In terms of planetary discoveries, Pluto is quite recent, having only been discovered in February of 1930 by Clyde Tombaugh. I mean, all of my grandparents were already born by that time!
Pluto was hard to find because of its diminutive size, but by comparing photos taken six days apart, Tombaugh - who was just 23 years of age at the time - managed to find the dwarf planet.
The first modern photos of Pluto were taken with the Hubble Space Telescope in the 1990s.
At the time, its images were mind-blowing in terms of their quality.
Of course, the quality of the instruments improved with time, as did the photos.
Here's a quick timeline of some of NASA's greatest photos of Pluto.
1994 - Hubble Space Telescope Faint Object Camera
Original image caption from NASA:
"This is the clearest view yet of the distant planet Pluto and its moon, Charon, as revealed by NASA's Hubble Space Telescope (HST). The image was taken by the European Space Agency's Faint Object Camera on February 21, 1994 when the planet was 2.6 billion miles (4.4 billion kilometers) from Earth; or nearly 30 times the separation between Earth and the sun.
Hubble's corrected optics show the two objects as clearly separate and sharp disks. This now allows astronomers to measure directly (to within about 1 percent) Pluto's diameter of 1440 miles (2320 kilometers) and Charon's diameter of 790 miles (1270 kilometers).
The Hubble observations show that Charon is bluer than Pluto. This means that both worlds have different surface composition and structure. A bright highlight on Pluto suggests it has a smoothly reflecting surface layer.
A detailed analysis of the Hubble image also suggests there is a bright area parallel to the equator on Pluto. This result is consistent with surface brightness models based on previous ground-based photometric observations. However, subsequent HST observations will be required to confirm whether the feature is real.
Though Pluto was discovered in 1930, Charon wasn't detected until 1978. That is because the moon is so close to Pluto that the two worlds are typically blurred together when viewed through ground-based telescopes. (If our moon were as close to Earth, it would be as big in the night sky as an apple held at arm's length). The new HST image was taken when Charon was near its maximum elongation from Pluto of .9 arc seconds. The two worlds are 12,200 miles apart (19,640 kilometers).
Hubble's ability to distinguish Pluto's disk at a distance of 2.6 billion miles (4.4 billion kilometers) is equivalent to seeing a baseball at a distance of 40 miles (64 kilometers).
Pluto typically is called the double planet because Charon is half the diameter of Pluto (our Moon is one-quarter the diameter of Earth).
This image and other images and data received from the Hubble Space Telescope are posted on the World Wide Web on the Space Telescope Science Institute home page at URL http://oposite.stsci.edu/."
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1996 - Hubble Space Telescope Faint Object Camera
Original image caption from NASA:
"The never-before-seen surface of the distant planet Pluto is resolved in these NASA Hubble Space Telescope pictures, taken with the European Space Agency's (ESA) Faint Object Camera (FOC) aboard Hubble.
Discovered in 1930, Pluto has always appeared as nothing more than a dot of light in even the largest Earth-based telescopes because Pluto's disk is much smaller than can be resolved from beneath the Earth's turbulent atmosphere. Pluto is 2/3 the size of Earth's Moon but 12,000 times farther away. Viewing surface detail is as difficult as trying to read the printing on a golf ball located thirty-three miles away!
Hubble imaged nearly the entire surface of Pluto, as it rotated through its 6.4-day period, in late June and early July 1994. These images, which were made in blue light, show that Pluto is an unusually complex object, with more large-scale contrast than any planet, except Earth.
Pluto itself probably shows even more contrast and perhaps sharper boundaries between light and dark areas than is shown here, but Hubble's resolution (just like early telescopic views of Mars) tends to blur edges and blend together small features sitting inside larger ones.
The two smaller inset pictures at the top are actual images from Hubble. North is up. Each square pixel (picture element) is more than 100 miles across. At this resolution, Hubble discerns roughly 12 major "regions" where the surface is either bright or dark.
The larger images (bottom) are from a global map constructed through computer image processing performed on the Hubble data. The tile pattern is an artifact of the image enhancement technique.
Opposite hemispheres of Pluto are seen in these two views. Some of the variations across Pluto's surface may be caused by topographic features such as basins, or fresh impact craters. However, most of the surface features unveiled by Hubble, including the prominent northern polar cap, are likely produced by the complex distribution of frosts that migrate across Pluto's surface with its orbital and seasonal cycles and chemical byproducts deposited out of Pluto's nitrogen-methane atmosphere.
The picture was taken in blue light when Pluto was at a distance of 3 billion miles from Earth.
This image and other images and data received from the Hubble Space Telescope are posted on the World Wide Web on the Space Telescope Science Institute home page at URL http://oposite.stsci.edu/."
2002 - Hubble Space Telescope
Original image caption from NASA:
The image was created from Hubble data from proposals 5330: A. Stern (Southwest Research Institute), L. Trafton (University of Texas, Austin), and M. Buie (Southwest Research Institute); and 9391: M. Buie (Southwest Research Institute), W. Grundy (Lowell Observatory), and E. Young, L. Young, and A. Stern (Southwest Research Institute). The science team comprises: M. Buie (Southwest Research Institute), W. Grundy (Lowell Observatory), and E. Young, L. Young, and A. Stern (Southwest Research Institute).
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2005 - Hubble Space Telescope Advanced Camera for Surveys
Original image caption from NASA:
"A pair of small moons that NASA's Hubble Space Telescope discovered orbiting Pluto now have official names: Nix and Hydra. Photographed by Hubble in 2005, Nix and Hydra are roughly 5,000 times fainter than Pluto and are about two to three times farther from Pluto than its large moon, Charon, which was discovered in 1978."
2006 - New Horizons LORRI Cam
Original image caption from NASA:
"A white arrow marks Pluto in this New Horizons Long Range Reconnaissance Imager (LORRI) picture taken Sept. 21, 2006. Seen at a distance of about 4.2 billion kilometers (2.6 billion miles) from the spacecraft, Pluto is little more than a faint point of light among a dense field of stars. Mission scientists knew they had Pluto in their sights when LORRI detected an unresolved "point" in Pluto's predicted position, moving at the planet's expected motion across the constellation of Sagittarius near the plane of the Milky Way galaxy."
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2015 - New Horizons LORRI Cam
Original image caption from NASA:
"This image of Pluto was taken by New Horizons' Long Range Reconnaissance Imager (LORRI) at 4:18 UT on July 9, 2015, from a range of 3.9 million miles (6.3 million kilometers). It reveals new details on the surface of Pluto, including complex patterns in the transition between the very dark equatorial band (nicknamed "the whale"), which occupies the lower part of the image, and the brighter northern terrain. The bright arc at the bottom of the disk shows that there is more bright terrain beyond the southern margin of the "whale." The side of Pluto that will be studied in great detail during the close encounter on July 14 is now rotating off the visible disk on the right hand side, and will not be seen again until shortly before closest approach.
Three consecutive images were combined and sharpened, using a process called deconvolution, to create this view. Deconvolution enhances real detail but can also generate spurious features, including the bright edge seen on the upper and left margins of the disk (though the bright margin on the bottom of the disk is real).
The wireframe globe shows the orientation of Pluto in the image: thicker lines indicate the equator and the prime meridian (the direction facing Charon). Central longitude on Pluto is 86°."
For more information about the New Horizons mission, visit http://www.nasa.gov/newhorizons and http://pluto.jhuapl.edu."
2015 - New Horizons LORRI Cam
Original image caption from NASA:
"The latest two full-frame images of Pluto and Charon were collected separately by NASA's New Horizons during approach on July 13 and July 14, 2015. The relative reflectivity, size, separation, and orientations of Pluto and Charon are approximated in this composite image, and they are shown in approximate true color."
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2015 - New Horizons LORRI Cam & MVIC
Original image caption from NASA:
"Imagine a future spacecraft following New Horizons' trailblazing path to Pluto, but instead of flying past its target -- as New Horizons needed to do to explore Pluto and the Kuiper Belt beyond -- the next visitor touches down near the tall mountains on the frozen icy, plains of Pluto's heart.
A video produced by New Horizons scientists that offers that very perspective. Made from more than 100 New Horizons images taken over six weeks of approach and close flyby, the video offers a trip in to Pluto -- starting with a distant spacecraft's-eye view of Pluto and its largest moon, Charon, to an eventual ride in for a "landing" on the shoreline of Pluto's informally named Sputnik Planum. The video shows what it would be like to ride aboard an approaching spacecraft and see Pluto grow from a "dot" to become a world, and then to swoop down over Pluto's spectacular terrains.
New Horizons scientists had to interpolate some of the frames in the movie based on what they know Pluto looks like to make it as smooth and seamless as possible.
After a 9.5-year voyage covering more than three billion miles, New Horizons flew through the Pluto system on July 14, 2015, coming within 7,800 miles (12,500 kilometers) of Pluto itself. Carrying powerful telescopic cameras that could spot features smaller than a football field, New Horizons has sent back hundreds of images of Pluto and its moons that show how dynamic and fascinating their surfaces are - and what great targets they'd make for follow-up mission one day."
2015 - New Horizons LORRI Cam & MVIC
Original image caption from NASA:
"This is the highest-resolution color departure shot of Pluto's receding crescent from NASA's New Horizons spacecraft, taken when the spacecraft was 120,000 miles (200,000 kilometers) away from Pluto. Shown in approximate true color, the picture was constructed from a mosaic of six black-and-white images from the Long Range Reconnaissance Imager (LORRI), with color added from a lower resolution Ralph/Multispectral Visible Imaging Camera (MVIC) color image, all acquired between 15:20 and 15:45 UT -- about 3.5 hours after closest approach to Pluto -- on July 14, 2015. The resolution of the LORRI images is about 0.6 miles (1 kilometer) per pixel; the sun illuminates the scene from the other side of Pluto and somewhat toward the top of this image.
The image is dominated by spectacular layers of blue haze in Pluto's atmosphere. Scientists believe the haze is a photochemical smog resulting from the action of sunlight on methane and other molecules in Pluto's atmosphere, producing a complex mixture of hydrocarbons such as acetylene and ethylene. These hydrocarbons accumulate into small haze particles, a fraction of a micrometer in size, which preferentially scatter blue sunlight -- the same process that can make haze appear bluish on Earth.As they settle down through the atmosphere, the haze particles form numerous intricate, horizontal layers, some extending for hundreds of miles around large portions of the limb of Pluto. The haze layers extend to altitudes of over 120 miles (200 kilometers). Pluto's circumference is 4,667 miles (7,466 kilometers).Adding to the beauty of this picture are mountains and other topographic features on Pluto's surface that are silhouetted against the haze near the top of the image. Sunlight casts dramatic and beautiful finger-like shadows from many of these features onto the haze (especially on the left, near the 11 o'clock position), forming crepuscular rays like those often seen in Earth's atmosphere near sunrise or sunset."
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2015 - New Horizons LORRI Cam & MVIC
Original image caption from NASA:
"Pluto's bladed terrain as seen from NASA's New Horizons during its July 2015 flyby."
2015 - New Horizons MVIC
Original image caption from NASA:
NASA’s New Horizons spacecraft captured this high-resolution enhanced color view of Pluto on July 14, 2015. The image combines blue, red and infrared images taken by the Ralph/Multispectral Visual Imaging Camera (MVIC). Pluto’s surface sports a remarkable range of subtle colors, enhanced in this view to a rainbow of pale blues, yellows, oranges, and deep reds. Many landforms have their own distinct colors, telling a complex geological and climatological story that scientists have only just begun to decode. The image resolves details and colors on scales as small as 0.8 miles (1.3 kilometers). The viewer is encouraged to zoom in on the full resolution image on a larger screen to fully appreciate the complexity of Pluto’s surface features.
Via PetaPixel