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where the resulting crater shape becomes less circular and more elliptical. The primary impact angle is much more influential on the morphology (shape) of secondary impacts. Experiments conducted from lunar craters suggests that the ejection angle is at its highest for the early-stage ejecta, that which is ejected from the primary impact at its earliest moments, and that the ejection angle decreases with time for the late-stage ejecta. For example, a primary impact that is vertical to the body surface may produce early-stage ejection angles of 60°-70°, and late-stage ejection angles that have decreases to nearly 30°.
153:
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toward flatness. The morphology, and size, of secondary craters is limited. Secondary craters exhibit a maximum diameter of < 5% of its parent primary crater. The size of a secondary crater is also dependent on its distance from its primary. The morphology of secondaries is simple but distinctive. Secondaries that form closer to their primaries appear more elliptical with shallower depths. These may form rays or crater chains. The more distant secondaries appear similar in circularity to their parent primaries, but these are often seen in an array of clusters.
186:
277:≤1 km. Unfortunately, age research stemming from these crater databases is restrained due to the pollution of secondary craters. Scientists are finding it difficult to sort out all the secondary craters from the count, as they present false assurance of statistical vigor. Contamination by secondaries is often misused to calculate age constraints due to the erroneous attempts of using small craters to date small surface areas.
118:
211:(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. Secondary crater sizes and morphology also are affected by the distribution of rock sizes in the regolith of the target body.
17:
44:. In addition, secondary craters are often seen as clusters or rays surrounding primary craters. The study of secondary craters exploded around the mid-twentieth century when researchers studying surface craters to predict the age of planetary bodies realized that secondary craters contaminated the crater statistics of a body's
245:
are observed. Two factors dominate the morphologies of these craters: material strength and gravity. The bowl-shaped morphology suggests that the topography is supported by the strength of the material, while the topography of the basin-shaped craters is overcome by gravitational forces and collapses
198:
For primary impacts, based on geometry, the most probable impact angle is 45° between two objects, and the distribution falls off rapidly outside of the range 30° – 60°. It is observed that impact angle has little effect on the shape of primary craters, except in the case of low angle impacts,
177:
It can be increasing difficult to distinguish primary craters from secondaries craters when the projectile fractures and breaks apart prior to impact. This depends on conditions in the atmosphere, coupled with projectile velocity and composition. For instance, a projectile that strikes the moon will
92:
Self-secondary craters are a those that form from ejected material of a primary crater but that are ejected at such an angle that the ejected material makes an impact within the primary crater itself. Self-secondary craters have caused much controversy with scientists who excavate cratered surfaces
82:
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
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databases are further sorted according to each craters size, depth, morphology, and location. The observations and characteristics of both primaries and secondaries are used in distinguishing impact craters within small crater cluster, which are characterized as clusters of craters with a diameter
109:
Secondary craters are formed around primary craters. When a primary crater forms following a surface impact, the shock waves from the impact will cause the surface area around the impact circle to stress, forming a circular outer ridge around the impact circle. Ejecta from this initial impact is
285:
Secondary craters are common on rocky bodies in the Solar System with no or thin atmospheres, such as the Moon and Mars, but rare on objects with thick atmospheres such as Earth or Venus. However, in a study published in the
Geological Society of America Bulletin the authors describe a field of
173:
Primary craters form from high-velocity impacts whose foundational shock waves must exceed the speed of sound in the target material. Secondary craters occur at lower impact velocities. However, they must still occur at high enough speeds to deliver stress to the target body and produce strain
223:
in
Germany and of ejecta blocks circling lunar and martian crater rims suggest that ejecta fragments having a similar density would likely express the same depth of penetration, as opposed to ejecta of differing densities creating impacts of varying depths, such as primary impactors, i.e.
258:. 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:
74:
If ejected material is within an atmosphere, such as on Earth, Venus, or Titan, then it is more difficult to retain high enough velocity to create secondary impacts. Likewise, bodies with higher resurfacing rates, such as Io, also do not record surface cratering.
182:, possibly breaking up. In that case, the smaller chunks, now separated from the large impacting body, may impact the surface of the planet in the region outside the primary crater, which is where many secondary craters appear following primary surface impact.
286:
secondary impact craters they believe was formed by the material ejected from a larger, primary meteor impact around 280 million years ago. The location of the primary crater is believed to be somewhere between Goshen and
Laramie counties in
240:
Secondary crater size is dictated by the size of its parent primary crater. Primary craters can vary from microscopic to thousands of kilometers wide. The morphology of primary craters ranges from bowl-shaped to large, wide basins, where
56:
When a velocity-driven extraterrestrial object impacts a relatively stationary body, an impact crater forms. Initial crater(s) to form from the collision are known as primary craters or
189:
Illustration of projectile fracturing prior to primary impact to show the chronological procedure of the creation of primary and secondary impacts from projectile fractures.
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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. These
125:(upper center, yellow), ejecta blanketed the surrounding area. Blue denotes the outline of the ejecta deposit; secondary craters and crater chains are orange.
142:
Secondary craters may appear as small-scaled singular craters similar to a primary crater with a smaller radius, or as chains and clusters. A secondary
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is simply a row or chain of secondary craters lined adjacent to one another. Likewise, a cluster is a population of secondaries near to one another.
510:
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Scientists have long been collecting data surrounding impact craters from the observation that craters are present all throughout the span of the
152:
367:
McEwan, Alfred S.; Bierhaus, Edward B. (31 January 2006). "The
Importance of Secondary Cratering to Age Constraints on Planetary Surfaces".
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The gravitational acceleration of the extraterrestrial body must be great enough to drive the ejected material back toward the surface.
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685:
Xiao, Zhiyong; Strom, Robert G (July 2012). "Problems determining relative and absolute ages using the small crater population".
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The velocity by which the ejected material returns toward the body's surface must be large enough to form a crater.
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The calculation of depth of secondary crater can be formulated based on the target body's density. Studies of the
60:. Material expelled from primary craters may form secondary craters (secondaries) under a few conditions:
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thrust upward out of the impact circle at an angle toward the surrounding area of the impact ridge. This
404:"Lunar crater forms on melt sheets–Origins and implications for self-secondary cratering and chronology"
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with the intent to identify its age based on the composition and melt material. An observed feature on
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results that exceed the limits of elasticity, that is, secondary projectiles must break the surface.
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express the location at which secondary craters will form outside of or away from the impact center.
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Gault, Donald E; Wedekind, John A (13 March 1978). "Experimental studies of oblique impact".
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725:"Large impact crater histories of Mars: The effect of different model crater age techniques"
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Robbins, Stuart J; Hynek, Brian M (8 May 2014). "The secondary crater population of Mars".
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probably hit intact; whereas if it strikes the earth, it will be slowed and heated by
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Robbins, Stuart J; Hynek, Brian M; Lillis, Robert J; Bottke, William F (July 2013).
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537:"Using lunar boulders to distinguish primary from distant secondary impact craters"
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450:"Lunar self-secondary cratering: implications for cratering and chronology"
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has been interpreted to be a self-secondary crater morphology known as
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590:. Washington: Philosophical Society of Washington. pp. 3843–75
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that was thrown out of a larger crater. They sometimes form radial
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Head, James N; Melosh, H. Jay; Ivanov, Boris A (7 November 2002).
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630:"Martian Meteorite Launch:High-Speed Ejecta from Small Craters"
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size frequency distribution (SFD) of primary craters is known.
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image of secondary craters surrounding a primary impact site.
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craters exist as independently, contingent occurrences.
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Distinguishing factors of primary and secondary craters
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The Moon's Face, a study of the origin of its features
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Group of secondary craters on Mars, as seen by HiRISE
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Secondary crater chain of
Copernicus in Mare Imbrium
535:Bart, Gwendolyn D.; Melosh, H. J. (6 April 2007).
457:46th Annual Lunar and Planetary Science Conference
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792:Scientists discover Moon-like craters on Earth
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290:and Banner, Cheyenne, and Kimball counties in
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369:Annual Review of Earth and Planetary Sciences
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268:cratering rate relative to time is known.
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250:Age constraints due to secondary craters
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64:Primary craters must already be present.
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611:Lunar and Planetary Science Conference
448:Plescia, J.B.; Robinson, M.S. (2015).
389:10.1146/annurev.earth.34.031405.125018
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807:Thomas Kenkmann et al (11 Feb 2022)
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207:Mechanical properties of a target's
313:Earth and Planetary Science Letters
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584:Gilbert, Grove Karl (April 1893).
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766:"Mars Crater Database Search"
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810:Secondary cratering on Earth
752:10.1016/j.icarus.2013.03.019
707:10.1016/j.icarus.2012.05.012
541:Geophysical Research Letters
121:From the impact that formed
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770:Mars Crater Database Search
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333:10.1016/j.epsl.2014.05.005
789:Jon Kelvey (16 Feb 2022)
655:10.1126/science.1077483
325:2014E&PSL.400...66R
243:multi-ringed structures
429:Cite journal requires
402:Plescia, J.B. (2015).
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511:"Secondary Cratering"
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88:Self-secondary crater
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562:10.1029/2007GL029306
744:2013Icar..225..173R
699:2012Icar..220..254X
646:2002Sci...298.1752H
553:2007GeoRL..34.7203B
465:2015LPI....46.2535P
381:2006AREPS..34..535M
236:Size and Morphology
130:Chains and clusters
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834:Planetary geology
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640:(5599): 1752–56.
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375:: 535–567.
203:Target type
99:palimpsests
828:Categories
496:2007-08-07
298:References
281:Occurrence
123:Copernicus
105:Appearance
571:106395684
230:asteroids
52:Formation
22:MESSENGER
775:29 March
664:12424385
292:Nebraska
209:regolith
740:Bibcode
695:Bibcode
672:2969674
642:Bibcode
634:Science
594:1 March
549:Bibcode
470:2 March
461:Bibcode
412:2 March
377:Bibcode
321:Bibcode
288:Wyoming
732:Icarus
687:Icarus
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520:15 May
516:. 2006
226:comets
38:ejecta
728:(PDF)
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567:S2CID
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95:Tycho
777:2015
660:PMID
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435:help
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228:and
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