A paper just posted online by two Caltech astronomers describes observations at an 8-metre telescope of more than 300 faint trans-Neptunian objects (TNOs), small lumps of ice orbiting out beyond Neptune. These are leftover chunks of the materials that went into the planets, witnesses to the events that formed our solar system. The shapes of their orbits tells us how the large planets near them have pulled on their paths over time; patterns in the evolution of their surfaces hint at events in our solar system over the past 4 billion years.

Nearly 20 years ago I started working on just such observations with Steve Tegler (Northern Arizona University) and Bill Romanishin (University of Oklahoma). Back then, Steve and Bill had noticed that the first handful of TNOs they had observed did not show a range of colours but rather fell into two distinct colour classes: red and grey. Looking for a telescope where they could continue their survey, they asked to use our 2-metre Vatican Advanced Technology Telescope. I operated the telescope, while chiming in on their all-night speculations as to what it all meant.