Data released from NASA's New Horizons on Thursday probe showed that the distant dwarf planet has a blue atmospheric haze.
The space agency released an image that showed a blue layer surrounding Pluto, taken by the spacecraft's camera.
Blue skies often results from scattering of sunlight by very small particles. "On Earth, those particles are very tiny nitrogen molecules," said science team researcher Carly Howett, from the Southwest Research Institute (SwRI). "On Pluto they appear to be larger - but still relatively small - soot-like particles we call tholins."
The particles are thought to accumulate condensed gases on their surfaces, eventually falling to the planet's surface and adding to its red coloring.
New Horizons launched from Earth in 2006 to study the Pluto system, as well as other objects in the Kuiper Belt zone - at the frozen distant edge of our solar system.
"Who would have expected a blue sky in the Kuiper Belt? It's gorgeous," said Alan Stern, one of the principal investigators on the New Horizons project.
Puzzle of water ice distribution
Researchers were also able to map out areas of water ice on various parts of Pluto's surface, and will now puzzle out why it appears to be distributed where it is.
"Large expanses of Pluto don't show exposed water ice," said team member Jason Cook, also of SwRI. "Understanding why water appears exactly where it does, and not in other places, is a challenge that we are digging into."
Last week, NASA released the best color pictures it has obtained so far of Pluto's largest moon, Charon, which has a diameter more than half that of Pluto itself.
The images showed canyons that stretched more than 1,000 miles (1,600 kilometers) above the equator. Each surface fracture appeared to be about four times as long as the Grand Canyon and, in places, twice as deep.
The first close-ups of Pluto awed the world this week. A couple of decades ago, photos of Venus or Saturn taken from space had a similar effect on scientists. Join DW on an interplanetary photo safari!
Image: Reuters/NASA/APL/SwRI/HandoutDepending on who you ask, there are eight or nine planets in our solar system - some experts still count Pluto, while the International Astronomical Union (IAU) took away its planetary status in 2006. People were still excited when NASA presented the first high-res images of Pluto this week. Its neighbors all had their portrait taken as early as the 1960s.
The spacecraft Mariner 10 left for the planet closest to the Sun in 1973. It took this picture of Mercury's moon-like surface in March 1974. The planet's distance to the Sun varies between 28.5 million miles (46 kilometers) and 43.5 million miles (70 kilometers), because its orbit isn't a perfect circle. Scientists were surprised to discover that Mercury had a small magnetic field.
Mariner 10 took this first close-up of Mercury's direct neighbor on February 5, 1974. The picture was color-enhanced by NASA to bring out Venus' cloudy atmosphere - the planet is perpetually blanketed by a thick veil of clouds rich in carbon dioxide. Mariner 10's journey to Venus was a rocky one: the spacecraft's high-gain antenna developed problems and a mechanical issue caused a large fuel-loss.
The first full-on photo of our planet as seen from outer space was taken by Lunar Orbiter 1 in August 1966. That was three years before a human being had ever set foot on the Moon, which can be seen in the foreground of this picture as a shadow. The now-iconic photo was one of a series of pictures taken in preparation for the Apollo missions that would eventually put a human on the Moon.
This close-up of Earth's neighbor is the first picture ever taken of another planet by a spacecraft. Mariner 4 snapped it on July 15, 1965. Scientists who had expected to see lakes, valleys and mountains were disappointed - instead of an Earth-like planet, they were treated to craters similar to those on the Moon. The New York Times wrote: "Mars is probably a dead planet."
Spacecraft Pioneer 10 took the planet's first close-up from roughly 80,780 miles (130,000 kilometers) away on November 19, 1973. Jupiter is our solar system's largest planet. At its equator, Jupiter's diameter is a whopping 88,846 miles (142,984 kilometers). Its mass is two-and-a-half times larger than the masses of all other planets combined.
This first shot of the ringed planet was taken on Pioneer 10's follow-up mission, Pioneer 11, on August 31, 1979. It was a perilous adventure: as the spacecraft flew through Saturn's outer rings, it almost crashed into one of two new moons it discovered. Visible at the upper left-hand corner in this photo is Saturn's moon Titan.
One of the first glimpses scientists got of Uranus was of its rings. Voyager 2 took this shot of them in 1986. Scientists had to remote-fix the spacecraft's camera for it to be able to photograph the planet with the coldest atmosphere in our solar system (as low as -366 degrees Fahrenheit or -221 degrees Celsius). The device had malfunctioned while Voyager 2 was passing Saturn.
Voyager 2 also took the first picture of Neptune in August 1989. The planet has four cloud features that scientists know about. For those who don't count Pluto, Neptune is the planet in our solar system that's furthest away from the sun: at an average of 2.8 billion miles (4.5 billion kilometers), that distance is 30 times greater than the one between the Sun and Earth.
The fact that Pluto is not officially a planet anymore didn't detract from the excitement scientists and lay-people all over the world experienced when NASA released this first close-up of the copper-colored (dwarf-) planet taken by New Horizons on July 13, 2015. The spacecraft traveled 3 billion miles (4.88 billion kilometers) to the solar system's farthest reaches for this shot.
rc/jr (AFP, AP)
