terrace Road, Tempe, AZ 85281 (United States)
  4. Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)
  5. Department of Physics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)
  6. NASA Ames Research Center, Moffett Field, CA 94035 (United States)
Publication Date:
OSTI Identifier:
22663862
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (Online); Journal Volume: 153; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CLOUDS; DISSIPATION FACTOR; EMISSION; HEATING; LUMINOSITY; MASS; METALLICITY; METALS; NEPTUNE PLANET; ORBITS; PHOTOCHEMISTRY; PHOTOMETRY; SATELLITE ATMOSPHERES; SATELLITES; TELESCOPES; WAVELENGTHS

Citation Formats

Morley, Caroline V., Knutson, Heather, Line, Michael, Fortney, Jonathan J., Teal, Dillon, Thorngren, Daniel, Marley, Mark S., and Lupu, Roxana, E-mail: caroline.morley@cfa.harvard.edu. FORWARD AND INVERSE MODELING OF THE EMISSION AND TRANSMISSION SPECTRUM OF GJ 436B: INVESTIGATING METAL ENRICHMENT, TIDAL HEATING, AND CLOUDS. United States: N. p., 2017. Web. doi:10.3847/1538-3881/153/2/86.
Morley, Caroline V., Knutson, Heather, Line, Michael, Fortney, Jonathan J., Teal, Dillon, Thorngren, Daniel, Marley, Mark S., & Lupu, Roxana, E-mail: caroline.morley@cfa.harvard.edu. FORWARD AND INVERSE MODELING OF THE EMISSION AND TRANSMISSION SPECTRUM OF GJ 436B: INVESTIGATING METAL ENRICHMENT, TIDAL HEATING, AND CLOUDS. United States. doi:10.3847/1538-3881/153/2/86.
Morley, Caroline V., Knutson, Heather, Line, Michael, Fortney, Jonathan J., Teal, Dillon, Thorngren, Daniel, Marley, Mark S., and Lupu, Roxana, E-mail: caroline.morley@cfa.harvard.edu. Wed . "FORWARD AND INVERSE MODELING OF THE EMISSION AND TRANSMISSION SPECTRUM OF GJ 436B: INVESTIGATING METAL ENRICHMENT, TIDAL HEATING, AND CLOUDS". United States. doi:10.3847/1538-3881/153/2/86.
@article{osti_22663862,
title = {FORWARD AND INVERSE MODELING OF THE EMISSION AND TRANSMISSION SPECTRUM OF GJ 436B: INVESTIGATING METAL ENRICHMENT, TIDAL HEATING, AND CLOUDS},
author = {Morley, Caroline V. and Knutson, Heather and Line, Michael and Fortney, Jonathan J. and Teal, Dillon and Thorngren, Daniel and Marley, Mark S. and Lupu, Roxana, E-mail: caroline.morley@cfa.harvard.edu},
abstractNote = {The Neptune-mass GJ 436b is one of the most studied transiting exoplanets with repeated measurements of its thermal emission and transmission spectra. We build on previous studies to answer outstanding questions about this planet, including its potentially high metallicity and tidal heating of its interior. We present new observations of GJ 436b’s thermal emission at 3.6 and 4.5 μ m, which reduce uncertainties in estimates of GJ 436b’s flux at those wavelengths and demonstrate consistency between Spitzer observations spanning more than 7 yr. We analyze the Spitzer thermal emission photometry and Hubble WFC3 transmission spectrum. We use a dual-pronged modeling approach of both self-consistent and retrieval models. We vary the metallicity, intrinsic luminosity from tidal heating, disequilibrium chemistry, and heat redistribution. We also study clouds and photochemical hazes, but do not find strong evidence for either. The self-consistent and retrieval models combine to suggest that GJ 436b has a high atmospheric metallicity, with best fits at or above several hundred times solar metallicity, tidal heating warming its interior with best-fit intrinsic effective temperatures around 300–350 K, and disequilibrium chemistry. High metal enrichments (>600× solar) occur from the accretion of rocky, rather than icy, material. Assuming the interior temperature T {sub int} ∼ 300–350 K, we find a dissipation factor Q ′ ∼ 2 × 10{sup 5}–10{sup 6}, larger than Neptune’s Q ′, implying a long tidal circularization timescale for the orbit. We suggest that Neptune-mass planets may be more diverse than imagined, with metal enhancements spanning several orders of magnitude, to perhaps over 1000× solar metallicity. High-fidelity observations with instruments like the James Webb Space Telescope will be critical for characterizing this diversity.},
doi = {10.3847/1538-3881/153/2/86},
journal = {Astronomical Journal (Online)},
number = 2,
volume = 153,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}