Beyond The Last Planet

- Amy Thompson

ULTIMA THULE IS A SPECK IN the cosmos, barely 20 miles wide, that orbits our sun a billion miles past Pluto. It is so small and distant that it cannot be seen from Earth, even with the most powerful ground-based telescopes. To find it, astronomers had to use the Hubble Space Telescope, which sits above the Earth’s atmosphere—and even then, it appeared only as a faint dot. Astronomers named it with an ancient Greek phrase that refers to a distant place far to the north, beyond what is known.