Cloud features on Kepler-7b

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Cloud features on Kepler-7b

Post by Sirius_Alpha on 30th September 2013, 8:27 pm

Inference of Inhomogeneous Clouds in an Exoplanet Atmosphere
http://arxiv.org/abs/1309.7894

We present new visible and infrared observations of the hot Jupiter Kepler-7b to determine its atmospheric properties. Our analysis allows us to 1) refine Kepler-7b's relatively large geometric albedo of Ag=0.35+-0.02, 2) place upper limits on Kepler-7b thermal emission that remains undetected in both Spitzer bandpasses and 3) report a westward shift in the Kepler optical phase curve. We argue that Kepler-7b's visible flux cannot be due to thermal emission or Rayleigh scattering from H2 molecules. We therefore conclude that high altitude, optically reflective clouds located west from the substellar point are present in its atmosphere. We find that a silicate-based cloud composition is a possible candidate. Kepler-7b exhibits several properties that may make it particularly amenable to cloud formation in its upper atmosphere. These include a hot deep atmosphere that avoids a cloud cold trap, very low surface gravity to suppress cloud sedimentation, and a planetary equilibrium temperature in a range that allows for silicate clouds to potentially form in the visible atmosphere probed by Kepler. Our analysis does not only present evidence of optically thick clouds on Kepler-7b but also yields the first map of clouds in an exoplanet atmosphere.

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Re: Cloud features on Kepler-7b

Post by Stalker on 1st October 2013, 2:11 am

http://www.jpl.nasa.gov/news/news.php?release=2013-296

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Re: Cloud features on Kepler-7b

Post by Sunchaser on 1st October 2013, 2:42 pm

I thought this was really neat. How likely is this?

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Re: Cloud features on Kepler-7b

Post by Edasich on 1st October 2013, 2:47 pm

The Kepler-7 b's artistic rendering is so neat I wish it to be posted in this thread.
 
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Re: Cloud features on Kepler-7b

Post by Sirius_Alpha on 1st October 2013, 6:29 pm

Sunchaser wrote:I thought this was really neat.  How likely is this?
It's pretty likely. Here's 14 quarters of Kepler secondary eclipse photometry, folded by the period of the planet, and binned into 5 minute averages.



The peak reflectivity does not correspond to the secondary eclipse of the planet, but is clearly offset a bit (the secondary eclipse does not happen at the "top" of the sine curve made by the data). Clearly, the west side of the day-side hemisphere is brighter than the eastern side. Spitzer infrared photometry fails to detect the secondary eclipse, ruling out a thermal origin for the brightness difference in visible light. Clouds are the best solution.

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Re: Cloud features on Kepler-7b

Post by Sunchaser on 2nd October 2013, 9:32 pm

And the clouds we see in the rendering are based on this data? (I'm just trying to figure this out.)

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Re: Cloud features on Kepler-7b

Post by Stalker on 3rd October 2013, 1:37 am

Yep, you are looking at the planet with a point of view from the star.

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Re: Cloud features on Kepler-7b

Post by Sirius_Alpha on 3rd October 2013, 4:08 am

Yes. The paper has the actual map.

The artists rendering is overwhelmingly artistic, but what we do know is that the reflective clouds are on the west side of the dayside hemisphere.


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Re: Cloud features on Kepler-7b

Post by Sunchaser on 3rd October 2013, 9:06 pm

I'm speechless. This is one of the coolest things I've ever seen.

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Re: Cloud features on Kepler-7b

Post by Shellface on 19th January 2015, 6:36 pm

Further study of Kepler-7's uniquely high S/N phase curve (and also Kepler-10):

A Semi-Analytical Model of Visible-Wavelength Phase Curves of Exoplanets and Applications to Kepler-7 b and Kepler-10 b

Kepler has detected numerous exoplanet transits by precise measurements of stellar light in a single visible-wavelength band.
In addition to detection, the precise photometry provides phase curves of exoplanets, which can be used to study the dynamic processes
on these planets. However, the interpretation of these observations can be complicated by the fact that visible-wavelength
phase curves can represent both thermal emission and scattering from the planets. Here we present a semi-analytical model
framework that can be applied to study Kepler and future visible-wavelength phase curve observations of exoplanets. The model
efficiently computes reflection and thermal emission components for both rocky and gaseous planets, considering both homogeneous
and inhomogeneous surfaces or atmospheres. We analyze the phase curves of the gaseous planet Kepler-7 b and the
rocky planet Kepler-10 b using the model. In general, we find that a hot exoplanet’s visible-wavelength phase curve having a
significant phase offset can usually be explained by two classes of solutions: one class requires a thermal hot spot shifted to one
side of the substellar point, and the other class requires reflective clouds concentrated on the same side of the substellar point. The
two solutions would require very different Bond albedos to fit the same phase curve; atmospheric circulation models or eclipse
observations at longer wavelengths can effectively rule out one class of solutions, and thus pinpoint the albedo of the planet,
allowing decomposition of the reflection and the thermal emission components in the phase curve. Particularly for Kepler-7 b,
reflective clouds located on the west side of the substellar point can best explain its phase curve. We further derive that the
reflectivity of the clear part of the atmosphere should be less than 7% and that of the cloudy part should be greater than 80%, and
that the cloud boundary is located at 11±3 degree to the west of the substellar point. For Kepler-10 b, the phase curve does not
show a significant phase offset, and any model with a Bond albedo greater than 0.8 would provide an adequate fit. We suggest
single-band photometry surveys could yield valuable information on exoplanet atmospheres and surfaces.
This work shows the extent of the reflection - thermal emission degeneracy for observations in a single wavelength, as two fits of similar quality can be derived with very different atmospheric parameters. However, the Spitzer non-detection in the work at the top of the page can be used to reject the thermal emission model:

For Kepler-7 b, the dayside equilibrium temperature for the best-fit homogeneous atmosphere model is 1820 K, which is higher than the 3-σ upper limit of the brightness temperature measured at the Spitzer 3.6 µm band (Demory et al. 2013). With the caveat that Kepler and Spitzer may probe different pressure levels and have different brightness temperatures, the homogeneous atmosphere scenario appears to be inconsistent with the Spitzer observations. Based on the atmospheric circulation model results and the Spitzer observations, the homogeneous atmosphere scenario is unlikely, which effectively makes the patchy cloud scenario to only plausible scenario for Kepler-7 b.
In simpler terms, the cloudy model for Kepler-7 b remains favourable.

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Re: Cloud features on Kepler-7b

Post by Stalker on 3rd March 2015, 9:11 am

New technique allows analysis of clouds around exoplanets
Analysis of data from the Kepler space telescope has shown that roughly half of the dayside of the exoplanet Kepler-7b is covered by a large cloud mass. Statistical comparison of more than 1,000 atmospheric models show that these clouds are most likely made of Enstatite, a common Earth mineral that is in vapor form at the extreme temperature on Kepler-7b. These models varied the altitude, condensation, particle size, and chemical composition of the clouds to find the right reflectivity and color properties to match the observed signal from the exoplanet.

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Re: Cloud features on Kepler-7b

Post by Lazarus on 4th March 2015, 6:42 pm

Now on arXiv: http://arxiv.org/abs/1503.01028
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Re: Cloud features on Kepler-7b

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