Near-Earth Asteroids


Learning GoalsThe goal of this lab is to use observations to determine properties of aаnear-earth object (NEO) and the effect an impact produced by one can have.

Suggested Observations:аa near-earth asteroid (NEO) that is currently near Earth in its orbit - A list of NEOs and their distances can be found on the Minor Planet Center website.

Challenge: а

Determine the size of an asteroid from astronomical images.

Resources: аWorksheetImagesImpact: Earth

Terminology:аmeteor, meteoroid, meteorite, impactor

Tutorials: аnone



Impact craters are the dominant landforms on many solid Solar System objects. Although the Earth’s active surface processes quickly destroy the impact record, about 170 terrestrial impact craters have been identified. These range in diameter from a few tens of meters up to about 300 km, and in age from recent times (e.g. the Sikhote-Alin craters in Russia whose creation were witnessed in 1947) to more than two billion years.

Impact cratering involves high velocity collisions between solid objects, typically much greater than the velocity of sound in those objects. Such hyper-velocity impacts produce physical effects such as melting and vaporization that do not occur in familiar sub-sonic collisions. The velocity of impacts on Earth range from 11 km/s (escape velocity) to more than 70 km/s, with the median impact velocity on Earth being about 20 to 25 km/s.

In impacts at these speeds, both impactor and the material impacted are rapidly compressed to high density. Following initial compression, the high-density, over-compressed region rapidly depressurizes, exploding violently. Since craters are caused by explosions, they are nearly always circular – only very low-angle impacts cause significantly elliptical craters. The impact process is divided conceptually into three stages: (1) initial contact and compression, (2) excavation, (3) modification and collapse.

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