PHYSICS 20E Lecture Notes - Lecture 10: Escape Velocity, Low Mass, Robotic Spacecraft
Document Summary
Mass extinctions have occurred a number of times during the history of the earth. Sharp decrease in the number of species. 5 major events during the past 500 myr. Most recent one was late cretaceous mass extinction of asteroids. Largest was the great dying at the permian-triassic boundary 251 mya killed 98% of marine species and 77% of land species. Extinctions have the effect of opening up ecological niches and accelerating evolution. For <300m objects, if we have early warning of several years to a decade, a weighted robotic spacecraft could nudge the trajector enough to avoid impact. Nuclear standoff explosions required for more massive objects. 30-80% of neos are in orbits that cannot be reached by planned launch systems. Life on earth would not be possible without earth"s atmosphere. Atmospheric pressure drops by 50% for every 5. 6km you go up in altitude. Gases are made of molecule or atoms moving in random directions.
