Pluto, barely visible by telescope in the night sky. (Adler Planetarium)
This combination of images made by NASA's Hubble Space Telescope in 2002 and 2003 shows Pluto at different angles. (AP Photo/ NASA, ESA, M. Buie)
An artist's rendering of the New Horizon's spacecraft passing by pluto. (NASA)
This combination of images from July 1 to July 3, 2015, provided by NASA shows Pluto at different distances from the New Horizons spacecraft. (AP Photo/NASA via Pluto)
A composite image of Pluto and its largest moon Charon, as seen from the New Horizon's spacecraft, showing the planet's rust color. (NASA)
Pluto as seen by the New Horizons spacecraft on July 11, 2015. The spacecraft traveled 3 billion miles over 9 and a half years to reach Pluto. (NASA)
A false-color image taken on July 13, 2015 of Pluto and its moon, Charon, with differences in surface material and features depicted in exaggerated colors. (NASA/APL/SwRI via AP)
An accurate-color image of Pluto on July 13, 2015, the day before New Horizon's completed its flyby, showing geological features. (NASA)
This Tuesday, July 14, 2015 image provided by NASA on Wednesday shows a region near Pluto's equator with a range of mountains captured by the New Horizons spacecraft. (NASA/JHUAPL/SwRI via AP)
This Tuesday, July 14, 2015 image provided by NASA on Wednesday shows Pluto's largest moon, Charon, made by the New Horizons spacecraft. (NASA/JHUAPL/SwRI via AP)
This July 14, 2015 image provided by NASA on Wednesday shows one of Pluto's five moons, Hydra, about 27 miles by 20 miles wide, made by the New Horizons spacecraft. (NASA/JHUAPL/SwRI via AP)