The United States is the only nation to visit every single planet in the solar system.
Pluto was number nine in the lineup when the New Horizons spacecraft departed Cape Canaveral, Fla., on Jan. 19, 2006. Although Pluto has since been downgraded to the status of a dwarf planet, its photos are just as remarkable.
Photos of the (other) planets, shot by NASA over the years, have offered a tantalizing glimpse of our solar system:
NASA / JHU Applied Physics Lab
The colours of the solar system's innermost planet are enhanced in this tantalizing view, based on global image data from the Mercury-orbiting Messenger spacecraft. Human eyes would not discern the clear colour differences, but they are real nonetheless. Notable at the upper right, the Caloris basin was created by a comet or asteroid during the solar system's early years. The ancient basin was subsequently flooded with lava from volcanic activity. Mercury is the smallest of the eight planets and the closest to the sun. According to NASA, it would take more than 18 Mercurys to be as big as Earth. The surface of Mercury looks like Earth's moon. It is covered with impact craters made by rocks from space hitting the planet. Earth has a blanket of air around it. Mercury does not. This is what helps keep Earth from getting too hot or cold. Because it is so close to the sun, Mercury is extremely hot, although it can become very cold at night.
On Feb. 5, 1974, NASA's Mariner 10 mission took this first close-up photo of Venus. Made using an ultraviolet filter in its imaging system, the photo was colour-enhanced to bring out Venus's cloudy atmosphere as the human eye would see it. According to NASA, Venus is perpetually blanketed by a thick veil of clouds high in carbon dioxide and its surface temperature approaches 480 C.
NASA Johnson Space Center Gateway
This classic photograph of the Earth, as seen by the Apollo 17 crew travelling toward the moon, was taken Dec. 7, 1972.
NASA / JPL-Caltech
This global view of Mars is composed of about 100 Viking Orbiter images. Mars is the fourth planet from the sun. It is about one-sixth the size of Earth, and is known as the Red Planet for the colour from the iron in its soil. Mars is very cold; the average temperature there is way below freezing. The planet is home to vast dust storms. Mars has about one-third the gravity of Earth.
NASA / JPL
Here is the first close-up view of Jupiter from Voyager 1, taken in 1979. Jupiter is the fifth planet from the sun and the largest planet in the solar system. It is so large that all of the other planets in the solar system could fit inside it. More than 1,000 Earths would fit inside Jupiter. The planet is covered in thick red, brown, yellow and white clouds of gas and has winds that blow more than 650 km/h. Jupiter is famous for its Great Red Spot, a giant spinning storm. The planet has three thin rings made up mostly of tiny bits of dust. It rotates faster than any other planet. A day on Jupiter is about 10 hours long, and a year there is equivalent to 12 years on Earth. The planet, which has more than 60 moons, is very cold and has 2.4 times the gravity of Earth.
NASA / JPL
Voyager 1 looked back at Saturn on Nov. 16, 1980, four days after the spacecraft flew past the planet, to observe the appearance of the planet and its rings. Here, Saturn's shadow falls upon the rings. According to NASA, the rings are made of ice and rock of different sizes; some are as small as a grain of sand, while others are as large as a house. Saturn has at least 60 moons and it's possible the rings are made up of the fragments of moons destroyed by the impact of asteroids and meteroids. Saturn is much larger than Earth; more than 700 Earths could fit inside it.
NASA / JPL
NASA's Voyager 2 spacecraft flew closely past distant Uranus, the seventh planet from the Sun, in January 1986. According to NASA, Uranus is the only giant planet with an equator nearly at right angles to its orbit. A collision with an Earth-sized object may explain the unique tilt. Nearly a twin in size to Neptune, Uranus has more methane in its mainly hydrogen and helium atmosphere than Jupiter or Saturn. Methane gives Uranus its blue tint. If Earth was the size of a nickel, Uranus would be as big as a baseball.
NASA / JPL
This picture of Neptune was produced from images taken through the green and orange filters on the Voyager 2 narrow angle camera. The picture shows the Great Dark Spot and its companion bright smudge. The average temperature on Neptune is about minus 200 C, according to the Jet Propulsion Lab, which is managed for NASA by the California Institute of Technology in Pasadena. Neptune is the furthest known planet of our solar system, located about 30 times farther away from the sun than Earth is. Only about one thousandth of the sunlight received by our planet reaches Neptune.
NASA / APL / SwRI
The colours in this July 13, 2015, image of Pluto and its largest moon, Charon, seen from the New Horizons spacecraft show the varying surface composition of the planetary bodies, including ice and craters. Pluto was the ninth planet in the solar system, when New Horizons departed Cape Canaveral, Fla., on Jan. 19, 2006. It was subsequently declared to be a dwarf planet. Pluto is 2,300 km. wide. It is slightly smaller than Earth's moon. One day on Pluto is about 6 1/2 days on Earth. Pluto is very, very cold. The temperature on Pluto is -225 C to -230 C. Pluto has about one-fifteenth the gravity of Earth.