[meteorite-list] New Solar System World Has A Moon (2003 EL61)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Jul 29 15:54:41 2005
Message-ID: <200507291953.j6TJrlF27758_at_zagami.jpl.nasa.gov>

http://www.newscientistspace.com/article/dn7758-new-solar-system-world-has-a-moon.html

New solar system world has a moon
Jeff Hecht
New Scientist
29 July 2005

Newly disclosed observations of the giant world revealed on Friday to
orbit in the outer solar system show that it has a moon.

But although initial calculations suggested the Kuiper Belt object could
be up to twice as big as Pluto, the new data
indicates it is about 70% the diameter of that planet. This makes its
size second only to Pluto itself among objects beyond Neptune.

The new object has been temporarily named 2003 EL61 by the Minor Planet
Center at the Harvard-Smithsonian Center for Astrophysics in
Massachusetts, US, and was first spotted by Jose-Luis Ortiz at the
Sierra Nevada Observatory in Spain in 2003. Ortiz's group uncovered
observations as far back as 1955, and after additional observations
reported its orbit to the Minor Planet Center.

When he first saw how bright the object was, Gareth Williams of the
Minor Planet Center could not believe it was as far from the Sun as
Ortiz claimed - 51 times further away than the Earth. However, he
quickly found two images of the object in the online Digital Sky Survey,
and posted it on a confirmation page on the Minor Planet Center's
website. Half an hour later, German amateur astronomers announced they
had found it where predicted.

But more was to come. After Williams put out a notice of the new object
and its orbit the evening of 28 July, Mike Brown of Caltech in
California, US, said his group had discovered the same object in 2004 -
and in January 2005 had spotted a moon orbiting it using the Keck
Observatory in Hawaii.

Mass by moon

The moon is not the first discovered around a Kuiper Belt object, but it
is the smallest, only about 1% the mass of 2003 EL61. More importantly,
observations of the satellite's 49-day orbit allowed Brown to precisely
calculate the masses of both 2003 EL61 and its moon.

Brown's results - posted on his website
<http://www.gps.caltech.edu/~mbrown/> - show the object is about 32% as
massive as Pluto. Assuming its composition is similar, that implies its
diameter is about 70% of Pluto's, or about 1600 kilometres. That would
probably make it larger than Sedna, an object beyond the Kuiper Belt
discovered earlier by Brown's group.

Brown had not made his findings public because he was waiting for
infrared data from the Spitzer Space Telescope, which he could use to
calculate how much visible light 2003 EL61 reflected. That would allow
him to calculate its size more precisely.

Taking a chance

He finally received that data on 22 July, and is still in process of
analysing it. "We could have announced the object earlier, but we took a
chance that no one else would find it while we were awaiting our
observations" from Spitzer, Brown writes on his web site. "We were
wrong," so the Spanish group earned credit for the discovery.

Williams is surprised the object had not been spotted earlier. Although
its motion in the sky is very slow: "It's bloody bright," he told New
Scientist.

If it was in the main asteroid belt, it would be visible to the unaided
eye in a dark sky, one to two magnitudes brighter than Vesta, the
brightest object in the main belt. Even far beyond Neptune, it is bright
enough for amateur astronomers to have captured images of it without
recognising its motion.

----------------------------------------------------------


Large New World Discovered Beyond Neptune
By Robert Roy Britt
space.com
29 July 2005

A newfound object in our solar system's outskirts may be larger than any
known world after Pluto, scientists said today.

It also has a moon.

Designated as 2003 EL61, the main object in the two-body system is 32
percent as massive as Pluto and is estimated to be about 70 percent of
Pluto's diameter.

Other news reports that the object could be twice as big as Pluto are
false, according to two astronomers who found the object in separate
studies and another expert who has analyzed the data.

If the mass is only one-third that of Pluto, then theory holds that it
can't be larger than Pluto, according to Brian Marsden of the Minor
Planet Center, which serves as a clearinghouse for data on all newfound
objects in the solar system.

Marsden, who was not involved in the discovery but has reviewed the
data, told SPACE.com that the mass estimate is very firm, within 1 or 2
percent. "I don't think it is bigger than Pluto," he said.

Where it fits in

This is still a big world, once again raising the prospect that
something larger than Pluto might still lurk out there.

Scientists base their size calculations in part on the object's
reflectivity. Since they don't know exactly how much the surface
brightness of distant objects varies, there is some wiggle room in their
size estimates.

A team led by Mike Brown of Caltech has been observing 2003 EL61 for a
year but was seeking more data before announcing the discovery. Brown
said today it may possibly be larger than Sedna, which
has been the largest known world beyond Neptune other than Pluto.

Sedna is between 800 and 1,100 miles in diameter. Pluto is about 1,400
miles across.

Brown figures 2003 EL61 has a diameter of around 930 miles.

Is there any chance it is bigger than Pluto?

"No," Brown said in a telephone interview. "Definitely not."

In fact, Brown's team got the new data they had been waiting for, from
the Spitzer Space Telescope, last week. While not fully analyzed, he
said the Spitzer observations show "absolutely" that the object is not
bigger than Pluto.

Who gets credit?

The object was spotted independently by a group led by Jose-Luis Ortiz
of the Sierra Nevada Observatory in Spain. Ortiz' team announced the
finding in astronomy circles recently and the finding, including the
claim that it might be twice as big as Pluto, was reported by an online
news site today.

Ortiz said that based on his team's observations, there was one outlying
theory could allow 2003 EL61 to be larger than Pluto, but he does not
think it is right.

"I do not think it is larger than Pluto," Ortiz told SPACE.com today.

Brown was surprised last night to learn that Ortiz' group had
independently found the object, which only yesterday gained the tag 2003
EL61 from the Minor Planet Center. It was a rare case of one group of
astronomers unwittingly scooping another.

Brown said that Ortiz' group rightfully deserves credit for making the
discovery.

About that moon

2003 EL61 orbits the Sun on an elliptical path beyond Neptune in a
region of space known as the Kuiper Belt. It
is significantly inclined to the main plane of the solar system where
most of the planets travel. It is one of several objects
out there now known to have a satellite.

The moon around 2003 EL61 is small, making up only about 1 percent of
the mass of the system, Brown said.

"This satellite is the smallest satellite relative to its primary known
in the Kuiper belt," Brown said. "Pluto's satellite, Charon, is about 10
percent of the mass of Pluto.

Marsden, of the Minor Planet Center, said it is surprising the object
was not discovered earlier. He said it was probably just barely too
faint to be spotted in the sky survey done by Clyde Tombaugh that led to
the discovery of Pluto 75 years ago.

Brown's team first spotted 2003 EL61, which had no name at the time,
using the Samuel Oschin Telescope at Palomar Observatory on May 6, 2004.
They did not realized they had found it until Dec. 28, 2004, after
scrutinizing their data in and ongoing effort to find Kuiper Belt Objects.

In a series of three images, the object is seen moving across the sky in
relation to relatively fixed background stars.

Ortiz's group initially detected the object in 2003 and spotted it again
this year, leading to their announcement yesterday.
Received on Fri 29 Jul 2005 03:53:47 PM PDT