Introduction to Planetary Sciences: Terrestrial Planet Interiors II

These flashcards cover key concepts and facts related to planetary magnetism, dynamos, and the magnetic characteristics of terrestrial planets.

What is the dynamo process in planetary sciences?

The inductive process by which motion of conducting fluids in planetary interiors generates large-scale magnetic fields.

What does the growth and decay of magnetic fields depend on?

It is governed by advective growth and decay as well as the diffusive decay of the magnetic field.

What happens in the limiting situation where magnetic diffusivity approaches zero?

The magnetic induction equation simplifies to the diffusion equation.

What is the frozen flux theorem?

It states that field lines cannot pass in or out of a perfect conductor.

What is the Elsasser number?

It is a ratio between the Lorentz and Coriolis forces, important for understanding dynamo action.

What is the significance of a magnetic Reynolds number greater than 10-100?

It is necessary for dynamo action to occur.

What is the relationship between the dipole field strength and total core field strength?

Only the poloidal field emerges from the core, and higher-order terms fall off more rapidly than the dipole term.

How is the magnetic field at the surface of a planet estimated from the core?

Using the ratio of dipole field strength to total core field strength.

How is paleointensity measured in ancient rocks?

By measuring the natural remanent magnetization and comparing it to thermoremanent magnetization produced in a known laboratory field.

What is one proposed reason for Mercury’s weak magnetic field?

The field generated in the inner part of the core may be shielded by an outer layer, preventing convection.

What indicates that Venus does not currently have a dynamo?

Its magnetic field is less than 10 nT, suggesting insufficient heat flow for an active dynamo.

What does crustal remanence indicate about the Moon's history?

The Moon likely had an active dynamo in the past, but does not have one today.

What is the significance of the strength of magnetic fields in asteroids?

Strong crustal remanence indicates that at least 4 asteroids inferred to have generated dynamos.

What has paleointensity measurements revealed about Mars?

Mars once had a dynamo indicated by strong crustal remanence in ancient rocks.