As many as 1,400 icy objects inhabit a region of our solar system some 2.9 to 4.7 billion miles from the sun. The European Space Agency's Herschel Space Observatory has studied 132 of them, revealing a striking diversity of shapes, sizes and colors.
These trans-Neptunian objects (TNOs )— which include worlds such as Pluto, Eris, Haumea and Makemake — are extremely cold, at around -382 Fahrenheit. But these low temperatures lend themselves to observations by Herschel, which collects long-wavelength infrared radiation from some of the coldest and most distant objects in the universe.
Herschel was able to measure the sizes and albedos, the fraction of visible light reflected from the surface, of 132 TNOs (represented in the graphic above). They range from just below 31 miles to almost 1,491 miles in diameter. Pluto and Eris are the largest. Two worlds have distinctly elongated shapes: Haumea (seen in white) and Varuna (light brown). Some even host their own moons (not shown).
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.
TNOs are thought to be among the most primitive remnants of the planet-forming era, so astronomers intend to use this data in testing different models of how the solar system evolved.