THE INFLUENCE OF NONUNIFORM CLOUD COVER ON TRANSIT TRANSMISSION SPECTRA

By M. Line, V. Parmentier. 2015

139 citations recorded by the source corpus.

We model the impact of nonuniform cloud cover on transit transmission spectra. Patchy clouds exist in nearly every solar system atmosphere, brown dwarfs, and transiting exoplanets. Our major findings suggest that fractional cloud coverage can exactly mimic high mean molecular weight atmospheres and vice versa over certain wavelength regions, in particular, over the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) bandpass (1.1–1.7 μm). We also find that patchy cloud coverage exhibits a signature that is different from uniform global clouds. Furthermore, we explain analytically why the “patchy cloud-high mean molecular weight” degeneracy exists. We also explore the degeneracy of nonuniform cloud coverage in atmospheric retrievals on both synthetic and real planets. We find from retrievals on a synthetic solar composition hot Jupiter with patchy clouds and a cloud-free high mean molecular weight warm Neptune that both cloud-free high mean molecular weight atmospheres and partially cloudy atmospheres can explain the data equally well. Another key finding is that the HST WFC3 transit transmission spectra of two well-observed objects, the hot Jupiter HD 189733b and the warm Neptune HAT-P-11b, can be explained well by solar composition atmospheres with patchy clouds without the need to invoke high mean molecular weight or global clouds. The degeneracy between high molecular weight and solar composition partially cloudy atmospheres can be broken by observing the molecular Rayleigh scattering differences between the two. Furthermore, the signature of partially cloudy limbs also appears as a ∼100 ppm residual in the ingress and egress of the transit light curves, provided that the transit timing is known to seconds.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/9fdec7bba32fed327ed181ce0d939f26e757bfd7

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. N. Madhusudhan
2. R. MacDonald
3. Suzanne Aigrain
4. D. Sing
5. J. Barstow
6. P. Irwin
7. Jon Fortney
8. D. Deming

In Instrumentation

1. N. Madhusudhan
2. R. MacDonald
3. Suzanne Aigrain
4. D. Sing
5. J. Barstow
6. P. Irwin
7. D. Deming
8. Jon Fortney

Citations in the corpus

• HD 209458b in new light: evidence of nitrogen chemistry, patchy clouds and sub-solar water (2017, methodology): “The effect of partial clouds on transmission spectra retrieval has recently been examined by Line & Parmentier (2016).”
• A CONSISTENT RETRIEVAL ANALYSIS OF 10 HOT JUPITERS OBSERVED IN TRANSMISSION (2016, background): “As pointed out by Line & Parmentier (2015), the best method of distinguishing is to examine a high signalto-noise light curve for asymmetries, which may become possible with JWST. 5.6.”
• Exoplanetary Atmospheres: Key Insights, Challenges, and Prospects (2019, background): “The low spectral amplitudes may indicate either lower H2O abundances than assumed in equilibrium models (166), the presence of high-altitude clouds obscuring part of the atmosphere (80, 63), or a high mean molecular weight (150).”