81P/Wild 2

Small icy comet sampled by NASA's Stardust mission, which found glycine in its dust.

What it is

Comet: A dirty snowball that grows a tail near the Sun. Every kind of thing there is →

Can you see it?

No. No telescope on Earth will show you this one; it is here to be understood, not seen. It is here because it is worth knowing about — and because leaving it out would make the sky look emptier than it is.

Worth knowing about 81P/Wild 2

81P/Wild 2 is about the size of a small mountain, with a surface covered in pits, cliffs, and spires. Ranges from about as far as Mars to nearly twice Jupiter's distance. Sunlight takes 29 minutes to reach 81P/Wild 2 — on average, because that distance changes as it goes round.

Its weather: Icy and dusty, with jets of gas and dust erupting from many small vents across its surface.
How it moves: About 6 and a half years.
The machines we sent: NASA's Stardust flew straight through its tail in 2004, caught dust in a sponge-like material called aerogel, and parachuted the sample back to Earth in 2006.
What makes it worth knowing: Scientists discovered glycine -- a basic building block of proteins -- in the returned dust, the first amino acid ever confirmed to come from a comet, supporting the idea that some ingredients of life may have first formed out in space.

The numbers