The energy released by an asteroid impact is determined by its mass and velocity. Asteroids are denser than comets, which affects the impact’s consequences. Size, impact angle, and surface area also play a role. Large impacts can incinerate forests, bathe areas in magma, and block the Sun, leading to the collapse of food chains. Impacts larger than 20 km in diameter could wipe out complex life.
The most important factor determining the damage of an asteroid impact is the energy it releases upon impact. This is calculated by multiplying half the asteroid’s mass by the square of its velocity. The typical range of asteroid velocities is quite limited: most measured values are between 12 and 20 km/sec (7.5 – 12.4 mi/sec). Comets are much faster, ranging between 50 and 70 km/sec (31 – 43.5 mi/sec).
However, what asteroids lack in velocity, they make up for in density – while comets are thought to consist mostly of ice, with a density of only 1000kg/m3, asteroids made of solid rock have a density of around 3000kg /m3 , while the rarest metallic asteroids (8%) have a density of 8000 kg/m3. These density values intimately influence the final consequences of the asteroid impact.
Other factors that affect the environmental effects of an asteroid impact include its size (obviously), impact angle (most likely 45 degrees), and impact surface area (water, silicate or crystalline rock). The size of asteroids is distributed along a power law, where asteroids above a certain size are exponentially rarer than smaller ones.
Asteroids about a meter in diameter are thought to enter Earth’s atmosphere about once a month, leaving behind 100-foot (30 m) craters. Asteroids one kilometer in diameter impact only once every million years or so, releasing up to 100 gigatons of TNT, 200 times stronger than the most powerful nuclear weapon ever tested. Such an impact would shatter glass windows up to 500 km away, leaving a 20 km (12 mi) crater. The largest asteroid impact in the past 4 billion years is thought to be the asteroid that created Vredefort crater in South Africa, about 20 km (12 mi) in diameter.
Large asteroids do their damage in three ways: the initial airburst and heat wave, which can be strong enough to incinerate forests; the ejecta, which can bathe land-sized areas in magma, and the blocking of the Sun by soot particles in the upper atmosphere. The last factor is the most terminal to life, as without photosynthesis, food chains collapse and only decomposers and scavengers would be able to survive for more than a decade. In the case of impacts with asteroids larger than 20 km (12 mi) in diameter, scientists believe that all complex life (including all higher animals and plants) would be wiped out, leaving only microbes, similar to the situation on Earth about a year ago. billion years ago.
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