**Sedna (dwarf planet)**
**Definition**
Sedna is a large trans-Neptunian object and a likely dwarf planet located in the outer reaches of the Solar System. Discovered in 2003, it is notable for its extremely distant and elongated orbit, which takes it far beyond the Kuiper Belt into the inner Oort Cloud region.
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## Sedna (dwarf planet)
### Introduction
Sedna is one of the most distant known objects orbiting the Sun and is classified as a likely dwarf planet due to its size and shape. It resides in a region of space beyond the Kuiper Belt, often referred to as the inner Oort Cloud or the extended scattered disc. Its discovery in 2003 expanded our understanding of the Solar System’s outer frontier and raised questions about the formation and evolution of distant small bodies.
### Discovery
Sedna was discovered on November 14, 2003, by a team led by Michael E. Brown, Chad Trujillo, and David L. Rabinowitz at the Palomar Observatory in California. The discovery was made using the Samuel Oschin Telescope during a survey aimed at finding distant Solar System objects. The object was initially designated 2003 VB12 before being named Sedna, after the Inuit goddess of the sea.
### Naming
The name Sedna was chosen to reflect the mythological figure from Inuit culture who is the goddess of the sea and marine animals. This name was fitting given Sedna’s remote and cold environment, analogous to the deep, icy waters of the Arctic. The International Astronomical Union (IAU) officially adopted the name in 2004.
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## Physical Characteristics
### Size and Shape
Sedna is estimated to have a diameter of approximately 995 kilometers (about 618 miles), making it one of the largest known trans-Neptunian objects. Its size places it within the range of objects considered likely to be in hydrostatic equilibrium, a key criterion for dwarf planet status. However, its exact shape and size remain uncertain due to its great distance and faintness.
### Surface and Composition
The surface of Sedna is extremely red in color, one of the reddest among known Solar System bodies. This coloration is thought to be caused by the presence of complex organic molecules called tholins, which form when solar radiation and cosmic rays interact with simple carbon-containing compounds like methane and nitrogen ices. Spectroscopic observations suggest that Sedna’s surface is covered with a mixture of water ice, methane ice, and nitrogen ice.
### Temperature
Due to its vast distance from the Sun, Sedna’s surface temperature is extremely low, estimated to be around 12 Kelvin (-261 degrees Celsius or -438 degrees Fahrenheit). This makes it one of the coldest known objects in the Solar System.
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## Orbit and Rotation
### Orbital Characteristics
Sedna has an exceptionally elongated and distant orbit, with a perihelion (closest approach to the Sun) of about 76 astronomical units (AU) and an aphelion (farthest distance) estimated at around 937 AU. One AU is the average distance between the Earth and the Sun, approximately 150 million kilometers (93 million miles). Sedna’s orbital period is roughly 11,400 years, meaning it takes over ten millennia to complete one orbit around the Sun.
### Orbital Inclination and Eccentricity
Sedna’s orbit is highly eccentric, with an eccentricity of approximately 0.85, and inclined about 11.9 degrees relative to the ecliptic plane. This unusual orbit places Sedna far beyond the Kuiper Belt and scattered disc populations, suggesting it may be part of the inner Oort Cloud.
### Rotation
The rotation period of Sedna is not precisely known, but estimates based on light curve observations suggest it rotates approximately once every 10 to 20 hours. Its rotation period and axial tilt remain subjects of ongoing research.
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## Classification and Status
### Dwarf Planet Status
Sedna is considered a likely dwarf planet due to its size and probable hydrostatic equilibrium. However, it has not been officially classified as such by the International Astronomical Union (IAU), partly because of limited observational data. Its size is comparable to other recognized dwarf planets such as Haumea and Makemake.
### Trans-Neptunian Object and Inner Oort Cloud Member
Sedna is classified as a detached object or inner Oort Cloud object, distinct from typical Kuiper Belt objects. Its orbit is too distant and elongated to be influenced significantly by Neptune, suggesting a different origin or dynamical history.
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## Origin and Formation Theories
### Formation in the Early Solar System
Sedna’s unusual orbit challenges traditional models of Solar System formation. It is believed to have formed closer to the Sun and later scattered outward by gravitational interactions. However, its current orbit is too distant and stable to be explained solely by interactions with the known giant planets.
### Possible Perturbations
Several hypotheses have been proposed to explain Sedna’s orbit:
– **Stellar Encounter:** A passing star in the Sun’s birth cluster may have perturbed Sedna’s orbit, sending it into its current distant trajectory.
– **Planet Nine Hypothesis:** The presence of an undiscovered massive planet in the outer Solar System, often referred to as Planet Nine, could gravitationally influence Sedna and other distant objects.
– **Solar System Capture:** Sedna might be a captured object from another star system during the Sun’s early history in a dense stellar cluster.
### Implications for Solar System Structure
Sedna’s discovery suggests the Solar System’s boundary is more complex than previously thought, with a population of distant, detached objects that may represent the inner edge of the Oort Cloud. Studying Sedna and similar bodies provides insight into the Solar System’s formation environment and the processes shaping its outer regions.
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## Exploration and Observation
### Observational Challenges
Sedna’s great distance and faintness make it difficult to observe with ground-based telescopes. Its apparent magnitude is about 20.5, requiring large telescopes and sensitive instruments for detailed study.
### Space Missions
No spacecraft has yet been sent to Sedna, and its extreme distance poses significant challenges for future missions. However, Sedna remains a target of interest for potential flyby or rendezvous missions that could provide direct measurements of its surface, composition, and environment.
### Future Observations
Ongoing and future surveys with advanced telescopes, such as the James Webb Space Telescope and large ground-based observatories, aim to refine Sedna’s physical and orbital parameters. These observations will help clarify its status and role in the Solar System.
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## Significance in Astronomy
### Understanding the Outer Solar System
Sedna’s discovery has expanded the known boundaries of the Solar System and highlighted the existence of a population of distant, detached objects. These bodies provide clues about the Solar System’s early environment and the processes that shaped its architecture.
### Constraints on Planet Nine
Sedna’s orbit is one of the key pieces of evidence supporting the Planet Nine hypothesis. Its unusual trajectory cannot be easily explained without invoking additional gravitational influences beyond the known planets.
### Insights into Solar System Evolution
Studying Sedna helps astronomers understand the dynamical evolution of small bodies and the interactions between the Solar System and its galactic environment. It also informs models of planet formation and migration.
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## Summary
Sedna is a distant, large trans-Neptunian object with an exceptionally elongated orbit that places it in the inner Oort Cloud region. Discovered in 2003, it is a likely dwarf planet with a reddish surface rich in organic compounds. Its unique orbit challenges traditional models of Solar System formation and suggests the presence of additional gravitational influences, such as a hypothetical Planet Nine or past stellar encounters. Sedna remains an object of great interest for understanding the outer Solar System’s structure and history.
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**Meta Description:**
Sedna is a distant trans-Neptunian object and likely dwarf planet with an elongated orbit in the inner Oort Cloud. Discovered in 2003, it provides key insights into the Solar System’s outer frontier and formation history.