Our understanding of Pluto has changed a lot since it was discovered in 1930.
When American astronomer Clyde Tombaugh first trained the Lowell Observatory's gaze on Pluto's patch of sky, the small dwarf planet appeared as a pinprick of light in distant space. As the years went by, scientists continued to get better and better views of Pluto from powerful telescopes on Earth and in space.
Now, NASA's New Horizons spacecraft will get the first close-up images of the tiny planet on the outskirts of the solar system for the first time in history. The New Horizons mission will bring the surface features of the small world into sharp focus for the first time when it speeds past Pluto, making science observations along the way on Tuesday.
New Horizons has already revealed Pluto as a red world with strange dark and light patches dotting its surface. It looks completely unique within the context of the solar system, according to scientists working on the mission's team.
"This object is unlike any other that we have observed," New Horizons principal investigator Alan Stern said during a news conference this week.
Before New Horizons, scientists used data collected by the Hubble Space Telescope and other observatories to learn more about Pluto and hunt for moons around the tiny planet. The small planet's largest moon Charon was discovered in 1978 by U.S. Naval Observatory astronomer James Christy peering through a telescope in Arizona.
The Hubble telescope, however, is responsible for discovery of the vast majority of Pluto's known moons.
The intrepid eye on the sky discovered Pluto's moons Nix and Hydra in 2005 and another moon, Kerberos, in 2011. Pluto's family wasn't complete until 2012, however, when its last known moon -- now called Styx -- was discovered by the Hubble.
At one point, scientists thought that New Horizons might actually uncover new moons of Pluto during its flyby, but the craft hasn't found any new rings or moons orbiting the small body.
“Not finding new moons or rings present is a bit of a scientific surprise to most of us,” Stern said in a statement earlier in July.
It has been a long road to Pluto for New Horizons.
The spacecraft launched to the dwarf planet in January 2006, right before the International Astronomical Union -- the organization responsible for naming and categorizing cosmic objects -- reclassified Pluto as a dwarf planet instead of a "major" solar system planet.