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Skywatching

Another near miss

This autumn, we will have a close encounter with asteroid 2006 QV89.

At its closest, it is estimated to be about 6.7 million kilometres away (around 17 times the distance between the Earth and moon).

Taking into account possible errors in the orbit calculations, the chance it might come closer, and actually hit us, is around 1 in 7,300.

This object is about 40 metres in diameter, and its mass roughly 80,000 tonnes. This is far smaller than the one that sealed the fate of the dinosaurs, 64 million years ago, but is still not something to be taken lightly.

If it were moving at, say, 20 km/sec, its impact would liberate about the same amount of energy as a four megaton nuclear bomb. If it misses us this time, as is most likely, it will swoop by us again in 2032, 2045 and 2062.

It is not yet possible to predict exactly how close those encounters will be.

The moon is covered with craters formed by impacts like these. We can find similar scars on Earth, for example on the Canadian Shield and in Arizona, although weather erosion and plate tectonics remove them, which does not happen on the airless, tectonically-quiet moon.

On July 30, 1908 something fairly large plowed into the atmosphere over the Tunguska River in Siberia and exploded. The blast flattened 2,000 square kilometres of trees.

The object is believed to have been 50-100 metres across, depending on what it was made of. A small change in the time of arrival would have put the impact over Western Europe, with catastrophic results.

As our ways of life becomes more interconnected and interdependent, our vulnerability to natural disasters increases. The historical record shows that over human time-scales asteroid impacts are very rare, but their consequences make it worth doing our best to avoid them.

There are three facets to this.

First we need to detect and identify asteroids that are potential threats, and to maintain an up-to-date threat catalogue.

The next step is to estimate the threat potential of each close encounter, preferably in enough time to do something about it.

The final step is to do that something.

Work on the first step is well advanced, and there are purpose-built instruments sweeping the sky for asteroids, particularly those with orbits that cross or get close to the Earth's.

Assessment of threat potential in time to do something to mitigate the situation is more difficult. At the moment, we usually see the asteroids as they move in for their close approaches, which leaves us with little time to do anything.

We need predictions years in advance. With the asteroid orbits being constantly perturbed by the gravitational attractions of the giant planets, particularly Jupiter and Saturn, this is proving a challenge.

Work on this continues.

 

Mitigation is difficult. The method used in the movies, namely flying adventurously to the object and putting a great big bomb on it to blow it to pieces would actually make things worse.

Instead of being hit by one object at one location, we would instead be hit by multiple objects, all over the Earth. The idea getting most attention is to identify the threats long enough in advance for us to send a space mission to install a low-thrust rocket motor on the surface of the asteroid.

It could use the asteroid's material as fuel. The efficiency and thrust would be low, but the engine would run for years, gradually nudging the asteroid into a different orbit. The idea would be to push it far enough to accommodate any reasonable error in our orbit calculations.

Of course, to make this solution feasible we will need a launcher big enough to get to the asteroid in a reasonable time.

We are nowhere near there yet.

  • At 8:54 a.m. June 21, the sun reaches its northernmost point in its annual travels — the summer solstice.
  • Jupiter, shining brilliantly, rises around 10 p.m.
  • Saturn rises at 11 p.m.
  • The moon will reach Last Quarter on the 25th.

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About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]



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The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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