Day 1/5, Session 2: Low-mass planets


After the ski break (11:00-15:00), we reconvene in the 100-seats auditorium at the Aspen Center for Physics, with the snow still coming down hard outside. Some of the attendees look red in the face, presumably from the cold wind while skiing earlier.

First off, we have Geoffrey Vallis, from Princeton University, giving a keynote lecture on the atmospheric dynamics of terrestrial planets. He presented his book Atmospheric and Oceanic Fluid Dynamics: Fundamentals and Large-scale Circulation, which complements Pierrehumbert’s Principles of Planetary Climate.

Now he’s talking about Hadley cell dynamics. In mid-latitudes, baroclinic instability creates eddies, leading to Rossby waves forcing momentum to converge and generate an eastward jet. Next, he touches on superrotation, whereby the atmosphere of a planet rotates faster than the surface. He shows that the Earth atmosphere is not superrotating, but Jupiter, Titan and Venus are. It appears that the Earth atmosphere could have superrotated at high enough temperatures, for example in the past “hot-house” regimes that the Earth visited. Superrotation could also warm the dark side of tidally-locked exoplanets.

Next, we have Edwin Kite, from the University of California at Berkeley, presenting his recent paper on climate instability on tidally locked planets in the habitable zone around M-dwarfs. If his theory is correct, we would find a bimodal distribution of rocky planets in the galaxy, with planets with a sharp temperature contrast, and planets with a uniform temperature.

Now we have Feng Tian, from the University of Colorado, talking about nitrogen and habitability around M-dwarfs. The talk was highly technical. I spoke to Feng later, and he explained that the bottom line was this:  a CO2-poor atmosphere in the habitable zone around an M-dwarf can lose all the nitrogen very quickly and make the planet useless for life as we know it, which depends on nitrogen compounds.

It’s now time for the afternoon coffee break, and many people around me seem like they seriously need it.

The penultimate talk of the day is given by Jonathan Fortney, focussing on the atmospheres of low-mass and low-density planets, which are believed to be common in the Galaxy. The transmission spectrum can inform us on the composition. GJ-1214 has a flat transmission spectrum, suggesting the atmosphere has a high molecular weight, or has clouds obscuring the atmosphere. Sub-Neptune planets vastly outnumber gas giants, so core-accretion planet formation models must be explored in more detail for low mass objects.

It’s been a long day, and now we have the closing talk, given by Angela Zalucha, on General Circulation Modelling and spectral modelling of GJ 1214b. She uses the MIT GCM (, applied to Mars, Pluto and super-Earth exoplanets. She spent a large part of the talk on technical details of the simulations, and then showed her results. She finds eastward jets which match results by other teams, but she also showed jets along longitudes, crossing the poles.

This concludes the second session of Exoclimes 2012.


About Author

I graduated from the University of Manchester in 2009 with an MPhys "Physics with Astrophysics" degree. I am currently studying for a PhD in astrophysics at the University of Exeter, where I work with Prof. Frederic Pont. My primary research for my thesis is about tidal effects in close-in transiting gas giant exoplanets. I am also interested in the atmospheric physics of exoplanets - specifically simple radiative transfer models. (More)