Canberra scientist and author Dr Duncan Steel says while most people think of the ''killer asteroid'' that wiped out the dinosaurs about 65 million years ago, that was not the only global catastrophe of its type.

''There have been five major mass extinction events that we know of,'' he said. ''They are well known and well documented [in scientific circles].''

He says that given the existential threat such impacts pose for the human race it makes sense to invest a small proportion of the housekeeping money in a ''Spaceguard'' program such as the one outlined by Arthur C. Clarke in his novel, Rendezvous With Rama.

''I'm not saying the end is nigh, what I am saying is that there is a demonstrable risk and that it would be imprudent not to take action. It is like screening for cancer: most of the time the results are good but when they are bad then the consequences can be dire.''

Steel said the Chelyabinsk meteor impact in western Russia on February 15 was both a wake-up call and a lucky escape.

A small asteroid, believed to be about 17 metres in diameter, plunged into the Earth's atmosphere at about 60,000km/h, or 50 times the speed of sound. The resulting air burst explosion released 20 to 30 times more energy than the 1945 Hiroshima bomb, injured almost 1500 people and damaged 7200 buildings in six cities.

Because it was so small and coming from sunwards the asteroid was not detected until it exploded due to the heat of entering the Earth's atmosphere. The resulting fireball was recorded on hundreds, possibly thousands, of phone and car cameras, home video recorders and CCTV cameras.

The incident occurred on the same day as the closest ever ''observed near miss'' by an asteroid, but scientists have concluded the two events were not related.

''We were lucky (with Chelyabinsk) in a variety of ways,'' Steel said. ''First of all, it entered the Earth's atmosphere on a very shallow angle; about 20 degrees rather than the 45 degrees that is the most likely entry angle for objects of this type.''

This meant the object punched through a lot of air at a high altitude, dissipating most of its energy at between 40 and 28 kilometres above the Earth. ''It finally petered out about 20 kilometres,'' Steel said. ''That is twice the altitude a jumbo jet flies at.'' If the object had come in on a sharper angle the fireball would have occurred closer to the surface of the Earth and the damage, and the casualties, would have been much greater.

The five-megatonne airburst from the famous Tunguska event in Siberia in 1908, which felled trees over an area of about 2000 square kilometres, occurred at about eight to 10 kilometres above the earth. It is believed to have been caused by the arrival of an object about 40 metres in diameter.

''We are very fortunate nobody was killed [at Chelyabinsk],'' Steel said. ''It was the shock wave that caused the damage; it was not bright enough to start fires on the ground [which happened at Tunguska].''

Steel, who was born in the English town of Midsomer Norton at the beginning of the space race, has been fascinated by the heavens and space exploration since his childhood.

''I was 14 when Apollo 11 landed on the moon,'' he said. ''It was late at night [when it occurred] in England and we watched it at home.

''I thought it was wonderful. I was already reading science fiction and doing a lot of maths and physics. I could see no reason why I couldn't get involved [in space] and I did.''

While Steel, who had been working in the defence sector in Canberra until a year ago, is best known for his interest in Spaceguard, his interests are far more wide reaching.

He has just been appointed a visiting professor of astrobiology at the University of Buckingham in Britain and is in the final stages of being appointed an adjunct professor of physics and astronomy at a New Zealand university.

''In the past I have (also) been an associate professor of space technology,'' he said. ''None of these strictly define what I do. I am an educator, author, broadcaster and space researcher.''

Steel says astrobiology is about much more than the search for extraterrestrial intelligence (SETI) and life on other planets. ''Much of it is about understanding the evolution of life on Earth, particularly in extreme environments, where it is either hot or cold, acid or alkali or extremely dry.''

Earth's ''extremophilic'' life forms are evidence of the diverse range of environments life can adapt to and indicate where scientists can look when it comes to other worlds.

''Half of the Earth's biomass is believed to be deep underground; it consists of organisms that eat rock.''

Steel, who has worked for NASA and the European Space Agency in the past, worked at the Anglo-Australian Observatory at Coonabarabran, directing a now defunct program to find and track near-earth asteroids in the early 1990s. Australia's Spaceguard program was axed by the Howard government in 1996.

It alarms him that the Americans are the only people on the planet currently funding such work and cites a comment by Australia's then science minister, Peter McGauran, on 60 Minutes in 2002 as evidence of this country's ongoing indifference.

''I'm not going to be spooked, or panicked, into spending scarce research dollars on a fruitless attempt to predict the next asteroid,'' Mr McGauran said. ''I'm just not convinced that the hype and alarm and even fear mongering is enough to justify an instant investment.''

Steel puts this remark, and the remarkable replies the minister's office sent to some distinguished scientists who tried to point out the short-sightedness of this view, in the same basket as arguments that money spent on space research is a waste and produces no discernible benefit.

''I just don't have anything to say in the face of such profound ignorance,'' he said. ''Unless you are living in the deep bush and have no connection to the modern world then every aspect of your life is affected by space research in some way.''

And, of course, there is the chance that endeavours such as Spaceguard will one day save the planet.

Four weeks ago Steel was the only Australian at a Planetary Defence Conference in Flagstaff, Arizona, which involved a simulation of a meteor strike off the southern coast of France. Former astronauts ''Rusty'' Schweickart (Apollo 9) and ''Buzz'' Aldrin (Gemini 12 and Apollo 11) also attended. They, along with senior officials in the US administration, take the threat of asteroid impact very seriously and believe being forewarned is forearmed.

''The idea is to know about a threat as early as possible so something can be done about it,'' Steel said. ''America's next manned space mission will not be to the moon or to Mars. It will be to a near-Earth asteroid and the intent will be to develop the capability to intervene if we have to.''