An endorsement by astronomers meeting in Prague would require school and university textbooks to be rewritten.

The proposal recognises eight classical planets, three planets belonging to a new category called "plutons" and the largest asteroid Ceres.

Pluto remains a planet, but becomes the basis for the new pluton category.

The plan has been drawn up by the International Astronomical Union (IAU) with the aim of settling the question of what does and does not count as a planet.

Some 2,500 astronomers gathered at the IAU General Assembly in Prague will vote on the plan next Thursday.

New era

"For the first time in more than 75 years, we will be able to discover new planets in our Solar System. This is a fascinating prospect," said Richard Binzel, a member of the IAU planet definition committee which put together the proposal.

Dr Andrew Coates of the Mullard Space Science Laboratory in Dorking said he thought the plan was "a good compromise".

He explained: "It keeps the idea of eight classical planets, while Pluto is allowed to retain its status. But other objects are allowed in, which I suppose makes life more interesting."

Experts have been divided over whether Pluto - further away and considerably smaller than the eight other planets in our Solar System - deserves the title.

Since the early 1990s, astronomers have found several other objects of comparable size to Pluto in an outer region of the Solar System called the Kuiper Belt.

Some astronomers believe Pluto belongs with this population of "icy dwarfs", not with the objects we call planets.

Allowances could once be made for Pluto on account of its size. At just 2,360km (1,467 miles) across, Pluto is significantly smaller than the other planets. But until recently, it was still the biggest known object in the Kuiper Belt.

That changed with the discovery of 2003 UB313 by Professor Mike Brown and colleagues at the California Institute of Technology (Caltech). After being measured with the Hubble Space Telescope, it was shown to be some 3,000km (1,864 miles) in diameter, making it larger than the ninth planet.

Kicked upstairs?

The IAU draft resolution recognises eight "classical" planets - Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune - three "plutons" - Pluto, Charon and UB313 - and the asteroid Ceres.

Charon is currently described as a moon of Pluto, but because of its size some experts consider it a twin planet.

Professor Owen Gingerich, who chairs the IAU planet definition committee, said: "In a sense we're demoting Pluto by taking it off the list of classical planets. But we're promoting it by making it the prototype of this new category of plutons."

Dr Coates commented: "Something had to be done about the definition. It does change the textbooks somewhat, but it also demonstrates that this is a vibrant area of research.

"The surprise is Ceres, because most people thought of it as an asteroid."

Ceres is the largest object in the asteroid belt between Mars and Jupiter, and like a planet is spherical in shape.

Seeking endorsement

The basis for this re-evaluation is a new scientific definition of a planet which uses gravity as the determining factor.

According to this definition, two conditions must be satisfied for an object to qualify as a planet:

* The object must be in orbit around a star, but must not itself be a star
* It must have enough mass for the body's own gravity to pull it into a nearly spherical shape

On whether he was confident the resolution would be passed, Professor Gingerich told the BBC News website: "It will be a very awkward situation if they don't.

"On Sunday afternoon, we proposed it out of the blue for the division chairmen and they voted unanimously that they would be prepared to back it. That's a good cross-section of astronomers.

"I'm sure it will be controversial to those with a stake in some other solution, but I hope we will get an overwhelming endorsement."

More objects are likely to be announced as planets in the future. The IAU has a "watchlist" of at least a dozen other potential candidates that could become planets once more is known about their sizes and orbits.

These include the distant objects Sedna, Orcus, Quaoar and 2003 EL61 and the asteroids Vesta, Pallas and Hygiea.

The IAU spent two years debating the matter among its membership. A seven-member committee was set up to consider the findings and produce a draft proposal.

The body has been responsible for the naming of planets and moons since 1919.

Chilton said his goal was to learn all this in the object's first orbit of the Earth so the United States could take unspecified actions "before an adversary can cripple us."

The increased "situational awareness" he had in mind could be achieved largely through improved computer work that would present information in easy-to-understand displays, he said.

Foes would be foolish not to be thinking of how to deny the United States the advantages of space, on which it relies heavily for military and commercial purposes, said Chilton, who took over the space command a month and a half ago.

"And in the future, I'm convinced they'll strike at these capabilities, if nothing else to attempt to level the playing field," he said.

Chilton said the United States had a duty to secure "the entire space domain not just for our own military but for our allies and for the benefit of the free world."

In other remarks to the missile-defense conference, Gil Nolte of the code-making Information Assurance Directorate at the Pentagon's National Security Agency said his agency believed unspecified foreign intelligence agencies had been behind attacks on U.S. computer networks.

He said there had been insufficient investment in cyber security at all levels of the U.S. government while attackers were very well financed and used "a wide range of tradecraft."

A desperate search has begun amid concerns the tapes will disintegrate to dust before they can be found.

It is not widely known that the Apollo 11 television broadcast from the moon was a high-quality transmission, far sharper than the blurry version relayed instantly to the world on that July day in 1969.

Among those battling to unscramble the mystery is John Sarkissian, a CSIRO scientist stationed at Parkes for a decade. "We are working on the assumption they still exist," Mr Sarkissian told the Herald.

"Your guess is a good as mine as to where they are."

Mr Sarkissian began researching the role of Parkes in Apollo 11's mission in 1997, before the movie The Dish was made. However, when he later contacted NASA colleagues to ask about the tapes, they could not be found.

"People may have thought 'we have tapes of the moon walk, we don't need these'," said the scientist who hopes a new, intensive hunt will locate them.

If they can be found, he proposes making digitalised copies to treat the world to a very different view of history.

But the searchers may be running out of time. The only known equipment on which the original analogue tapes can be decoded is at a Goddard centre set to close in October, raising fears that even if they are found before they deteriorate, copying them may be impossible.

"We want the public to see it the way the moon walk was meant to be seen," Mr Sarkissian said.

"There will only ever be one first moon walk."

Originally stored at Goddard, the tapes were moved in 1970 to the US National Archives. No one knows why, but in 1984 about 700 boxes of space flight tapes there were returned to Goddard.

"We have the documents to say they were withdrawn, but no one knows exactly where they went," Mr Sarkissian said.

Many people involved had retired or died.

Also among tapes feared missing are the original recordings of the other five Apollo moon landings. The format used by the original pictures beamed from the moon was not compatible with commercial technology used by television networks. So the images received at Parkes, and at tracking stations near Canberra and in California, were played on screens mounted in front of conventional television cameras.

"The quality of what you saw on TV at home was substantially degraded" in the process, Mr Sarkissian said, creating the ghostly images of Armstrong and Aldrin that strained the eyes of hundreds of millions of people watching around the world.

Even Polaroid photographs of the screen that showed the original images received by Parkes are significantly sharper than what the public saw. While the technique looks primitive today, Mr Sarkissian said it was the best solution that 1969 technology offered.

Among the few who saw the original high-quality broadcast was David Cooke, a Parkes control room engineer in 1969.

"I can still see the screen," Mr Cook, 74, said. "I was amazed, the quality was fairly good."