Description: Trans-Neptunian objects (TNOs) are a class of small objects and dwarf planets that orbit the Sun beyond the orbit of Neptune. These are defined as having a typical distance from the Sun (the semi-major axis of their orbit) that is greater than Neptune's typical distance from the Sun (30.1 astronomical units or Earth–Sun distances). There are over 2000 known TNOs. Most are members of the Kuiper Belt although more distant objects are members of a population called the scattered disk.

Related Terms:

• Astronomical Unit
• Dwarf Planet
• Kuiper Belt
• Neptune
• Solar System
• Semi-Major Axis

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".