Astronomers may have found two new moons orbiting Pluto.
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November
1, 2005: Using NASA's Hubble Space Telescope to probe
the ninth planet in our solar system, astronomers have discovered
that Pluto may have not one, but three moons.
Right:
An artist's concept of the Pluto system as seen from the surface
of one of the candidate moons. [More]
Pluto
was discovered in 1930. The planet resides 3 billion miles
from the sun in the heart of the Kuiper Belt, a vast region
of icy, rocky bodies beyond Neptune's orbit. In 1978, astronomers
discovered Charon, Pluto's only confirmed moon.
"If,
as our new Hubble images indicate, Pluto has not one, but
two or three moons, it will become the first body in the Kuiper
Belt known to have more than one satellite," said Hal
Weaver of the Johns Hopkins Applied Physics Laboratory, Laurel,
Md. He is co-leader of the team that made the discovery.
The
candidate moons, provisionally designated S/2005 P1 and S/2005
P2, are approximately 27,000 miles (44,000 kilometers) away
from Pluto--in other words, two to three times as far from
Pluto as Charon.
These
are tiny moons. Their estimated diameters lie between 40 and
125 miles (64 and 200 kilometers). Charon, for comparison,
is about 730 miles (1170 km) wide, while Pluto itself has
a diameter of about 1410 miles (2270 km).
The
team plans to make follow-up Hubble observations in February
to confirm that the newly discovered objects are truly Pluto's
moons. Only after confirmation will the International Astronomical
Union consider permanent (and catchier) names for S/2005 P1
and S/2005 P2.
The
Hubble telescope's Advanced Camera for Surveys observed the
two new candidate moons on May 15, 2005. "The new satellite
candidates are roughly 5,000 times fainter than Pluto, but
they really stood out in these Hubble images," said Max
Mutchler of the Space Telescope Science Institute and the
first team member to identify the satellites.
Three
days later, Hubble looked at Pluto again. The two objects
were still there and appeared to be moving in orbit around
Pluto.
Above:
Hubble Space Telescope images taken in May 2005 show the candidate
moons apparently rotating counterclockwise around Pluto. [More]
"A
re-examination of [older] Hubble images taken on June 14,
2002 has essentially confirmed the presence of both P1 and
P2 near the predicted locations based on the 2005 Hubble observations,"
said Marc Buie of Lowell Observatory, Flagstaff, Ariz., another
member of the research team.
The
team looked long and hard for other potential moons around
Pluto, but they didn't find any.
"These
Hubble images represent the most sensitive search yet for
objects around Pluto," said team member Andrew Steffl
of the Southwest Research Institute, "and it is unlikely
that there are any other moons larger than about 10 miles
across in the Pluto system," he concludes.
The
Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency. The Space Telescope
Science Institute in Baltimore conducts Hubble science operations.
The Institute is operated for NASA by the Association of Universities
for Research in Astronomy, Inc., Washington, under contract
with Goddard.
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Source: NASA
Press Release | Production Editor:
Dr. Tony Phillips | Credit: Science@NASA
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