New Moons for Pluto!

NOTE: Astronomers are making exciting new discoveries every day. So, be sure to look for updates to the Star Witness stories for newer developments.

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Artist's conception: View from one of the moons

For 28 years, Charon was the only known moon orbiting the planet* Pluto. Now, Charon (pronounced “karon”) has company. A recent Hubble Space Telescope observation has revealed two new moons orbiting Pluto, the smallest planet in the solar system.

Where is
the Kuiper
Belt?

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Pluto is farther from the Sun than any of the planets. It resides in a region of space called the Kuiper (pronounced “kiper”) Belt. Scientists believe many comets occupy the Kuiper Belt.

Hubble peeks at Pluto in 1996

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Pluto, 1996: Maps of the surface

Little is known about the makeup of this tiny planet. In 1996, the Hubble Space Telescope observed Pluto. The resulting maps of Pluto's surface revealed that it is more complex than scientists had imagined, with large-
scale features, including icy-bright polar caps.

Pluto is the only planet in the solar system that has not been visited by a spacecraft. In January 2006, NASA launched the New Horizons mission to Pluto and the Kuiper Belt, but it will take more than nine years for the spacecraft to arrive at its targets.

Pluto moon hunt in 2005

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Pluto, 2005:
Possible new
moons

In anticipation of the New Horizons mission, astronomers used the Hubble telescope in May 2005 to hunt for moons in Pluto’s vast outer region. Many other telescopes had studied the region close to Pluto, but none had found anything interesting. To the surprise of astronomers, the Hubble snapshots revealed two objects close to Pluto that had never before been noticed.

The newly discovered objects are much smaller than Charon. Charon is about half Pluto’s size. The two new objects are about twice as far away from Pluto as Charon, but still close to the planet.

A second image of Pluto taken three days later showed the objects in the same area. Scientists thought the objects were two new moons. However, they had to confirm that the objects really were moons and not just icy rocks from the Kuiper Belt that were passing by Pluto. Before a new moon can be validated, astronomers must establish its orbit, or path around the planet, by making another observation.

Findings confirmed

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Pluto, 2006:
New moons confirmed

Scientists used the Hubble telescope in February 2006 to search again for these suspected moons — and found them. Finding the moons in the positions predicted from their orbits meant they are valid moons.

Where did they come from?

It was possible that the two new moons were icy rocks from the Kuiper Belt that had been “captured” by Pluto — attracted into orbit by Pluto’s gravity. However, scientists discovered that the new moons and the “old” moon, Charon, orbit Pluto in the same way. From this information, astronomers think all three moons formed at the same time as Pluto.

The confirmation of the new moons makes Pluto the first Kuiper Belt resident known to have more than one moon.

*UPDATE:

This article was published before the August 2006 International Astronomical Union decision to reclassify Pluto as a "dwarf planet" and change the number of solar system planets to eight.

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PDF of story and photos:
Pluto moons story and photos PDF

Illustration:
Pluto as seen from one of its three moons

Illustration:
Where is the Kuiper Belt?

Photo:
Hubble's views of Pluto, 1996

Photo:
Pluto, Charon, and two possible new moons of Pluto, 2005

Photo:
Pluto's two new moons confirmed, 2006

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