Meteorites
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Listed here are answers to the most commonly asked meteorite questions we get asked at Armagh Planetarium. Visit the Planetarium to find out more or to see our meteorite collection.

What are meteorites?
How fast do they travel through space?
What is the difference between a meteor, a shooting star and a meteorite?
Has the Earth ever been hit by an asteroid?
Will an asteroid ever strike the earth again?
Has a meteorite ever hit or killed anyone on Earth?
Where can I see meteorites?
Where can I find meteorites?
I heard that a robot found a meteorite on Mars
What are meteorites worth?
What is the biggest meteorite?
What is a fireball?
If I find a meteorite, who can identify it for me?
Are there different types of meteorites?

Where do meteorites come from?
What is a chondrite?

Do meteorites show signs of life?
What are iron meteorites?

What is a pallasite?
What are Martian and Lunar meteorites?
Why are meteorites so destructive?
Where can I see an impact crater?
What are tektites?
How can I tell if I have found a meteorite?


What are meteorites?

Meteorites are samples of space rock that fall on to the Earth’s surface from space. Until 1969 when we obtained lunar samples for the first time, meteorites were the only extraterrestrial samples that we had studied.

How fast do they travel through space?

As they enter Earth’s atmosphere at velocities from 11 to 70 km per second, friction slows them down and heats them up, so that their outer surface starts to burn (ablate).  This is also what happened to the heat shields of Apollo crew capsules.  This means that the space rock glows brightly.

What is the difference between a meteor, a shooting star and a meteorite?

Fleeting trails of light are called meteors or shooting stars and they are created by small particles, some no bigger than a grain of rice, as they are completely burned up high in the atmosphere: about 100 km (or 60 miles) above the Earth.  They are over literally in the blink of an eye.  Space debris is collectively termed meteoroids, those larger fragments that reach the ground are called meteorites. Very big meteoroids are also known as asteroids.  If one collides with Earth it would cause a major catastrophe.

Has the Earth ever been hit by an asteroid?

It is now generally accepted that the dinosaurs were pushed into extinction by a collision between a large chunk of space rock and the Earth: the evidence for this collision is provided by the large 180 km diameter impact crater near the town of Chicxulub on the Yucatan Peninsula, Mexico.  Other impact craters on Earth include Manicouagan in Canada, Roter Kamm in Namibia and craters.

Will an asteroid ever strike the earth again?

Yes.  It is a certainty that another collision will occur at some time in the future.

Has a meteorite ever hit or killed anyone on Earth?

There are no records of any human being killed hit by a space rock.  It is recorded that a dog was killed by a meteorite fall at Nakhla in Egypt in 1911.  A woman in Sylacauga, Alabama was lying on her sofa when a meteorite crashed through her house and bounced off her radio TV and hit her leg.  She survived but had a huge bruise to show where the space rock almost got her.

Where can I see meteorites?

The best place to see them is in a museum or you can see our collection at Armagh Planetarium.  We also have meteorite specimens that you can touch and hold.

Where can I find meteorites?

If you want to find one you have a few choices.  The first is to be very lucky and to observe one falling.  The second is to travel to Antarctica, or one of Earth’s hot deserts.  In the cold ice desert at Earth’s South Pole, rocky and metallic meteorites are easy to spot as the nearest rock is often under kilometres of ice, so rocks on the ice cap are likely to have fallen from space.
The deserts of Earth also make it easy to spot rocks that are sitting on their own miles from any dried up river bed, or rocky outcrop.  Many meteorites have been collected from such sites in Australia, the Sahara, Oman, and South America.

I heard that a robot found a meteorite on Mars  Is t

Yes.  Opportunity, one of the Martian rovers has found a couple of meteorites and you can see images of them here.  On Earth a prototype space robot has also found meteorites on the Antarctic ice cap.

What are meteorites worth?

Meteorites that are sold on the internet vary in size from very small to quite big.  The bigger they are the more expensive they are to buy.  Some sell for thousands of pounds.  There are relatively few collectors, and some people collect tiny flecks of meteorites that you can only really see with a magnifying glass as this is the cheapest way to build a collection.  But a big heavy iron meteorite is very special.  It allows you to touch something that was formed in space, and which is very old, at around 4600 million years old (=4.6 billion years).

What is the biggest meteorite?

The biggest and heaviest meteorite on Earth is at Hoba in Namibia.  It is a huge iron meteorite and is so heavy that it has been left where it fell.  The Namibian government has built a small amphitheatre around it so that visitors can sit and look at it, half buried in the sandy semi-desert soil.

What is a fireball?

Bigger meteors about the size of a football can produce a fireball which can be brighter than the full Moon.  When a fireball explodes and showers the ground below with fragments of the object, then it may be called a bolide.  The elongated oval area of land that is littered with the debris of a fall is called a strewn field. 

If I find a meteorite, who can identify it for me?

Your best plan if you think that you have found a meteorite is to show it to an expert.  Take it to your local museum, and they may have an expert there.  If not they can send it away to someone who can identify it.  It would be best if it met some of the critical signs that it might be a space rock as almost all of the experts have seen hundreds of things that are not meteorites.  We have an expert at the Planetarium in Armagh, who can look at it if you bring it along.

Are there different types of meteorites?

The simplest classification divides all meteorites into three groups: irons, stony irons and stones.  In terms of how common they are the table below shows the correlation between finds and observed falls.

Composition Observed to fall Found, not seen falling
Irons 6% 66%
Stony irons 2% 8%
Stones 92% 26%

(after Pasachoff, 2002)

It is obvious from this table that observed falls are more likely to be stones, thus they must be the commonest type of meteorite in space.  Unobserved falls, also known as finds, are objects that someone stumbles over in the wild.  They are much more likely to be irons.  It is fairly obvious that most of us do not usually stumble over big bits of very heavy rusty iron lying around in the fields, and therefore irons are over represented in finds.  It is also true that once a stony meteorite hits the surface unobserved, it quickly blends into the general rocky background.  Only the very observant will notice that it will have a thin fusion crust.  This is created by its fiery fall through the atmosphere, and is caused by frictional heating and melting of the rock. Almost all meteorites will have some metal in them, so all are at least faintly magnetic.  They are heavier than typical terrestrial rocks, and especially with the irons, the density is a striking property. The metallic content usually includes nickel, and the two forms of nickel iron (NiFe) alloy that prevail in samples are the minerals taenite and kamacite.  The first mineral has 16 % Ni, the second around 19 %. Metallic meteorites also contain the minerals troilite, graphite, cohenite and schriebersite, along with trace amounts of chromium, iridium, cobalt and rare earth elements like gallium and germanium. 

 

 

 

Where do meteorites come from?

Most meteorites are fragments of small planets shattered by collisions early in the history of the Solar System. These remnants now form the Asteroid Belt, where many thousands of small objects endlessly circle the Sun between the orbits of Mars and Jupiter.

Fragments of these asteroids may be knocked out of their orbits by collisions. If their path through space crosses the Earth’s orbit they may eventually hit the Earth and fall as meteorites.  The best analogy is to compare the Earth to a car driving along the motorway, and the meteorites are the bugs that hit the windscreen.

A few rare meteorites have been identified as fragments of rock from the Moon or Mars. These were blasted into space by the impact of large meteorites or asteroids on these other celestial bodies.  They are identified by their chemistry which is subtly different from the rocks that make up the Earth.

What is a chondrite?

The young Solar System was crowded with many small planets. Collisions were commonplace. In the first few million years, collisions between very hot planetismals (tiny planets) created showers of molten droplets. These droplets cooled quickly to form small stony beads, or chondrules: it is believed that the chondrules clumped together (accreted) to form larger extraterrestrial bodies with a tell-tale signature: if they fall to Earth they are classified as chondritic meteorites.
About 90% of meteorites that fall to Earth are chondrites. There are more than 15 types. Most belong to just three types of ordinary Chondrite.

Do meteorites show signs of life?

Carbonaceous chondrite meteorites contain some of the original material from which the Earth and everything on it, both living and non-living, ultimately is made.  They contain a mixture of stony mineral dust, spherical chondrules, iron, nickel and even organic carbon compounds, including amino acids!  Armagh Planetarium’s collection includes a fragment of the Allende Meteorite from Mexico which is a carbonaceous chondrite, and which is rich in organic material.

The Planetarium’s chondrite collection is best represented by the Bovedy meteorite which has excellent examples of chondrules.  It also has a well preserved fusion crust and contains veins of nickel iron metal.

What are iron meteorites?

Iron meteorites come from the solidified core of small planets or planetismals, that were shattered by collisions. More than 90 different types of iron meteorite have been found. Each represents a different planetismal.  Their crystal structure shows that the planetismal core cooled very slowly, perhaps at only a few °C per million years.  This allowed large metal crystals to nucleate and grow.

What is a pallasite?

Between the iron core of a planet and the rocky crust is the mantle. It is made largely of dark green to black minerals including olivine, pyroxene, spinel and garnet. Pallasites are a rare and beautiful type of meteorite, made of a nickel iron alloy studded with fragments of olivine. Pallasites are thought to be derived from the core - mantle boundary of a  shattered planetismal (a small planet).  They are stony irons in the simple classification scheme.

What are Martian and Lunar meteorites?

In the Planetarium’s collection we have a small piece of the Zagami Meteorite.  This is very like a basaltic rock from Earth, but it is classified as a shergottite. It fell in Nigeria on 3rd October 1962. It is believed to be a piece of the surface of Mars.  Sometime in the past an asteroid impact on Mars was so energetic that surface fragments from the planet were blown into space.  After millions of years some of these pieces fell to Earth as meteorites.  They are identified by their unique chemistry.

Why are meteorites so destructive?

Small meteorites are slowed by friction with the Earth’s atmosphere from more than 11km per second to less than 100 metres per second. This means that they have enormous kinetic energy, based on the well known equation KE = 1/2 mass x Velocity2.  The hole that they make when hitting soft ground is normally only a little bigger that the meteorite itself.  Very large meteorites, of 100 tonnes or more are not slowed by atmospheric drag as much as their smaller cousins, they are still travelling so fast that they explode or vaporize on impact. They will explode with the effect of a nuclear bomb. This forms a crater far bigger than the meteorite. Immense volumes of rock, melted and blasted out by the explosion, eventually fall back to Earth hundreds or even thousands of kilometres from the impact crater. 

Tektites are also a result of such a blast, and small spherical glass spheres are found preserved in Earth’s rocks as evidence of very large impact events in the past.  As glass devitrifies over time, the original small glassy beads are often now converted to clays.  The Planetarium collection includes a sample from 214 million years old rocks found near Bristol, England. It contains many small green “beads” which are microtektites, glassy beads formed from a spray of impact melted rock. They form a thin layer in the rock.  These small spheres were once glassy beads that have been altered to green clay; they represent some of the fallout from a giant impact which took place at that time. 


Where can I see an impact crater?

The best preserved meteorite impact crater on Earth is in the USA.  The 30 metre diameter iron meteorite which formed the 1 km wide Meteor Crater in Arizona (also known as Canyon Diablo Crater) was vaporised on impact. However, many pieces broke away from the main mass shortly before the impact and lie strewn to the northwest of the crater. This crater is also known as the Barringer Crater the after the family who own the site.

What are tektites?

Tektites are pieces of natural glass formed by the melted material thrown out of the impact site by a large meteorite striking the Earth.  The largest known tektite field covers a tenth of the Earth’s surface around Australasia. They are thought to have formed around 780 000 years ago when a giant meteorite exploded high in the atmosphere, blasting the ground beneath with a superheated ‘fireball’ that melted rock, sand and soil.


Tektites are usually very well rounded and appear to be black.  If you cut them thinly enough so that light can pass through, they are actually a very dark green colour.  When the first nuclear bombs were tested in the Arizona desert in 1945, the enormous temperatures generated by the atomic fireball fused the desert sand into a dark green radioactive glass.

How can I tell if I have found a meteorite? Top tips for identifying a meteorite.

So you think that you have found a meteorite?  Use the following checklist to discover if you have really found a meteorite, or just an odd rock.

Is it heavy? 
Most meteorites are heavy for their size as almost all contain metal.

Does it attract a magnet?
Most meteorites are magnetic because they contain nickel and iron which are both magnetic.  But many Earth rocks are magnetic too, so this is not conclusive.  Suspend a magnet on a string and it should be attracted to genuine meteorites.

Does it have a dark coloured fusion crust? 
When they fall through the atmosphere a fusion crust is formed.  This is a thin layer of rock material that coats the meteorite.  Sometimes the edges or rounded corners are knocked off and the lighter coloured inside is quite different from the fusion crust.

Is the outer dark surface covered in what look like thumb prints, or are there oriented lines? 
Remaglypts and flow lines are seen in meteorites that have flown through the atmosphere in a specific orientation. Meteorites almost never have holes in them.  They are almost never angular with sharp jagged edges, nor are they spherical like cannon balls.  They can be light coloured, but are mostly dark.