Planetary atmospheres in 2011 (2/2)

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An overview of the scientific literature on exoclimes in 2011 (if you notice some glaring omission, give us a shout in the comment section). This is part 2 of 2. You can find part 1 of 2 here.

Theory

Atmospheric circulation

Showman & Povlani (2011), building on their circulation simulations for hot Jupiters, study the circulation regime of tidally-locked super-Earths. They find that super-rotating equatorial jets also develop in this case, as in hot Jupiters. Heng et al. (2011) provide a suite of benchmark tests for circulation models of tidally-locked super-Earths. Showman et al. (2011b) calculate scaling laws for the atmospheric jets on gas giant planets.

Edson et al. (2011) use the same type of models to explore in sweeping generality the circulation regimes possible for tidally-locked Earth-like planets near the habitable zone with and without a global ocean. They quantify several rather intuitive features: wet planets are hotter, spin separates the circulation into two different regimes, with a transition at rotation periods of 3-5 days.

Wordsworth et al. (2011) run a general-circulation-model designed for Earth studies and adapted to exoplanets to address the question of the habitability of GJ581d. They answer with a very definite positive answer in the paper, although when you talk to them they are less confident of the possibility of circulation models to give fool-proof results in the absence of any data.

Pierrehumbert (2011) and Heng & Vogt (2011) get caught out in the cold by modelling the climate of a planet, GJ581g, that doesn’t not actually exist (see previous yearly literature overview). Nevertheless, Pierrehumbert’s simulations highlight an interesting case: an Earth-like planet covered by ice except for a circular open ocean around the sub-stellar point (advertised as “eyeball planets” by Ray – if like me you find the idea of a titanic eyeball rather disgusting, there is the earlier “pool planet” designation for this amusing member of the zoo of possible exotic worlds).

 

Atmospheric Composition

Moses et al. (2011) study the photochemistry effects in the high atmosphere of hot Jupiters for carbon, oxygen and nitrogen. The results are that abundances change a lot in the high atmosphere, although probably higher up than the altitudes that we probe with transit and eclipse data. Meanwhile the Zahnle et al. preprint on carbon soot photochemistry in hot Jupiters spends its second year in the purgatory of submitted, unpublished manuscript, suggesting that at least one expert in the world thinks that things are not so simple – too bad.

 

Internal Structure

Miller & Fortney (2011) calculate the size of hot Jupiters as a function of their heavy element content, and Rogers et al. (2011) study the formation and structure of hot Neptunes with large hydrogen/helium envelope.

Following up on the pioneering work of Cowan et al. (2009), Fujii et al. (2011) study how clouds affect the mapping of exo-Earths from their lightcurve.

 

Future

Finally, Shabram et al (2011) and Belu et al. (2011) study the potential of JWST for transit and eclipse spectroscopy. There was something of a scare for JWST in 2011 as some confused republican congressman scrapped it from the proposed budget at the commission level, but everything ended well after we got hold of his dog.

 

Solar System

For the first time this year, we make a little foray in Solar System studies. No attempt to be complete of course, we simply try to highlight a few papers with possible relevance to comparative planetology.

Venus Express and Cassini/Huygens provide the main sources of new results. Taking planets from the Sun out:

The Cloudy One

Venus Express keeps providing very precise measurements about the atmosphere of Venus, such as its sulphur content (Marcq et al. 2011, Sandor et al. 2011, Belyaev et al. 2011, Zhang et al. 2011), cloud morphology (Titov et al. 2011, Lee et al. 2011, Barstow et al. 2011), oxygen glow on the night side (Soret et al. 2011), carbon monoxide (Cotton et al. 2011) .

Parish et al. (2011) run an Earth-based climate model to study the decade-timescale variability of the Venusian climate. They find that the jets do wax and wane over these timescales.

The Red One

Zahnle et al. (2011) argue against the claims of methane detection on Mars.

The Boss

Orton et al. (2011) and Fletcher et al. (2011) study the 2009 asteroid impact on Jupiter. The impactor heated the atmosphere near 60 bars by “as much as 6 K”, and produce a detectable local contamination of silicates in Jupiter’s atmosphere. So ends the life of a random asteroid, in an echo of what must have been the last stages of giant planet formation in planetary systems. Fletcher et al. (2011b) study the famous “fading” of Jupiter’s Southern equatorial belt of clouds. Garcia-Malendo et al. (2011) and Asay-Davis et al. (2011) study the equatorial clouds of Jupiter from Cassini and HST data. The issue is weather the north-south differences and temporal changes observed are fundamental or due to transient features and waves.

The Hazy One
Cassini instruments (Hayes et al. 2011, Turtle et al. 2011) see the shoreline of methane lakes receding on Titan, a direct evidence of on-going “hydro”logical cycle on another planet. Ontario Lacus has lost about 1 metre per year since 2005. They know it is the lake getting shallower rather than another phenomenon because the drop is inversely proportional to the local slope.
Barnes et al. (2011) constrain the size of the waves from the Cassini data. Jingpo Lacus, Kraken Lacus, Arrakis Planitia – the Titan nomenclature is as evocative as that of Mars[1]. 

Clouds on Titan have been observed by Cassini since 2004, and Rodriguez et al. (2011) analyse the changing clouds over this 6-year period, which corresponds to about one season on Titan (the northern winter lasted from 2002 to 2009). Cassini results also provide data on photochemical haze shrouding the planet (Lavvas et al. 2011, Anderson & Samuelson 2011).
 
The Blue Ones
Karkoshka & Tomasko (2011) analyse HST/STIS data of Neptune, detecting the thin haze and a few discrete, bright clouds, and Irwin et al. (2011) study the clouds of Uranus with Gemini-North and UKIRT data. The atmosphere of Uranus gets more convective near the northern spring equinox, another “exoclimate”.
 
The Lost One
… and Zalucha et al. (2011) study the tiny atmosphere of no-longer-a-planet Pluto, using stellar occultations.
 
 
[1] a challenge to exoplanetologist.

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About Author

I am a professor of planetary science at the University of Exeter. My specialty is the study of exoplanets, in particular the observation and modelling of exoplanet atmospheres. I have done my PhD a the University of Geneva and worked in Chile, France and Switzerland.