ESA's Herschel space observatory has observed 132 of the known 1400 cold worlds that inhabit a region of the Solar System beyond the orbit of Neptune, some 4.5-7.5 billion km from the Sun. These "trans-Neptunian objects", or TNOs, include worlds such as Pluto, Eris, Haumea and Makemake, and make up a vast population of such objects thought to occupy these far-flung reaches of the Solar System. This graphic shows a sample of the population of TNOs observed with Herschel, arranged to showcase their sizes and albedos (the fraction of visible light reflected from the surface). They range from just below 50 km to almost 2400 km in diameter; Pluto and Eris are the largest. Two worlds have distinctly elongated shapes: Haumea (seen in white) and Varuna (brown). The albedo measurement implies a variety of surface compositions: low albedo (brown) is an indication of dark surface materials, such as organic material, while higher albedo (white) suggests pure ices.