1862 Apollo:
and the Earth-Grazers
- Apollo asteroids named for 1862 Apollo.
- It is a tiny - 1.5 km (1 mile) in diameter.
- 1862 Apollo is a classic example of this group.
- Apollo asteroids are related to Amor asteroids.
- These cross the orbit of Earth.
- Closest to the sun is typically 0.5-0.9 AU.
- Farthest extent of their elliptical orbits are:
- Typically 2-4 AU from the Sun.
- Usually in the Asteroid Belt.
- Referred to as "Earth-Crossers" or "Earth-Grazers."
- Some pass very clsoe to Earth.
- Related to another phenomenon - Meteorites.
- They are essentially giant meteroids.
- Largest known are about 8-10 km (5-6 miles) in diameter.
- Nearly all are larger than 1 km.
- Many smaller Apollo asteroids also exist:
- Most of these are too small to be seen via telescope.
- Very numerous - many hit the Earth each year.
- These break into pieces in the atmosphere.
- They strike the ground as meteorites.
- Spectroscopic stuides reveal many differnt rock types.
- All very similar to asteroids of the main belt.
- Also match rock types of the various meteorites.
- Some almost perfectly match spectroscopic properties of common meteorites.
- Some Apollo asteroids likely to be fragments of main-belt asteroids.
- Orbits may have been originally altered by Mars or Jupiter until they became Earth-Grazers.
- Some may even be burned-out cores of comets.
- Fresh comets are believed comprised of ice with a certain amount of rocky material.
- Orbits of comets often altered by planets of inner solar system.
- Continued orbit within the inner system causes ices to eventually evaporate or sublime into space.
- Rocky material remains in a loosely consolidated clump.
- Apollo asteroids do occasionally impact the Earth.
- 1908: an A-bomb-sized asteroid crashed in Siberia.
- Heard 600 miles away.
- Trees flattened for a radius of 9 miles around impact site.
- Statistically, large impacts occur about every century or so.
- Most usually occur in the ocean.
- Little or no historical record exists.
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