[extropy-chat] SPACE: Yet more about KBO 2004 DW

Joseph S. Barrera III joe at barrera.org
Sat Feb 21 22:51:18 UTC 2004

Here's a very nice article, including this tidbit: "We've traced 2004 DW 
back to November 23, 1954, when it was photographed as part of the first 
Palomar Sky Survey" and also a bit about getting a better estimate of 
its size in the next couple of weeks via the IRAM telescope in Spain.

- Joe


2004 DW: The largest Kuiper Belt Object?
Astronomers discover an icy world at the fringes of the solar system.
by Francis Reddy

Icy discovery: Is 2004 DW the largest KBO?
Courtesy Chad Trujillo, Gemini Observatory
Posted February 20, 2004

Astronomers at the California Institute of Technology (Caltech) and Yale 
University discovered an icy world at the outer fringes of the solar 
system on February 17. The object, currently known only as 2004 DW, may 
be the largest find in the solar system since 1930, the year astronomers 
discovered Pluto.

The object currently lies 4.4 billion miles (7.1 billion kilometers) 
away from Earth. Its orbital tilt, about 20.6°, is larger even than that 
of Pluto, which itself has an unusually high orbital inclination — far 
larger than any other planet.

"We've traced 2004 DW back to November 23, 1954, when it was 
photographed as part of the first Palomar Sky Survey," says codiscoverer 
Chad Trujillo of the Gemini Observatory in Hawaii. The team, which 
included Mike Brown of Caltech and David Rabinowitz of Yale University, 
found the new object using the same 48-inch (1.2 meter) Schmidt 
telescope on Palomar Mountain, California, used for that survey. 
Astronomers at Australia's Siding Spring Observatory also found 2004 DW 
on a pre-discovery photograph taken November 8, 1951. Thanks to these 
images, Trujillo told Astronomy, "We know the orbit much better now. 
It's quite similar to Pluto's."

The object's distance from the Sun varies between 30.9 AU and 48.1 AU. 
One AU, or astronomical unit, equals the Earth's average distance from 
the Sun: 93 million miles (150 million km).

The object takes 248 years to complete its orbit and reached its 
farthest point from the Sun in 1989. It's now inbound, Trujillo says, 
"But don't hold your breath — it won't reach perihelion until 2113."

The team found the object one day short of the 74th anniversary of when 
Pluto was discovered, February 18, 1930. That's appropriate because 2004 
DW's orbit places it in a class of icy objects sometimes called 
"plutinos." These objects occupy Pluto-like orbits in the Kuiper Belt, a 
collection of frozen worldlets circling the solar system in a realm 
beyond Neptune. Astronomers have cataloged some 800 Kuiper Belt Objects 
(KBOs) since 1992.

Until the discovery of 2004 DW, the largest-known KBO was an object 
named Quaoar, which was discovered in 2002 by Brown and Trujillo. With 
an estimated diameter of 780 miles (1,250 km), Quaoar is larger than 
Pluto's moon Charon and has a volume big enough to hold all 50,000 of 
the numbered asteroids in the solar system.

Because astronomers know the distance to 2004 DW, its brightness should 
indicate its size relative to Quaoar if both objects reflect the same 
proportion of sunlight. At the moment, says Trujillo, 2004 DW appears to 
be about 870 miles (1,400 km) across, making it the new record holder. 
"We'll be attempting to measure that in the next week or two with the 
IRAM telescope in Spain," Trujillo adds. This is the same heat-sensitive 
telescope Trujillo and Brown previously used to refine estimates of 
Quaoar's size. In addition, the team will attempt to obtain images with 
the Hubble Space Telescope and, possibly, the Spitzer Space Telescope.

Both Brown and Trujillo believe on the basis of statistical arguments 
that a few objects larger than Pluto eventually will be found in the 
Kuiper Belt. "Since there are only a few really large ones, you have to 
cover a lot of sky to find them," explains Trujillo. "We have a 
dedicated program to find objects like this in the outer solar system." 
For a few hours each night, the team images the sky with the 
170-million-pixel QUEST CCD camera attached to the 48-inch Schmidt 

"If Pluto were discovered today, it would be called a Kuiper Belt 
Object, not a planet," adds Trujillo. "Scientists have not yet created a 
good definition of planet that encompasses the Kuiper Belt."
"It's now only a matter of time before something is going to be 
discovered out there that will change our entire view of the outer solar 
system," Mike Brown notes.

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