AuthorMoses, J. I.
Marley, Mark S.
Line, Michael R.
Fortney, Jonathan J.
Barman, Travis S.
Lewis, N. K.
Wolff, M. J.
AffiliationUniv Arizona, Lunar & Planetary Lab
planets and satellites: atmospheres
planets and satellites: composition
planets and satellites: gaseous planets
planets and satellites: individual (51 Eri b, HR 8799 b)
MetadataShow full item record
PublisherIOP PUBLISHING LTD
CitationON THE COMPOSITION OF YOUNG, DIRECTLY IMAGED GIANT PLANETS 2016, 829 (2):66 The Astrophysical Journal
JournalThe Astrophysical Journal
Rights© 2016. The American Astronomical Society. All rights reserved.
Collection InformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at email@example.com.
AbstractThe past decade has seen significant progress on the direct detection and characterization of young, self-luminous giant planets at wide orbital separations from their host stars. Some of these planets show evidence for disequilibrium processes like transport-induced quenching in their atmospheres; photochemistry may also be important, despite the large orbital distances. These disequilibrium chemical processes can alter the expected composition, spectral behavior, thermal structure, and cooling history of the planets, and can potentially confuse determinations of bulk elemental ratios, which provide important insights into planet-formation mechanisms. Using a thermo/photochemical kinetics and transport model, we investigate the extent to which disequilibrium chemistry affects the composition and spectra of directly imaged giant exoplanets. Results for specific "young Jupiters" such as HR 8799 b and 51 Eri b are presented, as are general trends as a function of planetary effective temperature, surface gravity, incident ultraviolet flux, and strength of deep atmospheric convection. We find that quenching is very important on young Jupiters, leading to CO/CH4 and N-2/NH3 ratios much greater than, and H2O mixing ratios a factor of a few less than, chemical-equilibrium predictions. Photochemistry can also be important on such planets, with CO2 and HCN being key photochemical products. Carbon dioxide becomes a major constituent when stratospheric temperatures are low and recycling of water via the H-2 + OH reaction becomes kinetically stifled. Young Jupiters with effective temperatures less than or similar to 700 K are in a particularly interesting photochemical regime that differs from both transiting hot Jupiters and our own solar-system giant planets.
VersionFinal published version
SponsorsNational Aeronautics and Space Administration through NASA Exoplanet Research Program [NNX15AN82G, NNX16AC64G]
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EFFECT OF SURFACE-MANTLE WATER EXCHANGE PARAMETERIZATIONS ON EXOPLANET OCEAN DEPTHSKomacek, Thaddeus D.; Abbot, Dorian S.; Univ Arizona, Dept Planetary Sci, Lunar & Planetary Lab (IOP PUBLISHING LTD, 2016-11-16)Terrestrial exoplanets in the canonical habitable zone may have a variety of initial water fractions due to random volatile delivery by planetesimals. If the total planetary water complement is high, the entire surface may be covered in water, forming a "waterworld." On a planet with active tectonics, competing mechanisms act to regulate the abundance of water on the surface by determining the partitioning of water between interior and surface. Here we explore how the incorporation of different mechanisms for the degassing and regassing of water changes the volatile evolution of a planet. For all of the models considered, volatile cycling reaches an approximate steady state after similar to 2 Gyr. Using these steady. states, we find that if volatile cycling is either solely dependent on temperature or seafloor pressure, exoplanets require a high abundance (greater than or similar to 0.3% of total mass) of water to have fully inundated surfaces. However, if degassing is more dependent on seafloor pressure and regassing mainly dependent on mantle temperature, the degassing rate is relatively large at late times and a steady. state between degassing and regassing is reached with a substantial surface water fraction. If this hybrid model is physical, super-Earths with a total water fraction similar to that of the Earth can become waterworlds. As a result, further understanding of the processes that drive volatile cycling on terrestrial planets is needed to determine the water fraction at which they are likely to become waterworlds.
Tides Between the TRAPPIST-1 PlanetsHay, Hamish C. F. C.; Matsuyama, Isamu; Univ Arizona, Lunar & Planetary Lab (IOP PUBLISHING LTD, 2019-04-10)The TRAPPIST-1 system is sufficiently closely packed that tides raised by one planet on another are significant. We investigate whether this source of tidal heating is comparable to eccentricity tides raised by the star. Assuming a homogeneous body with a Maxwell rheology, we find that energy dissipation from stellar tides always dominates over that from planet–planet tides across a range of viscosities. TRAPPIST-1 g may experience the greatest proportion of planet–planet tidal heating, where it can account for between 2% and 20% of the total amount of tidal heating, for high-viscosity (1021 Pa s) and low-viscosity (1014 Pa s) regimes, respectively. If planet–planet tidal heating is to exceed that from stellar eccentricity tides, orbital eccentricities must be no more than e = 10−3–10−4 for most of the TRAPPIST-1 planets.