Definition

Noun: An Apollo asteroid is a specific class of near-Earth asteroid. Its defining characteristic is an orbital path that crosses Earth's orbit around the Sun. These asteroids have orbital periods greater than one year and semi-major axes larger than one astronomical unit (AU), meaning their average distance from the Sun is greater than Earth's.

Usage

The term is used in astronomy to categorize and discuss asteroids based on their orbital parameters and potential for close approaches to Earth. * Astronomers are tracking a newly discovered Apollo asteroid to refine its trajectory. * The Chelyabinsk meteor was caused by a small Apollo asteroid entering Earth's atmosphere.

Advanced Usage

• Planetary Defense Context: Apollo asteroids are of particular interest in planetary defense studies due to their Earth-crossing orbits, which classify them as potentially hazardous objects (PHOs) if they are large enough and pass close enough to Earth.
  • The conference focused on mitigation strategies for a hypothetical impact from an Apollo asteroid.

Variants and Related Words

• Amor asteroid: A class of near-Earth asteroids whose orbits approach but do not cross Earth's orbit; they have perihelion distances between 1.017 and 1.3 AU.
• Aten asteroid: A class of near-Earth asteroids with orbits mostly inside Earth's orbit; they have semi-major axes less than 1 AU and aphelion distances greater than 0.983 AU.
• Potentially Hazardous Asteroid (PHA): A designation for asteroids (which can include Apollo asteroids) that come within a certain minimum distance of Earth and are large enough to cause significant regional damage upon impact.

Synonyms

• Earth-crossing asteroid (This is a descriptive synonym, though "Apollo asteroid" is the formal scientific classification.)
• Near-Earth Asteroid (NEA) (This is a broader category that includes Apollo, Amor, and Aten asteroids.)

Related Concepts

• Orbital crossing: The key characteristic of an Apollo asteroid is that its orbital path intersects with Earth's orbital path around the Sun.
• Semi-major axis: A fundamental orbital element used to define an Apollo asteroid (must be > 1 AU).
• 1566 Icarus: A famous example of an Apollo asteroid.

Noun

1. an asteroid whose orbit crosses the Earth's orbit