148 results on '"Cowan, Nicolas B."'
Search Results
2. Transmission Spectroscopy of the Habitable Zone Exoplanet LHS 1140 b with JWST/NIRISS.
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Cadieux, Charles, Doyon, René, MacDonald, Ryan J., Turbet, Martin, Artigau, Étienne, Lim, Olivia, Radica, Michael, Fauchez, Thomas J., Salhi, Salma, Dang, Lisa, Albert, Loïc, Coulombe, Louis-Philippe, Cowan, Nicolas B., Lafrenière, David, L'Heureux, Alexandrine, Piaulet-Ghorayeb, Caroline, Benneke, Björn, Cloutier, Ryan, Charnay, Benjamin, and Cook, Neil J.
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- 2024
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3. Constraining Exoplanet Metallicities and Aerosols with the Contribution to ARIEL Spectroscopy of Exoplanets (CASE)
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Zellem, Robert T., Swain, Mark R., Cowan, Nicolas B., Bryden, Geoffrey, Komacek, Thaddeus D., Colavita, Mark, Ardila, David, Roudier, Gael M., Fortney, Jonathan J., Bean, Jacob, Line, Michael R., Griffith, Caitlin A., Shkolnik, Evgenya L., Kreidberg, Laura, Moses, Julianne I., Showman, Adam P., Stevenson, Kevin B., Wong, Andre, Chapman, John W., Ciardi, David R., Howard, Andrew W., Kataria, Tiffany, Kempton, Eliza M.-R., Latham, David, Mahadevan, Suvrath, Meléndez, Jorge, and Parmentier, Vivien
- Published
- 2019
4. A Framework for Prioritizing the TESS Planetary Candidates Most Amenable to Atmospheric Characterization
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Kempton, Eliza M.-R., Bean, Jacob L., Louie, Dana R., Deming, Drake, Koll, Daniel D. B., Mansfield, Megan, Christiansen, Jessie L., López-Morales, Mercedes, Swain, Mark R., Zellem, Robert T., Ballard, Sarah, Barclay, Thomas, Barstow, Joanna K., Batalha, Natasha E., Beatty, Thomas G., Berta-Thompson, Zach, Birkby, Jayne, Buchhave, Lars A., Charbonneau, David, Cowan, Nicolas B., Crossfield, Ian, de Val-Borro, Miguel, Doyon, René, Dragomir, Diana, Gaidos, Eric, Heng, Kevin, Hu, Renyu, Kane, Stephen R., Kreidberg, Laura, Mallonn, Matthias, Morley, Caroline V., Narita, Norio, Nascimbeni, Valerio, Pallé, Enric, Quintana, Elisa V., Rauscher, Emily, Seager, Sara, Shkolnik, Evgenya L., Sing, David K., Sozzetti, Alessandro, Stassun, Keivan G., Valenti, Jeff A., and von Essen, Carolina
- Published
- 2018
5. Uniformly hot nightside temperatures on short-period gas giants
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Keating, Dylan, Cowan, Nicolas B., and Dang, Lisa
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- 2019
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6. Near-infrared transmission spectroscopy of HAT-P-18 b with NIRISS: Disentangling planetary and stellar features in the era of JWST.
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Fournier-Tondreau, Marylou, MacDonald, Ryan J, Radica, Michael, Lafrenière, David, Welbanks, Luis, Piaulet, Caroline, Coulombe, Louis-Philippe, Allart, Romain, Morel, Kim, Artigau, Étienne, Albert, Loïc, Lim, Olivia, Doyon, René, Benneke, Björn, Rowe, Jason F, Darveau-Bernier, Antoine, Cowan, Nicolas B, Lewis, Nikole K, Cook, Neil J, and Flagg, Laura
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NEAR infrared spectroscopy ,LIGHT sources ,STELLAR atmospheres ,NATURAL satellite atmospheres ,NATURAL satellites ,LIGHT curves - Abstract
The JWST Early Release Observations (ERO) included a NIRISS/SOSS (0.6–2.8 μ m) transit of the ∼ 850 K Saturn-mass exoplanet HAT-P-18 b. Initial analysis of these data reported detections of water, escaping helium and haze. However, active K dwarfs like HAT-P-18 possess surface heterogeneities – star-spots and faculae – that can complicate the interpretation of transmission spectra, and indeed, a spot-crossing event is present in HAT-P-18 b's NIRISS/SOSS light curves. Here, we present an extensive reanalysis and interpretation of the JWST ERO transmission spectrum of HAT-P-18 b, as well as HST /WFC3 and Spitzer /IRAC transit observations. We detect H
2 O (12.5σ), CO2 (7.3σ), a cloud deck (7.4σ), and unocculted star-spots (5.8σ), alongside hints of Na (2.7σ). We do not detect the previously reported CH4 (log CH4 < −6 to 2σ). We obtain excellent agreement between three independent retrieval codes, which find a sub-solar H2 O abundance (log H2 O ≈ −4.4 ± 0.3). However, the inferred CO2 abundance (log CO2 ≈ −4.8 ± 0.4) is significantly super-solar and requires further investigation into its origin. We also introduce new stellar heterogeneity considerations by fitting for the active regions' surface gravities – a proxy for the effects of magnetic pressure. Finally, we compare our JWST inferences to those from HST /WFC3 and Spitzer /IRAC. Our results highlight the exceptional promise of simultaneous planetary atmosphere and stellar heterogeneity constraints in the era of JWST and demonstrate that JWST transmission spectra may warrant more complex treatments of the transit light source effect. [ABSTRACT FROM AUTHOR]- Published
- 2024
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7. Quantifying the Impact of Spectral Coverage on the Retrieval of Molecular Abundances from Exoplanet Transmission Spectra
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Chapman, John W., Zellem, Robert T., Line, Michael R., Vasisht, Gautam, Bryden, Geoff, Willacy, Karen, Iyer, Aishwarya R., Bean, Jacob, Cowan, Nicolas B., Fortney, Jonathan J., Griffith, Caitlin A., Kataria, Tiffany, Kempton, Eliza M.-R., Kreidberg, Laura, Moses, Julianne I., Stevenson, Kevin B., and Swain, Mark R.
- Published
- 2017
8. The role of magma oceans in maintaining surface water on rocky planets orbiting M-dwarfs.
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Moore, Keavin, Cowan, Nicolas B, and Boukaré, Charles-Édouard
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PLANETARY orbits , *MAGMAS , *HABITABLE planets , *INNER planets , *SEAWATER , *DWARF stars , *OCEAN - Abstract
Earth-like planets orbiting M-dwarf stars, M-Earths, are currently the best targets to search for signatures of life. Life as we know it requires water. The habitability of M-Earths is jeopardized by water loss to space: high flux from young M-dwarf stars can drive the loss of 3–20 Earth oceans from otherwise habitable planets. We develop a 0-D box model for Earth-mass terrestrial exoplanets, orbiting within the habitable zone, which tracks water loss to space and exchange between reservoirs during an early surface magma ocean phase and the longer deep-water cycling phase. A key feature is the duration of the surface magma ocean, assumed concurrent with the runaway greenhouse. This time-scale can discriminate between desiccated planets, planets with desiccated mantles but substantial surface water, and planets with significant water sequestered in the mantle. A longer-lived surface magma ocean helps M-Earths retain water: dissolution of water in the magma provides a barrier against significant loss to space during the earliest, most active stage of the host M-dwarf, depending on the water saturation limit of the magma. Although a short-lived basal magma ocean can be beneficial to surface habitability, a long-lived basal magma ocean may sequester significant water in the mantle at the detriment of surface habitability. We find that magma oceans and deep-water cycling can maintain or recover habitable surface conditions on Earth-like planets at the inner edge of the habitable zone around late M-dwarf stars – these planets would otherwise be desiccated if they form with less than ∼10 terrestrial oceans of water. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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9. Chasing rainbows and ocean glints: Inner working angle constraints for the Habitable Worlds Observatory.
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Vaughan, Sophia R, Gebhard, Timothy D, Bott, Kimberly, Casewell, Sarah L, Cowan, Nicolas B, Doelman, David S, Kenworthy, Matthew, Mazoyer, Johan, Millar-Blanchaer, Maxwell A, Trees, Victor J H, Stam, Daphne M, Absil, Olivier, Altinier, Lisa, Baudoz, Pierre, Belikov, Ruslan, Bidot, Alexis, Birkby, Jayne L, Bonse, Markus J, Brandl, Bernhard, and Carlotti, Alexis
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EARTH (Planet) ,RAINBOWS ,OBSERVATORIES ,RAYLEIGH scattering ,HABITABLE planets - Abstract
NASA is engaged in planning for a Habitable Worlds Observatory (HabWorlds ), a coronagraphic space mission to detect rocky planets in habitable zones and establish their habitability. Surface liquid water is central to the definition of planetary habitability. Photometric and polarimetric phase curves of starlight reflected by an exoplanet can reveal ocean glint, rainbows, and other phenomena caused by scattering by clouds or atmospheric gas. Direct imaging missions are optimized for planets near quadrature, but HabWorlds ' coronagraph may obscure the phase angles where such optical features are strongest. The range of accessible phase angles for a given exoplanet will depend on the planet's orbital inclination and/or the coronagraph's inner working angle (IWA). We use a recently created catalog relevant to HabWorlds of 164 stars to estimate the number of exo-Earths that could be searched for ocean glint, rainbows, and polarization effects due to Rayleigh scattering. We find that the polarimetric Rayleigh scattering peak is accessible in most of the exo-Earth planetary systems. The rainbow due to water clouds at phase angles of ∼20
○ − 60○ would be accessible with HabWorlds for a planet with an Earth equivalent instellation in ∼46 systems, while the ocean glint signature at phase angles of ∼130○ − 170○ would be accessible in ∼16 systems, assuming an IWA = 62 mas (3λ/ D). Improving the IWA = 41 mas (2λ/ D) increases accessibility to rainbows and glints by factors of approximately 2 and 3, respectively. By observing these scattering features, HabWorlds could detect a surface ocean and water cycle, key indicators of habitability. [ABSTRACT FROM AUTHOR]- Published
- 2023
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10. Warm Jupiters Beyond the Tidal Synchronization Limit May Exhibit a Wide Range of Secondary Eclipse Depths
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Rauscher, Emily, Cowan, Nicolas B., and Luger, Rodrigo
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Earth and Planetary Astrophysics (astro-ph.EP) ,FOS: Physical sciences ,Astrophysics - Earth and Planetary Astrophysics - Abstract
With JWST we can now characterize the atmospheres of planets on longer orbital planets, but this moves us into a regime where we cannot assume that tidal forces from the star have eroded planets' obliquities and synchronized their rotation rates. These rotation vectors may be tracers of formation and evolution histories and also enable a range of atmospheric circulation states. Here we delineate the orbital space over which tidal synchronization and alignment assumptions may no longer apply and present three-dimensional atmospheric models of a hypothetical warm Jupiter over a range of rotation rates and obliquities. We simulate the secondary eclipses of this planet for different possible viewing orientations and times during its orbital, seasonal cycle. We find that the eclipse depth can be strongly influenced by rotation rate and obliquity through the timing of the eclipse relative to the planet's seasonal cycle, and advise caution in attempting to derive properties such as albedo or day-night transport from this measurement. We predict that if warm Jupiters beyond the tidal limit have intrinsic diversity in their rotation vectors, then it will manifest itself as dispersion in their secondary eclipse depths. We explore eclipse mapping as a way to uniquely constrain the rotation vector of warm Jupiters but find that the associated signals are likely at the edge of JWST performance. Nevertheless, as JWST begins to measure the secondary eclipses of longer orbital period planets, we should expect to observe the consequences of a wider range of rotation states and circulation patterns., 14 pages, 6 figures, animated figures available in the journal's online version
- Published
- 2023
11. Awesome SOSS: Transmission Spectroscopy of WASP-96b with NIRISS/SOSS
- Author
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Radica, Michael, Welbanks, Luis, Espinoza, Néstor, Taylor, Jake, Coulombe, Louis-Philippe, Feinstein, Adina D., Goyal, Jayesh, Scarsdale, Nicholas, Albert, Loic, Baghel, Priyanka, Bean, Jacob L., Blecic, Jasmina, Lafrenière, David, MacDonald, Ryan J., Zamyatina, Maria, Allart, Romain, Artigau, Étienne, Batalha, Natasha E., Cook, Neil James, Cowan, Nicolas B., Dang, Lisa, Doyon, René, Fournier-Tondreau, Marylou, Johnstone, Doug, Line, Michael R., Moran, Sarah E., Mukherjee, Sagnick, Pelletier, Stefan, Roy, Pierre-Alexis, Talens, Geert Jan, Filippazzo, Joseph, Pontoppidan, Klaus, and Volk, Kevin
- Subjects
Earth and Planetary Astrophysics (astro-ph.EP) ,FOS: Physical sciences ,Astrophysics - Earth and Planetary Astrophysics - Abstract
The future is now - after its long-awaited launch in December 2021, JWST began science operations in July 2022 and is already revolutionizing exoplanet astronomy. The Early Release Observations (ERO) program was designed to provide the first images and spectra from JWST, covering a multitude of science cases and using multiple modes of each on-board instrument. Here, we present transmission spectroscopy observations of the hot-Saturn WASP-96b with the Single Object Slitless Spectroscopy (SOSS) mode of the Near Infrared Imager and Slitless Spectrograph, observed as part of the ERO program. As the SOSS mode presents some unique data reduction challenges, we provide an in-depth walk-through of the major steps necessary for the reduction of SOSS data: including background subtraction, correction of 1/f noise, and treatment of the trace order overlap. We furthermore offer potential routes to correct for field star contamination, which can occur due to the SOSS mode's slitless nature. By comparing our extracted transmission spectrum with grids of atmosphere models, we find an atmosphere metallicity between 1x and 5x solar, and a solar carbon-to-oxygen ratio. Moreover, our models indicate that no grey cloud deck is required to fit WASP-96b's transmission spectrum, but find evidence for a slope shortward of 0.9$\mu$m, which could either be caused by enhanced Rayleigh scattering or the red wing of a pressure-broadened Na feature. Our work demonstrates the unique capabilities of the SOSS mode for exoplanet transmission spectroscopy and presents a step-by-step reduction guide for this new and exciting instrument., Comment: MNRAS, in press. Updated to reflect published version
- Published
- 2023
12. Clearing up the clouds on hot gas giants
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Cowan, Nicolas B. and Rauscher, Emily
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- 2020
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13. Detection of a westward hotspot offset in the atmosphere of hot gas giant CoRoT-2b
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Dang, Lisa, Cowan, Nicolas B., Schwartz, Joel C., Rauscher, Emily, Zhang, Michael, Knutson, Heather A., Line, Michael, Dobbs-Dixon, Ian, Deming, Drake, Sundararajan, Sudarsan, Fortney, Jonathan J., and Zhao, Ming
- Published
- 2018
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14. Transiting Exoplanet Studies and Community Targets for JWST ʼs Early Release Science Program
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Stevenson, Kevin B., Lewis, Nikole K., Bean, Jacob L., Beichman, Charles, Fraine, Jonathan, Kilpatrick, Brian M., Krick, J. E., Lothringer, Joshua D., Mandell, Avi M., Valenti, Jeff A., Agol, Eric, Angerhausen, Daniel, Barstow, Joanna K., Birkmann, Stephan M., Burrows, Adam, Charbonneau, David, Cowan, Nicolas B., Crouzet, Nicolas, Cubillos, Patricio E., Curry, S. M., Dalba, Paul A., de Wit, Julien, Deming, Drake, Désert, Jean-Michel, Doyon, René, Dragomir, Diana, Ehrenreich, David, Fortney, Jonathan J., Muñoz, Antonio García, Gibson, Neale P., Gizis, John E., Greene, Thomas P., Harrington, Joseph, Heng, Kevin, Kataria, Tiffany, Kempton, Eliza M.-R., Knutson, Heather, Kreidberg, Laura, Lafrenière, David, Lagage, Pierre-Olivier, Line, Michael R., Lopez-Morales, Mercedes, Madhusudhan, Nikku, Morley, Caroline V., Rocchetto, Marco, Schlawin, Everett, Shkolnik, Evgenya L., Shporer, Avi, Sing, David K., Todorov, Kamen O., Tucker, Gregory S., and Wakeford, Hannah R.
- Published
- 2016
15. CO or no CO? Narrowing the CO abundance constraint and recovering the H2O detection in the atmosphere of WASP-127 b using SPIRou.
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Boucher, Anne, Lafreniére, David, Pelletier, Stefan, Darveau-Bernier, Antoine, Radica, Michael, Allart, Romain, Artigau, Étienne, Cook, Neil J, Debras, Florian, Doyon, René, Gaidos, Eric, Benneke, Björn, Cadieux, Charles, Carmona, Andres, Cloutier, Ryan, Cortés-Zuleta, Pía, Cowan, Nicolas B, Delfosse, Xavier, Donati, Jean-François, and Fouqué, Pascal
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ORIGIN of planets ,NATURAL satellite atmospheres ,SPACE telescopes ,ATMOSPHERE ,NATURAL satellites - Abstract
Precise measurements of chemical abundances in planetary atmospheres are necessary to constrain the formation histories of exoplanets. A recent study of WASP-127 b, a close-in puffy sub-Saturn orbiting its solar-type host star in 4.2 d, using Hubble Space Telescope (HST) and Spitzer revealed a feature-rich transmission spectrum with strong excess absorption at 4.5 μm. However, the limited spectral resolution and coverage of these instruments could not distinguish between CO and/or CO
2 absorption causing this signal, with both low and high C/O ratio scenarios being possible. Here we present near-infrared (0.9–2.5 μm) transit observations of WASP-127 b using the high-resolution SPIRou spectrograph, with the goal to disentangle CO from CO2 through the 2.3 μm CO band. With SPIRou, we detect H2 O at a t -test significance of 5.3 σ and observe a tentative (3σ) signal consistent with OH absorption. From a joint SPIRou + HST + Spitzer retrieval analysis, we rule out a CO-rich scenario by placing an upper limit on the CO abundance of log10 [CO] <−4.0, and estimate a log10 [CO2 ] of −3.7 |$^{+0.8}_{-0.6}$| , which is the level needed to match the excess absorption seen at 4.5 μm. We also set abundance constraints on other major C-, O-, and N-bearing molecules, with our results favouring low C/O (0.10 |$^{+0.10}_{-0.06}$|), disequilibrium chemistry scenarios. We further discuss the implications of our results in the context of planet formation. Additional observations at high and low resolution will be needed to confirm these results and better our understanding of this unusual world. [ABSTRACT FROM AUTHOR]- Published
- 2023
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16. The feeding zones of terrestrial planets and insights into Moon formation
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Kaib, Nathan A. and Cowan, Nicolas B.
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- 2015
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17. Cloud Atlas: Rotational Modulations in the L/T Transition Brown Dwarf Companion HN Peg B
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Zhou, Yifan, Apai, Daniel, Metchev, Stanimir, Lew, Ben W. P, Schneider, Glenn, Marley, Mark S, Karalidi, Theodora, Manjavacas, Elena, Bedin, Luigi R, Cowan, Nicolas B, Miles-Paez, Paulo A, Lowrance, Patrick J, Radigan, Jacqueline, and Burgasser, Adam J
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Astrophysics - Abstract
Time-resolved observations of brown dwarfs' rotational modulations provide powerful insights into the properties of condensate clouds in ultra-cool atmospheres. Multi-wavelength light curves reveal cloud vertical structures, condensate particle sizes, and cloud morphology, which directly constrain condensate cloud and atmospheric circulation models. We report results from Hubble Space Telescope/Wide Field Camera 3 (WFC3) near-infrared G141 taken in six consecutive orbits observations of HNPeg B, an L/T transition brown dwarf companion to a G0V type star. The best-fit sine wave to the 1.1 to 1.7 micron broadband light curve has the amplitude of and period of hour. The modulation amplitude has no detectable wavelength dependence except in the 1.4 micron water absorption band, indicating that the characteristic condensate particle sizes are large (greater than 1 micron). We detect significantly (4.4 sigma) lower modulation amplitude in the 1.4 micron water absorption band, and find that HN Peg B's spectral modulation resembles those of early T type brown dwarfs. We also describe a new empirical interpolation method to remove spectral contamination from the bright host star. This method may be applied in other high-contrast time-resolved observations with WFC3.
- Published
- 2018
18. Rotational Spectral Unmixing of Exoplanets: Degeneracies Between Surface Colors and Geography
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Fujii, Yuka, Lustig-Yaeger, Jacob, and Cowan, Nicolas B
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Lunar And Planetary Science And Exploration - Abstract
Unmixing the disk-integrated spectra of exoplanets provides hints about heterogeneous surfaces that we cannot directly resolve in the foreseeable future. It is particularly important for terrestrial planets with diverse surface compositions like Earth. Although previous work on unmixing the spectra of Earth from disk-integrated multi-band light curves appeared successful, we point out a mathematical degeneracy between the surface colors and their spatial distributions. Nevertheless, useful constraints on the spectral shape of individual surface types may be obtained from the premise that albedo is everywhere between 0 and 1. We demonstrate the degeneracy and the possible constraints using both mock data based on a toy model of Earth, as well as real observations of Earth. Despite the severe degeneracy, we are still able to recover an approximate albedo spectrum for an ocean. In general, we find that surfaces are easier to identify when they cover a large fraction of the planet and when their spectra approach zero or unity in certain bands.
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- 2017
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19. K2 and Spitzer phase curves of the rocky ultra-short-period planet K2-141 b hint at a tenuous rock vapor atmosphere
- Author
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Zieba, Sebastian, Zilinskas, Mantas, Kreidberg, Laura, Nguyen, T. Giang, Miguel, Yamila, Cowan, Nicolas B., Pierrehumbert, Raymond, Carone, Ludmila, Dang, Lisa, Hammond, Mark, Louden, Tom, Lupu, Roxana, Malavolta, Luca, and Stevenson, Kevin B.
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Earth and Planetary Astrophysics (astro-ph.EP) ,Planets and satellites: individual: K2-141 b ,Spitzer ,planets and satellites: atmospheres ,planets and satellites: individual: K2-141 b ,techniques: photometric ,Exoplanets ,K2-141 b ,lava planet ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Space and Planetary Science ,atmospheres ,Astrophysics::Solar and Stellar Astrophysics ,Planets and satellites: atmospheres ,Astrophysics::Earth and Planetary Astrophysics ,Techniques: photometric ,Astrophysics - Earth and Planetary Astrophysics - Abstract
K2-141 b is a transiting, small (1.5 Re) ultra-short-period (USP) planet discovered by Kepler orbiting a K-dwarf host star every 6.7 hours. The planet's high surface temperature makes it an excellent target for thermal emission observations. Here we present 65 hours of continuous photometric observations of K2-141 b collected with Spitzer's IRAC Channel 2 at 4.5 micron spanning 10 full orbits of the planet. We measure an infrared eclipse depth of 143 +/- 39 ppm and a peak to trough amplitude variation of 121 +/- 43 ppm. The best fit model to the Spitzer data shows no significant thermal hotspot offset, in contrast to the previously observed offset for the well-studied USP planet 55 Cnc e. We also jointly analyze the new Spitzer observations with the photometry collected by Kepler during two separate K2 campaigns. We model the planetary emission with a range of toy models that include a reflective and a thermal contribution. With a two-temperature model, we measure a dayside temperature of 2049 +/- 361 K and a night-side temperature that is consistent with zero (Tp,n < 1712 K at 2 sigma). Models with a steep dayside temperature gradient provide a better fit to the data than a uniform dayside temperature (DeltaBIC = 22.2). We also find evidence for a non-zero geometric albedo Ag = 0.28 +/- 0.07. We also compare the data to a physically motivated, pseudo-2D rock vapor model and a 1D turbulent boundary layer model. Both models fit the data well. Notably, we find that the optical eclipse depth can be explained by thermal emission from a hot inversion layer, rather than reflected light. A thermal inversion may also be responsible for the deep optical eclipse observed for another USP, Kepler-10 b. Finally, we significantly improve the ephemerides for K2-141 b and c, which will facilitate further follow-up observations of this interesting system with state-of-the-art observatories like JWST., 31 pages, 27 figures, 12 tables, accepted for publication in A&A
- Published
- 2022
20. GJ 1252b: A Hot Terrestrial Super-Earth with No Atmosphere.
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Crossfield, Ian J. M., Malik, Matej, Hill, Michelle L., Kane, Stephen R., Foley, Bradford, Polanski, Alex S., Coria, David, Brande, Jonathan, Zhang, Yanzhe, Wienke, Katherine, Kreidberg, Laura, Cowan, Nicolas B., Dragomir, Diana, Gorjian, Varoujan, Mikal-Evans, Thomas, Benneke, Björn, Christiansen, Jessie L., Deming, Drake, and Morales, Farisa Y.
- Published
- 2022
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21. Transiting Exoplanet Studies and Community Targets for JWST's Early Release Science Program
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Stevenson, Kevin B, Lewis, Nikole K, Bean, Jacob L, Beichman, Charles, Fraine, Jonathan, Kilpatrick, Brian M, Krick, J. E, Lothringer, Joshua D, Mandell, Avi M, Valenti, Jeff A, Agol, Eric, Angerhausen, Daniel, Barstow, Joanna K, Birkmann, Stephan M, Burrows, Adam, Charbonneau, David, Cowan, Nicolas B, Crouzet, Nicolas, Cubillos, Patricio E, Curry, S. M, Dalba, Paul A, de Wit, Julien, Greene, Thomas P, Line, Michael R, and Wakeford, Hannah R
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Lunar And Planetary Science And Exploration - Abstract
The James Webb Space Telescope (JWST) will likely revolutionize transiting exoplanet atmospheric science, due to a combination of its capability for continuous, long duration observations and its larger collecting area, spectral coverage, and spectral resolution compared to existing space-based facilities. However, it is unclear precisely how well JWST will perform and which of its myriad instruments and observing modes will be best suited for transiting exoplanet studies. In this article, we describe a prefatory JWST Early Release Science (ERS) Cycle1 program that focuses on testing specific observing modes to quickly give the community the data and experience it needs to plan more efficient and successful transiting exoplanet characterization programs in later cycles. We propose a multi-pronged approach wherein one aspect of the program focuses on observing transits of a single target with all of the recommended observing modes to identify and understand potential systematics, compare transmission spectra at overlapping and neighboring wavelength regions, confirm throughputs, and determine overall performances. In our search for transiting exoplanets that are well suited to achieving these goals, we identify 12 objects (dubbed community targets) that meet our defined criteria. Currently, the most favorable target is WASP-62b because of its large predicted signal size, relatively bright host star, and location in JWSTs continuous viewing zone. Since most of the community targets do not have well-characterized atmospheres, we recommend initiating preparatory observing programs to determine the presence of obscuring cloudshazes within their atmospheres. Measurable spectroscopic features are needed to establish the optimal resolution and wavelength regions for exoplanet characterization. Other initiatives from our proposed ERS program include testing the instrument brightness limits and performing phase-curve observations. The latter are a unique challenge compared to transit observations because of their significantly longer durations. Using only a single mode, we propose to observe a full-orbit phase curve of one of the previously characterized, short-orbital-period planets to evaluate the facility-level aspects of long, uninterrupted time-series observations.
- Published
- 2016
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22. Stratospheric clouds do not impede JWST transit spectroscopy for exoplanets with Earth-like atmospheres.
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Doshi, Dhvani, Cowan, Nicolas B, and Huang, Yi
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EXTRASOLAR planets , *HABITABLE planets , *DWARF stars , *ATMOSPHERE , *PLANETARY orbits , *SPACE telescopes - Abstract
The James Webb Space Telescope (JWST) will provide an opportunity to investigate the atmospheres of potentially habitable planets. Aerosols significantly mute molecular features in transit spectra because they prevent light from probing the deeper layers of the atmosphere. Earth occasionally has stratospheric/high tropospheric clouds at 15–20 km that could substantially limit the observable depth of the underlying atmosphere. We use solar occultations of Earth's atmosphere to create synthetic JWST transit spectra of Earth analogues orbiting dwarf stars. Unlike previous investigations, we consider both clear and cloudy sightlines from the SCISAT satellite. We find that the maximum difference in effective thickness of the atmosphere between a clear and globally cloudy atmosphere is 8.5 km at 2.28 |$\mu$| m, with a resolution of 0.02 |$\mu$| m. After incorporating the effects of refraction and Pandexo's noise modelling, we find that JWST would not be able to detect Earth-like stratospheric clouds if an exo-Earth was present in the TRAPPIST-1 system, as the cloud spectrum differs from the clear spectrum by a maximum of 10 ppm. These stratospheric clouds are also not robustly detected by TauREx when performing spectral retrieval for a cloudy TRAPPIST-1 planet. However, if an Earth-sized planet were to orbit in a white dwarf's habitable zone, then we predict that JWST 's NIRSpec would be able to detect its stratospheric clouds after only four transits. We conclude that stratospheric clouds would not impede JWST transit spectroscopy or the detection of biosignatures for Earth-like atmospheres. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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23. Deep Two-phase, Hemispherical Magma Oceans on Lava Planets.
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Boukaré, Charles-Édouard, Cowan, Nicolas B., and Badro, James
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MAGMAS , *LAVA , *PLANETS , *PLANETARY surfaces , *PLANETARY interiors , *LUNAR craters , *EXTRASOLAR planets - Abstract
Astronomers have discovered a handful of exoplanets with rocky bulk compositions but orbiting that orbit so close to their host star that the surface of the planet must be at least partially molten. It is expected that the dayside of such “lava planets” harbors a rock-vapor atmosphere that flows quickly toward the airless nightsideâ€"this partial atmosphere is critical to the interpretation of lava planet observations, but transports negligible heat toward the nightside. As a result, the surface temperature of the magma ocean may range from 3000 K near the substellar point down to 1500 K near the dayâ€"night terminator. We use simple models incorporating the thermodynamics and geochemistry of partial melt to predict the physical and chemical properties of the magma ocean as a function of the distance from the substellar point. Our principal findings are that: (1) the dayside magma ocean is much deeper than previously thought, probably extending down to the coreâ€"mantle boundary below the substellar point of an Earth-sized planet; (2) much of the dayside is only partially molten, leading to gradients in the surface chemistry of the magma ocean; and (3) the temperature at the base of the silicate mantle is as important as the surface temperature. In the most extreme cases, lava planet interiors could be cold enough such that thermal stratification below the substellar point is gravitationally stable. These findings have important implications for the dynamics of the magma ocean, as well as the composition and dynamics of the atmosphere. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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24. TOI-1452 b: SPIRou and TESS Reveal a Super-Earth in a Temperate Orbit Transiting an M4 Dwarf.
- Author
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Cadieux, Charles, Doyon, René, Plotnykov, Mykhaylo, Hébrard, Guillaume, Jahandar, Farbod, Artigau, Étienne, Valencia, Diana, Cook, Neil J., Martioli, Eder, Vandal, Thomas, Donati, Jean-François, Cloutier, Ryan, Narita, Norio, Fukui, Akihiko, Hirano, Teruyuki, Bouchy, François, Cowan, Nicolas B., Gonzales, Erica J., Ciardi, David R., and Stassun, Keivan G.
- Published
- 2022
- Full Text
- View/download PDF
25. impact of ultraviolet heating and cooling on the dynamics and observability of lava planet atmospheres.
- Author
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Nguyen, T Giang, Cowan, Nicolas B, Pierrehumbert, Raymond T, Lupu, Roxana E, and Moores, John E
- Subjects
- *
PLANETARY atmospheres , *TURBULENT boundary layer , *TEMPERATURE inversions , *LAVA , *ATMOSPHERIC circulation , *LUNAR craters - Abstract
Lava planets have non-global, condensible atmospheres similar to icy bodies within the Solar system. Because they depend on interior dynamics, studying the atmospheres of lava planets can lead to understanding unique geological processes driven by their extreme environment. Models of lava planet atmospheres have thus far focused on either radiative transfer or hydrodynamics. In this study, we couple the two processes by introducing ultraviolet (UV) and infrared (IR) radiation to a turbulent boundary layer model. We also test the effect of different vertical temperature profiles on atmospheric dynamics. Results from the model show that UV radiation affects the atmosphere much more than IR. UV heating and cooling work together to produce a horizontally isothermal atmosphere away from the substellar point regardless of the vertical temperature profile. We also find that stronger temperature inversions induce stronger winds and hence cool the atmosphere. Our simulated transmission spectra of the bound atmosphere show a strong SiO feature in the UV that would be challenging to observe in the planet's transit spectrum due to the precision required. Our simulated emission spectra are more promising, with significant SiO spectral features at 4.5 and 9 |$\mu$| m that can be observed with the James Webb Space Telescope. Different vertical temperature profiles produce discernible dayside emission spectra, but not in the way one would expect. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
26. Atmospheric Gravitational Tides of Earth-like Planets Orbiting Low-mass Stars.
- Author
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Navarro, Thomas, Merlis, Timothy M., Cowan, Nicolas B., and Gomez, Natalya
- Published
- 2022
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- View/download PDF
27. A map of the day-night contrast of the extrasolar planet HD 189733b
- Author
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Knutson, Heather A., Charbonneau, David, Allen, Lori E., Fortney, Jonathan J., Agol, Eric, Cowan, Nicolas B., Showman, Adam P., Cooper, Curtis S., and Megeath, S. Thomas
- Subjects
Environmental issues ,Science and technology ,Zoology and wildlife conservation - Abstract
Author(s): Heather A. Knutson (corresponding author) [1]; David Charbonneau [1]; Lori E. Allen [1]; Jonathan J. Fortney [2, 3]; Eric Agol [4]; Nicolas B. Cowan [4]; Adam P. Showman [5]; [...]
- Published
- 2007
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- View/download PDF
28. Astronomy in a Low-Carbon Future
- Author
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Matzner, Christopher, Cowan, Nicolas B., Doyon, Rene, Hénault-Brunet, Vincent, Lafrenière, David, Lokken, Martine, Martin, Peter G., Morsink, Sharon, Nomandeau, Magdalen, Ouellette, Nathalie, Rahman, Mubdi, Roediger, Joel, Taylor, James, Thacker, Rob, and van Kerkwijk, Marten
- Subjects
astrophysics - Abstract
The consequences of climate change are developing into a vast and unparalleled crisis, which is planetary in scale and yet very human in its causes and impacts. Faced with this truth, inaction and delay are neither ethical nor wise: every field of human activity, astronomy included, must take urgent steps to mitigate the crisis and avoid the worst potential outcomes, while adapting to those that are inevitable. We outline a strategy for climate-responsible scholarship and communication that we hope will resonate with the astronomical community's aspirations for a stable future in which there is room for curiosity and discovery. In light of the crisis, greenhouse gas emissions must be understood as significant research costs to be justified, budgeted, and rationed. Air travel is a major contributor. We must remove incentives in tenure and promotions for profligate travel, codify low-carbon practices, and reward efforts to minimize emissions while maximizing research. Any essential travel emissions must be fully offset, with carbon offsets that are reimbursable if not covered by the institution. The frequency, timing, and locations of conferences and colloquia should be planned to minimize air travel, with remote participation encouraged using online platforms. Conferences should favour lowest-impact food options by default, taking steps to minimize food waste (and other waste as well). Infrastructure must be planned with climate impacts in mind for both construction and operation. For buildings, this means pushing for designs and materials at the forefront of sustainable technology. For observatories and computing facilities, it includes justifying and thoroughly vetting the emissions footprint at the proposal stage and fully considering low-impact options, such as cloud computing. In education and outreach, we must strive to be reliable sources of scientific information on climate change, prepared to connect this to astrophysics and ready to direct curious people to authoritative sources. We recommended that CASCA support this transformation by establishing a sustainability committee (or office) to be tasked with conducting a community-wide survey of our greenhouse gas emissions and developing a decarbonization road map for the discipline. This committee would host sustainability forums and provide resources to support each of our other recommendations, especially climate-related materials and references for education and outreach. We recommend that CASCA push for climate-responsible governance. Governments, granting agencies, and universities must implement climate-responsible policies, like rationing the carbon budget of the entire discipline, using climate impacts to evaluate proposals, permitting the use of funds for offsets, and allowing climate-friendly but more costly travel options. Moreover, these entities must ultimately ration emissions to ensure that targets are met. To have an impact beyond the bounds of professional astronomy, we encourage astronomers to press their institutions to divest from fossil fuel extraction and its financing. Finally, we recommend that climate responsibility be an explicit priority in the 2020 Long Range Plan, and that it be used to guide all aspects of our profession, from our research and education practices to our infrastructure., White paper identifier W021
- Published
- 2019
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29. Astronomy in a Low-Carbon Future
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Matzner, Christopher D., Cowan, Nicolas B., Doyon, Ren��, H��nault-Brunet, Vincent, Lafren��re, David, Lokken, Martine, Martin, Peter G., Morsink, Sharon, Normandeau, Magdalen, Ouellette, Nathalie, Rahman, Mubdi, Roediger, Joel, Taylor, James, Thacker, Rob, and van Kerkwijk, Marten
- Subjects
Earth and Planetary Astrophysics (astro-ph.EP) ,High Energy Astrophysical Phenomena (astro-ph.HE) ,Cosmology and Nongalactic Astrophysics (astro-ph.CO) ,Astrophysics of Galaxies (astro-ph.GA) ,FOS: Physical sciences ,Astrophysics - Instrumentation and Methods for Astrophysics ,Astrophysics - High Energy Astrophysical Phenomena ,Instrumentation and Methods for Astrophysics (astro-ph.IM) ,Astrophysics - Astrophysics of Galaxies ,Astrophysics - Cosmology and Nongalactic Astrophysics ,Astrophysics - Earth and Planetary Astrophysics - Abstract
The global climate crisis poses new risks to humanity, and with them, new challenges to the practices of professional astronomy. Avoiding the more catastrophic consequences of global warming by more than 1.5 degrees requires an immediate reduction of greenhouse gas emissions. According to the 2018 United Nations Intergovernmental Panel report, this will necessitate a 45% reduction of emissions by 2030 and net-zero emissions by 2050. Efforts are required at all levels, from the individual to the governmental, and every discipline must find ways to achieve these goals. This will be especially difficult for astronomy with its significant reliance on conference and research travel, among other impacts. However, our long-range planning exercises provide the means to coordinate our response on a variety of levels. We have the opportunity to lead by example, rising to the challenge rather than reacting to external constraints. We explore how astronomy can meet the challenge of a changing climate in clear and responsible ways, such as how we set expectations (for ourselves, our institutions, and our granting agencies) around scientific travel, the organization of conferences, and the design of our infrastructure. We also emphasize our role as reliable communicators of scientific information on a problem that is both human and planetary in scale., 16 pages. A White Paper prepared for the Canadian Long Range Plan 2020
- Published
- 2019
30. Mapping the surface of partially cloudy exoplanets is hard.
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Teinturier, Lucas, Vieira, Nicholas, Jacquet, Elisa, Geoffrion, Juliette, Bestavros, Youssef, Keating, Dylan, and Cowan, Nicolas B
- Subjects
ALBEDO ,EXTRASOLAR planets ,LIGHT curves ,PLANETARY surfaces ,CLOUD physics ,NATURAL satellite atmospheres ,CONTINENTS - Abstract
Reflected light photometry of terrestrial exoplanets could reveal the presence of oceans and continents, hence placing direct constraints on the current and long-term habitability of these worlds. Inferring the albedo map of a planet from its observed light curve is challenging because different maps may yield indistinguishable light curves. This degeneracy is aggravated by changing clouds. It has previously been suggested that disc-integrated photometry spanning multiple days could be combined to obtain a cloud-free surface map of an exoplanet. We demonstrate this technique as part of a Bayesian retrieval by simultaneously fitting for the fixed surface map of a planet and the time-variable overlying clouds. We test this approach on synthetic data and then apply it to real disc-integrated observations of the Earth. We find that 8 d of continuous synthetic observations are sufficient to reconstruct a faithful low-resolution surface albedo map, without needing to make assumptions about cloud physics. For light curves with negligible photometric uncertainties, the minimal top-of-atmosphere albedo at a location is a good estimate of its surface albedo. When applied to observations from the Earth Polychromating Imaging Camera aboard the Deep Space Climate Observatory spacecraft, our approach removes only a small fraction of clouds. We attribute this difficulty to the full-phase geometry of observations combined with the short correlation length for Earth clouds. For exoplanets with Earth-like climatology, it may be hard to do much better than a cloud-averaged map. We surmise that cloud removal will be most successful for exoplanets imaged near quarter phase that harbour large cloud systems. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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31. Atmospheric characterization of hot Jupiters using hierarchical models of Spitzer observations.
- Author
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Keating, Dylan and Cowan, Nicolas B
- Subjects
- *
HOT Jupiters , *BRIGHTNESS temperature , *PLANETARY observations , *PLANETS - Abstract
The field of exoplanet atmospheric characterization is trending towards comparative studies involving many planetary systems, and using Bayesian hierarchical modelling is a natural next step. Here we demonstrate two use cases. We first use hierarchical modelling to quantify variability in repeated observations by reanalysing a suite of 10 Spitzer secondary eclipse observations of the hot Jupiter XO-3 b. We compare three models: one where we fit 10 separate eclipse depths, one where we use a single eclipse depth for all 10 observations, and a hierarchical model. By comparing the widely applicable information criterion of each model, we show that the hierarchical model is preferred over the others. The hierarchical model yields less scatter across the suite of eclipse depths – and higher precision on the individual eclipse depths – than does fitting the observations separately. We find that the hierarchical eclipse depth uncertainty is larger than the uncertainties on the individual eclipse depths, which suggests either slight astrophysical variability or that single eclipse observations underestimate the true eclipse depth uncertainty. Finally, we fit a suite of published dayside brightness measurements for 37 planets using a hierarchical model of brightness temperature versus irradiation temperature. The hierarchical model gives tighter constraints on the individual brightness temperatures than the non-hierarchical model. Although we tested hierarchical modelling on Spitzer eclipse data of hot Jupiters, it is applicable to observations of smaller planets like hot Neptunes and super-Earths, as well as for photometric and spectroscopic transit or phase-curve observations. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
32. Thermal Phase Variations of WASP-12b: Defying Predictions
- Author
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Cowan, Nicolas B, Machalek, Pavel, Croll, Bryce, Shekhtman, Louis M, Burrows, Adam, Deming, Drake, Greene, Tom, and Hora, Joseph L
- Subjects
Astrophysics - Abstract
We report Warm Spitzer full-orbit phase observations of WASP-12b at 3.6 and 4.5 micrometers. This extremely inflated hot Jupiter is thought to be overflowing its Roche lobe, undergoing mass loss and accretion onto its host star, and has been claimed to have a C/O ratio in excess of unity. We are able to measure the transit depths, eclipse depths, thermal and ellipsoidal phase variations at both wavelengths. The large-amplitude phase variations, combined with the planet's previously measured dayside spectral energy distribution, are indicative of non-zero Bond albedo and very poor day-night heat redistribution. The transit depths in the mid-infrared-(R(sub p)/R(sub ∗))(sup 2) = 0.0123(3) and 0.0111(3) at 3.6 and 4.5 micrometers, respectively-indicate that the atmospheric opacity is greater at 3.6 than at 4.5 micrometers, in disagreement with model predictions, irrespective of C/O ratio. The secondary eclipse depths are consistent with previous studies: F(sub day)/F(sub ∗) = 0.0038(4) and 0.0039(3) at 3.6 and 4.5 micrometers, respectively. We do not detect ellipsoidal variations at 3.6 micrometers, but our parameter uncertainties-estimated via prayer-bead Monte Carlo-keep this non-detection consistent with model predictions. At 4.5 micrometers, on the other hand, we detect ellipsoidal variations that are much stronger than predicted. If interpreted as a geometric effect due to the planet's elongated shape, these variations imply a 3:2 ratio for the planet's longest:shortest axes and a relatively bright day-night terminator. If we instead presume that the 4.5 micrometer ellipsoidal variations are due to uncorrected systematic noise and we fix the amplitude of the variations to zero, the best-fit 4.5 micrometer transit depth becomes commensurate with the 3.6 micrometer depth, within the uncertainties. The relative transit depths are then consistent with a solar composition and short scale height at the terminator. Assuming zero ellipsoidal variations also yields a much deeper 4.5 micrometer eclipse depth, consistent with a solar composition and modest temperature inversion. We suggest future observations that could distinguish between these two scenarios.
- Published
- 2012
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33. Constraining Exoplanet Metallicities and Aerosols with ARIEL: An Independent Study by the Contribution to ARIEL Spectroscopy of Exoplanets (CASE) Team
- Author
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Zellem, Robert T., Swain, Mark R., Cowan, Nicolas B., Bryden, Geoffrey, Komacek, Thaddeus D., Colavita, Mark, Ardila, David, Roudier, Gael M., Fortney, Jonathan J., Bean, Jacob, Line, Michael R., Griffith, Caitlin A., Shkolnik, Evgenya L., Kreidberg, Laura, Moses, Julianne I., Showman, Adam P., Stevenson, Kevin B., Wong, Andre, Chapman, John W., Ciardi, David R., Howard, Andrew W., Kataria, Tiffany, Kempton, Eliza M.-R., Latham, David, Mahadevan, Suvrath, Meléndez, Jorge, and Parmentier, Vivien
- Subjects
Earth and Planetary Astrophysics (astro-ph.EP) ,Astrophysics::Instrumentation and Methods for Astrophysics ,FOS: Physical sciences ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Astrophysics - Instrumentation and Methods for Astrophysics ,Instrumentation and Methods for Astrophysics (astro-ph.IM) ,Physics::Atmospheric and Oceanic Physics ,Astrophysics - Earth and Planetary Astrophysics - Abstract
Launching in 2028, ESA's Atmospheric Remote-sensing Exoplanet Large-survey (ARIEL) survey of $\sim$1000 transiting exoplanets will build on the legacies of Kepler and TESS and complement JWST by placing its high precision exoplanet observations into a large, statistically-significant planetary population context. With continuous 0.5--7.8~$\mu$m coverage from both FGS (0.50--0.55, 0.8--1.0, and 1.0--1.2~$\mu$m photometry; 1.25--1.95~$\mu$m spectroscopy) and AIRS (1.95--7.80~$\mu$m spectroscopy), ARIEL will determine atmospheric compositions and probe planetary formation histories during its 3.5-year mission. NASA's proposed Contribution to ARIEL Spectroscopy of Exoplanets (CASE) would be a subsystem of ARIEL's FGS instrument consisting of two visible-to-infrared detectors, associated readout electronics, and thermal control hardware. FGS, to be built by the Polish Academy of Sciences' Space Research Centre, will provide both fine guiding and visible to near-infrared photometry and spectroscopy, providing powerful diagnostics of atmospheric aerosol contribution and planetary albedo, which play a crucial role in establishing planetary energy balance. The CASE team presents here an independent study of the capabilities of ARIEL to measure exoplanetary metallicities, which probe the conditions of planet formation, and FGS to measure scattering spectral slopes, which indicate if an exoplanet has atmospheric aerosols (clouds and hazes), and geometric albedos, which help establish planetary climate. Our design reference mission simulations show that ARIEL could measure the mass-metallicity relationship of its 1000-planet single-visit sample to $>7.5\sigma$ and that FGS could distinguish between clear, cloudy, and hazy skies and constrain an exoplanet's atmospheric aerosol composition to $>5\sigma$ for hundreds of targets, providing statistically-transformative science for exoplanet atmospheres., Comment: accepted to PASP; 23 pages, 6 figures
- Published
- 2019
34. Eccentricity is Not Responsible for Odd Harmonics in HAT-P-7 and Kepler-13A
- Author
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Bielecki, Claudia I. and Cowan, Nicolas B.
- Subjects
Earth and Planetary Astrophysics (astro-ph.EP) ,Astrophysics - Solar and Stellar Astrophysics ,FOS: Physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,Astrophysics - Earth and Planetary Astrophysics - Abstract
The exquisite photometry of Kepler has revealed reflected light from exoplanets, tidal distortion of host stars and Doppler beaming of a star's light due to its motion (Borucki 2016; Demory et al. 2012; Welsh et al. 2010; Bloemen et al. 2012). Esteves et al. (2013, 2015) and Shporer et al. (2014) reported additional odd harmonics in the light curves of two hot Jupiters: HAT-P-7b and Kepler-13Ab. They measured non-zero power at three times the orbital frequency that persisted while the planet was eclipsed and hence must originate in the star (Esteves et al. 2015). Penoyre & Sandford (2018) showed that orbital eccentricity could result in time-dependent tidal deformation of the star that manifests itself at three times the orbital frequency and suggested this could be the origin of the measured odd modes. In this Research Note, we show that the small orbital eccentricities of HAT-P-7b and Kepler-13Ab cannot generate the odd harmonics observed in these systems. Esteves et al. (2015) hypothesized that the odd modes could be due to tidal distortion of the star if its spin is misaligned with the system's orbital motion, as is the case in both of these systems (Benomar et al. 2014; Herman et al. 2018), but this mechanism has yet to be verified theoretically or numerically., 2 pages, 1 figure, RNAAS in press
- Published
- 2018
35. Longitudinally Resolved Spectral Retrieval (ReSpect) of WASP-43b.
- Author
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Cubillos, Patricio E., Keating, Dylan, Cowan, Nicolas B., Vos, Johanna M., Burningham, Ben, Ygouf, Marie, Karalidi, Theodora, Zhou, Yifan, and Gonzales, Eileen C.
- Subjects
TEMPERATURE lapse rate ,SPACE telescopes ,SOLAR system ,LEGACY systems ,MOLECULAR spectra - Abstract
Thermal phase variations of short-period planets indicate that they are not spherical cows: day-to-night temperature contrasts range from hundreds to thousands of degrees, rivaling their vertical temperature contrasts. Nonetheless, the emergent spectra of short-period planets have typically been fit using one-dimensional (1D) spectral retrieval codes that only account for vertical temperature gradients. The popularity of 1D spectral retrieval codes is easy to understand: they are robust and have a rich legacy in solar system atmospheric studies. Exoplanet researchers have recently introduced multidimensional retrieval schemes to interpret the spectra of short-period planets, but these codes are necessarily more complex and computationally expensive than their 1D counterparts. In this paper we present an alternative: phase-dependent spectral observations are inverted to produce longitudinally resolved spectra that can then be fit using standard 1D spectral retrieval codes. We test this scheme on the iconic phase-resolved spectra of WASP-43b and on simulated observations for the James Webb Space Telescope (JWST) using the open-source Pyrat Bay 1D spectral retrieval framework. Notably, we take the model complexity of the simulations one step further from previous studies by allowing for longitudinal variations in composition in addition to temperature. We show that performing 1D spectral retrieval on longitudinally resolved spectra is more accurate than applying 1D spectral retrieval codes to disk-integrated emission spectra, even though this is identical in terms of computational load. We find that for the extant Hubble and Spitzer observations of WASP-43b, the difference between the two approaches is negligible, but JWST phase measurements should be treated with longitudinally re solved spect ral retrieval (ReSpect). [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
36. A comprehensive reanalysis of Spitzer's 4.5 μm phase curves, and the phase variations of the ultra-hot Jupiters MASCARA-1b and KELT-16b.
- Author
-
Bell, Taylor J, Dang, Lisa, Cowan, Nicolas B, Bean, Jacob, Désert, Jean-Michel, Fortney, Jonathan J, Keating, Dylan, Kempton, Eliza, Kreidberg, Laura, Line, Michael R, Mansfield, Megan, Parmentier, Vivien, Stevenson, Kevin B, Swain, Mark, and Zellem, Robert T
- Subjects
PHOTOMETRY - Abstract
We have developed an open-source pipeline for the analysis of Spitzer /IRAC channel 1 and 2 time-series photometry, incorporating some of the most popular decorrelation methods. We applied this pipeline to new phase curve observations of ultra-hot Jupiters MASCARA-1b and KELT-16b, and we performed the first comprehensive reanalysis of 15 phase curves. We find that MASCARA-1b and KELT-16b have phase offsets of |$6^{+11}_{-11}~^{\circ }$| W and |$38^{+16}_{-15}~^{\circ }$| W, dayside temperatures of |$2952^{+100}_{-97}$| and |$3070^{+160}_{-150}$| K, and nightside temperatures of |$1300^{+340}_{-340}$| and |$1900^{+430}_{-440}$| K, respectively. We confirm a strong correlation between dayside and irradiation temperatures with a shallower dependence for nightside temperature. We also find evidence that the normalized phase curve amplitude (peak-to-trough divided by eclipse depth) is correlated with stellar effective temperature. In addition, while our different models often retrieve similar parameters, significant differences occasionally arise between them, as well as between our preferred model and the literature values. Nevertheless, our preferred models are consistent with published phase offsets to within −8 ± 21 degrees (−1.6 ± 3.2 sigma), and normalized phase curve amplitudes are on average reproduced to within −0.01 ± 0.24 (−0.1 ± 1.6 sigma). Finally, we find that BLISS performs best in most cases, but not all; we therefore recommend future analyses consider numerous detector models to ensure an optimal fit and to assess model dependencies. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
37. The Science Case for an Extended Spitzer Mission
- Author
-
Yee, Jennifer C., Fazio, Giovanni G., Benjamin, Robert, Kirkpatrick, J. Davy, Malkan, Matt A., Trilling, David, Carey, Sean, Ciardi, David R., Apai, Daniel, Ashby, M. L. N., Ballard, Sarah, Bean, Jacob L., Beatty, Thomas, Berta-Thompson, Zach, Capak, P., Charbonneau, David, Chesley, Steven, Cowan, Nicolas B., Crossfield, Ian, Cushing, Michael C., Wit, Julien, Deming, Drake, Dickinson, M., Dittmann, Jason, Dragomir, Diana, Dressing, Courtney, Emery, Joshua, Faherty, Jacqueline K., Jonathan Gagné, Gaudi, B. Scott, Gillon, Michael, Grillmair, Carl J., Harris, Alan, Hora, Joseph, Ingalls, James G., Kataria, Tiffany, Kreidberg, Laura, Krick, Jessica E., Lowrance, Patrick J., Mahoney, William A., Metchev, Stanimir A., Mommert, Michael, Migo Mueller, Michael, Shvartzvald, Yossi, Smith, Howard, Stevenson, Kevin B., Teplitz, H. I., and Willner, S. P.
- Subjects
Earth and Planetary Astrophysics (astro-ph.EP) ,astro-ph.SR ,astro-ph.GA ,Astrophysics::Instrumentation and Methods for Astrophysics ,FOS: Physical sciences ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Astrophysics - Solar and Stellar Astrophysics ,Astrophysics of Galaxies (astro-ph.GA) ,astro-ph.EP ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,Astrophysics::Galaxy Astrophysics ,Astrophysics - Earth and Planetary Astrophysics - Abstract
Although the final observations of the Spitzer Warm Mission are currently scheduled for March 2019, it can continue operations through the end of the decade with no loss of photometric precision. As we will show, there is a strong science case for extending the current Warm Mission to December 2020. Spitzer has already made major impacts in the fields of exoplanets (including microlensing events), characterizing near Earth objects, enhancing our knowledge of nearby stars and brown dwarfs, understanding the properties and structure of our Milky Way galaxy, and deep wide-field extragalactic surveys to study galaxy birth and evolution. By extending Spitzer through 2020, it can continue to make ground-breaking discoveries in those fields, and provide crucial support to the NASA flagship missions JWST and WFIRST, as well as the upcoming TESS mission, and it will complement ground-based observations by LSST and the new large telescopes of the next decade. This scientific program addresses NASA's Science Mission Directive's objectives in astrophysics, which include discovering how the universe works, exploring how it began and evolved, and searching for life on planets around other stars., 75 pages. See page 3 for Table of Contents and page 4 for Executive Summary
- Published
- 2017
38. Visible extreme adaptive optics on extremely large telescopes: towards detecting oxygen in Proxima Centauri b and analogs.
- Author
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Fowler, J., Haffert, Sebastiaan Y., van Kooten, Maaike A. M., Landman, Rico, Bidot, Alexis, Hours, Adrien, N'Diaye, Mamadou, Absil, Olivier, Altinier, Lisa, Baudoz, Pierre, Belikov, Ruslan, Bonse, Markus Johannes, Bott, Kimberly, Brandl, Bernhard, Carlotti, Alexis, Casewell, Sarah L., Choquet, Elodie, Cowan, Nicolas B., Desai, Niyati, and Doelman, David
- Published
- 2023
- Full Text
- View/download PDF
39. Integrated photonic-based coronagraphic systems for future space telescopes.
- Author
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Desai, Niyati, König, Lorenzo, Por, Emiel, Juanola-Parramon, Roser, Belikov, Ruslan, Laginja, Iva, Guyon, Olivier, Pueyo, Laurent, Fogarty, Kevin, Absil, Olivier, Altinier, Lisa, Baudoz, Pierre, Bidot, Alexis, Bonse, Markus Johannes, Bott, Kimberly, Brandl, Bernhard, Carlotti, Alexis, Casewell, Sarah L., Choquet, Elodie, and Cowan, Nicolas B.
- Published
- 2023
- Full Text
- View/download PDF
40. Modelling the atmosphere of lava planet K2-141b: implications for low- and high-resolution spectroscopy.
- Author
-
Nguyen, T Giang, Cowan, Nicolas B, Banerjee, Agnibha, and Moores, John E
- Subjects
- *
ATMOSPHERIC models , *STEADY-state flow , *SPECTROMETRY , *OCEAN circulation , *NATURAL satellite atmospheres , *PLANETARY atmospheres - Abstract
Transit searches have uncovered Earth-size planets orbiting so close to their host star that their surface should be molten, so-called lava planets. We present idealized simulations of the atmosphere of lava planet K2-141b and calculate the return flow of material via circulation in the magma ocean. We then compare how pure Na, SiO, or SiO2 atmospheres would impact future observations. The more volatile Na atmosphere is thickest followed by SiO and SiO2, as expected. Despite its low vapour pressure, we find that a SiO2 atmosphere is easier to observe via transit spectroscopy due to its greater scale height near the day–night terminator and the planetary radial velocity and acceleration are very high, facilitating high dispersion spectroscopy. The special geometry that arises from very small orbits allows for a wide range of limb observations for K2-141b. After determining the magma ocean depth, we infer that the ocean circulation required for SiO steady-state flow is only 10−4 m s−1, while the equivalent return flow for Na is several orders of magnitude greater. This suggests that a steady-state Na atmosphere cannot be sustained and that the surface will evolve over time. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
41. Cloud Atlas: Unraveling the Vertical Cloud Structure with the Time-series Spectrophotometry of an Unusually Red Brown Dwarf.
- Author
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Lew, Ben W. P., Apai, Dániel, Marley, Mark, Saumon, Didier, Schneider, Glenn, Zhou, Yifan, Cowan, Nicolas B., Karalidi, Theodora, Manjavacas, Elena, Bedin, L. R., and Miles-Páez, Paulo A.
- Subjects
BROWN dwarf stars ,ATMOSPHERIC circulation ,TIME series analysis ,SPACE telescopes ,MOLECULAR spectra ,SPATIAL distribution (Quantum optics) - Abstract
Rotational modulations of emission spectra in brown dwarf and exoplanet atmospheres show that clouds are often distributed non-uniformly in these ultracool atmospheres. The spatial heterogeneity in cloud distribution demonstrates the impact of atmospheric dynamics on cloud formation and evolution. In this study, we update the Hubble Space Telescope (HST) time-series data analysis of the previously reported rotational modulations of WISEP J004701+680352—an unusually red late-L brown dwarf with a spectrum similar to that of the directly imaged planet HR 8799e. We construct a self-consistent spatially heterogeneous cloud model to explain the HST and the Spitzer time-series observations, as well as the time-averaged spectra of WISE 0047. In the heterogeneous cloud model, a cloud thickness variation of around one pressure scale height explains the wavelength dependence in the HST near-IR spectral variability. By including disequilibrium CO/CH
4 chemistry, our models also reproduce the redder color of WISE 0047 compared to that of field brown dwarfs. We discuss the impact of vertical cloud structure on atmospheric profile and estimate the minimum eddy diffusivity coefficient for other objects with redder colors. Our data analysis and forward modeling results demonstrate that time-series spectrophotometry with a broad wavelength coverage is a powerful tool for constraining heterogeneous atmospheric structure. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF
42. Phase Curves of Hot Neptune LTT 9779b Suggest a High-metallicity Atmosphere.
- Author
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Crossfield, Ian J. M., Dragomir, Diana, Cowan, Nicolas B., Daylan, Tansu, Wong, Ian, Kataria, Tiffany, Deming, Drake, Kreidberg, Laura, Mikal-Evans, Thomas, Gorjian, Varoujan, Jenkins, James S., Benneke, Björn, Collins, Karen A., Burke, Christopher J., Henze, Christopher E., McDermott, Scott, Mireles, Ismael, Watanabe, David, Wohler, Bill, and Ricker, George
- Published
- 2020
- Full Text
- View/download PDF
43. Keeping M-Earths habitable in the face of atmospheric loss by sequestering water in the mantle.
- Author
-
Moore, Keavin and Cowan, Nicolas B
- Subjects
- *
DWARF stars , *MARTIAN atmosphere , *EARTH'S mantle , *SURFACE of the earth , *PLANETARY orbits , *PLANETARY surfaces , *UPPER atmosphere , *NUCLEOSYNTHESIS - Abstract
Water cycling between Earth's mantle and surface has previously been modelled and extrapolated to rocky exoplanets, but these studies neglected the host star. M-dwarf stars are more common than Sun-like stars and at least as likely to host temperate rocky planets (M-Earths). However, M dwarfs are active throughout their lifetimes; specifically, X-ray and extreme ultraviolet (XUV) radiation during their early evolution can cause rapid atmospheric loss on orbiting planets. The increased bolometric flux reaching M-Earths leads to warmer, moister upper atmospheres, while XUV radiation can photodissociate water molecules and drive hydrogen and oxygen escape to space. Here, we present a coupled model of deep-water cycling and water loss to space on M-Earths to explore whether these planets can remain habitable despite their volatile evolution. We use a cycling parametrization accounting for the dependence of mantle degassing on seafloor pressure, the dependence of regassing on mantle temperature, and the effect of water on mantle viscosity and thermal evolution. We assume the M dwarf's XUV radiation decreases exponentially with time, and energy-limited water loss with 30 per cent efficiency. We explore the effects of cycling and loss to space on planetary water inventories and water partitioning. Planet surfaces desiccated by loss can be rehydrated, provided there is sufficient water sequestered in the mantle to degas once loss rates diminish at later times. For a given water loss rate, the key parameter is the mantle overturn time-scale at early times: if the mantle overturn time-scale is longer than the loss time-scale, then the planet is likely to keep some of its water. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
44. Mass loss from the exoplanet WASP-12b inferred from Spitzer phase curves.
- Author
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Bell, Taylor J, Zhang, Michael, Cubillos, Patricio E, Dang, Lisa, Fossati, Luca, Todorov, Kamen O, Cowan, Nicolas B, Deming, Drake, Zellem, Robert T, Stevenson, Kevin B, Crossfield, Ian J M, Dobbs-Dixon, Ian, Fortney, Jonathan J, Knutson, Heather A, and Line, Michael R
- Subjects
INFRARED radiation ,CURVES ,ACCRETION (Astrophysics) ,STARS ,EXTRASOLAR planets - Abstract
The exoplanet WASP-12b is the prototype for the emerging class of ultrahot, Jupiter-mass exoplanets. Past models have predicted – and near-ultraviolet observations have shown – that this planet is losing mass. We present an analysis of two sets of 3.6 and 4.5 |$\mu \rm{m}$| Spitzer phase curve observations of the system which show clear evidence of infrared radiation from gas stripped from the planet, and the gas appears to be flowing directly toward or away from the host star. This accretion signature is only seen at 4.5 |$\mu \rm{m}$| , not at 3.6 |$\mu \rm{m}$| , which is indicative either of CO emission at the longer wavelength or blackbody emission from cool, ≲600 K gas. It is unclear why WASP-12b is the only ultrahot Jupiter to exhibit this mass-loss signature, but perhaps WASP-12b's orbit is decaying as some have claimed, while the orbits of other exoplanets may be more stable; alternatively, the high-energy irradiation from WASP-12A may be stronger than the other host stars. We also find evidence for phase offset variability at the level of 6.4σ (46.2°) at 3.6 |$\mu \rm{m}$|. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
45. Estimating dayside effective temperatures of hot Jupiters and associated uncertainties through Gaussian process regression.
- Author
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Pass, Emily K, Cowan, Nicolas B, Cubillos, Patricio E, and Sklar, Jack G
- Subjects
- *
KRIGING , *HOT Jupiters , *GAUSSIAN processes , *UNCERTAINTY - Abstract
In this work, we outline a new method for estimating dayside effective temperatures of exoplanets and associated uncertainties using Gaussian process (GP) regression. By applying our method to simulated observations, we show that the GP method estimates uncertainty more robustly than other model-independent approaches. We find that unbiased estimates of effective temperatures can be made using as few as three broad-band measurements (white-light HST WFC3 and the two warm Spitzer IRAC channels), although we caution that estimates made using only IRAC can be significantly biased. We then apply our GP method to the 12 hot Jupiters in the literature whose secondary eclipse depths have been measured by WFC3 and IRAC channels 1 and 2: CoRoT-2 b; HAT-P-7 b; HD 189733 b; HD 209458 b; Kepler-13A b; TrES-3 b; WASP-4 b; WASP-12 b; WASP-18 b; WASP-33 b; WASP-43 b; and WASP-103 b. We present model-independent dayside effective temperatures for these planets, with uncertainty estimates that range from ±66 to ±136 K. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
46. An empirical infrared transit spectrum of Earth: opacity windows and biosignatures.
- Author
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Macdonald, Evelyn J R and Cowan, Nicolas B
- Subjects
- *
INFRARED spectra , *FOURIER transform spectrometers , *HABITABLE planets , *ATMOSPHERIC boundary layer , *ATMOSPHERIC chemistry , *TROPOSPHERIC aerosols , *REFRACTIVE index - Abstract
The Atmospheric Chemistry Experiment Fourier Transform Spectrometer on the SCISAT satellite has been measuring infrared (IR) transmission spectra of Earth during Solar occultations since 2004. We use these data to build an IR transit spectrum of Earth. Regions of low atmospheric opacity, known as windows, are of particular interest, as they permit observations of the planet's lower atmosphere. Even in the absence of clouds or refraction, imperfect transmittance leads to a minimum effective thickness of h min ≈ 4 km in the 10–12 |$\mu \mathrm{m}$| opacity window at a spectral resolution of R = 103. None the less, at R = 105, the maximum transmittance at the surface is around |${70}{{{\ \rm per\ cent}}}$|. In principle, one can probe the troposphere of an Earth-like planet via high-dispersion transit spectroscopy in the mid-IR; in practice aerosols and/or refraction likely make this impossible. We simulate the transit spectrum of an Earth-like planet in the TRAPPIST-1 system. We find that a long-term near-IR (NIR) campaign with the James Webb Space Telescope (JWST) could readily detect CO2 and H2O, establishing the presence of an atmosphere. A mid-IR campaign or longer NIR campaign would be more challenging, but in principle could detect the biosignatures O3 and CH4. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
47. 3.6 AND 4.5 mu m SPITZER PHASE CURVES OF THE HIGHLY IRRADIATED HOT JUPITERS WASP-19b AND HAT-P-7b
- Author
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Wong, Ian, Knutson, Heather A, Kataria, Tiffany, Lewis, Nikole K, Burrows, Adam, Fortney, Jonathan J, Schwartz, Joel, Shporer, Avi, Agol, Eric, Cowan, Nicolas B, Deming, Drake, Desert, Jean-Michel, Fulton, Benjamin J, Howard, Andrew W, Langton, Jonathan, Laughlin, Gregory, Showman, Adam P, and Todorov, Kamen
- Subjects
photometric [techniques] ,Particle and Plasma Physics ,astro-ph.EP ,Molecular ,Nuclear ,Astronomy & Astrophysics ,Atomic ,Physical Chemistry ,planetary systems ,individual [stars] ,Astronomical and Space Sciences ,Physical Chemistry (incl. Structural) ,individual (WASP-19 and HAT-P-7) [stars] - Abstract
We analyze full-orbit phase curve observations of the transiting hot Jupiters WASP-19b and HAT-P-7b at 3.6 and 4.5 $\mu$m obtained using the Spitzer Space Telescope. For WASP-19b, we measure secondary eclipse depths of $0.485\%\pm 0.024\%$ and $0.584\%\pm 0.029\%$ at 3.6 and 4.5 $\mu$m, which are consistent with a single blackbody with effective temperature $2372 \pm 60$ K. The measured 3.6 and 4.5 $\mu$m secondary eclipse depths for HAT-P-7b are $0.156\%\pm 0.009\%$ and $0.190\%\pm 0.006\%$, which are well-described by a single blackbody with effective temperature $2667\pm 57$ K. Comparing the phase curves to the predictions of one-dimensional and three-dimensional atmospheric models, we find that WASP-19b's dayside emission is consistent with a model atmosphere with no dayside thermal inversion and moderately efficient day-night circulation. We also detect an eastward-shifted hotspot, suggesting the presence of a superrotating equatorial jet. In contrast, HAT-P-7b's dayside emission suggests a dayside thermal inversion and relatively inefficient day-night circulation; no hotspot shift is detected. For both planets, these same models do not agree with the measured nightside emission. The discrepancies in the model-data comparisons for WASP-19b might be explained by high-altitude silicate clouds on the nightside and/or high atmospheric metallicity, while the very low 3.6 $\mu$m nightside planetary brightness for HAT-P-7b may be indicative of an enhanced global C/O ratio. We compute Bond albedos of 0 ($
- Published
- 2016
48. Exoplanet Exploration Program Analysis Group (ExoPAG) Report to Paul Hertz Regarding Large Mission Concepts to Study for the 2020 Decadal Survey
- Author
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Gaudi, B. Scott, Agol, Eric, Apai, Daniel, Bendek, Eduardo, Boss, Alan, Breckinridge, James B., Ciardi, David R., Cowan, Nicolas B., Danchi, William C., Domagal-Goldman, Shawn, Fortney, Jonathan J., Greene, Thomas P., Kaltenegger, Lisa, Kasting, James F., Leisawitz, David T., Leger, Alain, Lille, Charles F., Lisman, Douglas P., Lo, Amy S., Malbet, Fabian, Mandell, Avi M., Meadows, Victoria S., Mennesson, Bertrand, Nemati, Bijan, Plavchan, Peter P., Rinehart, Stephen A., Roberge, Aki, Serabyn, Eugene, Shaklan, Stuart B., Shao, Michael, Stapelfeldt, Karl R., Stark, Christopher C., Swain, Mark, Taylor, Stuart F., Turnbull, Margaret C., Turner, Neal J., Turyshev, Slava G., Unwin, Stephen C., and Walkowicz, Lucianne M.
- Subjects
Earth and Planetary Astrophysics (astro-ph.EP) ,FOS: Physical sciences ,Astrophysics - Instrumentation and Methods for Astrophysics ,Instrumentation and Methods for Astrophysics (astro-ph.IM) ,Astrophysics - Earth and Planetary Astrophysics - Abstract
This is a joint summary of the reports from the three Astrophysics Program Analysis Groups (PAGs) in response to the "Planning for the 2020 Decadal Survey" charge given by the Astrophysics Division Director Paul Hertz. This joint executive summary contains points of consensus across all three PAGs. Additional findings specific to the individual PAGs are reported separately in the individual reports. The PAGs concur that all four large mission concepts identified in the white paper as candidates for maturation prior to the 2020 Decadal Survey should be studied in detail. These include the Far-IR Surveyor, the Habitable-Exoplanet Imaging Mission, the UV/Optical/IR Surveyor, and the X-ray Surveyor. This finding is predicated upon assumptions outlined in the white paper and subsequent charge, namely that 1) major development of future large flagship missions under consideration are to follow the implementation phases of JWST and WFIRST; 2) NASA will partner with the European Space Agency on its L3 Gravitational Wave Surveyor; 3) the Inflation Probe be classified as a probe-class mission to be developed according to the 2010 Decadal Survey report. If these key assumptions were to change, this PAG finding would need to be re-evaluated. The PAGs find that there is strong community support for the second phase of this activity - maturation of the four proposed mission concepts via Science and Technology Definition Teams (STDTs). The PAGs find that there is strong consensus that all of the STDTs contain broad and interdisciplinary representation of the science community. Finally, the PAGs find that there is community support for a line of Probe-class missions within the Astrophysics mission portfolio (condensed)., 22 pages, 2 tables, no figures
- Published
- 2015
49. Water On -and In- Terrestrial Planets
- Author
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Cowan, Nicolas B.
- Subjects
Earth and Planetary Astrophysics (astro-ph.EP) ,Physics - Geophysics ,FOS: Physical sciences ,Astrophysics::Earth and Planetary Astrophysics ,Geophysics (physics.geo-ph) ,Physics::Geophysics ,Astrophysics - Earth and Planetary Astrophysics - Abstract
Earth has a unique surface character among Solar System worlds. Not only does it harbor liquid water, but also large continents. An exoplanet with a similar appearance would remind us of home, but it is not obvious whether such a planet is more likely to bear life than an entirely ocean-covered waterworld---after all, surface liquid water defines the canonical habitable zone. In this proceeding, I argue that 1) Earth's bimodal surface character is critical to its long-term climate stability and hence is a signpost of habitability, and 2) we will be able to constrain the surface character of terrestrial exoplanets with next-generation space missions., 4 pages, 1 figure; to appear in the proceedings of the Comparative Climates of Terrestrial Planets II conference
- Published
- 2015
50. Brief follow-up on recent studies of Theia’s accretion
- Author
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Kaib, Nathan A. and Cowan, Nicolas B.
- Published
- 2015
- Full Text
- View/download PDF
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