We have completed maintenance on DiscoverMagazine.com and action may be required on your account. Learn More

A History of Pluto Exploration

As New Horizons' journey culminates in the July 14 Pluto flyby, explore how a search for Planet X over a century ago led scientists on a wild ride of dwarf planet discovery.

By Discover Staff
Jul 13, 2015 5:00 PMNov 13, 2019 5:41 PM
Pluto New Horizons 2015
(Credit: NASA/APL/SwRI)


Sign up for our email newsletter for the latest science news

1905: Beyond Neptune

Percival Lowell launches a search for "Planet X." His calculations are based on inaccurate contemporary estimates of Uranus' mass, but his quest will eventually turn up a different world.

(Credit: Lowell Observatory)

Clyde Tombaugh discovers Pluto from Lowell Observatory in Arizona by seeing it move on photographic plates over a six-day period.

(Credit: Lowell Observatory)

1950: More to the story

Gerard Kuiper and others propose the existence of a large belt of icy objects beyond Neptune.

(Credit: Lunar and Planetary Laboratory)

November 19, 1976: Methane measurement

Dale Cruikshank, Carl Pilcher, and David Morrison discover methane ice on Pluto, providing the first indication that the planet's surface is icy rather than rocky.

June 22, 1978: A Pluto companion

James Christy and Robert Harrington discover Pluto's largest moon, Charon. It appears as a slight elongation in these images of Pluto.

(Credit: U.S. Navel Observatory)

1985: Size matters

A series of mutual occultations between Pluto and Charon begins, allowing scientists to measure the objects' diameters and much more.

1987: Icy out there

Marc Buie and Robert Marcialis lead teams that discover water ice on Charon.

(Credit: Mark Buie)

1988: Thin air

James Elliot and colleagues discover Pluto's thin atmosphere.

May 1, 1989: A call for exploration

About a dozen planetary scientists gather for dinner at a small Italian restaurant in downtown Baltimore. They call themselves the Pluto Underground, and the group decides to force the issue to get NASA on board with a mission to Pluto.

(Credit: NASA)

May 27, 1992: More and more icy

Toby Owen and colleagues discover nitrogen and carbon monoxide ices on Pluto.

August 30, 1992: No longer alone

David Jewitt and Jane Luu discover 1992 QB1, the first sighted partner to Pluto orbiting beyond Neptune, opening up a whole new realm of the solar system, that of the Kuiper Belt objects. Today, scientists know of more than 1,200 such trans-Neptunian objects.

(Credit: ESO)

March 8, 1996: Speckled surface

Using the Hubble Space Telescope, Alan Stern and colleagues create the first "world maps" of Pluto, showing color and brightness changes on the planet's surface.

(Credit: A. Stern (SwRI)/Marc Buie (Lowell)/NASA/ESA)

November 29, 2001: Mission set

NASA selects the space probe New Horizons for a mission to Pluto.

(Credit: NASA)

May 15, 2005: More companions

Hal Weaver and Alan Stern lead a team that uses the Hubble Space Telescope to discover Pluto's moons Nix and Hydra.

(Credit: NASA/ESA/H. Weaver (JHU/APL)/A. Stern (SwRI)/HST Pluto Companion Search Team)

January 19, 2006: Launch day

New Horizons launches from Cape Canaveral, Florida, to begin its nine-year, 3-billion-mile journey to Pluto.

(Credit: NASA/Ken Thornsley)

August 24, 2006: Dwarf demotion

The International Astronomical Union redefines the term "planet," demoting Pluto to dwarf planet status and lumping it with Eris, a Kuiper Belt object similar in size to Pluto discovered in 2005.

(Credit: NASA/ESA/A. Feild (STScI))

February 28, 2007: Passing through

New Horizons flies past Jupiter, receiving a gravity assist that allows it to reach Pluto more quickly.


December 29, 2009: 1.5 billion miles down

New Horizons reaches its halfway point (in distance) to Pluto.

June 28, 2011: Party of five

Using the Hubble Space Telescope, Mark Showalter and colleagues discover Pluto's moon Kerberos.

July 7, 2012: Family of six

Using the Hubble Space Telescope, Mark Showalter and colleagues discover Pluto's moon Styx.

(Credit: NASA/ESA/M. Showalter (SETI Institute))

December 4, 2014: Go time

New Horizons awakens from hibernation and prepares for its Pluto flyby.

(Credit: NASA)

July 14, 2015: Hello Pluto!

New Horizons makes its closest approach to Pluto, flying some 7,700 miles from the planet's surface.

(Credit: NASA/APL/SwRI)

Read our latest coverage of the New Horizons mission here »

1 free article left
Want More? Get unlimited access for as low as $1.99/month

Already a subscriber?

Register or Log In

1 free articleSubscribe
Discover Magazine Logo
Want more?

Keep reading for as low as $1.99!


Already a subscriber?

Register or Log In

More From Discover
Recommendations From Our Store
Shop Now
Stay Curious
Our List

Sign up for our weekly science updates.

To The Magazine

Save up to 40% off the cover price when you subscribe to Discover magazine.

Copyright © 2024 Kalmbach Media Co.