asteroids Flashcards
what is an asteroid
relatively small rock (1000km or less) or metal-rich planetary object orbiting the sun
- most asteroids are in the asteroid belt: main belt asteroid
- some in earth crossing orbits: most concerning
what is a comet
a small (10km or less) ice and dust rich object orbiting the sun
- formed out beyond jupiter
- reside in outer solar system (kuiper belt and oort cloud)
- further out, knocked into inner solar system near the sun, ice on the inside sublimates, forms a tail
- sit in sky for many days at a time
what is a meteor
atmospheric phenomenon created by a meteoroid in transit through atmosphere; streak of light you see in sky
- cannot hold in hand
- shooting star or fireball
what is a meteoroid
rock that enters the earth’s atmosphere from space, before it reaches the earth’s surface (the ground); still in sky, not on ground
- enters at 58000 to 150000km/hr)
- slows down, fragments, friction produces heat and light
what is a meteorite
particle of solid matter that has fallen to earth, the moon, or another planet from space
- most derived from asteroids in asteroid belt
- on earth, an extraterrestrial rock
- has survived becoming a meteor and is now on earth
what is a fireball?
exceptionally bright meteor
- heat with friction from atmosphere produces light and different colors common
- stops being bright 20km in altitude
- terminal speed of 200km/hr
describe the order in which a rock from space comes and lands on earth?
meteoroid (space) –> meteor (atmosphere) –> meteorite (earth)
what happens if meteoroid loses its cosmic velocity (velocity relative to the earth, 60,000km/hr)?
ablates / erodes completely
- fragments, slows –> meteorites
- no significant damage
what happens if the meteoroid retains its cosmic velocity (relative to earth, 60,000km/hr)?
impacts the earth at >12km/sec
- creates an impact crater
what does NEO stand for and mean?
near earth objects
- asteroids or comets
- brings them within 50 million km of earth
what does PHA stand for and mean
potentially hazardous asteroids
- come within 7.5 million km of earth
- greater than 140m across (significant regional / global damage)
- bennu and ryugu (rubble piles)
when something is within __X the earth-moon distance, it is a PHA?
20
who are the most massive asteroid residents on the main belt?
ceres and vesta
- investigated in DAWN mission
- protoplanets
what are asteroids physical characteristics
irregularly shaped, though a few are nearly spherical, and they are often pitted or cratered
- basins
- can contain some water / ice
what is the importance of asteroid sample return
- compare properties to meteorites and identify common parent bodies / processes
- provide links between asteroids and meteorites
- provide info on PHAs
