Small-Body Mission Control

A comet is a small icy body that releases gas and dust as it warms near the Sun, forming a visible tail. Most originate from the Oort Cloud or Kuiper Belt — the outer edges of our solar system. Most are a few kilometers across.

Asteroids are rocky or metallic bodies orbiting the Sun. Near-Earth Asteroids (NEAs) cross or approach Earth's orbit. Most are small and pose no risk. Sizes range from pebbles to hundreds of kilometers.

"Potentially Hazardous Asteroid" is a technical classification, not an alarm. It means the object is large enough (>140 m) and comes close enough to Earth's orbital path (<0.05 AU) that scientists track it carefully. No currently listed PHA has a credible near-term impact prediction.

Magnitude measures brightness but the scale runs backwards: magnitude 1 is brighter than magnitude 6. The naked eye limit under dark skies is about magnitude 6.5. Each step of 1 is 2.5× in brightness. Binoculars typically reach magnitude 9–10; a small telescope ~12–13.

1 Lunar Distance (LD) ≈ 384,400 km — 30× the Earth's diameter. An object at 5 LD is 1.9 million km away. For reference, geostationary satellites orbit at just 0.1 LD. "Very Close" by asteroid standards is still enormously far — no alarm warranted.

Periodic comets (like 67P or Halley's) orbit the Sun on a schedule. Hyperbolic comets are deep-space visitors on escape trajectories — they won't return. Interstellar objects like ʻOumuamua and Borisov originate from other star systems entirely and are extremely rare.