As Giang Nguyen gets deeper into his PhD, the atmospheric conditions he is analyzing just keep getting more and more extreme! Above, the subject of his latest project: looking at winds on a ultra-short period planet which orbits incredibly close to its parent star.
By Giang Nguyen
As I progress with my PhD research hoping to graduate in a couple of years, I delve deeper and deeper into the field of exoplanets. No longer working on Mars, I now model the atmospheres of distant planets as well as hypothetical planets yet to be discovered. Continuing my work from my internship in the UK where I started with modelling the thin SO2 atmosphere of Io, I now expand my model to analyze icy-Earths and lava planets.
For the icy-Earth cases, I inferred what kind of atmosphere would arise from a water dominated world with sub-freezing surface temperatures (50 K - 270 K). With an atmosphere generated from the sublimation of ice/frost at the surface on the dayside, this creates a pressure gradient which causes the wind to blow from the dayside to the nightside. To give an example, one water-vapour dominant atmosphere has a maximum pressure of 0.45 kPa (0.4% of the Earth’s atmosphere) where winds reach up to 950 m/s. With winds going much faster than Mach 1 and there’s precipitation too! It’s rather exciting to think that somewhere in the universe there’s a blizzard blowing at twice the speed of sound.
For the icy-Earth cases, I inferred what kind of atmosphere would arise from a water dominated world with sub-freezing surface temperatures (50 K - 270 K). With an atmosphere generated from the sublimation of ice/frost at the surface on the dayside, this creates a pressure gradient which causes the wind to blow from the dayside to the nightside. To give an example, one water-vapour dominant atmosphere has a maximum pressure of 0.45 kPa (0.4% of the Earth’s atmosphere) where winds reach up to 950 m/s. With winds going much faster than Mach 1 and there’s precipitation too! It’s rather exciting to think that somewhere in the universe there’s a blizzard blowing at twice the speed of sound.
Having presented this work as a poster at the EPSC-DPS joint meeting conference in Geneva this past September, I was delighted to see enthusiasm from others. Of course, there were many qualms about the simplicity of the model I used. For an atmospheric pressure less than 1% of Earth’s atmosphere composed of water-vapour, there can still be a greenhouse effect that I have yet to consider. Also, water-vapour is prone to be dissociated into Hydrogen and Oxygen through photolysis which will change the composition as the hydrogen escapes to space. This has the effect of diluting the water-vapour in the atmosphere over time with molecular oxygen. However, the idealistic model used for my work serves as good basis for additional processes to be implemented and can be applied to any compositionally pure atmospheres.
Having dealt with made up planets, it was finally time to try my hand on an observed exoplanet. With a mission to determine the atmospheric properties of a planet named k2-141b, I am to collaborate with Nicolas Cowan at McGill University for a proposal of observing the distant exoplanet via JWST (James Webb Space Telescope). I’ve gotten some preliminary results which I’d like to share but first, let’s start off with some background information about our planet of interest.
Discovered in 2018 by the K2 mission (originally Kepler mission), K2-141b is 50% larger than Earth but is 5 times the mass of Earth. Its ultra-short orbital period of 0.3 days and a semi-major axis of 0.00716 AU makes K2-141b a prime subject since its transit can be frequently observed. The tidally locked planet has an extremely large surface temperature gradient with an inferred maximum temperature of 3000 K on the dayside and near absolute zero temperature on the nightside.
For my part in the project, I am using the parameters above to model the atmospheric flow on K2-141b under the assumption of a silicate dominated composition on both the surface and in the atmosphere. Here the maximum pressure is 12 kPa on the dayside and winds can reach up to 700 m/s. Since the dayside temperatures are so hot, the entirety of the dayside surface is one giant magma ocean.
As you move away from the subsolar point, the air cools and precipitation happens. Since the temperature gradient is much larger than my previous icy-Earth scenarios, there can be a phase change in the precipitation. Imagine liquid rock rain going at the speed of sound which then transitions to snow or hail going even faster. This is pretty enticing stuff: getting a peek into extreme weather on planets hundreds of lightyears away is as good as it gets, in this field!
Thus concludes the update on what I have been doing since being evicted from Mars. Although my focus has shift significantly, I find that there is a bunch of things have stayed the same: I still model how ice melts and sublimates, study how wind carries material, and I still need to get hastily written code to run with a 50% success rate. And by the look of things, I’m going to be still doing that for a while longer. I’ll tell you more interesting things next time when it’s my turn to write a blogpost, dear reader, but until then, cheers.
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