Sedna
What is Sedna?
Dwarf planets· Diameter ~1,000 km. One of the bodies that travel farthest from the Sun. Even at its closest it is 76 AU away; at its farthest it reaches 937 AU, and one orbit takes about 11,400 years.
Orbit and size
| Diameter | ~1,000 km |
|---|---|
| Distance | 76~937 AU |
| Year | ~11,400 yr |
| Next perihelion | ~2076 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
The pinprick Sun in Sedna's sky
When Sedna is at its farthest, 937 AU from the Sun, sunlight there is about 900,000 times weaker than at Earth. The Sun looks not like a disk but like the single brightest star in the sky. Sedna is now about 84 AU away, in the closer part of its orbit, yet sunlight is still about 7,000 times weaker than at Earth. The surface is estimated to be colder than minus 240 degrees Celsius.
Sedna is one of the reddest bodies in the solar system. Its surface ice has probably been turned into reddish material by particles from space over a very long time. In 2023 the James Webb Space Telescope detected ices such as ethane, acetylene and ethylene on its surface. After passing its closest point around 2076, Sedna will head away again for more than ten thousand years, so the coming decades are a good time to study it.
Soon after its discovery, Sedna's brightness seemed to change over a period of 20 to 40 days. Such a slow spin led to guesses that a moon had braked it. But the Hubble Space Telescope found no moon, and later observations corrected the spin period to about ten hours. No moon of Sedna has been found to this day.
The dwarf planet in depth
Sedna was discovered in November 2003 by Michael Brown, Chad Trujillo and David Rabinowitz. It is named after the Inuit sea goddess who lives at the bottom of the Arctic Ocean. It was about 90 AU from the Sun when found, and it is about 1,000 km across.
Its orbit turned out to be a very long ellipse. At its closest Sedna is 76 AU from the Sun; at its farthest, 937 AU, a distance that even light takes more than five days to cross. One lap takes about 11,400 years. The last time Sedna was at its closest point, people were just beginning to farm. The next time will be around 2076.
Sedna's orbit puzzles scientists. It stays too far from Neptune for Neptune's gravity to have shaped such a path. One explanation is that a nearby star in the cluster where the Sun was born passed close and pulled on it. Another is that an undiscovered planet exists. Neither has been confirmed. More bodies on similar orbits were found in 2014 and 2018.
Frequently asked
- How big is Sedna?
- The diameter of Sedna is ~1,000 km.
- How far is Sedna from Earth?
- The distance of Sedna is 76~937 AU.
- When does Sedna return?
- The next perihelion of Sedna is ~2076.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.