What happened on October 10 in History

Triton was discovered on October 10, 1846 by British astronomer William Lassell, just 17 days after Neptune itself was discovered.

Triton is the largest of Neptune's 13 moons. It is unusual because it is the only large moon in our solar system that orbits in the opposite direction of its planet's rotation―a retrograde orbit.

Scientists think Triton is a Kuiper Belt Object captured by Neptune's gravity millions of years ago. It shares many similarities with Pluto, the best known world of the Kuiper Belt.

Like our own moon, Triton is locked in synchronous rotation with Neptune―one side faces the planet at all times. But because of its unusual orbital inclination both polar regions take turns facing the Sun.

Triton has a diameter of 1,680 miles (2,700 kilometers). Spacecraft images show the moon has a sparsely cratered surface with smooth volcanic plains, mounds and round pits formed by icy lava flows. Triton consists of a crust of frozen nitrogen over an icy mantle believed to cover a core of rock and metal. Triton has a density about twice that of water.