Pluto in pictures: a visual timeline of our changing view of icy orb

The former ninth planet received its first visit by Earthlings with a flyby by the New Horizons spacecraft on Tuesday, the result of nearly a century of research and discovery.

New close-up images of a region near Pluto’s equator reveal a giant surprise: a range of youthful mountains.

NASA

July 16, 2015

NASA's historic flyby of Pluto this week has brought the world some breathtakingly crisp images of the dwarf planet. The New Horizons spacecraft began its 3.6-billion-mile journey to Pluto nine years ago. But the fascination with Pluto began nearly a century ago, when a young astronomer first identified our solar system's ninth planet.

Pluto has since been demoted to the status of dwarf planet, but the icy orb has continued to capture the Earthling imaginations.

Here's a visual chronology of our evolving view of Pluto, from the beginning.

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In this 1931 file photo, Clyde Tombaugh poses with the telescope through which he discovered the Pluto at the Lowell Observatory on Observatory Hill in Flagstaff, Ariz. On Tuesday, July 14, 2015, NASA's New Horizons spacecraft, carrying a small canister with his ashes, is scheduled to pass within 7,800 miles of Pluto which he discovered 85 years ago
File/AP

Clyde Tombaugh, a 23-year-old newcomer to Arizona's Lowell Observatory was charged with the task of locating "Planet X," the mysterious ninth planet that had been hypothesized based on gravitational pattens.

Plates from the original discovery of Pluto in 1930.
Lowell Observatory Archives

Over a period close to a year, Dr. Tombaugh scanned the night sky and took images of space in an attempt to see whether any object had changed position. Using photographic plates taken on Jan. 23 and Jan. 29, 1930, the young astronomer first discovered an apparent motion, later confirming that he in fact had found what he was looking for, a celestial object that would eventually be given the name Pluto. 

These images, released by NASA Thursday, March 6, 1996, show the never-before-seen surface of the planet Pluto as seen fron the Hubble Space Telescope's Faint Object Camera. The two smaller inset pictures at top are the actual Hubble images. Opposite hemispheres of Pluto are seen in the bottom images, which are from a global map constructed through computer image processing of the Hubble data. The picture was taken when Pluto was 3 billion miles from Earth.
NASA/AP

Ideas about the appearance of Pluto and its surface were mainly relegated to conjecture until NASA's launch of the Hubble Space Telescope in 1990. Using images from Hubble's Faint Object Camera along with data gathered from the telescope, scientists were able to construct an image of the planet's surface for the first time.

Pluto and its satellites, Charon, Hydra and Nix taken by the Hubble Telescope in 2005.
NASA

In 2005, the Hubble Space Telescope was able to capture another image of Pluto which and discovered the possibility of additional natural satellites around the planet besides its main moon, Charon. The two moons captured as specks of light to the right of the planet would later be named Hydra and Nix.

Harry, age 11, submitted this drawing to NASA which envisions Pluto as a little speck on the edge of the Solar System.
NASA

In 2006, the International Astronomical Union developed an official definition of planet and booted Pluto off the list because it had not "cleared the neighborhood around its orbit." The decision was controversial and led to petitions to reinstate Pluto among the planets of the solar system that students had been drawing in elementary school for decades. 

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The most detailed view to date of the entire surface of the dwarf planet Pluto as constructed from multiple NASA Hubble Space Telescope photographs taken from 2002 to 2003 and released on February 4, 2010. Hubble reveals a complex-looking and variegated world with white, dark-orange, and charcoal-black terrain. The overall color is believed to be a result of ultraviolet radiation from the distant Sun breaking up methane that is present on Pluto's surface, leaving behind a dark, molasses-colored, carbon-rich residue. This series of pictures took four years and 20 computers operating continuously and simultaneously to accomplish.
Reuters/NASA

Another series of higher-resolution shots of the planet's surface was constructed using images taken in 2002 and 2003 by the Hubble Space Telescope and released in 2010. Construction of the images took four years and 20 computers working simultaneously and they revealed, for the first time, the possible color and landscape of the now-dwarf planet's surface.

An artist’s impression of NASA’s New Horizons spacecraft encountering Pluto and its largest moon, Charon, is seen in this NASA image from July 2015. The first spacecraft to visit distant Pluto, a dwarf planet in the solar system's frozen backyard, is still three months away from a close encounter, but already in viewing range, newly released photos show.
Reuters/NASA

In 2006, the New Horizons space probe was launched by NASA with the mission of visiting and studying Pluto and its moons, as well as the objects and bodies in the mostly unexplored Kuiper Belt, of which the dwarf planet is a part.

Guests and New Horizons team members countdown to the spacecraft's closest approach to Pluto, Tuesday, July 14, 2015.
NASA

The spacecraft made its way 3.6 billion miles through the solar system, flying by Jupiter along the way, until it approached Pluto earlier this month. The countdown until Pluto's flyby gathered massive media attention as scientists and the public waited for the first images to be transmitted back across space. 

Members of the New Horizons science team react to seeing the spacecraft's last and sharpest image of Pluto.
NASA

Scientists who had worked on New Horizons project for more than a decade received word of a successful flyby of Pluto on July 14. With New Horizons' brief visit it became the first spacecraft to visit the dwarf planet and the United States became the first country to send spacecraft to the nine pre-2006 planets. 

New Horizons has obtained impressive new images of Pluto and its large moon Charon that highlight their compositional diversity.
NASA

Scientists at NASA started receiving high-resolution images of Pluto and its main moon Charon, culminating with the highest resolution snapshot, which cast a new light on the Pluto's surface and landscape.

This July 13, 2015 image provided by NASA shows Pluto, seen from the New Horizons spacecraft. The United States is now the only nation to visit every single planet in the solar system. Pluto was No. 9 in the lineup when New Horizons departed Cape Canaveral, Fla, on Jan. 19, 2006
NASA/AP

Earthlings were particularly smitten by a particular shot of Pluto with a formation in the shape of a heart.

New close-up images of a region near Pluto’s equator reveal a giant surprise: a range of youthful mountains.
NASA

New Horizons was also able to capture images of Pluto's vast mountain ranges, which some scientists say could be a clue that there may be water on the dwarf planet.