Description: Plasma is a quasi-neutral (i.e. charge balanced) gas where a significant fraction of the particles are positive ions and negative electrons, often mixed with molecules and neutral atoms. The properties of plasma are so different from those of ordinary neutral gases that plasma is considered a "fourth state of matter". The positive ions and negative electrons allow a plasma to conduct electricity. Plasma can form at high temperatures (as in stars) or by photoionization (as in interstellar gas). Plasma is found in stars, the interstellar medium, in the space between the planets in the Solar System in the form of the solar wind, within the planetary magnetosphere, and in the space between galaxies. It is estimated that more than 99% of the ordinary matter in the observable Universe (excluding dark matter and dark energy) is in the plasma state.

Related Terms:

• Dark Energy
• Dark Matter
• Gas
• Ion
• Electron
• Interstellar Medium

Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".