Dark Star book review by Western Daily Press journalist Geoff Ward

Andy Lloyd, 37, of Longlevens, Gloucester, who carefully assesses the evidence in a new book, puts forward a convincing case for the existence of the mysterious "dark star", or "Planet X", as it has also been called.

Scientists have speculated about a hidden body orbiting the Sun for a century at least, and there has been mounting interest in the subject of such a binary star system since the 1980s, with a variety of theories being put forward - but, as yet, no discovery.

A possible contender for the companion star was located in 1983 by the Infra-Red Astronomical Satellite (IRAS), but the findings were never confirmed. Another was the "Nemesis" star, discussed by the American astronomer Carl Sagan following results of research announced in 1984 by the University of Louisiana. It was the late Sagan and his Cosmos TV series in the 1980s that inspired Andy to take up science and gain a first-class honours degree in chemistry at Lancaster University. Now he has put forward his own formulation of the Nemesis theory.

He told me that he believes the dark star is a small version of what astronomers call a "brown dwarf" - a body caught half way between being a star and a planet - with its own retinue of satellites and a 10,000-year orbit around the Sun. It is now at its furthest point from us - a thousand times the distance from the Earth to the Sun - and so would be a vanishingly small object and, because of the enormous distance, apparently stationary, giving it the misleading appearance of a fixed star.

Indeed, Andy says it may already have been detected and catalogued erroneously as a star in the Milky Way galaxy.

It would be about the size of Jupiter, the largest planet in our solar system, but much heavier and denser and capable of generating both heat and light.

Andy has calculated that Planet X lies in the constellation of Sagittarius, in what is known as the "Oort cloud", the deep-space origin of many comets that pass through the solar system. "Two new space telescopes are due to be launched in the next couple of years, and if these between them don't spot the star then it's not there," he admitted. "If it hasn't been found within five years, it doesn't exist.

"But my book is basically a prediction that the star will be found within five years. The discovery will create a whole new structure in astronomy.

"I have had to be as scientific as I can to make this leap into the unknown. But in the last year or two science has really turned in my direction on this issue, which is really exciting."

Andy believes that evidence for an approach by the dark star, when one of its planets swung through the outer reaches of our solar system and became visible from Earth, can be found in the writings of the ancient Sumerian civilisation which flourished in the Middle East 5,000-6,000 years ago.

This is when the star would have last passed, if it is on a 10,000-year orbit, coinciding, significantly, with the invention of the calendar about 3,800BC.

Andy takes a cue from the Russian scholar Zecharia Sitchin whose book The Twelfth Planet caused a stir when it was published in 1976.

Sitchin proposed that the Sumerian creation myth of a cosmic battle between the gods was actually an account of a new celestial body entering the solar system four billion years ago which created the Earth through a collision with another planet, the remains of which are the belt of asteroids which lie between the orbits of Mars and Jupiter.

Andy thinks this body was indeed the binary companion star.

He says it may hold the key to long-term shifts in the climate of the Earth, and that the changes we are experiencing now may be "symptomatic of adjustments in that cosmic balance of power".