Atira asteroid
Atira asteroids or Apohele asteroids, also known as interior-Earth objects (IEOs), are asteroids whose orbits are entirely confined within Earth's orbit; that is, their orbit has an aphelion (farthest point from the Sun) smaller than Earth's perihelion (nearest point to the Sun), which is 0.983 astronomical units (AU). Atira asteroids are by far the smallest group of near-Earth objects, compared to the Aten, Apollo and Amor asteroids. Asteroids. The first suspected was , and the first confirmed, was 163693 Atira in 2003. , there are 28 known Atiras, of which 24 have robust orbit determinations, of  which seven have been computed with sufficient precision to receive a permanent number. An additional 127 objects (not listed below) have aphelia smaller than Earth's aphelion (Q = 1.017 AU). The Near Earth Object Surveillance Satellite is intended to find more. Atiras do not cross Earth's orbit and are not immediate impact event threats, but their orbits may be perturbed outward by a close approach to either Mercury or Venus and become Earth-crossing asteroids in the future. Although the dynamics of many of these objects somehow resemble the one induced by the Kozai-Lidov mechanism (coupled oscillations  in eccentricity and inclination), which contributes to enhanced long-term stability, there is no libration of the value of the argument of perihelion. Vatira asteroids. Vatira asteroids are a subclass of Atiras that orbit entirely interior to the orbit of Venus (whose perihelion q = 0.718 AU). The name "Vatira" is provisional, combining "Venus" with "Atira". They were theorized to exist at least since 2012, and in early 2020, the first Vatira asteroid was discovered: 594913 ꞌAylóꞌchaxnim. It was discovered on 4 January 2020 by the Zwicky Transient Facility. Its aphelion distance is only 0.656 AU. Being the prototype, its  name will be used to refer to this population. , it is the asteroid with the smallest known aphelion, followed by with Q = 0.774 AU and with Q = 0.794 AU. Vulcanoid asteroids. No asteroids have yet been discovered to orbit entirely inside the orbit of Mercury (q = 0.307 AU). Such hypothetical asteroids would likely be termed vulcanoids, although the term often refers to asteroids which more specifically have remained in the intra-Mercurian region over the age of the solar system. Name. There is no standard name for the class. Following the general practice to name a new  class of asteroids for the first recognized member of that class, some astronomers, and this article, use the designation "Atira asteroids". The name "Apohele" was proposed by the discoverers of . It is the Hawaiian word for orbit, from "apo" 'circle' and "hele" 'to go'; it was chosen partly because of its similarity to the words "aphelion (apoapsis)" and "helios". Other authors adopted the designation "Inner Earth Objects" (IEOs). Members. The following table lists the known and suspected Atiras . The sole known Vatira asteroid 594913 ꞌAylóꞌchaxnim has been highlighted in pink. The planets Mercury and Venus have been included for comparison  (grey rows).