Impacts with Space Objects. Moon shows many impact scars though most are prior to 3.8 billion years ago. Earth destroys most evidence over time. Why?. ASTEROIDS Originate in the asteroid belt between Mars and Jupiter. Mostly pieces of rock and metals that never coalesced to form a planet.
Earth destroys most evidence over time. billion years agoWhy?
Mostly billion years agopieces of rock and metals that never coalesced to form a planet
They are part of the Kuiper belt, a flattened disk of comets made up of icy debris left over from the formation of the outer planets.
Make a complete orbit in <200 years. billion years ago
Haley’s Comet every ~75 years
Long-period comets billion years ago
They are part of the Oort cloud, a vast diffuse envelope of encircling comets. Period may thousands of years of more.
Energy release depends on speed and size.
Asteroids may impact at >30,000mph.
Long-period comets >150,000mph.
M-16 rifle ~2250 mph.
Given equal size, the mass of an asteroid is greater than that of a comet.
Atmosphere may heat the asteroid to 3,000 that of a comet.oC.
Impact instantly released enormous heat and energy, melting and vaporizing not only rock but also much of the asteroid itself.
Crater may end up filled with crushed and shattered rock.
Fragment Q impacts on Jupiter. There were 21 discernable fragments up to 2km diameter.
Impact from nickel-iron metallic meteorite (asteroid).
Diameter ~40m (120ft.).
Speed at impact ~27,000mph.
Crater floor holds 365m (870ft.) of shattered rock.
Tektites fragments up to 2km diameter.– glassy spherules formed by in-air-cooling of impact melted rock.
Happens with large asteroid impacts.
~5km (3mi) diameter asteroid
~70km (40mi) diameter crater
Extinction of Dinosaurs fragments up to 2km diameter.
~65 Million Years B.P.
Figure 17.25 fragments up to 2km diameter.
Probably a stony meteorite or comet possibly smaller than 40m in diameter.
Exploded 5 – 10km (3 – 6mi.) above the earth’s surface.
Figure 17.26 fragments up to 2km diameter.
Monitors and identifies near earth-objects for potential impact of objects >1km (.62mi.) diameter.
Average time interval between impacts of this size >100,000 years.
However, objects 40m(or less) – 100m in diameter can cause devastating local effects (like Tunguska).
Smaller potentially damaging events occur perhaps every couple of centuries.
Would we have warning before an impact? devastating local effects (like Tunguska).
Maybe, maybe not.
Near Earth Objects Tracking