Asteroids, Comets, and Meteors: A Celestial Guide

Near Earth Asteroids (NEAs)

Asteroids that cross the orbits of inner planets.

Comets

Icy counterparts to asteroids, formed beyond the frostline.

Kuiper Belt

Objects outside the orbit of Neptune to the beginning of the Oort Cloud.

Asteroids

• Small, naturally formed solid bodies that orbit the Sun.
• Airless and show no detectable outflow of gas or dust.
• 18 different compositional types, ranging from solid metal to soggy dirt clods.
• Most are"rocky" consisting of common minerals and free metal. -"Iron" composed of almost pure metal (mostly iron and nickel). -"Carbonaceous Chondrite" composed of rocky material and carbon-rich compounds.

Asteroid Facts

• Rocky leftovers of planet formation.
• Largest is Ceres, diameter ~1,000 km.
• 150,000 in catalogs, and probably over a million with diameter >1 km.
• Small asteroids are more common than large asteroids.
• All the asteroids in the solar system wouldn't add up to even a small terrestrial planet.

The Asteroid Belt

• Jupiter's gravity disrupts the orbits of asteroids with periods of an integer fraction of Jupiter's.
• Orbital resonances created gaps... like in Saturn's rings, known as the Kirkwood gaps.
• This explains why no planet formed in the asteroid belt.

Origin of Meteorites

• Meteorites come from asteroids.

What Do We Learn from Meteorites?

What the original planetesimals were like.When solar system formation began.What asteroids are like on the inside.Proof that differentiation and volcanism happened on asteroids. Characteristics:Fusion Crust :Glassy, thin (~ 1mm) melted surface covering a meteorite,Metal: 95% of all meteorites have free iron*Density and Magnetism:Since most have iron, meteorites to be on the high side of density for most rocks.Also they tend (mostly) to be magnetic*Chondrules:Chondrules are millimeter sized bb-like grains.*Comets:Formed beyond the frostline, comets are icy counterparts to  asteroids.“Dirty snowballs” = the nucleus,Most comets remain perpetually frozen in the outer solar system. Only a few enter the inner solar system, where they can grow tails,A comet can only visit the Sun a few hundred times before losing all its ice to sublimation,the comet may then disintegrate,or the rocky remains may stick together as an asteroid,When a comet nears the Sun, its ices can sublimate into gas and carry off dust, creating a coma and long tails.*Meteors:Glowing light created by friction heating of a meteoroid as it enters the atmosphere.  These are typically small (dust-sized) and moving fast (12-70 km/s).Meteors typically burn up at about 90 km above the surface.Earth is impacted by an estimated 25 million small particles each day which cause meteors. When the Earth passes through the orbit of a comet, we get a meteor shower.upward of 1 meteor per minute from one location.Normal meteor rates are about 5-10 per hour visible from any dark location.  Meteor “storms” can have over 100,000 per hour.*Meteor Showers:Watching meteor showers can be thrilling (witness the 1833 meteor storm over the eastern US) or deadly dull,