About Meteorites | Southwest Meteorite Laboratory

What are meteorites?
Meteorites are bits of other planets, asteroid, or planetoids which are found on Earth. They once were moving along in space on a collision course with earth and survive entry into our atmosphere and the impact. back to top
What planets do they come from?
So far only two parent bodies have been positively identified; Earth’s moon and Mars. However, much evidence suggests that the origin of the HED group is the asteroid 4Vesta. back to top
How do you know it is from Mars?
For several years scientists were puzzled by the SNC group of meteorites. They are not only compositionally different from all other meteorites but they are also much younger (175 million to 1.3 billion years old compared to the average of other meteorites at ~4.5 billion years old). Originally it was by a process of elimination they reasonably concluded that these meteorites must have originated on Mars. This conclusion is now well accepted in the scientific community. In early 1983 scientists reported that the meteorites in this group contained chemical, isotopic, and petrologic features consistent with available data collected by the Viking landers. By late 1983 others showed that the isotopic concentrations of various noble gasses found in shergottioes (S) were consistent with the atmosphere of Mars as measured by the Viking landers. More recent data sets transmitted by Mars Global Surveyor, Pathfinder and other scout missions also confirm the origin of the SNC meteorites. back to top
Has anyone been hit by meteorite?
A woman was struck on the thigh by a stone meteorite that crashed through the roof of her home in Sylacauga, Alabama, USA. Though it was probably pretty painful the injury was not life-threatening.
Things reported to be struck by a meteorite fall are; several houses, a barn, paved roads, a dog, a cow, a car, a mail box, a large machine, and a pot on a stove. back to top
Fall or Find?
A “Fall” is a recovered meteorite that was witnessed to fall. A “Find” is a recovered meteorite whose fall was not witnessed. back to top
How are meteorites named?
Meteorites are typically named for the town, post office or other geographical landmark nearest the recovery sight. back to top
Is a meteor a meteorite?
No. A meteor is a streak in the sky and gets its name from the Greek word “meteoros” meaning something high in the sky. A meteor is a phenomenon that occurs when a solid object makes contact with Earth’s atmosphere causing an exchange of ions resulting in a bright streak of light in the sky. The object causing the meteor can be as small as a fleck of dust or as big as a mountain. Every meteorite started out as a meteor when it entered our atmosphere. However every meteor doesn’t produce a meteorite. Most of the objects burn completely up before reaching the ground. A meteorite is the portion of an object that survives passage through the atmosphere and lands on the ground. back to top
Why study meteorites?
Meteorites are a poor mans space probe and time machine. They teach us about planetary geology and the formation of our solar system. They also represent natural resources mankind may use to survive as they travel through space. back to top
Where do meteorites come from?
Most meteorites probably come from the asteroid belt; between Mars and Jupiter. Some have been linked to specific planetary bodies: Mars, Earth’s moon, and Asteroid 4 Vesta. Some meteorites contain pre solar grains that existed before the ignition of the Sun and predate our solar system. Generally speaking most meteorites are probably samples of the Near Earth Asteroids (NEAs). back to top
How many have been found?
The Meteoritical Bulletin has recorded 34,554 valid meteorite names (fall or find locations worldwide) since 1957. Each name represents a location where at least one meteorite was found. Often multiple (paired) specimens are recovered from the same site. In rare cases a single location has yielded thousands of pieces. Individual specimens range in size from sub-gram up to 60 tons. back to top
When was the first meteorite found?
The oldest meteorite find recorded was recovered from an archeological site, in Ur, circa 2500BC. back to top
How are meteorites found?
Most meteorites have been found by visual recognition; out of place rocks that don’t fit in with their surroundings. Some meteorites are seen to fall and recovered immediately and some are found with a metal detector. Not all meteorites have enough metal to register on a metal detector. back to top
Are meteorites radioactive?
Generally, no appreciable levels of radiation are found in meteorites. One meteorite which fell in Japan a few years ago had some measurable radioactivity. back to top
What are meteorites made of?
Meteorites are primarily made of stone, iron and a mixture of the two. Stone meteorites are primarily made of Iron/Magnesium silicates (olivine and pyroxene) and Aluminum silicates (feldspars) with minor amounts of other rock forming minerals. Iron meteorites are generally made of mostly iron with from ~5.5% to 18% nickel plus trace amounts of many siderophile elements. Relatively few iron meteorites contain more than 18% nickel. Stony-iron meteorites can be made of all of the above or combinations of them. back to top
Are meteorites hot when they hit the earth?
A freshly landed meteorite is never glowing red, in fact a freshly landed meteorite is seldom if ever even as hot as a hot potato. Considering the temperature of deep space is only a few degrees above absolute zero (~ 273°C, a theoretical limit where no heat remains), we know the meteoroid is very cold, frozen solid so to speak. The descent rarely lasts as much as 30 seconds. Imagine a solid ice cube fired through a blast furnace, the surviving portion is still very cold. back to top
What is fusion crust?
Fusion crust forms on all meteorites that survive passage through our atmosphere and land on the Earth. It is usually black, rarely cream colored and often weathered to brown or reddish-brown. Fusion crust is like a rind (rarely thicker than 1 millimeter) of melted rock that is caused by friction with our atmosphere. With a minimum entry velocity of 11.2 kilometers per second, the air in the meteorite’s path is compressed to the point of superheating. The outer surface of the meteorite melts and ablates as it races to the Earth’s surface; yet the interior of the meteorite remains cool. back to top
What is orientation?
Orientation is a term used to describe an aerodynamic shape resulting from a meteorite passing through our atmosphere remaining in fixed position. As the air superheats the surface directional melting and ablation occurs systematically sculpting the specimen and producing distinctive fusion crust with directional flow lines. back to top
What is secondary fusion crust?
Secondary fusion crust forms over a surface of a meteorite that broke in the upper atmosphere while still traveling at cosmic velocity. back to top
Are meteorites magnetic?
All nickel-iron meteorites are strongly attracted to a magnet. Most stone meteorites have varying magnetic susceptibility depending upon iron content. Some meteorites have no iron at all and are not attracted by a magnet. back to top
Do they magnetize?
Any iron can be magnetized but meteorites are not natural magnets. back to top
Why do meteorites affect a compass?
Because of their iron content. A compass needle is a magnet on one end and is attracted by the north pole of the earth. When a stronger source of magnetic material is close to the needle the magnet is attracted to it. back to top
What is a chondrule?
Chondrules are little round things found in primitive meteorites called chondrites hence their name from the Greek root “chondros” meaning rounded grain. Chondrules are considered the first solid objects to form in the solar nebula. They are generally spherical igneous droplets with various composition and structures, like: porphyritic, granular, barred, radiating, and cryptocrystalline. back to top
How old are meteorites?
Generally speaking meteorites are about the same age as our solar system 4.5 billion years old. A few meteorites are considerably younger; Martian meteorites at 175 million to 1.3 billion years and some Lunar meteorites with ages of <4.3 billion years. back to top
What is an impact structure?
Impact structures are craters formed by meteorite impact, like: Great Meteor Crater; Chesapeake Bay; Wolfe Creek; and Nordlinger Reis to name a few. back to top
How many impact structures are there?
Aside from small, relatively recent, impact events like Henbury and Sikhote-Alin with multiple craters and impact pits, some 174 impact structures have been identified worldwide. back to top
What is an impactite?
An impacite is glass formed as a result of meteorite impact. It is always associated with an impact structure. back to top
What is a tektite?
A tektite is glass formed as a result of meteorite impact. However a tektite has a very low or no water content and was transported by the meteorite impact blast. Some tektites show evidence of cosmic ray exposure and aerodynamic shapes produced by re-entry strongly suggesting they were ejected from Earth’s atmosphere and returned at a later date. back to top