Space Encyclopedia
🪨 Asteroids
Overview
Asteroids are rocky and metallic bodies left over from the formation of the Solar System. Most orbit the Sun in the main belt between Mars and Jupiter, but Near-Earth Asteroids (NEAs) come close enough to warrant continuous tracking by planetary defense programs.
Key facts
- •Main belt population: >1 million larger than 1 km
- •Largest: Ceres (~940 km) — now classified as a dwarf planet
- •Typical NEA velocity relative to Earth: 15–30 km/s
- •NASA tracks all NEOs ≥140 m
- •DART mission (2022): first successful asteroid deflection test
Why it matters
Asteroids are time capsules of the early Solar System — and a real long-term hazard. Continuous cataloging of Near-Earth Objects and missions like DART, Hera, and OSIRIS-REx build the technology to redirect a threatening object decades before impact.
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Frequently asked questions
Can I see an asteroid with the naked eye?
Almost never. Only Vesta occasionally reaches naked-eye brightness at opposition. Most asteroids require binoculars or a telescope.
Are any asteroids on a collision course with Earth?
No known asteroid larger than 140 m has a significant probability of impacting Earth in the next century, per NASA's catalog.
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