Here’s a pretty infographic that might come in handy when it comes to trying to explain the difference between different space rocks. Exactly what you might need when you’re just going about your normal day and you suddenly spot something from space hurtling towards earth.
The International Astronomical Union notes the difference between an asteroid and a meteoroid thusly:
A meteoroid is a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom.
Which kind of doesn’t clear things up much at all really. And as it turns out, the definitions and naming conventions are not as clear cut as the infographic suggests.
The IAU spends a lot of time trying to figure out the rules on nomenclature with it’s dedicated body, the perfectly named Committee on Small Body Nomenclature, and another commission for Meteors, Meteorites and Interplanetary Dust, which itself includes the Working Group on Meteor Shower Nomenclature.
Near Earth Asteroids (NEAs) are NEOs that are asteroids and come within 1.3AU from the Sun, or within 0.3AU of the Earth’s orbit, since an Astronomical Unit is the average distance from Earth to the Sun.
NEAs can then become the bad boys of space, Potentially Hazardous Asteroids (PHAs), when they come to within 0.05AU of the Earth’s orbit.