Impacts Flashcards
what is an asteroid?
a small (less than 1000 km) rock/metal rich body orbiting the sun
how many asteroids exists? vs the number identified?
millions vs 10,000
most asteroids are in the asteroid belt (some are near earth orbits). where is the belt?
between mars and jupiter
what is a comet?
a small (less than 10 km) ice & dust object orbiting around the sun
where are comets formed? where do they reside?
-past the orbit of jupiter
-outer solar system (Kuiper Belt -neptune and Oort Cloud)
what is a meteroite? there are two meanings. (on earth vs techinically)
-on earth: an extraterrestial rock
-technically: solid matter that has fallen to earth, moon, or other planet
what is a meteoroid? speed?
rock that enters the atmosphere from space (before it hits the ground)
16-42 km/s (58000-150000 km/h)
what happens as a meteroid enters the atmosphere?
it slows and fragments because of friction (produce light of different colour and heat)
what is a meteor?
the atmospheric phenomenon created by meteoroid (aka the light, aka shooting star, aka fireball)
what is a fireball?
a really bright meteror (light of different colours)
how many meteroites per day?
100 tons/day
what happens with meteoroid loses its cosmic velocity
ablate completely, fragments, slows —> meteorites (no reall damage)
what happens with meteoroid keeps its cosmic velocity
impacts surface at more than 12km/s -> impact crater
what is the source for most meteroites?
asteroids (hazardous if close to earth and large enough)
what are NEOs
Near Earth Objects (asteroids or comets)
whose orbits bring them within 50 million km of
Earth.
what are PHAs
Potentially Hazardous Asteroids, that come
within 7.5 million km of Earth and are > 140 m
across
what are largest resident of the belt?
ceres (946 km)
vesta (525 km)
they are protoplanets
what is the dawn mission?
mission by nasa launched in sep 27, 2007 using ion propulsion engine to investigate the asteroids vesta and ceres (ended nov 1, 2018)
what did dawn capture?
colour photograph, topographic map, elemental and mineral composition, gravity field
vesta has two impact basins. what are they?
-Rheasilvia’s central peak is more than twice the height of Mt. Everest (500 km , 1 bya)
-veneneia (400 km, 2 bya)
vesta has a core of ____ km diamater
220
ceres before dawn mission suggested what?
featureless ball (75% rock and the rest ice)
dawn mission:ceres
similar crater pop’n as vesta but large basins are not present
ceres hidden interior
-icy crust indicates differentiation
-strong shell (40-50 km thick) made of ice, salts, silicates with soft muddy mantle Irocky)
OSIRIS-REx mission
sampled bennu asteroid (rubble pile has breccias)
bennu mineral composition? ejection? spin rate? age?
-hydrated mineal (chondrites)
-ejected particles into space
-spin rate increasing over time
-100 million to 1 billion
what is a rubble pile asteroid?
asteroid made from other asteroids
Bennu and Ryugu are ____
PHAs
Sample return from Ryugu and Bennu can:____ (2)
– Provide links between asteroids and meteorites
– Provide information on the physical properties of PHA
Ryugu is most like a -_______
CI chondrite meteorite
the moon was formed by what?
giant impact 50 ma after earth was formed
how many craters formed on mars in the last 10 years
400
bolide aka ____
meteorite/comet
what are the stages of impact cratering
Compression (Shock wave expands out from
point of impact, Compresses rock to 1/3 its usual
volume, Rock can flow like a fluid)
Excavation (decompression wave follows shock front, target rock and bolide vaporized, flow, spray out of transient cavity, eject ravels out as conical sheet, crater rim overturned)
Modification (larg ones only, gravity can’t sustain cavity so walls slumps and central uplift occurs)
the bolide is typically _____ in impact
destroyed
features of impact cratering
- Ejecta blanket, (sometimes) rays
- Overturned rim
- Impact melt sheet
- (sometimes) Central uplift (peaks or rings)
ejecta rays, secondary craters,
tektites (glass)
breccia
The Cretaceous-Paleogene (K-Pg) Impact Event
-hit yucatan peninsula, 66 mya
-tsunami (global)
-melted rock falling = fires
-75 % of plant and animals species died out
crater: chicxulub is 180 km (one of largest on earth)
hazard vs risk
-something that may cause death, injury or other impacts (can be single, sequential)
-probability that hazard causes damage
hazards are either anthropogenic or non-anthropogenic?
-war, global warming, famine etc.
-pandemic (kinda), solar flar, volcanism, impact
What can we do to mitigate the risk of impact?
- OBSERVE (The more we look, the more we can identify PHAs and determine their orbits)
- Plan (Since 2013 there have been >10 exercises involving hypothetical simulations carried out by the planetary defense community)
- Prepare (Develop technology to deflect a PHA)
There are ~_____impact craters recorded in Earth’s crust
-200
The NASA DART Mission
-►Double Asteroid Redirect Test (NASA first planetary defence mission)
purpose: show that asteroid could be deflected by kinetic impact
