NASA-funded researchers have discovered the most distant object orbiting the sun. It’s a mysterious planet-like body three times farther from Earth than Pluto.
This is likely the first detection of the long-hypothesized “Oort 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 color. After Mars, it is the second reddest object in the solar system. It is estimated Sedna is approximately three- fourths the 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 Observatory, Hawaii, and David Rabinowitz of Yale University, New Haven, Conn., found the planet-like object, or planetoid, on Nov. 14, 2003. The researchers used the 48-inch Samuel Oschin Telescope at Caltech’s Palomar Observatory near San Diego. Within days, telescopes in Chile, Spain, Arizona and Hawaii observed the object. NASA’s new Spitzer Space Telescope also looked for it.
“The sun appears so small from that distance that you could completely block it out with the head of a pin,” said Dr. Mike Brown, California Institute of Technology (Caltech), Pasadena, Calif., associate professor of planetary astronomy and leader of the research team. The object, called Sedna for the Inuit goddess of the ocean, is 13 billion kilometers (8 billion miles) away, in the farthest reaches of the solar system.
Sedna is extremely far from the sun, in the coldest known region of our solar system, where temperatures never rise above minus 240 degrees Celsius (minus 400 degrees Fahrenheit). The planetoid is usually even colder, because it approaches the sun only briefly during its 10,500- year solar orbit. At its most distant, Sedna is 130 billion kilometers (84 billion miles) from the sun, which is 900 times Earth’s solar distance. Scientists used the fact that even the Spitzer telescope was unable to detect the heat of the extremely distant, cold object to determine it must be less than 1,700 kilometers (about 1,000 miles) in diameter, which is smaller than Pluto. By combining available data, Brown estimated Sedna’s size at about halfway between Pluto and Quaoar, a smaller planetoid discovered by the same team in 2002.
The elliptical orbit of Sedna is unlike anything previously seen by astronomers. It resembles the orbits of objects predicted to lie in the hypothetical Oort cloud–a distant reservoir of comets. But Sedna is 10 times closer than the predicted distance of the Oort cloud. Brown speculated that this “inner Oort cloud” might have been formed billions of years ago when a rogue star passed by the sun, nudging some of the comet-like bodies inward.