(153591) 2001 SN263 made a close pass by the earth in February 2008. On February 15 I was able to catch it passing by in a series of 15 30 second exposures. It was about 6.5 million miles away at the time but moving rather rapidly, a bit over 7" of arc per minute. My USB1.1 camera is slow downloading so there's a noticeable gap between each frame. It was about 6.1 million miles away when, a few days later, Arecibo discovered it had two satellite asteroids. So instead of imaging one asteroid, it turns out I was taking three. The main asteroid is a bit under 3 kilometers in size while the satellites are .77 and .43 kilometers in size.

Only two other trinary main belt asteroids are known that I'm aware of; (136617) 1994 CC and 3122 Florence. They were found to be trinaries in 2009 and 2017. That makes this one the first trinary asteroid known.

Normally I'd not post such a basic image as this one but after learning its history and my image being taken just before it was discovered to be trinary I decided to include it.

14" LX200R @ f/10, L=15x30", STL-11000XM, Paramount ME