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SEDNA : a new planet in the solar system , discovered in the year 2004 !
SEDNA : 'New planet' may have a moon
The object appears very red
The distant object that some astronomers think could be the Solar System's 10th planet may have a moon.
The new planetary candidate, which has been named Sedna, rotates more slowly on itself than expected, suggesting it may have a satellite orbiting it.
One of the scientists who found Sedna has been giving further details of its discovery at a news conference.
Observations show it measures less than 1,700km (about 1,000 miles) in diameter, which is smaller than Pluto.
"We think that there's evidence there is a satellite around Sedna," said Dr Mike Brown, of the California Institute of Technology, US, and leader of the research team that found the body.
"We're hoping in the very near future to get some observations from the Hubble Space Telescope that should put that question to rest."
It was first seen on 14 November 2003 with the 48-inch Samuel Oschin Telescope at California's Mount Palomar Observatory. Astronomers from the California Institute of Technology, Yale Observatory and the Gemini Observatory were involved in the discovery.
Sedna, which is named after the Inuit goddess of the ocean, is both very red and very shiny.
This combination is extremely unusual in the Solar System and has baffled scientists trying to determine what it is made of.
Further than Pluto
Sedna, or 2003 VB12, as it was originally designated, is the most distant object yet found orbiting our Sun. It is three times further away than Pluto (average distance to the Sun is 5.9 billion km or 3.6 billion miles).
"The Sun appears so small from that distance that you could completely block it out with the head of a pin," said Dr Brown.
Sedna is currently about 13 billion km from Earth
He added that, in his view, the object's apparently small size suggested it should not be classified as a true planet.
Dr Brown suggested the "planetoid" was about half-rock and half-ice mixed together, but further work was needed to verify this.
Follow-up studies by the Tanagra Observatory have measured the thermal radiation coming from Sedna to determine how hot it is, and help provide some estimate of its size.
Researchers believe that Sedna's surface temperature is about -240 degrees Celsius (-400 degrees Fahrenheit).
The object 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 km (84 billion miles) from the Sun, which is 900 times Earth's solar distance (149 million km or 93 million miles).
Although Sedna could be a so-called Kuiper Belt object, its discoverers are unsure if it is as they consider it to be unlike any other object yet found.
KUIPER BELT OBJECTS
Icy planetary bodies that orbit beyond Neptune in the distant region of the Solar System
More than 400 such objects are currently known
They are believed to be remnants of the formation of the Solar System and among the most primitive objects available for study
It could be the first detection of the long-hypothesized "Oort cloud", a faraway repository of small icy bodies that supplies the comets that streak by Earth.
In recent years, astronomical work has thrown up several big objects in the outer Solar System. Quaoar, found in 2002, is about 1,200km (745 miles) across. Ixion, discovered in 2001, is 1,065 km (660 miles) wide. Varuna, detected in 2000, has a diameter of approximately 900 km (560 miles).
And only in February this year, scientists picked up the object 2004 DW, which is though to be 1,800km (1,120 miles) across.
The new discovery will reignite the debate about what constitutes a planet.
One group of astronomers believe that Pluto is not a true planet but merely one of the largest of a vast number of minor objects in the outer Solar System.
The alternative standpoint is that Pluto is a planet and those who believe that will have to classify Sedna as the 10th planet
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