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Beware Of Buses From Deep Space

A 2km asteroid is something to be taken very seriously. The global climatic effects of an impact anywhere on Earth would be devastating for our civilisation and would probably lead to the death of more than a quarter of the world's population. It would however, not be nearly as severe as the impact 65 million years ago that is associated with the extinction of the dinosaurs.
by Michael Paine
Sydney - Jul 31, 2002
There was a flurry of interest by TV news studios and newspapers last week when it was realised there was a slight risk that a space rock, designated 2002 NT7, some two kilometres across might hit the Earth in 2019. As expected, by the end of the week additional observations had pinned down the orbit sufficiently for astronomers to rule out any possibility of an impact in 2019.

A debate ensued about whether the initial, tentative calculations should have been made available to the public and whether the media reporting was sensationalised. When the dust settles, so to speak, there are a few points to be made about this object.

Firstly, a 2km asteroid is something to be taken very seriously. The global climatic effects of an impact anywhere on Earth would be devastating for our civilisation and would probably lead to the death of more than a quarter of the world's population. It would however, not be nearly as severe as the impact 65 million years ago that is associated with the extinction of the dinosaurs.

Secondly this object has an unusual orbit and it appears to be fortunate that it was picked up by the LINEAR "Spaceguard" telescopes. With current search efforts we can expect a large proportion, perhaps 80%, of Near Earth Asteroids of this size to have been discovered to date so it was a bit of a surprise that 2002 NT7 turned up.

Thirdly, a world-wide effort by astronomers, who were mostly amateurs, was needed to track the asteroid so that calculations could be refined and the object eventually declared "safe" (there is still a slight risk of an impact in 2060, but once again further observations are expected to eliminate that possibility).

Estimates of the average impact rate of asteroids vary considerably. During the next 50 years there is perhaps a one in ten chance of an impact actually occurring but this would likely be an airburst event such as the 60m diameter asteroid that flattened 2000 square kilometres of forest in Siberia in 1908.

Small asteroids collide with the Earth (or more correctly, the atmosphere) much more frequently than large ones. They are not a threat to our civilisation but could easily destroy a city with an explosion similar to that of a nuclear bomb.

For now NASA has decided to concentrate on asteroids one kilometre and larger that pose a global threat. It aims to have detected 90% by 2008. The search effort also picks up many of the smaller asteroids so that after ten years it is expected that about 20% of asteroids 200m or larger will have been found.

Since an impact by an object this size could devastate a small country a 20% completion rate is likely to be seen as inadequate by future generations and the Spaceguard effort will no doubt be stepped up.

Up until 1996 Australia made a significant contribution to Spaceguard, accounting for about one third of discoveries. In that year Australian government funding stopped and the program closed down. In January this year more than 90 scientists from around the world signed an open letter to the Australian government supporting the revival of funding for "Spaceguard Australia". Most were experts in the field of asteroid research and the letter was a remarkable, spontaneous show of solidarity. Nevertheless during a subsequent TV interview, Australian Science Minister Peter McGauran dismissed the search for Earth-threatening asteroids as a "fruitless, unnecessary, self-indulgent exercise".

Fruitless? Spaceguard is finding objects like Asteroid 2002 NT7, and can provide decades of warning - sufficient time to nudge an Earth-threatening asteroid into a safe orbit.

Unnecessary? Only if we take the gamble that an impact will not happen in our lifetimes. Sadly it is all too easy for politicians to ignore our responsibilities to future generations - the ones who would benefit most from observations made today.

Self-indulgent? That is plain insulting to the many scientists who have recognised that the Earth is at risk and who have dedicated much of their career to addressing the hazard. It is also insulting to the hundreds of amateur astronomers who donate their time to follow-up observations.

In fact, the letter arose from a statement by a spokesperson for Minister McGauran who indicated that funding would be reconsidered, following another asteroid "near miss" around Christmas time.

Clearly asteroids do pose a hazard to our civilisation. The Spaceguard system has been shown to be effective in detecting objects like Asteroid 2002 NT7 but there are many more that we should be looking for. An international effort is needed and, in particular, the current blind spot in the southern hemisphere needs to be addressed.

Yes - there is an asteroid with our name on it. It might hit tomorrow or not for a thousand years. Every telescope that is added to the international Spaceguard program will reduce our chances of being caught with insufficient time to avoid the collision.

By reviving the search for rogue asteroids, Australia would fulfill its responsibility to protect its citizens, to help protect other citizens of the world and to provide a possible gift of survival for future generations.

Michael Paine is a consulting mechanical engineer based in Sydney. He is a member of the Planetary Society.

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