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.
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.
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
Pluto, 1996: Maps of the
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
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
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
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.
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.
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.