A dagger from the stars

In 1922, when archaeologist Howard Carter opened up the tomb of the Pharaoh Tutankhamun, the first undisturbed ancient Egyptian royal tomb to be discovered, he got many surprises.

One of them was quite small, and at first sight, not very dramatic looking. It was a small, iron dagger. What was unusual is that Tutankhamun lived and died in the Bronze Age, and the Iron Age started well after his death. Where did that iron come from?

The ancient Egyptians knew all about iron ore—haematite. They ground it up with oil and used it as the basis of red paint. They did not know how to smelt it to extract the iron. The Egyptian furnaces were nowhere near hot enough to do that.

A viable alternative, now proved by analysis of the iron from which the dagger is made, is that the iron arrived from space as an iron meteorite. These can be almost pure iron, with a little nickel and cobalt, and ready for forging into blades and other implements. Much less heat is required for that.

Meteorites come in two main types—rocky or stony ones, mainly made of basaltic rocks, and nickel/iron ones, which are lumps of almost pure metal. When cut in half, they show a clean, shiny metallic surface. Where did they come from? The explanation starts with stars.

Stars are born as big balls of hydrogen gas, with some helium. If hydrogen is compressed enough and hot enough, hydrogen atoms combine to form helium atoms, releasing energy, which makes the star shine.

When hydrogen starts to run short, the star shrinks and the pressure and temperature in the core rise until helium atoms combine to form larger atoms, such as nitrogen and carbon. When fuel runs short again, the fusion process goes on to produce larger and heavier atoms.

However, each generation of fusion processes produces smaller and smaller energy yields. Finally the fusion processes reach high enough temperatures to reach iron and related elements, such as nickel and cobalt. These atoms are the are the most stable.

Turning iron into other elements requires energy. This puts the star at the end of the road. It is out of fuel. It collapses and explodes, blasting its material out into space in the form of clouds of dust and fine particles. In the explosion all the elements heavier than iron are produced, such as lead, copper, gold, platinum and silver.

Over time these clouds of dust can become unstable, collapsing to form new stars, planets and other rocky bodies. The energy released by the impacts of in-falling material means the growing planets are molten. Also over time, the heavier elements sink to the middle and the lighter ones float on top. So these new bodies can have cores of iron and nickel. Our planet is a good example.

In the young Solar System, there were lots of bodies orbiting around the young Sun. Collisions were frequent.

If they were gentle enough, the bodies stuck together, helping the growing planets. However, some collisions were so violent the colliding bodies were smashed to bits, releasing lots of fragments that could be swept up by other planets.

If one or both of the smashed up planets had iron cores, the result was lumps of pure iron and nickel being sent off to orbit the Sun. Our museums have many specimens of iron meteorites that have hit our world. Impact sites have been found all over the world, including the Middle East.

Iron is not a precious metal to us, but in the Bronze Age, lumps of iron falling from the sky would have been regarded as very special. Artifacts made from them would have been important enough to be buried with a dead Pharaoh.

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• Venus shines very brightly in the west after sunset.

• Mars, much less bright, and reddish, lies higher in the southwest.

• Saturn, golden coloured and moderately bright, lies very low in the dawn glow.

• The Moon will be full on May 5.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory near Penticton, B.C.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.