When the original object enters the atmosphere, various factors such as friction, pressure, and chemical interactions with the atmospheric gases cause it to heat up and radiate energy.

It then becomes a meteor and forms a fireball, also known as a shooting star; astronomers call the brightest examples "bolides". Once it settles on the larger body's surface, the meteor becomes a meteorite. Meteorites vary greatly in size. For geologists, a bolide is a meteorite large enough to create an impact crater.

Meteorites that are recovered after being observed as they transit the atmosphere and impact the Earth are called meteorite falls. All others are known as meteorite finds.

Meteorites have traditionally been divided into three broad categories: stony meteorites that are rocks, mainly composed of silicate minerals; iron meteorites that are largely composed of ferronickel; and stony-iron meteorites that contain large amounts of both metallic and rocky material.

Modern classification schemes divide meteorites into groups according to their structure, chemical and isotopic composition and mineralogy. "Meteorites" less than ~1 mm in diameter are classified as micrometeorites, however micrometeorites differ from meteorites in that they typically melt completely in the atmosphere and fall to Earth as quenched droplets.

Extraterrestrial meteorites have been found on the Moon and on Mars.

Most meteoroids disintegrate when entering the Earth's atmosphere. Usually, five to ten a year are observed to fall and are subsequently recovered and made known to scientists. Few meteorites are large enough to create large impact craters. Instead, they typically arrive at the surface at their terminal velocity and, at most, create a small pit.

Large meteoroids may strike the earth with a significant fraction of their escape velocity (second cosmic velocity), leaving behind a hypervelocity impact crater. The kind of crater will depend on the size, composition, degree of fragmentation, and incoming angle of the impactor. The force of such collisions has the potential to cause widespread destruction.

The most frequent hypervelocity cratering events on the Earth are caused by iron meteoroids, which are most easily able to transit the atmosphere intact. Examples of craters caused by iron meteoroids include Barringer Meteor Crater, Odessa Meteor Crater, Wabar craters, and Wolfe Creek crater; iron meteorites are found in association with all of these craters. In contrast, even relatively large stony or icy bodies such as small comets or asteroids, up to millions of tons, are disrupted in the atmosphere, and do not make impact craters.

Although such disruption events are uncommon, they can cause a considerable concussion to occur; the famed Tunguska event probably resulted from such an incident. Very large stony objects, hundreds of meters in diameter or more, weighing tens of millions of tons or more, can reach the surface and cause large craters but are very rare. Such events are generally so energetic that the impactor is completely destroyed, leaving no meteorites. (The very first example of a stony meteorite found in association with a large impact crater, the Morokweng impact structure in South Africa, was reported in May 2006.)

Several phenomena are well documented during witnessed meteorite falls too small to produce hypervelocity craters.

The fireball that occurs as the meteoroid passes through the atmosphere can appear to be very bright, rivaling the sun in intensity, although most are far dimmer and may not even be noticed during the daytime. Various colors have been reported, including yellow, green, and red. Flashes and bursts of light can occur as the object breaks up. Explosions, detonations, and rumblings are often heard during meteorite falls, which can be caused by sonic booms as well as shock waves resulting from major fragmentation events. These sounds can be heard over wide areas, with a radius of a hundred or more kilometers. Whistling and hissing sounds are also sometimes heard but are poorly understood. Following the passage of the fireball, it is not unusual for a dust trail to linger in the atmosphere for several minutes. As meteoroids are heated during atmospheric entry, their surfaces melt and experience ablation. They can be sculpted into various shapes during this process, sometimes resulting in shallow thumbprint-like indentations on their surfaces called regmaglypts. If the meteoroid maintains a fixed orientation for some time, without tumbling, it may develop a conical "nose cone" or "heat shield" shape. As it decelerates, eventually the molten surface layer solidifies into a thin fusion crust, which on most meteorites is black (on some achondrites, the fusion crust may be very light-colored). On stony meteorites, the heat-affected zone is at most a few mm deep; in iron meteorites, which are more thermally conductive, the structure of the metal may be affected by heat up to 1 centimetre (0.39 in) below the surface. Reports vary; some meteorites are reported to be "burning hot to the touch" upon landing, while others are alleged to have been cold enough to condense water and form a frost.

Meteoroids that disintegrate in the atmosphere may fall as meteorite showers, which can range from only a few up to thousands of separate individuals. The area over which a meteorite shower falls is known as its strewn field. Strewn fields are commonly elliptical in shape, with the major axis parallel to the direction of flight. In most cases, the largest meteorites in a shower are found farthest down-range in the strewn field.

Ref: Wikipedia

At Henbury there are 13 to 14 craters ranging from 7 to 180 m (23 to 591 ft) in diameter and up to 15 m (49 ft) in depth that were formed when the meteor broke up before impact. Several tonnes of iron-nickel fragments have been recovered from the site. The site has been dated to ≤4.7 thousand years ago based on the cosmogenic 14C terrestrial age of the meteorite[6] and 4.2±1.9 thousand years ago using fission track dating.

The craters are named for Henbury Station, a nearby cattle station named in 1875 for the family home of its founders at Henbury in Dorset, England.

The craters were discovered in 1899 by the manager of the station, then went uninvestigated until interest was stirred when the Karoonda meteorite fell on South Australia in 1930.

The first scientific investigations of the site were conducted by A.R. Alderman of the University of Adelaide who published the results in a 1932 paper entitled The Meteorite Craters at Henbury Central Australia.

Numerous studies have been undertaken since.

The highlighted words are defined as follows:

Ordinary chondrite:

A major class of chondrites, distinguished by sub-solar Mg/Si and refractory/Si ratios, oxygen isotope compositions that plot above the terrestrial fractionation line, and a large volume percentage of chondrules, with only 10-15 vol% fine-grained matrix.

LL group:

The low-iron, low metal (LL) chemical group of ordinary chondrites, distinguished by their low siderophile element content, fairly large chondrules (~0.9 mm), and oxygen isotope compositions that are further above the terrestrial fractionation line than those of other ordinary chondrites.

Type 3:

Designates chondrites that are characterized by abundant chondrules, low degrees of aqueous alteration, and unequilibrated mineral assemblages. Many of the low-Ca pyroxene grains are monoclinic and exhibit polysynthetic twinning. The type 3 chondrites may be divided into subtypes ranging from 3.00 (least metamorphosed) to 3.9 (nearly metamorphosed to type 4 levels). If primary igneous glass occurs in the chondrules, it belongs to type 3.

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HISTORY

In 1911 an iron meteorite fragment of 112 g was found by Harry Kent, foreman in charge of camels for the Western Australian survey of the transcontinental railway route, at 31°1′S 127°23′E, on Premier Downs station on the Nullarbor Plain. The small meteorite was called Premier Downs I. Later in 1911 Kent found another small iron meteorite (116 g) about 13 kilometres (8.1 mi) west from the found location of Premier Downs I, named Premier Downs II. Both meteorites were medium octahedrites, believed to be part of the same fall.

In 1918 a third similar small iron meteorite of 99 g was found in the area by A. Ewing, named Premier Downs III.

In 1962 a small iron meteorite of 108 g with similar characteristics was found near Loongana railway station by a rabbit trapper named Harrison. It was suggested as a possible pairing with the previous Premier Downs samples.

In 1965 three small iron fragments (94.1 g, 45 g, 38.8 g) were found by Bill Crowle of the Geological Survey of Western Australia 16 kilometres (9.9 mi) north of Mundrabilla Siding on the Trans Australian Railway at 30°45′S 127°30′E.

In April 1966 two very large iron masses of 12.4 tonnes and 5.44 tonnes were found in the Nullarbor Plain at 30°47′S 127°33′E by geologists R.B. Wilson and A.M. Cooney during a geological survey. The two masses were lying 180 metres (590 ft) apart, in clayey soil within slight depressions. The masses were surrounded by a large number of small iron fragments. The meteorites were named Mundrabilla, while the largest fragment, the eleventh largest found in the world as of 2013, is distinguished as Mundrabilla I.

In 1967 a small iron fragment of 66.5 g found at 30°57′S 126°58′E by Harry Butler, was named Loongana Station West.

It has been suggested that the Mundrabilla meteorites are closely related to the Loongana Station and Premier Downs meteorites, and were shed from the same mass during atmospheric ablation.

Mundrabilla I, the main mass of 12.4 tonnes, is now conserved at the Western Australia Museum.

The secondary piece of the Mundrabilla meteorite, weighed at approximately 3.5 tons, was recovered in 1988. It was taken by train from Loongana to Perth where it was studied at the Western Australia Museum. It is now on display at the Museum of the Great Southern in Albany, Western Australia.

Ref: Wikipedia