Owing to its lack of known moons,[20] the Keplerian laws of planetary motion cannot be utilized for determining its mass, and the actual figure remains as yet unknown.

A transfer window for a probe fly-by in 2029 utilizing a gravitational assist from Jupiter was proposed, taking 25 years to travel to the dwarf planet, 80 AU (12 billion kilometers) distant.

The International Astronomical Union (IAU) initially considered Sedna to be a member of the scattered disc, a group of objects sent into high-eccentricity orbits by the gravitational influence of Neptune.

The dwarf planet is also the prototype of a new orbit class of objects named after itself, the sednoids, which include 2012 VP113 and Leleākūhonua, both celestial bodies with large perihelion distances and high eccentricities.

[30][31][32] Sedna (provisionally designated 2003 VB12) was discovered by Michael Brown (Caltech), Chad Trujillo (Gemini Observatory), and David Rabinowitz (Yale University) on 14 November 2003.

[35] He suggested to the International Astronomical Union's (IAU) Minor Planet Center that any objects discovered in Sedna's orbital region in the future should be named after mythical entities in Arctic mythologies.

[35] The team made the name "Sedna" public before the object had been officially numbered, which caused some controversy among the community of amateur astronomers.

[36] Brian Marsden, the head of the Minor Planet Center, stated that such an action was a violation of protocol, and that some members of the IAU might vote against it.

Near aphelion, Sedna is one of the coldest places in the Solar System, located far past the termination shock, where temperatures never exceed −240°C (−400°F) due to its extreme distance.

[53][54][12] The orbits of some long-period comets extend further than that of Sedna; they are too dim to be discovered except when approaching perihelion in the inner Solar System.

As Sedna nears its perihelion in mid-2076,[6][b] the Sun will appear merely as a very bright pinpoint in its sky, the G-type star too far away to be visible as a disc to the naked eye.

[56] It was initially speculated that Sedna's rotation was slowed by the gravitational pull of a large binary companion, similar to Pluto's moon Charon.

[56][c] Subsequent measurements from the MMT telescope showed that Sedna in reality has a much shorter rotation period of about 10 hours, more typical for a body its size.

[59] In 2012, measurements from the Herschel Space Observatory suggested that Sedna's diameter was 995 ± 80 km, which would make it smaller than Pluto's moon Charon.

[60] As Sedna has no known moons, the direct determination of its mass is as yet impossible without either sending a space probe or perhaps locating a nearby object which is gravitationally perturbed by the planetoid.

[64] Observations from the SMARTS telescope show that Sedna, in visible light, is one of the reddest objects known in the Solar System, nearly as red as Mars.

[60] Chad Trujillo and his colleagues suggest that Sedna's dark red color is caused by an extensive surface coating of hydrocarbon sludge, termed tholins.

[65] Its surface is homogeneous in color and spectrum; this may be because Sedna, unlike objects nearer the Sun, is rarely impacted by other bodies, which would expose bright patches of fresh icy material like that on 8405 Asbolus.

[60] Barucci and colleagues compared Sedna's spectrum with that of Triton and detected weak absorption bands belonging to methane and nitrogen ices.

[60] The European Southern Observatory's Very Large Telescope observed Sedna with the SINFONI near-infrared spectrometer, finding indications of tholins and water ice on the surface.

[68] In 2022, low-resolution near-infrared (0.7–5 μm) spectroscopic observations by the James Webb Space Telescope (JWST) revealed the presence of significant amounts of ethane ice (C2H6) and of complex organics on the surface of Sedna.

[72] On top of that, Sedna's initial orbit must have been approximately circular, otherwise its formation by the accretion of smaller bodies into a whole would not have been possible, because the large relative velocities between planetesimals would have been too disruptive.

[76][77] Computer simulations by Julio A. Fernandez and Adrian Brunini suggest that multiple close passes by young stars in such a cluster would pull many objects into Sedna-like orbits.

[30] A study by Morbidelli and Levison suggested that the most likely explanation for Sedna's orbit was that it had been perturbed by a close (approximately 800 AU) pass by another star in the first 100 million years or so of the Solar System's existence.

[81] Caltech researchers Konstantin Batygin and Mike Brown have hypothesized the existence of a super-Earth planet in the outer Solar System—Planet Nine—to explain the orbits of a group of extreme trans-Neptunian objects that includes Sedna.

[30][57] In 2007, astronomer Megan Schwamb outlined how each of the proposed mechanisms for Sedna's extreme orbit would affect the structure and dynamics of any wider population.

[87] Subsequent simulations incorporating the new data suggested about 40 Sedna-sized objects probably exist in this region, with the brightest being about Eris's magnitude (−1.0).

[90] With a perihelion of 65 AU and an even more distant orbit with a period of 40,000 years, its longitude of perihelion (the location where it makes its closest approach to the Sun) appears to be aligned with the directions of both Sedna and 2012 VP113, strengthening the case for an apparent orbital clustering of trans-Neptunian objects suspected to be influenced by a hypothetical distant planet, dubbed Planet Nine.

[106] It was calculated in 2011 that a flyby mission to Sedna could take 24.48 years using a Jupiter gravity assist, based on launch dates of 6 May 2033 or 23 June 2046.