From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Thu, 4 Aug 2011 04:46:36 -0500
Message-ID: <42558F23BE9345D291BE08EDE430A81E_at_ATARIENGINE2>


Astronomers have discovered three small, icy worlds
orbiting the sun near Pluto, on the outer reaches of
the solar system.

The three newfound bodies are likely big enough to
be rounded by their own gravity, which means they
may be "dwarf planets" like Pluto, researchers said.

Scientists discovered them and eleven other new
objects while performing a survey of the Kuiper Belt,
the ring of icy bodies beyond Neptune.

"Three of the discoveries would be in the dwarf planet
regime," said study lead author Scott Sheppard, of the
Carnegie Institution of Washington. "The others were
much smaller, and they're probably just irregular
chunks of ice or rock."

Surveying the southern sky

Sheppard and his colleagues surveyed the Kuiper
Belt, which is found roughly between 30 and 50
astronomical units (AU) from the sun. The distance
from the Earth to the sun, about 93 million miles
or 150 million kilometers, is 1 AU.

Using the 1.3-meter Warsaw Telescope at Las Campanas
Observatory in Chile, the team focused their search on
the southern skies and the galactic plane, areas that had
not been covered completely in previous Kuiper Belt surveys.
They found three objects that seem to be more than 250
miles (400 km) wide - for icy bodies, probably big enough
to be molded into a sphere by their own gravity, Sheppard
said. That would likely qualify them for "dwarf planet" status.

The International Astronomical Union (IAU) created the
dwarf planet category back in 2006, when it became clear
that Pluto wasn't alone on the cold outskirts of the solar
system. Basically, in the IAU's estimation, dwarf planets
are big enough to be spherical but too small to have
"cleared their neighborhoods" of other orbiting bodies.

So Pluto was demoted to dwarf planet, a status it shares
with the other icy, faraway bodies Eris, Haumea and
Makemake, as well as the giant asteroid Ceres. These
are the only five officially recognized dwarf planets
at the moment, although hundreds or even thousands
more may exist.

The new survey didn't find any objects as big as Pluto
or Eris, which are both roughly 1,450 miles (2,333 km)
wide. Before this search, the existence of other Pluto-size
bodies in the Kuiper Belt had been a real possibility,
Sheppard said, because the southern skies had not
been searched comprehensively.

"This survey basically completes the Belt for the big
stuff," Sheppard told SPACE.com. "So Pluto and Eris
are the kings of the Kuiper Belt area, basically."
The study has been accepted for publication in the
Astronomical Journal.

Looking farther out

While no more truly massive objects are likely awaiting
discovery in the Kuiper Belt, some may lurk even farther
away, Sheppard said.

For example, astronomers know of one object, called
Sedna, that orbits up to 940 AU from the sun. Sedna,
which appears to be at least 745 miles (1,200 km)
wide, has an extremely elliptical orbit that brings
it to within about 75 AU of the sun at its closest point.
Much about Sedna is a mystery at the moment -
including how busy its neck of the cosmic woods may be.
"Sedna is basically the frontier right now in the
solar system," Sheppard said. "We've found one
object, and it's likely there's a bunch more out
there. But the technology right now is just barely
 at the ability for us to efficiently detect these things."
Objects even bigger than Sedna may zip around the
sun undetected in the cold, dark depths of the far
outer solar system, Sheppard said. Even planet-size
bodies could have escaped notice to this point, if
they're far enough away.

"There could still be Mars- or even Earth-size objects
way out there, at hundreds of AU, that would be too
faint for us to detect," Sheppard said. "It's pretty
amazing when you think about it. It's unlikely,
but it's possible."
Received on Thu 04 Aug 2011 05:46:36 AM PDT

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