Welcome to the Pluto Portal!

HST/FOC Image

The Planet Pluto's Home on the Web

Click here to see What's New @ www.PlutoPortal.Net!

Updates on the New Horizons Mission:
- Check out this link for pressing issues related to New Horizons Funding in FY03

-Check out this article on New Horizons published at Astronomy.Com regarding the Student Dust Counter
- New Horizons Adds Student Dust Counter Experiment JHUAPL News Release (11/4/02)

Want to Explore Pluto? Support the Mission at: www.plutomission.com & www.planetary.org !

Long considered to be the smallest, coldest, and most distant planet from the Sun, Pluto may also be the largest of a group of objects that orbit in a disk-like zone of comets beyond the orbit of Neptune.

Discovered by American astronomer Clyde Tombaugh in 1930, Pluto takes 248 years to orbit the Sun. Pluto’s most recent close approach to the Sun was in 1989. Between 1979 and 1999, Pluto was actually closer to the Sun than Neptune, providing rare opportunities to study this small, cold, distant world and its companion moon, Charon.

Most of what we know about Pluto we have learned since the late 1970s from Earth-based observations, the Infrared Astronomical Satellite (IRAS), and the Hubble Space Telescope. Many of the key questions about Pluto, Charon, and the outer fringes of our solar system await close-up observations by a robotic space flight mission.

Pluto and Charon orbit the Sun in a region where there may be a population of hundreds or thousands of similar bodies that were formed early in solar system history. The gravitational influence of the giant planets may have ejected these bodies to much larger distances from the solar system. The recent discovery of several bodies about the size of Charon in the region beyond Pluto has bolstered this theory. These objects are currently referred to interchangeably as trans-Neptunian objects, Edgeworth-Kuiper Disk objects, Kuiper Belt objects, or ice dwarves.

Pluto is about two-thirds the diameter of Earth’s Moon and may have a rocky core surrounded by a mantle of water ice. Due to its lower density, its mass is about one-sixth that of the Moon. Pluto appears to have a bright layer of frozen methane, nitrogen, and carbon monoxide on its surface. While it is close to the Sun, these ices thaw, rise, and temporarily form a thin atmosphere, with a pressure one one-millionth that of Earth’s atmosphere. Pluto’s low gravity (about 6 percent of Earth’s) causes the atmosphere to be much more extended in altitude than our planet’s. Because Pluto’s orbit is so elliptical, Pluto grows much colder during the part of each orbit when it is traveling away from the Sun. During this time, the bulk of the planet’s atmosphere freezes.

In 1978, American astonomer James Christy discovered that Pluto has a satellite (moon) which he named Charon. Working with Christy's measurements of Charon's positions, Robert Harrington calculated the orbit of Charon and deduced that the rotations of both Pluto and Charon were synchronized with the orbital period.

No spacecraft have ever visited Pluto. Because Pluto is so small and far away, it is difficult to observe from Earth. In the late 1980s, Pluto and Charon passed in front of each other repeatedly for several years. Observations of these rare events allowed astronomers to make crude maps of each body. From these maps it was learned that Pluto has polar caps, as well as large, dark spots nearer its equator.

Plans are currently in place for NASA to visit Pluto within our lifetme, NASA's New Horizons Pluto-Kuiper Belt Mission is currently under development, and hopes to launch to Pluto in 2006, and hopes to swing by the double planet by 2015 or 2016.


A US Postage Service Stamp Issued in 1991, commemorating the exploration of the Solar System. Pluto was not yet explored then, and still has not been. The New Horizons Mission provides hope we will soon explore Pluto.

Above Pluto Description Courtesy of NASA/JPL's Solar System Website which is at http://solarystem.nasa.gov .


The Pluto Portal was envisioned by Dr. S. Alan Stern, Principal Investigator of the NASA New Horizons Pluto-Kuiper Belt Mission and Director of the Department Of Space Studies, in Boulder, CO. Website made possibly by funding from the New Horizons Pluto-Kuiper Belt Mission. Website created by Ted A. Nichols II. Banner and button artwork created by Daniel Durda of Southwest Research Insitute's Department of Space Studies in Boulder, CO. Imagery modified by Ted A. Nichols II, with permission. Site design help provided by Patricia Kurtz of Starfire Creations.

This site was last modified on February 1, 2003.

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