Trans-Neptunian object

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TheTransneptunians 73AU

Euler-Diagram bodies in the Solar System

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TheTransneptunians Color Distribution

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Trans-Neptunian objects (TNOs) are minor planets in the Solar System that orbit the Sun at a greater average distance than Neptune, the eighth and farthest known planet from the Sun. These objects reside in the Kuiper Belt, the Scattered Disc, and the Oort Cloud, which are regions filled with icy bodies and remnants from the early Solar System. The study of TNOs provides valuable insights into the formation and evolution of the Solar System, as well as the composition of the early solar nebula.

Discovery and Exploration

The first TNO, Pluto, was discovered in 1930 by Clyde Tombaugh. For many years, Pluto was considered the ninth planet of the Solar System until the discovery of similar-sized objects in the Kuiper Belt led to its reclassification as a dwarf planet in 2006. The discovery of the Kuiper Belt in the 1990s, starting with (15760) 1992 QB1, marked the beginning of the exploration of TNOs. Since then, thousands of TNOs have been identified, including notable objects like Eris, Haumea, and Makemake.

Classification

TNOs are classified into several groups based on their orbits:

• Kuiper Belt Objects (KBOs): These objects have orbits that are relatively close to the ecliptic plane and are further divided into the classical KBOs, which have more stable orbits, and the resonant KBOs, which are in orbital resonance with Neptune.
• Scattered Disc Objects (SDOs): These objects have highly elliptical and inclined orbits, suggesting they were scattered by Neptune's gravity.
• Detached Objects: Also known as extended scattered disc objects, these TNOs have orbits that are too far from Neptune to have been directly influenced by its gravity, suggesting other mechanisms for their current orbits.
• Oort Cloud Objects: Though not directly observed, these are theoretical objects believed to exist in a distant cloud surrounding the Solar System. Their existence is inferred from the long-period comets that enter the inner Solar System.

Physical Characteristics

TNOs are primarily composed of ices (such as water, methane, and ammonia) and rock. Their surfaces are often colored red due to the presence of tholins, organic compounds created by the irradiation of simpler compounds. The size of TNOs varies widely, from as small as 10 km in diameter to over 2,000 km for the largest known objects like Pluto and Eris.

Importance of Study

Studying TNOs is crucial for understanding the outer Solar System's dynamics and the distribution of small bodies beyond Neptune. These objects are considered pristine remnants from the formation of the Solar System, potentially holding clues about the early solar nebula's composition and the processes that led to the formation of planets and other solar system bodies.

Challenges in Observation

Observing TNOs poses significant challenges due to their small size, low brightness, and great distance from Earth. Advances in telescope technology and the development of specialized surveys have been crucial in identifying and studying these distant objects.