Robert Foot, who has been studying mirror matter since 1991, became interested in the Tunguska event when in 1999 he watched the television documentary As It Happened: The Day the Earth Was Hit. He became convinced that the event was not fully understood by scientists and that they were ignoring the crucial evidence such as the funnel-shaped holes discovered by
Kulik. He also thought it most unlikely that an ordinary matter asteroid or a comet could completely disappear in the air without leaving any traces, however minute.
In 2002, Foot proposed an interesting solution to the Tunguska puzzle. In his book Shadowlands: Quest for Mirror Matter in the Universe, he suggested that the event was caused by a mirror asteroid. As it dived into the atmosphere the heat caused it to explode at high altitude. The explosion caused a shock wave that wreaked havoc on the Tunguska taiga but didn't leave a trace of an impact crater. He estimated that the mirror matter space-body was roughly 100 metres in size and weighed about 1 million tonnes. Such a heavy (ordinary or mirror) body would not lose much of its velocity in the atmosphere if it remained intact. However, if it were to break up for any reason, the energy of the body would be rapidly dumped into the atmosphere, leading to a huge explosion.
As for the nature of the space-body, Foot said that it was most likely made from mirror matter ices, such as mirror H2O ice. An important difference between the mirror ices and the ordinary ices would be that the mirror ices would not be melted by light from the Sun, and therefore would be likely to be relatively abundant in the inner solar system. On entering the atmosphere, a mirror H2O ice body would vaporise during the flight, and any leftover fragments would eventually melt after striking the ground. 'This could explain why no substantial mirror matter fragments were found at Tunguska; most of the space-body had vaporized after it exploded in the atmosphere, any remaining fragments had melted by the time Kulik arrived there', he said. 'Once in the liquid state, mirror matter should seep into the ground, probably making its extraction impossible.'
However, Foot has left some hope for Tunguska trophy hunters. The mirror body might have some embedded amount of ordinary matter, so a tiny amount of ordinary extra-terrestrial material was possible. Also, any mirror matter fragments that survived and hit the ground could potentially cause small craters or holes. 'Perhaps the most interesting facet of this interpretation of the Tunguska event is that there should be large pieces of mirror matter still lodged in the ground at the Tunguska site', he said. 'Nobody has looked.'
Perhaps the most spectacular way to test Foot's idea is to actually find mirror matter in the ground at Tunguska. 'Any mirror matter fragments would have melted when they hit the ground and reformed becoming mixed with ordinary matter at some distance underground', he said. 'There may be some amount close to the surface which could potentially be extracted and purified.' He suggested that the mirror matter might be separated from the ordinary matter in a laboratory centrifuge. But there is a catch: once the heavier mirror matter had separated from the ordinary matter, it would fly out of the centrifuge test tubes. As you can't see it, you can't catch it. The experiments, however, would prove the existence of mirror matter if the mass of the test tubes and their contents after the experiment were less than they were before. The missing mass would be the mass of the mirror matter you failed to catch.
'It would be a very exciting experiment and lots of fun too!', Foot believes. If you were ever interested in making a name for yourself as an experimental scientist, here's your opportunity. However, you must heed Foot's warning before you pick up your shovel and head to Tunguska: 'It is possible that mirror matter could be hazardous to health.' He takes no responsibility for any cases of mirror matter poisoning.
Alice probably knew about mirror matter poisoning. Just before she stepped through the looking glass, she asked her cat: 'How would you like to live in a Looking-glass House, Kitty? I wonder if they'd give you milk in there? Perhaps Looking-glass milk isn't good to drink.' Now we know that this milk would be made of mirror molecules and perhaps it wouldn't be good to drink, for Kitty at least. Mirror-Kitty would love it, for sure.
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