Sedna is a small, distant world about 1,000 kilometers across that orbits the Sun far beyond Neptune. At the farthest point of its long, stretched orbit, it is about 140 billion kilometers from the Sun, about 940 times as far as Earth is. It will next reach that point around the year 7800.

Distance

Sedna's orbit is a long, stretched ellipse. Its closest point to the Sun, called perihelion, is about 76 astronomical units (au) away. One au is about 150 million kilometers, Earth's average distance from the Sun. Its farthest point, called aphelion, is about 937 au, or 140 billion kilometers, more than 12 times as far as its closest point.

One trip around the Sun takes about 11,400 years. As of September 2026, Sedna is about 83 au (12.4 billion kilometers) from the Sun and moving inward. It will reach perihelion around 2076.

These figures are calculated from Sedna's observed motion. NASA's Jet Propulsion Laboratory puts the aphelion at about 937 au, and a 2019 study describes it as about 1,000 au. Astronomers have followed Sedna along only a tiny part of its orbit, so its farthest point is known much less precisely than its closest.

Size comparisons

The aphelion is about 5.4 light-days from the Sun, which means sunlight takes about 5.4 days to reach it.
It is about 2.6 times as far from the Sun as the farthest point of Comet Hale-Bopp's orbit.
It is about 31 times as far from the Sun as Neptune, the outermost planet.
It is about 5.5 times as far from the Sun as Voyager 1, the most distant spacecraft, was in September 2026. At its present speed, Voyager 1 would need more than 200 years to get that far out.
If the Sun were shrunk to the size of a basketball, Earth would orbit about 26 meters (85 feet) away, and Sedna's aphelion would be about 24 kilometers (15 miles) away.

Discovery

Michael Brown, Chadwick Trujillo and David Rabinowitz discovered Sedna on November 14, 2003, at Palomar Observatory. It was then about 90 au from the Sun, more distant than any Solar System object seen before. It is named after Sedna, the Inuit goddess of the sea. In 2012, astronomers used the heat Sedna gives off, measured by the Herschel Space Observatory, to estimate its diameter at about 995 kilometers, give or take 80 kilometers.

A puzzling orbit

Sedna never comes closer than 76 au, so it always stays far from the planets. Its discoverers noted that Neptune's gravity can push the closest point of an object's orbit out only to about 36 au, and more complex effects to about 50 au at most. None of the known planets could have put Sedna in its orbit.

They suggested three possible causes: an undiscovered planet, a star that once passed unusually close to the Sun, or the Sun's birth in a cluster of stars. A 2019 study called the birth cluster the preferred explanation. In that picture, Sedna belongs to the inner Oort cloud, a vast, distant store of comets thought to surround the Solar System.

Sources

Horizons System. NASA Jet Propulsion Laboratory, 2026.
Small-Body Database Lookup: 90377 Sedna (2003 VB12). NASA Jet Propulsion Laboratory, 2026.
Discovery of a candidate inner Oort cloud planetoid. Brown et al., The Astrophysical Journal, 2004.
A New High Perihelion Inner Oort Cloud Object: 2015 TG387. Sheppard et al., The Astronomical Journal, 2019.
"TNOs are Cool": A survey of the trans-Neptunian region. VII. Size and surface characteristics of (90377) Sedna and 2010 EK139. Pál et al., Astronomy & Astrophysics, 2012.
Measuring the Universe. International Astronomical Union.
Speed of light in vacuum. NIST CODATA, 2022.
Neptune Fact Sheet. NASA.
Sun Fact Sheet. NASA.
Official Basketball Rules 2026: Basketball Equipment. FIBA, 2026.

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