Dynamos |

MagIC

Mon, 01 Jan 0001 00:00:00 +0000

MagIC is a numerical code that can simulate fluid dynamics in spherical geometry. It solves for the Navier-Stokes equation including Coriolis force, optionally coupled with an induction equation for Magneto-Hydro Dynamics (MHD), a temperature (or entropy) equation and an equation for chemical composition under both the anelastic and the Boussinesq approximations.

MagIC has been used in 174 publications (170 refereed) since 2002, according to .

MagIC is pseudo-spectral and makes use of spherical harmonics $Y_\ell^m(\theta,\phi)$ in the angular directions. In the radial direction, it offers two options : one can either make use of Chebyshev polynomials or finite differences.

I am one of the developers of MagIC, so feel free to reach out if you plan to use it for your work!

For more information, visit: .

Mars

Wed, 01 Jan 2020 00:00:00 +0000

Mars does not currently generate its own magnetic field. However, the crust of Mars has recorded its ancient magnetic field and it is quite unusual. It has a much higher magnetitude in the souther hemisphere compared to the northern.

We simulate the dynamo of Mars with a heat flux variation at the core-mantle boundary (CMB) such that there is greater heat flux coming out of the southern hemisphere. This enhances convection in one hemisphere compared to another and yields “hemispherical” dynamos - with one hemisphere having higher magnetic field than another.

Gas giant dynamos

Mon, 01 Jan 0001 00:00:00 +0000

The gas giants - Jupiter and Saturn - have a similar size and are composed mostly of Hydrogen and Helium. However, their magnetic fields are completely different. Jupiter has the strongest magnetic field among all the planets while Saturn’s field is comparable to that of Earth. The Juno and Cassini missions gave us a wealth of information about the the gas giants.

Radial magnetic field of Jupiter and Saturn

Both missions with contraints from gravity and magnetic data have revealed a few key features of the two planets:

A dilute “fuzzy” core at the interior
Presence of stably stratified layers
Zonal winds that penetrate to different depths on the two planets

Explaining all of these features at the same time requires three dimensional simulations of the dynamo being generated inside the planets, with realistic profiles of interior properties. A key features of the simulations are including stably stratified layers in different forms to account for, explain and constrain the above three features.

Moon

Sun, 01 Jan 2017 00:00:00 +0000

Paleomagnetic analysis of rock samples returned from the Apollo missions have revealed that the Moon used to have a very strong magnetic field, higher than that of present day Earth 100$\mu$ T, which then later dropped to values of around 10$\mu$ T and eventually, at present day the moon does not generate any magnetic field.

The problem with generating such a strong magnetic field on the moon is the size of its core. A core of this size cannot have the amount of power needed to generate a magnetic field of this magnitude at the surface, keeping in mind that the core is very far away from the surface.

In addition, any dynamo mechanism attempting to explain the lunar paleomagnetic record must explain the following three things:

High magnetic field in the ancient past
Low magnetic field thereafter
No magnetic field in present day

A few different dynamo mechanisms have been proposed, each with their pros and cons:

Thermochemical convection:
- Field intensity : low ❌
- Lifetime : long ✅
Basal magma ocean:
- Field intensity : high ✅
- Lifetime: limited ✅
- Requires high magma conductivity ❓
Mechanical driving (e.g.: precession):
- Field intensity : high ✅
- Lifetime: limited ✅
- Very hard to run simulations and scale to real values ❌

We followed a slightly different approach and found that a mix of convection and precession has the potential to explain all three features of the lunar paleomagnetic record.