Planet Sedna

March 15, 2004: NASA-funded researchers have discovered the most distantobject orbiting the sun. It's a mysterious planet-like three body times farther from Earth than Pluto.

"The sun appears so small from that distance that you could completely block it out with the head of the pin," said Dr.Mike Brown, California Institute of Technology (Caltech), Pasadena, Calif, associate professor of planetary astronomy and leader of research team. The object, called Sedna for the Inuit goddess of the ocean, is 13 billion kilometers (8 billion miles) away,in the farthest research of the solar system.

This is likely the first detections of the long-hypothesized "Ourt cloud", a faraway repository of small icy bodies that supplies the comets that streak by Earth. Other notable features of sedna include its size and reddish colour. After Mars, it is the second reddest object in the solar system. It is estimaded Sedna approximately three-fourth size of Pluto. Sedna is likely the largest object found in the solar system since Pluto was discovered in 1930.

Brown, along with Drs. Chad Trujillo of the Gemini Observator, Hawaii, and David Rabinowitz of Yale University, New Haven, Conn, found the planet-like object , or planetoid, on Nov. 14, 2003. The researches used the 48-inch Samuel Oshin Telescope at Caltech's Palomar Observatory near San Diego. Within days, telescope in Chilie, Spain, Arizona and Hawaii observed the object. NASA's new Spitzer Space Telescope also looked for it.

Sedna is extremly far from the sun, in the coldest known region of the solar system, where temperatures rise above minus 240 degrees Celcius (minus 400 degrees Fahrenheit). The planetoid is usually even colder, because it approches the sun only briefly during its 10,500 year solar orbit. At the most distant, Sedna is 13o billion kilometers (84 billion miles) from the sun, which 900 times Earth's solar distance.

Scientist used the fact than even Spitzer telescope was unable to defeat the heat of the extremly distant, cold object to determine it must be last then 1.700 kilometers (about 1.000 miles) in diameter, which is smaller than Pluto. By combining availalbe data, Brown estimated Sedna's size at about halfway beetwen Pluto and Quaror, a smaller planetoid discovered by the same team in 2002.

The eliptical orbit of Sedna is unlike anything previously seen by astronomers. It resembles the orbits of object predicted to lie in the hypotethical Ourt cloud--a distant reservoir of comets. But Sedna is 10 times closer than the predicted distance of the Ourt cloud. Brown speculated that this "inner Ourt cloud" might have been formed billions of years ago when a rouge star passed by the sun, nudging some of the comet-like bodies inward.

"The star would have been close enough to be brighther than the full moon, and it would have been visible in the daytime sky for 20.000 years," Brown explained. Worse, it would have dislodgeg comets farther out in the Ourt cloud, leading to intense comet shower that could have wiped out some or all forms life that existed on Earth at the time.

Rabinowitz said there is indirect evidence that Sedna may have a moon. The researches hope to check this possibility with NASA's Hubble Space Telescope. Trujillo has begun to examine the object's surface with one of the world's largest optical/infrared telescope, the 8-meters (26-foot) Frederick C. Gillet Gemini Telescope on Mauna Kea, Hawaii. "We still don't understand what is on the surface of the body. It is nothing like what we would have predicted or what we can explain," he said.

Sedna will come to closer to Earth in this years ahead, but even at closed approach, about 72 years from now, Sedna is very far away--farther than Pluto. Then it will begins its 10.500-years trip back to the far reaches of the solar system. "The last time Sedna was this close to the sun, Earth was just coming out of the last ice age. The next time it comes back, the world might again be a completely diffrent place," Brown said.