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What are near-Earth asteroids?
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Asteroid
This rock would take out more than just a T. rex.
Near-Earth asteroids (NEAs) are asteroids that can pass close to Earth. While the term is often used to describe these objects, not all NEAs actually cross Earth’s orbit. NEAs are categorized into several orbital classes based on their proximity to the planet:1
- Atira asteroids: Their orbits lie entirely inside Earth’s orbit; they do not cross it.1
- Aten asteroids: These have mean distances from the Sun of less than 1 AU and cross Earth’s orbit near the farthest points of their own orbits.1
- Apollo asteroids: These have mean distances greater than or equal to 1 AU and cross Earth’s orbit near their closest points to the Sun.1
- Amor asteroids: These have perihelion distances greater than Earth’s aphelion but no greater than 1.3 AU. They do not currently cross Earth’s orbit, though gravitational perturbations can cause their orbits to change over time, making some of them "part-time" Earth crossers.1
Because of the potential for collision, these objects are monitored as part of planetary defense efforts to identify and mitigate Earth impact hazards.23