University of Melbourne theoretical physicist, Dr Robert Foot suggests that many of the missing comets could be made of an exotic material called 'mirror matter', a new type of invisible matter that a small group of physicists believe could be the elusive 'dark matter'. Dark matter is considered the cosmic scaffolding that makes up most of the universe, but nobody can identify it.
"If mirror matter exists, then there should exist also mirror stars, mirror planets, even mirror life. Over the last few years almost every astrophysical and experimental prediction of the theory has actually been observed by observations and experiments," says Foot.
"Most tantalysing of all, is evidence that our planet is frequently bombarded by asteroids made of mirror matter, causing puzzling events such as the devastating Siberian explosion in 1908 and similar, but smaller recent events in Jordan and Spain," he says.
Foot has outlined his theories and those of other mirror matter proponents in a new book, Shadowlands-quest for mirror matter in the Universe.
The theory of mirror matter has been around for decades. The case of the missing comets has baffled scientists for nearly as long. Yet, if Foot is right, the two mysteries may have a common and potentially cataclysmic answer.
Astronomers have found that most comets disappear after their first pass through our solar system. The consensus is that they either disintegrate or 'turn off', having lost their volatile gases and ice that form their glowing head and tail. They become, in effect, chunks of rock similar to asteroids.
But some US scientists recently did some modelling and number crunching to determine the fate of the missing comets. They came to the striking conclusion that the number of dormant comets or asteroids being discovered is far too low to accommodate the predicted number - about 100 times too low. So where did they go?
Dr Foot says there is a good case for these missing comets to be made of mirror matter. He points to some freaky and, so far, inexplicable events to make his case.
Tunguska, Siberia was the site of a blast with the explosive power of 1000 atomic bombs that flattened 2100 square kilometres of forest in 1908. Scientists have blamed an asteroid, but remarkably they have found no crater, no evidence of meteorite fragments and no significant chemical traces.
In Jordan, April 2001, 100 witnesses on their way to a funeral watched a ball of light streak across the sky at low altitude, break into two, and then slam into a hill about one kilometre away. Again, local astronomers found neither a crater nor evidence of a meteorite; just a patch of scorched earth and burnt trees.
"These events cannot be explained in terms of a space-body made of ordinary matter. If the Jordan space-body was made of ordinary matter it should have lit up a large part of the Middle East. This was not observed," says Foot.
So what is mirror matter and how does it affect us?
Nearly 50 years ago physicists discovered that the way particles interact was not symmetrical. Instead, they are predominantly left-handed. This was contrary to the strongly held belief that all fundamental interactions were mirror symmetric. That is, for every left hand interaction there was a right hand interaction to balance it out.
This is where mirror matter makes its entrance. Mirror matter is the predicted right hand or mirror image of ordinary matter. For each of the known basic particles, such as the electron, proton and photon, there is a distinct mirror partner. Where the ordinary particles favour the left hand, the mirror particles favour the right hand.
It is thought that ordinary particles, for example, photons (light particles), cannot interact or couple with mirror particles directly. Because we are made of ordinary matter we are unable to see mirror photons and therefore the world of mirror matter remains invisible to us.
Theory predicts, however that mirror particles have a mass. This means one force that does act on both is gravity, which means we should be able to detect this effect. It is one fact that takes mirror matter out of the realms of science fiction and into reality. Another is the possibility of new forces connecting ordinary and mirror matter.
A recent experiment suggests one such force could exist. The force measured was a small electromagnetic coupling between mirror and ordinary particles. Two groups, including the world's largest physics research centre, CERN, are about to begin highly sensitive experiments to try and confirm the existence of this force.
Foot has calculated this force, should it exist, is sufficient to allow interactions between ordinary particles and those of a mirror asteroid entering the Earth's atmosphere.
These interactions could allow heat to build up within the mirror body, causing it to explode. It would also make the mirror body visible. If the events of Tunguska and Jordan are the results of mirror space-bodies, then tonnes of mirror matter might lie hidden just below the surface of these sites, waiting to be found. Nobody has looked," says Foot
"As for the missing comets, they could simply be mirror comets with embedded ordinary matter. Once they have passed the sun, their ordinary volatile components progressively burn off leaving an invisible mirror matter core. This would explain why so many simply fade away," he says.
Dr Foot's website on mirror matter can be found at http://www.ph.unimelb.edu.au/~foot/ It contains links to further information and his new book.