[meteorite-list] Researchers Describe Discovery of Pluto's New Moons

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Feb 23 12:30:49 2006
Message-ID: <200602231729.k1NHT6L10832_at_zagami.jpl.nasa.gov>

The Johns Hopkins University Applied Physics Laboratory
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Media Contact: Michael Buckley
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February 22, 2006



New Hubble Images Offer Best View yet of Distant Planet and its Three

In the Feb. 23 issue of the journal Nature, a team led by Dr. Hal Weaver of
the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel,
Md., describes its discovery of two new moons around Pluto - a finding that
made the ninth planet the first Kuiper Belt object known to have multiple

In a companion paper, discovery team members led by Dr. Alan Stern of the
Southwest Research Institute, Boulder, Colo., conclude that the two small
moons were very likely born in the same giant impact that gave birth to
Charon. They also argue that large binary Kuiper Belt objects like
Pluto-Charon may also have small moons accompanying them, and that Pluto's
small moons may generate debris rings that orbit the planet.

The Kuiper Belt is a band of icy, rocky objects and dwarf planets that
orbit the Sun in the outer region of our solar system, beyond the orbit of
Neptune. It has been known since 1992; Pluto is its most prominent member.

Using the Hubble Space Telescope's Advanced Camera for Surveys, the team
originally discovered the moons in two sets of Pluto observations in May
2005. Their discovery was confirmed in new Hubble images taken Feb. 15 and
released today.

"We used Hubble's exceptional resolution to peer close to Pluto and pick
out two small moons that had eluded detection for more than 75 years," says
Weaver, who also serves as project scientist for NASA's New Horizons
mission, which is on track to make the first close-up reconnaissance of the
Pluto system in 2015.

Pluto's previously known moon, Charon, was discovered in 1978, nearly half
a century after Pluto's discovery in 1930. With diameters estimated to lie
between 35 and 100 miles, the new moons, provisionally designated S/2005 P1
and S/2005 P2, are roughly 10 times smaller than Charon. They're also about
600 times fainter than Charon and 4,000 times fainter than Pluto, and
hidden in the glare of nearby Pluto and Charon when viewed by ground-based
optical telescopes. The scientists say this is the reason the moons evaded
detection before Hubble looked for them.

The Weaver team writes in Nature that the satellites were easy to see in
the Hubble pictures. "That was somewhat surprising because ground-based
observers had been trying for more than a decade to find new satellites
around Pluto," says Max Mutchler from the Space Telescope Science Institute
in Baltimore, the first person to spot the moons in the May 2005 images.
"But I felt almost certain even when I first saw them that they were real
objects -- not any sort of artifact -- and that they were exhibiting
orbital motion around Pluto."

That orbital motion -- inferred from the different locations of the moons
in pictures taken May 15 and May 18 -- is what convinced scientists that
they were indeed looking at moons and not stray light, cosmic rays or other
Kuiper Belt objects that happened to be passing by.

"If we assumed the orbits were circular and in the same orbit plane as
Charon, we could predict the exact positions of the objects on the second
day," says Dr. William Merline, a co-author and discovery team member from
Southwest Research Institute (SwRI). "When the objects on the second day
appeared almost exactly where we predicted, we were convinced -- no two
artifacts could follow the rules of orbital physics that 'real' objects
must obey."

"The presence of the new moons in orbits with so many similarities to
Charon's sheds light on the formation and evolution of the Pluto system, as
well as on the process by which satellites are formed in the Kuiper Belt,"
says SwRI's Stern, who is principal investigator of the New Horizons mission.

The new moons will be important targets of New Horizons, which was launched
Jan. 19 to provide the first detailed reconnaissance of Pluto and the
Kuiper Belt. The New Horizons spacecraft will fly within several thousand
miles of Pluto and its moons in July 2015.

Weaver says the APL-built Long Range Reconnaissance Imager (LORRI)
telescopic camera on New Horizons should be able to probe the new moons and
resolve surface features down to 600 yards wide. These observations build
on primary mission science plans to characterize the global geology and
geomorphology of Pluto and Charon, map their surface compositions and
temperatures, and examine Pluto's atmospheric composition and structure.
New Horizons also will map the two smaller satellites in color and
black-and white, and map their surface compositions and temperatures.

"We're getting four fascinating targets for the price of two," says Weaver.
"The opportunity to explore the 'bookends' of Kuiper Belt object size
distribution, with Pluto and Charon at one end and P1 and P2 at the other,
is an unexpected treat."

The team is already analyzing the new Hubble images, which confirm the
results published in the Nature paper and provide the most detailed view
yet of this fascinating mini solar system. Hubble is scheduled to take
another set of Pluto images in early March.

"The more we learn about the orbits and physical properties of P1 and P2,
the better we can fine-tune our spacecraft investigation and focus on the
objectives that are impossible to achieve from Earth-based observations,"
says Stern.

The Hubble Pluto companion search team also includes Dr. Marc Buie of
Lowell Observatory, Flagstaff, Ariz., and Dr. John Spencer, Dr. Eliot
Young, Dr. Leslie Young and Dr. Andrew Steffl of Southwest Research
Institute, Boulder. New Horizons is the first mission in NASA's New
Frontiers Program of medium-class spacecraft exploration projects. Stern
leads the mission and science team as principal investigator. APL manages
the mission for NASA's Science Mission Directorate and is operating the
spacecraft in flight.

On the Web:
Hubble/Pluto System images: http://hubblesite.org/news/2006/09
NASA's New Horizons mission: http://pluto.jhuapl.edu


The Applied Physics Laboratory (APL) is a not for profit laboratory and
division of The Johns Hopkins University. APL conducts research and
development primarily for national security and for nondefense projects of
national and global significance. For more information, visit
Received on Thu 23 Feb 2006 12:29:05 PM PST

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