I am currently writing my PhD Thesis in Computational Engineering applied to Civil Engineering. My background includes an MSc in Civil Engineering, an MSc in Computational Engineering, and a BSc in theoretical mathematics and physics. As part of my PhD, I am working intensively with weather data. I was wondering if that PhD could lead to a Postdoc within atmospheres studies of other planets, i.e., that postdoc wouldn't be in Civil Engineering, but rather in an Astrophysics department. Any thoughts?
Firstly, the topic you mentioned about studying the weather on other planets is extremely interesting. I used to listen to a weekly podcast, a decade ago where the speaker will talk about changing weather on planets. It was amazing.
Secondly, coming to your question; it is absolutely possible. It is dependent on two things, the acceptability criterion of the principal investigator of the project and the competition. You need to tune your resume for this purpose, communicate efficiently with the committee and effectively highlight your current work on weather data. Attend a related conference and talk to the potential PostDoc.
Finally, it won't be easy and you might need to push hard and maybe push for long. Luck could play a factor. You might have already spent many years coming this far in your studies; so you might look for stable opportunities.