Figure 1. Modeled plasma density about a magnetized asteroid.
Asteroids are mainly composed of mineral and rock, comets are composed of dust and ice. Asteroids formed closer to the sun. Meteorites are less than a meter in diameter.
Asteroids can be made of metals and therefore retain a magnetic field. The source of the field is often not known.
The asteroids travel through a background plasma, known as the solar wind. With a plasma density of about 2 particles per cc and an electron temperature of about 8 million degrees. The plasma is flowing with a speed of about 1 million Kilometers per hour. The magnetic fields of the asteroid, if it exists, is small about a 1000 times less than the earths magnetic field, because the asteroids are small – a few hundred kilometers across for the largest.
When ions from the solar plasma pass a large magnetized asteroid they will interact with the magnetic field and gyrate with a orbit which will be a few thousand kilometers, that is an orbit greater than the radius of the asteroid. Unlike, plasma at the earth where gyroradii are much smaller than the earth radius and the solar wind is trapped which results in the aurora, this is not possible on an asteroid.
Figure 2. Hybrid simulation results for a magnetized Psyche taken from showing the magnitude of the magnetic field normalized to the undisturbed upstream magnetic field Bsw=2 nT. (a) a cut in the xz plane at y=0, and (b) a cut in the xy plane at z=0. The solar wind flows along the -x axis, the IMF is along the +z axis, and the dipole moment of Psyche is along the -z axis. Streamlines in panel a show the magnetic field line tracing in the xz plane. Psyche is the white circle at the center of the coordinate system.