An ion engine is an engine that ionizes a gas in order to propel a spacecraft. This efficient type of engine delivers 10 times the thrust of conventional engines for the same mass of fuel. This engine is only used in outer space. The ionosphere is one of the highest layer of the Earth's atmosphere. The ions are created when sunlight hits atoms and tears off some electrons.
Auroras occur in the ionosphere.
An iron meteorite is a meteor made of the metal iron that has fallen to Earth. Irregular galaxies usually contain only 100 million to 10 billion stars. For example, the Magellanic Cloud is an irregular galaxy. The local group is an irregular galaxy cluster. A physical measurement made in one direction is the same as the measurement made in another direction.