Chapter 6 Flashcards
What is the name of a solid particle in orbit about the Sun: composed of silicates and hydrocarbons; typically lower density than common terrestrial rock?
Meteoroid
A meteoroid which survives entry into atmosphere and lands on Earth’s surface
Meteoroite
The light heat and sound phenomena produced when a meteoroid enters the Earth’s atmosphere and is heated through collision with air molecules
Meteor
Groups of meteoroids which move in
similar orbits after being ejected from a comet
Meteor Stream
When a meteor stream’s orbit intersects with Earth’s to produce meteors
Meteor Shower
A short-lived, usually strong meteor shower usually occurring at the perihelion passage of the parent comet
Meteor Storm
What are the 2 sources of meteorites?
Comets and asteroids
Where do small meteoroids come from?
Comet nucleus release silicate and other solids as they pass near the sun (dust tails)
When does gas vaporization stop turn into dust tail?
Around 1.5 to 2 AU
How many major meteor shower are their in one year?
13 major showers
Do small meteors ever reach the Earth’s surface?
No, they entirely turn to vapor in the Earth’s atmosphere, atoms are exited and radiate away as they relax
What is a sporadic meteoroid?
A meteoroid that used to be part of a stream, but has diffused away from the stream after a long period of time
What is the size at which a metor is too small to vaporize and survives to surface?
Less than 10 mu*m
What size meteors have portions which survive to the surface?
a few cm to tens of m (depends on initial velocities, >30km/s will totally ablate)
What is the primary source of meteorites?
Asteroid collisions (can send large particle into Earth’s orbit)
How many “fireballs” have be perturbed out of the asteroid belt?
Approx 25 have been recorded
What is ablation?
Vaporization due to firction with the atomsphere
Why are meteorites cold when they impact?
They move so fast that only the outer mm to cm are melted, when the reach the upper atmosphere they are in “dark fall” and cool down
What are the 4 major types of meteorites found?
Stony (chondrites/achondrites), Irons (Fe and Ni), Stony-Irons (mix of rock and metal), Lunar/Martian
Which of these subcategories fall under undifferentiated?
Chondrites (the rest are differentiated)
What is the difference between differentiated and undifferentiated meteorites?
Undifferentiated - unheated, differentiated - heated
Where are “old” meteorites found?
Found in hot or cold deserts (harder to spot)
How many “new” meteorites are found each year?
Approx 6, found all over the world
What percent of the SS meteorites are Stony?
Approx 60%
Which type of meteorite is the oldest?
Chondrites, grains (condrules) condensed out of the SS approx 4.5 billion years ago
how large does a pp have to be fore rock to begin melting?
It muct be greater the 100 km across
What is differentiation?
As rocks melt, heavier elements (ie. iron) sink to the center and lighter rock rises the the surface
What percent of SS meteorites are Iron? Where do they come from?
Approx 5% , come from broken, cooled down cores of larger bodies
What are regmeglypts
Thumb-print like depressions on iron meteroites, formed when melting in their Earth-decent
What are Widmanstatten patterns
Patterns made in pure iron-nickel alloy that occurs only in very slow cooling
What percent of SS meteorites are Stony-iron?
About 10%, can be very difficult to distinguish from just their surface
What type of meteorites do Lunar meteorites fall under?
Achondrites, most common are anothositic breccias (rich in Al-Ca)
How do we know which meteorites come from the moon?
Lunar meteorites all have composition similar to the samples taken from the Apollo Mission
Which planet is the only one whose meteorits have been found?
Mars, although its strong gravity makes it them more rare than lunar
Why is ALH84001.0 special?
It is the oldest/ largest Martian meteorite ever found, was thought to contain fossil bacteria (not believed anymore)
What are the 3 distinct ages of meteorites?
Formation (time since it was liquid/gas), Gas retention (last shocked/ strongly heated), Cosmic Ray Exposure
What was the largest meteoric impact in history?
The Tunguska Effect (June 30th, 1908)
On what scale would the damage be if Earth was impacted by a meteor 100m to 1km in diameter?
Country to continental scale
What diameter must an asteroid be to cause dust to be ejected into the atmosphere and cool the Earth?
Diameter >1km
About how many >1km diameter meteors cross the Earth’s orbit? How often should the globe be concerned?
Approx 1000, once every million years
How often should there be “local” concern for meteor impact?
Once every 1000 years, on average
What is currently the best strategy for avoiding meteor impact?
Improve out ability to detect these objects (bigger telescopes and better cameras)
