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More Moons for Pluto
By Ezra Billinkoff

This illustration shows the Pluto system from the surface of one of the newly discovered moons. The other members of the Pluto system are just above the moon's surface. Pluto is the large disk at center, right. Charon is the smaller disk to the right of Pluto, and the other moon is the bright dot on Pluto's far left.
This illustration shows the Pluto system from the surface of one of the newly discovered moons. The other members of the Pluto system are just above the moon's surface. Pluto is the large disk at center, right. Charon is the smaller disk to the right of Pluto, and the other moon is the bright dot on Pluto's far left.
(Photo: (NASA, ESA and G. Bacon (STScI))
The ninth planet in the solar system has plenty of company. Astronomers announced this week that Pluto has not one but three moons.

"We see this as a whole new chapter in the Pluto story," said astronomer Alan Stern, a member of the team that discovered two small moons.

Pluto is was discovered in 1930. It was thought to be moonless until 1978, when astronomers spotted what they thought was a rotating bump on the distant planet's surface. Closer inspection revealed the bump to be a moon, and astronomers named it Charon.

The two newly discovered moons were spotted in images taken by the Hubble Space Telescope, a powerful telescope that orbits Earth. They are tiny: One is about 100 miles wide, and the other is a little bit smaller. Other astronomers will double-check the discovery. Until then, Pluto's little neighbors have been temporarily named S/2005 P1 and S/2005 P2.

How the Moons Were Born

The bustle around Pluto excites some astronomers. "It's almost like a mini-solar system," said team member Hal Weaver. "How can [a planet] about 70 percent the size of Earth's moon have all these [moons]? How can that happen? We're going to have to explain that."

Scientists are already offering theories on the birth of Pluto's moons. One idea is that a large object smacked into Pluto, breaking pieces off the planet. After billions of years spinning around Pluto, those pieces could have come together to form moons.

Another theory is that the two little moons were originally just small asteroids pulled into orbit around Pluto. Pluto's neighborhood, the Kuiper Belt, is an area in space packed with asteroids.

Astronomers believe that the moons' orbit of Pluto will allow them to learn more about Pluto's size and structure. This winter, NASA will launch a spacecraft to Pluto for the first time ever. The probe will study Pluto, Charon and the unexpected guests.

"We'll have to divide our attention four ways instead of two," said Alan Stern.