Glossary term: Near-Earth Objects

Also known as NEO, NEA, Near-Earth Asteroid, PHA or Potentially Hazardous Asteroid

Description: In addition to the Sun and planets, our Solar System contains numerous smaller bodies, notably asteroids and comets. The collision of an asteroid or comet with Earth can have disastrous consequences. So far, none of the objects we know is on a collision course with Earth, but there are a number of objects it makes sense to keep an eye on, nonetheless. Any asteroid or comet that, on its orbit, comes closer to the Sun than 1.3 times the Earth–Sun distance (in astronomical terms: 1.3 astronomical units) is called a Near-Earth Object (NEO). Most NEOs are Near-Earth Asteroids (NEAs).

A NEO is called a Potentially Hazardous Object (PHO) if it has the following properties: For one, it needs to come closer to Earth's orbit than 5% of the Earth–Sun distance (closer than 0.05 astronomical units). In addition such an object needs to have a certain minimum size – otherwise, it would pose no danger to Earth. Size is difficult to measure for smaller objects in the Solar System, so astronomers instead use a minimal value for such an object's absolute brightness – after all, the larger an object is, the brighter it is likely to be. To qualify as a PHO, an object needs to have an absolute magnitude of 22.0 or brighter (using the magnitude system as astronomy's standard way of measuring brightness). Most PHOs are Potentially Hazardous Asteroids (PHAs).

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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".

Related Activities

Creating Asteroids

Creating Asteroids

astroEDU educational activity (links to astroEDU website)
Description: Have fun, building asteroids using clay!

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons

Tags: Hands-on , Model
Age Ranges: 4-6 , 6-8 , 8-10
Education Level: Pre-school , Primary
Areas of Learning: Modelling , Social Research
Costs: Medium Cost
Duration: 1 hour 30 mins
Group Size: Group
Skills: Communicating information , Developing and using models