SEDNA: Dwarf Planet on the outer regions of Solar System

Sedna is a dwarf planet on the far outer reaches of the solar system.

Credit: NASA

Sedna is a dwarf planet that is one of the most distant bodies found in our solar system.

The object's closest approach to the sun is far greater than Pluto's distance away from Earth, at a spot where the sun is so tiny, according to NASA, that you could blot it out with a pin.

At 8 billion miles (12.8 billion kilometers) away, it's hard to figure out things such as surface features, but one thing astronomers have been able to identify is Sedna's distinct reddish colour.

Mike Brown

In 2004, it was described as the second-reddest object in our solar system, after Mars.

Sedna was discovered by a team led by Mike Brown, an astronomer at the California Institute of Technology.

The discovery of Sedna and other objects similar to it was a large impetus behind demoting Pluto from planetary status in 2006.

Image of Sedna, taken by Hubble Space Telescope

Discovery and basic statistics
Brown's team found Sedna in 2003 as part of a larger survey of the solar system that began in 2001.

Using the Samuel Oschin Telescope at the Palomar Observatory (east of San Diego) as well as Palomar's Quasar Equatorial Survey Team (QUEST) camera, the astronomers would take pictures of a tiny spot in the sky, one per hour for three hours, and see if they could find something that moved, Brown said in an explanation page about the discovery.

"The many billions of stars and galaxies visible in the sky appear stationary, while satellites, planets, asteroids, and comets appear to move. Objects in the inner Oort Cloud are extremely distant and so move extremely slowly," he said.

The Oort Cloud expands from a narrow belt on its inner edge
 into a large sphere farther from the Sun.

The Oort Cloud is a theorized area far in the solar system that is supposed to contain billions of icy objects that, if they receive a gravitational push toward the sun and warm up, turn into comets as the sun's energy melts the ice.

Sedna, however, was much bigger than a comet. Estimates for Sedna's size vary, but it is believed to be slightly smaller than the size of Pluto (1,400 miles or 2,250 kilometers in diameter).

Sedna takes some time to orbit the sun, not only because of its vast distance but also because its orbit is so elliptical or oval-shaped.

The dwarf planet takes roughly 10,000 years to complete one circuit around the sun. At the time of its discovery, it was at one of the closest points of its orbit to the sun, making it easier to spot.

Credit: Nasa

More Information: An explanation page about the SEDNA discovery