An impact event is a collision between astronomical objects causing measurable effects. Impact events have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or meteoroids and have minimal effect. When large objects impact terrestrial planets such as the Earth, there can be significant physical and biospheric consequences, as the impacting body is usually traveling at several kilometres a second, though atmospheres mitigate many surface impacts through atmospheric entry. Impact craters and structures are dominant landforms on many of the Solar System's solid objects and present the strongest empirical evidence for their frequency and scale.
Damage to trees caused by the Tunguska event. The object, just 50–80 metres (150–240 feet) across, exploded 6–10 km (4–6 miles) above the surface, shattering windows hundreds of km away.
Frequency of small asteroids roughly 1 to 20 m in diameter impacting Earth's atmosphere.
A bolide undergoing atmospheric entry
Eugene Merle Shoemaker was first to prove that meteorite impacts have affected the Earth.
An asteroid is a minor planet—an object that is neither a true planet nor a comet—that orbits within the inner Solar System. They are rocky, metallic, or icy bodies with no atmosphere. The size and shape of asteroids vary significantly, ranging from small rubble piles under a kilometer across to Ceres, a dwarf planet almost 1000 km in diameter.
2013 EC, shown here in radar images, has a provisional designation
A composite image, to the same scale, of the asteroids imaged at high resolution prior to 2012. They are, from largest to smallest: 4 Vesta, 21 Lutetia, 253 Mathilde, 243 Ida and its moon Dactyl, 433 Eros, 951 Gaspra, 2867 Šteins, 25143 Itokawa.
Vesta (left), with Ceres (center) and the Moon (right) shown to scale
Phobos
