It is often said that when the average person imagines what a meteorite looks like, they think of an iron. It is easy to see why. Iron meteorites are dense, very heavy, and have often been forged into unusual or even spectacular shapes as they plummet, melting, through our planet's atmosphere.
Though irons may be synonymous with most people's perception of a typical space rock's appearance, they are only one of three main meteorite types, and rather uncommon compared to stone meteorites , especially the most abundant stone meteorite group-the ordinary chondrites.
Iron Meteorite: A superb 1,gram complete iron meteorite from the Sikhote-Alin meteorite shower which occurred in a remote part of eastern Siberia in the winter of This fine specimen is described as a complete individual, as it flew through the atmosphere in one piece, without fragmenting.
Its surface is covered with scores of small regmaglypts, or thumbprints, created by melting during flight. The Sikhote-Alin shower was the largest recorded witnessed meteorite fall in history.
Although there are a large number of sub classes, meteorites are divided into three main groups: irons, stones and stony-irons. Almost all meteorites contain extraterrestrial nickel and iron, and those that contain no iron at all are so rare that when we are asked for help and advice on identifying possible space rocks, we usually discount anything that does not contain significant amounts of metal.
Much of meteorite classification is based, in fact, on how much iron a specimen does contain. Stone Meteorite: A It was a witnessed fall and is a rare type of achondrite—a stone meteorite which does not contain chondrules. Eucrites are volcanic rocks from other bodies in the solar system, and Millbillillie is one of the very few meteorites which does not contain iron-nickel.
Note the glossy black fusion crust, and fine flow lines which were caused as the surface of the meteorite melted during flight. This specimen is also highly oriented, with a textbook snub-nosed leading edge pictured and a flat back. When I give lectures and slideshows about meteorites to rock and mineral societies, museums, and schools, I always enjoy commencing the presentation by passing around a softball-sized iron meteorite.
Most people have never held a space rock in their hands and when someone does pick up an iron meteorite for the first time their face lights up and their reaction is, almost without fail, to exclaim: "Wow, it's so heavy! Iron meteorites were once part of the core of a long-vanished planet or large asteroid and are believed to have originated within the Asteroid Belt between Mars and Jupiter.
They are among the densest materials on earth and will stick very strongly to a powerful magnet. Iron meteorites are far heavier than most earth rocks-if you've ever lifted up a cannon ball or a slab of iron or steel, you'll get the idea. Iron meteorites are subdivided into classes both by chemical composition and structure. Structural classes are determined by studying their two component iron-nickel alloys: kamacite and taenite. This remarkable lattice-like arrangement can be very beautiful and is normally only visible when iron meteorites are cut into slabs, polished, and then etched with a mild solution of nitric acid.
The kamacite crystals revealed by this process are measured and the average bandwidth is used to subdivide iron meteorites into a number of structural classes. An iron with very narrow bands, less than 1 mm, would be a "fine octahedrite" and those with wide bands would be called "coarse octahedrites.
Stone meteorite: Detail of prepared slice of the carbonaceous chondrite Allende, which was seen to fall in Chihuahua, Mexico on the night of February 8, , following a massive fireball. Allende contains carbonaceous compounds as well as calcium-rich inclusions large white circle near center.
NASA scientist Dr. More recently, in the world was startled by a brilliant fireball that streaked across the sky above Chelyabinsk, Russia. The house-sized meteoroid entered the atmosphere at over 11 miles 18 kilometers per second and blew apart 14 miles 23 kilometers above the ground.
The explosion released the energy equivalent of around , tons of TNT and generated a shock wave that blew out windows over square miles square kilometers and damaged buildings. More than 1, people were injured in the blast, mostly due to broken glass. The smaller piece in the foreground is called "Lebanon B. Meteor Crater in Arizona. Note vehicles in parking lot for scale.
Credit: USGS. Full Moon Guide: October - November Models and lab tests suggest the asteroid could be venting sodium vapor as it orbits close to the Sun, explaining its increase in brightness. The Perseids are already showing up in our night skies, and they peak in mid-August.
The Perseids are on the Rise! The next full Moon will be on Thursday afternoon, Oct. The Moon will appear full from Wednesday morning through Saturday morning. Despite its small size, this space rock is a colossal find. It's one of the best-preserved meteorites of its kind ever found. Ice-blue clouds are drifting over the Arctic and that means noctilucent cloud season is here. Australian Meteor Crater is the Oldest Known. What's Up for January? Morning meteors, Mars meets its "rival," and the Moon comes around for another visit with Venus.
What's Up for January This year, the peak is during the overnight hours of December 13 and into the morning of December Catch the Geminids Meteor Shower Dec.
Alpha Monocerotid meteor shower, predicted to peak around pm ET on Nov. An international team has found sugars essential to life in meteorites. The new discovery adds to the growing list of biologically important compounds found in meteorites.
New research shows streams of meteoroids striking the Moon infuse the thin lunar atmosphere with a short-lived water vapor. December brings the Geminids, a visible comet, and a fond farewell.
What's Up - December Photographing a meteor shower can be an exercise in patience, but with these tips — and some good fortune — you might be rewarded with a great photo. How to Photograph a Meteor Shower. November brings planets, an asteroid, a comet and the Leonids meteor shower. What's Up - November Elsewhere it can create a pattern of veins through solid metal. The scientific jury is still out on exactly how pallasite meteorites formed.
Some scientists believe they formed in melted asteroids in a similar way to iron meteorites, where dense iron metal sinks toward the centre to form an iron core. Pallasites are thought to be samples of the boundaries between a metal core and the silicate, olivine-rich mantle around it. If this is the case, they could tell us a lot about the formation of Earth and other terrestrial planets. However, other scientists think that there are very few olivine-rich meteorites in the asteroid belt, and too many pallasite meteorites for them all to have come from a core-mantle boundary.
These types of formations may also be formed by impact melting. Mesosiderite meteorites are breccias, a variety of rock composed of broken fragments of minerals or rock cemented together by a finer material. The fragments are roughly centimetre-sized and contain a mix of igneous solidified silicate and metal clasts rocks made of pieces of older rocks. Mesosiderites form when debris from a collision between two asteroids is mixed together. In the crash, molten metal mixes together with solid fragments of silicate rocks.
Mesosiderites can therefore both record the history of both meteorites and reveal a snapshot of the conditions required for asteroids to melt and form iron cores. There are two main types of stony meteorite: chondrites some of the oldest materials in the solar system and achondrites including meteorites from asteroids, Mars and the Moon.
Both chondrites and achondrites have many subgroups based on their compositions, structures and the minerals they contain. At over 4. Chondrites have a distinctive appearance, made from droplets of silicate minerals mixed with small grains of sulphides and iron-nickel metal. Their millimetre-sized granules give chondrites their name, from the Greek 'chondres' meaning sand grains.
There are many varieties of chondrite, with differences in mineralogy relating to the type of asteroid the meteorite came from.
Chondrites are the material from which the solar system formed. They have been little changed compared with rocks from larger planets, which have been subjected to geological activity.
Chondrites can tell us a lot about how the solar system formed. The most basic types, known as carbonaceous chondrites, are rich in water, sulphur and organic material. They are thought to have brought volatile material to Earth when it was newly formed, helping to establish the atmosphere and other conditions required to sustain life. Achondrites include meteorites from asteroids, Mars and the Moon.
They are igneous, meaning at some point they were melted into magma. When magma cools and crystallises, it creates a concentric layered structure. This process is known as igneous differentiation. The rocky planets Mercury, Venus, Earth and Mars were formed in this way, giving them planetary crusts, mantles and cores. Achondrites can tell us a lot about the internal structure and formation of the planets, including our own.
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