What Does an Impact Look Like?
Our early solar system was littered with the left-over building blocks of planets, called “planetesimals,” that were hitting the surfaces of everything that existed at the time - the planets, moons, asteroids and comets.
The period of heavy bombardment, estimated to have occurred between 4.1-3.8 billion years ago, must have looked like chaos! A large fraction of the impacts in the solar system occurred during this time. Impacts have continued throughout the history of the solar system, just at lower rates. Most of the impacting objects vaporize in the process, leaving only small fragments scattered over a wide area.
What happened at Barringer Meteorite Crater?
About 50,000 years ago a meteorite traveling about 15km/s (54,000km/h or 33,500 mph) slammed into what is now the Arizona desert, creating a hole about 180 meters (590 feet) deep and 1.2 kilometers (.75 mile) wide. The meteorite was composed of nickel-iron and thought to be about 30-50 meters (98-164 ft) across, weighing about 270,000 metric tons (300,000 tons). The force of the explosion was about 150 times the force of the bomb that destroyed Hiroshima, equal to 2.5 megatons of TNT!
In July 1994, Comet P/Shoemaker-Levy 9 crashed into Jupiter - this was the only time we have been able to actually observe a planetary impact. The rest of the time, scientists who study impacts must rely on models and experiments to help them understand impact processes. Watch the videos below to observe what happens as an impactor crashes into a surface using a water drop simulation and complex impact computer models.
Videos from the Planetary Science Institute
The following simulations illustrate computer models of asteroid impacts. In both cases, the simulation shows an asteroid with a diameter of 12 km, moving at 20 km/s at a 45-degree angle to the Earth. The different colors show the level of shock suffered by the material the asteroid hits: At the magenta/blue end of the spectrum, the material is broken up and starting to melt; at the red end, it is beginning to vaporize.
Computer simulation: Asteroid hitting land surface (AVI, 6.5 Mb)
(click to download)
Computer simulation: Asteroid hitting deep ocean (AVI, 5.9 Mb)
(click to download)
Where On Earth Are the Impacts? A Scavenger Hunt!
When you look at the Moon, Mars, or Mercury, it’s easy to see the craters on their surfaces. The Earth was also bombarded, yet the evidence for impact events is not easy to see. Processes such as plate tectonics, erosion, and metamorphism have altered the surface of Earth throughout its history. The Earth has impact craters scattered across its surface. Some are exposed and easily identifiable (like Barringer Meteorite Crater). Others have become eroded or hidden by vegetation, water, or metamorphism. Where on Earth are they? You can look for them in the Earth Impact Database or by using this interactive map.