Wesley C. Fraser

At the outskirts of the Solar System, beyond Neptune's orbit, millions of icy chunks circle the Sun — leftover building material from the era of planet formation. Astronomers call them trans-Neptunian objects, and they have a peculiarity: their surfaces are painted in various shades of red. Some are merely reddish, like rust, while others are very red, like dried blood.

Beyond Neptune's orbit lies an ocean of icy islands that has remained nearly unchanged for four billion years. These islands, known as trans-Neptunian objects, hold the recipe for planet formation. Until recently, astronomers could only see the large ones, while the small, city-sized ones stayed invisible.