Book raises spectre of ghost comets coming soon

By GREG ANSLEY Australia correspondent

CANBERRA - As the BBC reported yesterday that a continent-killing asteroid was racing toward Earth, an Australian physicist was speculating on an even more hair-raising probability - ghost comets we cannot see coming.

The BBC's report that the 2km-wide asteroid 2002 NT7 could slam into the planet on February 1, 2019, is bad enough.

Striking at 28km a second, the impact would be powerful enough to destroy a continent and cause global climate changes, although scientists optimistically hope further observations may show 2002 NT7 will miss the planet.

But in Australia, Dr Robert Foot, of the University of Melbourne, has just published a book, Shadowlands: quest for mirror matter in the Universe, which suggests we may never see our doom approaching.

Foot theorises that invisible comets made of a substance called mirror matter are spinning through space and may already have collided cataclysmically with Earth.

More, there may be entire solar systems with their own suns, planets and forms of life that are invisible to humans or their instruments, apart from a possible explanation for the equally mysterious "dark matter" scientists suggest may be the cosmic framework of the universe.

"It certainly seems fantastic," Foot said yesterday. "But so did antimatter. Before antimatter was discovered experimentally it was [also] a theoretical idea."

Antimatter is a substance comprised of atoms that have the mass and charge of ordinary electrons, protons or neutrons, but which have opposite charge and cannot exist close together.

The theory of mirror matter has been debated for decades, based on the apparent lack of symmetry in the interaction of particles such as electrons, protons and photons.

Instead of the balance that nature normally demands, the interactions are mainly left-handed, leading Foot and other physicists to argue the mathematical probability of mirror particles, invisible and unable to interact with ordinary particles but providing essential symmetry.

Foot suggests there may be dramatic evidence of the existence of mirror matter.

A large number of comets vanish after orbiting the sun because, astronomers commonly believe, their volatile gases and ice are burned off, leaving inert rocks like asteroids.

But United States researchers recently calculated that the number of dormant comets or asteroids being discovered was about 100 times less than there should be.

"One idea is that these comets could be mirror matter bodies with a bit of ordinary matter in them," Foot said.

"The ordinary matter gets burned off and you're left with this mirror matter core, which is virtually invisible." This could explain the destruction of 2100 sq km of forest around Tunguska, Siberia, in 1908, generally attributed to an asteroid strike.

But scientists have been unable to find a crater, evidence of meteor fragments or even significant chemical traces.

Similarly, a ball of light streaked across the sky above Jordan in April last year, split into two and slammed into a hill, scorching earth and trees, but left no crater. Foot believes if mirror matter does exist, proof may lie in Siberia and Jordan.

He said tonnes of the matter could lie beneath the surface of the impact zones, so far undiscovered but probably detectable through thermal imaging and chemical tests.