Sedna (dwarf planet)

Sedna is a dwarf planet located in the outermost reaches of our Solar System.

It orbits the Sun far beyond the orbit of Neptune. This distant world is approximately 900 to 1,000 kilometers in diameter. Sedna is a significant object for astronomers to study. It is the largest trans-Neptunian object known that does not have a moon. Because it lacks a moon, scientists cannot directly determine its mass or density. This makes Sedna a unique subject in our study of the solar system.

Sedna follows a very unusual and extreme orbit around the Sun. Its path is highly elliptical, which means it is shaped like a long, stretched-out oval. This orbit has an eccentricity of 0.85. At its farthest point from the Sun, called aphelion, it reaches 937 astronomical units (AU). This distance is about 19 times farther than the aphelion of Pluto. Its closest approach to the Sun, or perihelion, is 76.19 AU. One full trip around the Sun takes approximately 11,400 years. This is one of the longest orbital periods for an object of its size.

The surface of Sedna is chemically complex and very colorful. It is one of the reddest objects known in the Solar System. This deep red color is caused by a surface coating of tholins. Tholins are organic mixtures that form over billions of years. They are created when ultraviolet radiation and interstellar particles hit simple organic compounds. This process transforms those compounds into a reddish, amorphous sludge. The surface also contains various ices. Spectroscopic analysis shows a mixture of water ice, carbon dioxide ice, and ethane ice. Some models also suggest the presence of nitrogen and methanol ices.

Sedna was discovered on November 14, 2003. The discovery team included Michael Brown, Chad Trujillo, and David Rabinowitz. They used the Samuel Oschin telescope at Palomar Observatory in California. They also used the Gemini Observatory and tools from Yale University. The team noticed an object moving relative to the stars. Follow-up observations were made with telescopes in Chile, Arizona, and Hawaii. These observations helped scientists accurately determine its distant and eccentric orbit. Precovery images even showed the object as far back as September 1990.

The naming of the dwarf planet was a notable event in astronomy. Michael Brown initially nicknamed the object "The Flying Dutchman." This was a reference to a legendary ghost ship. He eventually chose the name Sedna from Inuit mythology. He felt the goddess Sedna, who lives at the bottom of the Arctic Ocean, reflected the object's great distance from the Sun. This choice caused some controversy among amateur astronomers. They felt the name was announced before official numbering protocols were met. However, the International Astronomical Union officially accepted the name in September 2004.

Because Sedna travels so far from the Sun, it is an extremely cold place. Near its aphelion, it is one of the coldest spots in the Solar System. At this distance, the Sun appears as a very bright star in the black sky. It is about 45% as bright as a full moon looks from Earth. At its furthest point, Sedna moves at a slow speed of only 377 meters per second. This is only about 1.3% of the average orbital speed of Earth. This extreme environment makes Sedna a distinct type of world.

Sedna is considered the prototype for a new class of objects called sednoids. These are objects characterized by highly eccentric orbits with very distant perihelia. Some astronomers believe Sedna might belong to the inner Oort cloud. This is because its closest approach to the Sun is too far to be caused by Neptune. Others suggest its orbit was changed by a close encounter with a hypothetical Planet Nine. Studying Sedna helps scientists understand the early evolution of our Solar System. It provides a window into the history of the outer reaches of space.