Ch 19 Homework - Meteorites and Comets

Meteorites, Asteroids, and Comets

• Most falls are stony meteorites, but most finds are iron meteorites due to stony meteorites being less weather-resistant and resembling Earth rocks.
• Meteor showers' radiants reveal sources of meteoroids, located where Earth crosses comet debris trails.
• Widmanstätten patterns in iron meteorites indicate slow cooling, suggesting some meteorites originated inside large bodies.
• Carbonaceous chondrites are rich in volatiles, providing the best samples of the solar nebula.
• Chondrites come from undifferentiated bodies; they are primitive and have not undergone significant changes.
• Short-lived radioactive isotopes like aluminum-26 are suspected as the heat source that melted small planetesimals (around 20 km wide).
• Evidence shows that meteorites are pieces of recently broken planetesimals.
• Despite most meteorites being asteroidal, most meteors can be cometary.
• Kirkwood gaps in the asteroid belt are formed due to orbital resonances with Jupiter, affecting asteroid distribution.
• Apollo and Amor objects are likely ejected asteroids from the Kirkwood gaps, as their orbits are unstable.
• The Hirayama families of asteroids share common origins and physical properties, grouping them together based on similarities.
• Objects in the Oort cloud are believed to have formed near the orbits of Uranus and Neptune.
• Asteroids can be categorized into three classes based on their infrared reflectance spectra: C-type (carbonaceous chondrites), S-type (most common stony meteorites), and M-type (iron meteorites).
• Comets are considered loosely consolidated mixtures of ice and rock due to their structure and behavior.
• Long-period comets exhibit randomly inclined orbits, differing from those of short-period comets.
• The impact that likely caused the extinction of the dinosaurs left a significant crater in northern Yucatan.
• A flaw in the falling-comet hypothesis for the Tunguska event is that small comet bodies would vaporize high in the atmosphere, rather than impacting the ground.
• Iron meteorites are the most commonly found type, whereas stony meteorites are the most commonly fallen.
• Despite being the most common meteorite type, stony meteorites are hard to find on Earth due to their resemblance to terrestrial rocks.
• The major source of meteoroids in meteor showers is comets, evidenced by tracking meteoroid origins back to comet orbits.
• Most meteors originate from comets, while most meteorites derive from asteroids.
• The origin of meteors and meteorites can be determined through observation and analysis of their characteristics.
• In Antarctica, ice flow concentrates meteorites, making stony meteorites easier to find on the ice compared to soil elsewhere.