Atira asteroid
An Atira asteroid orbits entirely inside Earth's orbit, never coming farther from the Sun than Earth does.
An Atira asteroid has its whole orbit inside Earth's, with its farthest point from the Sun less than about 0.983 astronomical units. Atiras are sometimes called inner-Earth objects.
They are hard to find because they always appear fairly close to the Sun in our sky, visible only in twilight. The first confirmed Atira, 163693 Atira, was discovered in 2003. Only a few dozen are known. In January 2020 the Zwicky Transient Facility found 2020 AV2, the first asteroid known to orbit entirely inside the orbit of Venus, sometimes called a vatira.
Atiras cannot hit Earth on their present orbits, but over long periods their paths may evolve. Understanding the population helps complete the census of objects near Earth. Space telescopes looking from positions away from Earth can search the sky close to the Sun more easily than ground-based ones.
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