Secondary crater

Likewise, bodies with higher resurfacing rates, such as Io, also do not record surface cratering.

This ejecta blanket, or broad area of impacts from the ejected material, surrounds the crater.

[6] Primary craters form from high-velocity impacts whose foundational shock waves must exceed the speed of sound in the target material.

However, they must still occur at high enough speeds to deliver stress to the target body and produce strain results that exceed the limits of elasticity, that is, secondary projectiles must break the surface.

[2] Mechanical properties of a target's regolith (existing loose rocks) will influence the angle and velocity of ejecta from primary impacts.

Research using simulations has been conducted that suggest that a target body's regolith decreases the velocity of ejecta.

The morphology of primary craters ranges from bowl-shaped to large, wide basins, where multi-ringed structures are observed.

[11] Most notably, impact craters are studied for the purposes of estimating ages, both relative and absolute, of planetary surfaces.

Dating terrains on planets from the according to density of craters has developed into a thorough technique, however 3 key assumptions control it:[2] Photographs taken from notable lunar and martian missions have provided scientists the ability to count and log the number of observed craters on each body.

Scientists are finding it difficult to sort out all the secondary craters from the count, as they present false assurance of statistical vigor.

However, in a study published in the Geological Society of America Bulletin the authors describe a field of secondary impact craters they believe was formed by the material ejected from a larger, primary meteor impact around 280 million years ago.

MESSENGER image of secondary craters surrounding a primary impact site.
Cartoon strip of the formation of impact craters and, subsequently, secondary craters. From left to right, shows the timeline of a mass impacting a body, ejecta propagating from the initial impact, shock wave motion and the resulting cratered surface. The right most rectangle features arrows, which express the location at which secondary craters will form outside of or away from the impact center.
From the impact that formed Copernicus (upper center, yellow), ejecta blanketed the surrounding area. Blue denotes the outline of the ejecta deposit; secondary craters and crater chains are orange.
Secondary crater chain of Copernicus in Mare Imbrium
Illustration of projectile fracturing prior to primary impact to show the chronological procedure of the creation of primary and secondary impacts from projectile fractures.