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Deep Field
29 September 2026 2518 stories tracked

Glossary · Comets & Asteroids

Oort cloud

A shell of icy bodies at the edge of the Sun's influence, inferred rather than observed.

Long-period comets arrive from every direction with orbits stretching tens of thousands of astronomical units out, which implies a roughly spherical reservoir at that distance. Nobody has ever directly observed an Oort cloud object out there — it is too far and too dark — so its existence rests on the orbits of the comets that leave it. Voyager 1, the most distant thing we have built, will take about three hundred years to reach the inner edge.

Related terms

Near-Earth object An asteroid or comet whose orbit brings it inside 1.3 astronomical units of the Sun. Asteroid and comet Rock that stays rock, and ice that grows a tail when it gets warm. Coma and tail A comet's atmosphere, and the two separate tails the Sun pushes off it. Kuiper belt The flat ring of icy bodies beyond Neptune, where Pluto lives and short-period comets come from.

Questions

What is Oort cloud?

A shell of icy bodies at the edge of the Sun's influence, inferred rather than observed.

Why does it matter?

Nobody has ever directly observed an Oort cloud object out there — it is too far and too dark — so its existence rests on the orbits of the comets that leave it. Voyager 1, the most distant thing we have built, will take about three hundred years to reach the inner edge.

Written and computed by . Corrections and errors to hello@cantinalabs.dev.