Magnetohydrodynamics is the study of how motions of electrically-conducting fluid layers inside of planets (or stars) act as the current source for huge magnetic fields that wrap around the planet as a shield that protects the planet’s atmosphere from potentially corrosive particles that come careening towards the planet from outer space. As a NASA researcher, I studied magnetohydrodynamics on Uranus and Neptune.

Observations show that the magnetic fields at Uranus and Neptune look like weird amoebas (i.e. “multipolar”) while the magnetic fields at Mercury, Earth, Jupiter, Saturn, and Ganymede (a moon around Jupiter) are all shaped like chonky donuts (i.e. “dipolar”). I was trying to figure out what was happening inside of Uranus and Neptune to cause their strange-looking magnetic fields.

The shape of a planetary magnetic field changes over time as the fluid motions inside of the planet change over time. The time-varying shape can be mathematically decomposed into a combo of constituent parts. A good analogy for this is if you go grocery shopping. The bag of groceries might consist of 5 apples, 4 chocolate-chip cookies, 2 cauliflowers, 2 bunches of spinach, and 1 box of tortellini. The total weight of the bag of groceries might change if you add an apple or remove the tortellini. So the total bag of groceries can be split into specific, constituent parts. And if the total bag weight changes over time, we automatically assume that it’s because the amounts of some ingredient in the bag must be changing with time too! Similarly, the fluid motions inside of a plant change over time, causing the constituent parts of the planet’s magnetic field to change over time, causing the total magnetic field shape to change over time, which is detected by a spacecraft.

Now suppose that I was indecisive about whether I wanted to make apple pie, so I spent a while at the grocery store adding apples and then taking them back out of the grocery bag again and again, and now I am plotting how the number of apples in the bag changed over time while I was struggling to choose. Maybe this plot will quantify my indecisive behavior by exhibiting when I was feeling like pie and when I wasn’t, over time, just by counting the weight of the apples in the bag. I did a similar thing for Uranus and Neptune. For my NASA research, I ran supercomputer simulations of how the fluid moves inside of either planet. The simulations also calculates and displays the magnetic field that is produced by those fluid motions. The simulated magnetic field can be decomposed into constituent parts, which change over simulated time. So I plot how the strength of each, constituent part changes over time for my Uranus and Neptune – like simulations (there were 2 of them). And then I did something called a correlation analysis to see if the different parts trade-off energy between each other so that when one part’s influence goes down, the other part’s influence goes up. (Or if they mirror each other, where when one part’s influence goes up, so does the other.)