";s:4:"text";s:3141:"The 4:7 resonance in particular has large instability. Although the centaurs share a reddish or neutral coloration with many SDOs, their nuclei are bluer, indicating a fundamental chemical or physical difference.Following the discovery of the planet Neptune in 1846, there was considerable speculation that another planet might exist beyond its orbit. 1) Classification: Sedna is a Trans-Neptunian Object (TNO), which just means that it is an object out past Neptune. Its discoverer Michael E. Brown has suggested instead that it should be considered an inner Oort-cloud object rather than a member of the scattered disc, because, with a perihelion distance of 76 AU, it is too remote to be affected by the gravitational attraction of the outer planets. The Oort cloud lies beyond the scattered disc. Sedna is well beyond the Kuiper Belt which lies at roughly 30-55 AU. Although the centaurs share a reddish or neutral coloration with many SDOs, their nuclei are bluer, indicating a fundamental chemical or physical difference.Rodney S. Gomes, Julio A. Fernandez, Tabare Gallardo, Adrian Brunini (2008). The Minor Planets Center lists Sedna as an SDO (Scattered Disc Object).