Theres another matter

And it's called quark matter. The incredibly tiny quarks come in six types or 'flavours': up, down, strange, charmed, bottom and top. Protons and neutrons are made from up and down quarks. Other quarks are not found in ordinary matter. Scientists, however, believe that a strange quark matter - a form of matter made of up, down and strange quarks - was formed in the big bang that marked the beginning of the universe some 13 billion years ago. This matter is so dense that a teaspoonful of it would weigh billions of tonnes.

In 2002, the orbiting Chandra X-Ray Observatory spotted a star which scientists believe is a quark star. Theorists have long suspected the existence of quark stars, collapsed stars that are denser than neutron stars but not dense enough to become black holes. The observed star has a radius of 5 to 6 kilometres. This radius, scientists believe, is about half of what would be expected if the object were a neutron star, but about right if it were a quark star. If the strange quark matter does really exist, it could destroy ordinary matter by converting protons and neutrons to quarks. This process could spread like cosmic wildfire through space.

In the same year, a team of researchers from Southern Methodist University in Dallas said that not only does the strange quark matter exist, but it passed through Earth twice in 1993. The first event occurred on 22 November, when an object entered Earth off Antarctica and left the Indian Ocean south of Sri Lanka 26 seconds later. In the second event, on 24 November, an object entered south of Australia and exited near Antarctica 19 seconds later. These entry and exit points imply that both objects were travelling with a speed of 144,000 kilometres per hour. Both events were recorded by several monitoring stations but no satisfactory explanation for the events has ever been suggested.

In 1984 Sheldon Glashow said that strange quark matter would pass through Earth with a dramatic effect: a 1-tonne object would release 50 kilotons of energy, which would be spread through Earth along the path of the object. The Southern Methodist researchers began looking for such events in 1993 and selected the two events mentioned above from more than a million records collected by the US Geological Survey between 1990 and 1993 which were not associated with traditional seismic disturbances. According to Eugene Herrin, one of the team members, normal earthquakes and explosions are point sources - the energy radiates from a single point. When a clump of strange quark matter - known as a strangelet or strange-quark nugget -passes through Earth, you have a linear source with energy radiating from the whole of the line through Earth, and this would give a different pattern in the way seismic stations record the data. The 1993 events -caused by strangelets just one-tenth the breadth of a hair and weighing nearly a tonne - left a distinct linear quark matter pattern. 'We can't prove that this was strange quark matter, but that is the only explanation that has been offered so far', Herrin said.

The impact of strangelets on an inhabited area would probably be less violent than that of a meteorite. 'It's very hard to determine what the effect would be', said Herrin. 'There would probably be a tiny crater but it would be virtually impossible to find anything.'

Did a quark matter rock strike Tunguska on 30 June 1908? There is a possibility, but no one has the definitive answer, yet.

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