The NASA spacecraft, New Horizons, only about the size of a baby grand piano, blasted off into space in January 2006 on it's flyby mission past Pluto in the Kuiper belt, a zone of frozen rocks and asteroids on the outer regions of our solar system. It has taken nine years, covering billions of miles, to reach Pluto and will continue into deep space for decades to come.
Speeding out into the Kuiper belt, it will rendezvous with another small planet – yet to be selected – in several years' time. Powered by a nuclear reactor that runs on plutonium, named after the dwarf planet itself, the generator is expected to run until the 2030s.
Pluto and Charon in false colour show compositional diversity. Note: These are not the actual colours of Pluto and Charon, and the apparent distance between the two bodies has been reduced for this side-by-side view. Image credit: NASA/APL/SwRI
During its flyby, which took place this month, July 2015, New Horizons has obtained impressive new images of Pluto and its large moon Charon that highlight their compositional diversity. The images shown here are not actual colour images of Pluto and Charon, but have been touched up in exaggerated colours that make it easy to note the differences in surface material and features on each planetary body.
The images were obtained using three of the color filters of the 'Ralph' instrument (one of seven science instruments on the spacecraft) on July 13 at 3:38 am EDT. "These images show that Pluto and Charon are truly complex worlds. There's a whole lot going on here," said New Horizons co-investigator Will Grundy, Lowell Observatory, Flagstaff, Arizona. "Our surface composition team is working as fast as we can to identify the substances in different regions on Pluto and unravel the processes that put them where they are."
The colour data helps scientists understand the molecular make-up of ices on the surfaces of Pluto and Charon, as well as the age of geologic features such as craters. They can also tell us about surface changes caused by space 'weather', such as radiation.
An artist's impression of New Horizons approaching Pluto and one of its moons. Photograph: NASA
The new colour images reveal that the 'heart' of Pluto actually consists of two remarkably different-coloured regions. In the false-colour image, the heart consists of a western lobe shaped like an ice cream cone that appears peach color in this image. A mottled area on the right (east) side looks bluish. A mid-latitude band appears in shades ranging from pale blue through red. Even within the northern polar cap, in the upper part of the image, various shades of yellow-orange indicate subtle compositional differences.
The surface of Charon is viewed using the same exaggerated colour. The red on the dark northern polar cap of Charon is attributed to hydrocarbon and other molecules, compounds called tholins. The mottled colours at lower latitudes point to the diversity of terrains on Charon. Both these images were obtained using three of the colour filters of the Ralph instrument on July 13 at 3:38 am EDT and received on the ground on at 12:25 pm.
Members of the New Horizons science team react to seeing the probe's last and sharpest image of Pluto before its closest approach. Photograph: Bill Ingalls/AP
"We make these colour images to highlight the variety of surface environments present in the Pluto system," said Dennis Reuter, co-investigator with the New Horizons Composition Team. "They show us in an intuitive way that there is much still to learn from the data coming down."
Discovered in 1930, by US astronomer Clyde Tombaugh, Pluto has an atmosphere of nitrogen and methane and a surface temperature of about minus 230 ºC. Sensors on New Horizons detected Pluto's thin nitrogen atmosphere extending far out into space. Scientists believe it may shed snow, with flakes tumbling down to the surface before vapourising back into the atmosphere. New Horizon measurements reveal Pluto is roughly two-thirds the size of the moon, and probably holds more ice beneath its surface than previously thought.
Other instruments onboard New Horizons confirmed that Pluto's north pole bears an icy cap. The latest measurements beamed to Earth from the probe picked up chemical signatures of methane and nitrogen ice in the polar cap.
The initial photograph of Pluto released by NASA on Monday 13th July 2015. Photograph: NASA/Press Association
The mission marks the end of the US space agency's bid to explore every planet in the solar system, starting with Venus in 1962. Tuesday's flyby (on 14 July 2015) coincided with the 50th anniversary of the first ever fly-by of Mars by the Mariner 4 probe.
Due to the three-billion-mile distance to Pluto, data takes 4 ½ hours to come to Earth, even at the speed of light. It will take 16 months for all of New Horizons' science data to be received, and the treasure trove from this mission will be studied for decades to come.
Compiled from information written by NASA official, Tricia Talbert, Robin McKie, science editor for the 'Observer' newspaper, London,and Ian Sample, 'Guardian' science editor.