If it gains two more electrons, it becomes an ion with a positive charge. If it loses electrons, it becomes an ion with a negative charge. A magnetomer measures the magnetic field around the sun. The magnetic field, invisible to the eye, act like iron filings around a magnet and form lines of force. When Ulysses crossed into the comet's tail, the magnetic fields changed, slowed by the gas and dust emitted by the comet.
Comet tails are like signatures for individual comets.
Hyakutake had a long, thin, bluish tail. Comet Hale-Bopp had a definite split between its gas and dust tails, giving it its own particular look. As these dirty balls of ice and rock approach the sun from the deep freeze of the outer solar system, they begins to warm. As they heat up, they give off gas and dust, which form the tails. Pressure from the sun and solar wind always blows a comet's tail away from the sun.