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Sednoid

The orbits of the three known sednoids with Neptune's 30 AU circular orbit in blue.
The apparent magnitudes of the three known sednoids.
Discovery image of Sedna, the eponymous and first known sednoid

A sednoid is a trans-Neptunian object with a large semi-major axis and a high perihelion, similar to the orbit of the dwarf planet Sedna. The consensus among astronomers is that there are only three objects that are known from this population: Sedna, 2012 VP113, and 541132 Leleākūhonua (2015 TG387).[1] All three have perihelia greater than 60 AU.[2] These objects lie outside an apparently nearly empty gap in the Solar System and have no significant interaction with the planets. They are usually grouped with the detached objects. Some astronomers[3] consider the sednoids to be Inner Oort Cloud (IOC) objects, though the inner Oort cloud, or Hills cloud, was originally predicted to lie beyond 2,000 AU, beyond the aphelia of the three known sednoids.

One attempt at a precise definition of sednoids is any body with a perihelion greater than 50 AU and a semi-major axis greater than 150 AU.[4][5] However, this definition applies to objects such as 2013 SY99 and 2021 RR205,[6] which have perihelia beyond 50 AU and semi-major axes over 700 AU. Despite this, these objects are thought to not belong to the sednoids, but rather to the same dynamical class as 474640 Alicanto, 2014 SR349 and 2010 GB174.[7][1]

With their high eccentricities (greater than 0.8), sednoids are distinguished from the high-perihelion objects with moderate eccentricities that are in a stable resonance with Neptune, namely 2015 KQ174, 2015 FJ345, (612911) 2004 XR190 ("Buffy"), 2014 FC72 and 2014 FZ71.[8]

  1. ^ a b Cite error: The named reference Huang2024 was invoked but never defined (see the help page).
  2. ^ Cite error: The named reference JPL-sednoid was invoked but never defined (see the help page).
  3. ^ Cite error: The named reference Sheppard-Inner-Oort-Cloud was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference nature letter was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference Sheppard-Extreme was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference Sheppard-disc was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference Bannister2017 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference Like Buffy was invoked but never defined (see the help page).

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