Lunar craters are
impact crater
An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...
s on
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surf ...
's
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width ...
. The Moon's surface has many craters, all of which were formed by impacts. The
International Astronomical Union
The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach ...
currently recognizes 9,137 craters, of which 1,675 have been dated.
History
The word ''crater'' was adopted from the
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
word for "vessel" (, a Greek vessel used to mix wine and water).
Galileo built his
first telescope in late 1609, and turned it to the Moon for the first time on November 30, 1609. He discovered that, contrary to general opinion at that time, the Moon was not a perfect sphere, but had both mountains and cup-like depressions. These were named craters by
Johann Hieronymus Schröter
Johann Hieronymus Schröter (30 August 1745, Erfurt – 29 August 1816, Lilienthal) was a German astronomer.
Life
Schröter was born in Erfurt, and studied law at Göttingen University from 1762 until 1767, after which he started a ten-y ...
(1791), extending its previous use with
volcano
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often found where tectonic plates ...
es.
Robert Hooke
Robert Hooke FRS (; 18 July 16353 March 1703) was an English polymath active as a scientist, natural philosopher and architect, who is credited to be one of two scientists to discover microorganisms in 1665 using a compound microscope that h ...
in ''
Micrographia
''Micrographia: or Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses. With Observations and Inquiries Thereupon.'' is a historically significant book by Robert Hooke about his observations through various lenses. It ...
'' (1665) proposed two hypotheses for lunar crater formation: one, that the craters were caused by projectile bombardment from space, the other, that they were
the products of subterranean lunar
volcanism
Volcanism, vulcanism or volcanicity is the phenomenon of eruption of molten rock (magma) onto the Earth#Surface, surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics, and volcanic gases erupt through a break in the su ...
.
Scientific opinion
An opinion is a judgment, viewpoint, or statement that is not conclusive, rather than facts, which are true statements.
Definition
A given opinion may deal with subjective matters in which there is no conclusive finding, or it may deal with ...
as to the origin of craters swung back and forth over the ensuing centuries. The competing theories were:
#
volcanic eruption
Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are ...
s blasting holes in the Moon
#
meteoric impact
# a theory known as the
Welteislehre developed in Germany between the two
world wars
A world war is an international conflict which involves all or most of the world's major powers. Conventionally, the term is reserved for two major international conflicts that occurred during the first half of the 20th century, World WarI (1914 ...
which suggested
glacial motion creating the craters.
Grove Karl Gilbert
Grove Karl Gilbert (May 6, 1843 – May 1, 1918), known by the abbreviated name G. K. Gilbert in academic literature, was an American geologist.
Biography
Gilbert was born in Rochester, New York and graduated from the University of Rochester. D ...
suggested in 1893 that the Moon's craters were formed by large asteroid impacts.
Ralph Baldwin in 1949 wrote that the Moon's craters were mostly of impact origin. Around 1960,
Gene Shoemaker revived the idea. According to
David H. Levy
David Howard Levy (born May 22, 1948) is a Canadian amateur astronomer, science writer and discoverer of comets and minor planets, who co-discovered Comet Shoemaker–Levy 9 in 1993, which collided with the planet Jupiter in 1994.
Biography
...
, Shoemaker "saw the craters on the Moon as logical impact sites that were formed not gradually, in
eons, but explosively, in seconds."
Evidence collected during the
Apollo Project and from unmanned spacecraft of the same period proved conclusively that meteoric impact, or impact by
asteroids
An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...
for larger craters, was the origin of almost all lunar craters, and by implication, most craters on other bodies as well.
The formation of new craters is studied in the lunar impact monitoring program at
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeedi ...
. The biggest recorded creation was caused by an impact recorded on March 17, 2013. Visible to the
naked eye
Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to normal ...
, the impact is believed to be from an approximately meteoroid striking the surface at a speed of .
In March 2018, the discovery of around 7,000 formerly unidentified lunar craters via
convolutional neural network
In deep learning, a convolutional neural network (CNN, or ConvNet) is a class of artificial neural network (ANN), most commonly applied to analyze visual imagery. CNNs are also known as Shift Invariant or Space Invariant Artificial Neural Netwo ...
developed at the
University of Toronto Scarborough
The University of Toronto Scarborough, also known as U of T Scarborough or UTSC, is one of the three campuses that make up the tri-campus system of the University of Toronto. Located in Scarborough, Toronto, Ontario, Canada, the campus is set upo ...
, Canada was announced. A similar study in December 2020 identified around 109,000 new craters using a
deep neural network.
Characteristics
Because of the Moon's lack of
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
,
atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. ...
, and
tectonic plates, there is little erosion, and craters are found that exceed two billion years in age. The age of large craters is determined by the number of smaller craters contained within it, older craters generally accumulating more small, contained craters.
The smallest craters found have been microscopic in size, found in rocks returned to Earth from the Moon. The largest crater called such is about across in diameter, located near the
lunar south pole. However, it is believed that many of the
lunar maria were formed by giant impacts, with the resulting depression filled by upwelling
lava
Lava is molten or partially molten rock ( magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or ...
.
Craters typically will have some or all of the following features:
*a surrounding area with materials splashed out of the ground when the crater was formed; this is typically lighter in shade than older materials due to exposure to
solar radiation
Solar irradiance is the power per unit area ( surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre ...
for a lesser time
*raised rim, consisting of materials ejected but landing very close by
*crater wall, the downward-sloping portion of the crater
*crater floor, a more or less smooth, flat area, which as it ages accumulates small craters of its own
*central peak, found only in some craters with a diameter exceeding ; this is generally a splash effect caused by the kinetic energy of the impacting object being turned to heat and melting some lunar material.
Statistics
There are at least 1.3 million craters larger than in diameter; of these, 83,000 are greater than in diameter, and 6,972 are greater than in diameter.
Lunar crater categorization
In 1978,
Chuck Wood
David Strassman (born September 6, 1957) is an American ventriloquist, stand-up comedian, actor, voice artist, and comedian. He is best known for his ventriloquism act with Chuck Wood and Ted E. Bare.
Early life and education
Strassman, the seco ...
and
Leif Andersson of the Lunar & Planetary Lab devised a system of categorization of lunar impact craters.
[
They used a sampling of craters that were relatively unmodified by subsequent impacts, then grouped the results into five broad categories. These successfully accounted for about 99% of all lunar impact craters.
The LPC Crater Types were as follows:
* ''ALC'' — small, cup-shaped craters with a diameter of about or less, and no central floor. The ]archetype
The concept of an archetype (; ) appears in areas relating to behavior, historical psychology, and literary analysis.
An archetype can be any of the following:
# a statement, pattern of behavior, prototype, "first" form, or a main model that ...
for this category is Albategnius C.
* ''BIO'' — similar to an ALC, but with small, flat floors. Typical diameter is about . The lunar crater archetype is Biot.
* ''SOS'' — the interior floor is wide and flat, with no central peak. The inner walls are not terraced. The diameter is normally in the range of . The archetype is Sosigenes.
* ''TRI'' — these complex craters are large enough so that their inner walls have slumped to the floor. They can range in size from in diameter. The archetype crater is Triesnecker.
* ''TYC'' — these are larger than 50 km, with terraced inner walls and relatively flat floors. They frequently have large central peak formations. Tycho Tycho is a masculine given name, a latinization of Greek Τύχων, from the name of Tyche ( grc-gre, Τύχη, link=no), the Greek goddess of fortune or luck.
The Russian form of the name is '' Tikhon'' (Тихон).
People
Given name
* Tych ...
is the archetype for this class.
Beyond a couple of hundred kilometers diameter, the central peak of the TYC class disappear and they are classed as basins. Large craters, similar in size to maria, but without (or with a small amount of) dark lava filling, are sometimes called thalassoids.[
Beginning in 2009 ]Nadine G. Barlow
Nadine G. Barlow (1958–2020) was an American planetary scientist. She was a professor in the Department of Physics and Astronomy at Northern Arizona University (NAU). She became Associate Chair of the NAU Department of Physics and Astronomy in ...
of Northern Arizona University
Northern Arizona University (NAU) is a public research university based in Flagstaff, Arizona. It was founded in 1899 as the final public university established in the Arizona Territory, 13 years before Arizona was admitted as the 48th state.
...
, U.S. began to convert the Wood and Andersson lunar impact-crater database into digital format. Barlow is also creating a new lunar impact crater database similar to Wood and Andersson's, except hers will include all impact craters greater than or equal to five kilometers in diameter and is based on the '' Clementine'' spacecraft's images of the lunar surface.
The Moon Zoo project within the Zooniverse
Zooniverse is a citizen science web portal owned and operated by the Citizen Science Alliance. It is home to some of the Internet's largest, most popular and most successful citizen science projects. The organization grew from the original Gal ...
program aimed to use citizen scientists to map the size and shape of as many craters as possible using data from the NASA Lunar Reconnaissance Orbiter
The Lunar Reconnaissance Orbiter (LRO) is a NASA robotic spacecraft currently orbiting the Moon in an eccentric polar mapping orbit. Data collected by LRO have been described as essential for planning NASA's future human and robotic missions to ...
. However, it has since been retired.
Names
Craters constitute 95% of all named lunar features.[ Usually they are named after deceased scientists and other explorers.][ This tradition comes from ]Giovanni Battista Riccioli
Giovanni Battista Riccioli, SJ (17 April 1598 – 25 June 1671) was an Italian astronomer and a Catholic priest in the Jesuit order. He is known, among other things, for his experiments with pendulums and with falling bodies, for his discussion ...
, who started it in 1651.[ Riccioli's map of the Moon (1651)] Since 1919, assignment of these names is regulated by the International Astronomical Union
The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach ...
.[
Small craters of special interest (for example, visited by lunar missions) receive human first names (Robert, José, Louise etc.). One of the biggest lunar craters, ]Apollo
Apollo, grc, Ἀπόλλωνος, Apóllōnos, label=genitive , ; , grc-dor, Ἀπέλλων, Apéllōn, ; grc, Ἀπείλων, Apeílōn, label=Arcadocypriot Greek, ; grc-aeo, Ἄπλουν, Áploun, la, Apollō, la, Apollinis, label= ...
, is named after Apollo missions. Many smaller craters inside and near it bear the names of deceased American astronauts, and many craters inside and near Mare Moscoviense bear the names of deceased Soviet cosmonauts.[ Besides this, in 1970 twelve craters were named after twelve living astronauts (6 Soviet and 6 American).][
The majority of named lunar craters are ''satellite craters'': their names consist of the name of a nearby named crater and a capital letter (for example, , , and so on).][
Lunar crater chains are usually named after a nearby crater. Their Latin names contain the word ''Catena'' ("chain"). For example, '']Catena Davy
Davy is a small lunar impact crater that is located on the eastern edge of the Mare Nubium. It was named after British physicist Humphry Davy. It overlies the lava-flooded remains of the satellite crater Davy Y to the east, a formation which co ...
'' is situated near the crater Davy.[
]
Locations of major craters
The red marker on these images illustrates the location of the named crater feature on the near side of the Moon.
Image:Location of albategnius crater.jpg,
Image:Location of lunar aristarchus crater.jpg,
Image:Location of lunar aristoteles crater.jpg,
Image:Location of lunar bailly crater.jpg,
Image:Location of lunar crater clavius.jpg,
Image:Location of lunar crater copernicus.jpg,
Image:Location of lunar crater fra mauro.jpg,
Image:Location of lunar crater humboldt.jpg,
Image:Location of lunar crater janssen.jpg,
Image:Location of lunar crater langrenus.jpg,
Image:Location of lunar crater longomontanus.jpg,
Image:Location of lunar crater maginus.jpg,
Image:Location of lunar crater metius.jpg,
Image:Location of lunar crater moretus.jpg,
Image:Location of lunar crater petavius.jpg,
Image:Location of lunar crater picard.jpg,
Image:Location of lunar crater piccolomini.jpg,
Image:Location of lunar crater pitatus.jpg,
Image:Location of lunar crater plinius.jpg,
Image:Location of lunar crater rheita.jpg,
Image:Location of lunar crater russell.jpg,
Image:Location of lunar crater schickard.jpg,
Image:Location of lunar crater seleucus.jpg,
Image:Location of lunar crater stadius.jpg,
Image:Location of lunar crater stofler.jpg,
Image:Location of lunar crater thebit.jpg,
Image:Location of lunar crater theophilus.jpg,
Image:Lage des Mondkraters Tycho.jpg,
Image:Location of lunar crater vendelinus.jpg,
Image:Location of lunar crater wargentin.jpg,
See also
*List of craters on the Moon
This is a list of named lunar craters. The large majority of these features are impact craters. The crater nomenclature is governed by the International Astronomical Union, and this listing only includes features that are officially recognized b ...
Notes
References
{{DEFAULTSORT:Lunar Craters