Given a scientific passage and an answer, generate a question for the given answer.

[Q]: Passage: Wavelength is one way of measuring the size of waves. It is the distance between two corresponding points on adjacent waves, and it is usually measured in meters. How it is measured is a little different for transverse and longitudinal waves. Answer: waves
[A]: What do wavelengths measure the size of?

[Q]: Passage: Neutrons consist of fundamental particles known as quarks and gluons. Gluons carry the strong nuclear force that binds together the quarks in a neutron. Answer: gluons
[A]: The two main fundamental particles that make up neutrons are quarks and what else?

[Q]: Passage: Figure 22.13 (a) In the planetary model of the atom, an electron orbits a nucleus, forming a closed-current loop and producing a magnetic field with a north pole and a south pole. (b) Electrons have spin and can be crudely pictured as rotating charge, forming a current that produces a magnetic field with a north pole and a south pole. Neither the planetary model nor the image of a spinning electron is completely consistent with modern physics. However, they do provide a useful way of understanding phenomena. Answer: planetary model
[A]:
What model of the atom features an electron orbiting a nucleus, forming a closed-current loop and producing a magnetic field with a north pole and a south pole?.