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Skywatching

Dealing with asteroids before they collide with Earth

Killer asteroids

Sixty-five million years ago, after ruling the Earth for some 200 million years, the dinosaurs and many other forms of life were in decline. Then came the asteroid.

By the time things settled down again after the impact, the dinosaurs and 75% of the living species on Earth had gone, leaving our mammalian ancestors to take over. The geological record shows multiple occasions over our world's history where we have been hit by large objects from space.

It will certainly happen again, and on a world crowded with people and resources pushed to the limit, the consequences for us could be very serious. That is why there is a growing effort to do what we can to avoid such a disaster.

The science fiction movies show the threatening object being blown up at the last minute and the world being saved. In reality, doing that could make things worse. Lots of impacts scattered all over half the Earth would be nastier than one big impact in one place. Instead, plans are to change the orbit of threatening objects so they miss us.

A one-kilometre diameter asteroid would have a mass of more than a billion tonnes.

The object that finally ended the rule of the dinosaurs was several kilometres in diameter. Something that big will not be deflected easily. A thousand of the most powerful rocket engines available today applied a month before impact would not make much of an impression on the speed and direction of such an asteroid, apart from the challenge of getting all that hardware to the asteroid, installing and testing it.

The only feasible option we have at the moment is to spot the threat as early as possible. Then we can attach a small engine that will apply a tiny, continuous push that over years will change the asteroid's orbit enough for it to miss us.

We have the technology to do this. There are telescopes monitoring large areas of the sky, searching for objects moving against the background stars. Such objects would have to be nearby, well inside the Solar System.

The faster they seem to be moving, the closer they are likely to be to us, unless of course they are coming straight at us. Once an object has revealed itself, more precise observations are made to determine its orbit and its threat potential. In principle, the earlier we detect an object the more time we have to do something about it. It can take months or even years to deliver the equipment intended to deflect the asteroid. However, there is a problem. Although we see the Solar System as a collection of planets and other objects orbiting the Sun, held there by the Sun's gravity, there are other forces at work.

All the planets gravitationally tug at each other too; especially giant planets like Jupiter. These forces are tiny compared with the gravitational attraction of the Sun, but over time they cause orbits to change. The result is that precisely predicting where an asteroid might be in five years could be very difficult.

We have to predict the orbit and also estimate the errors that might build up over a few years of perturbations due to the other bodies in the Solar System.

To be sure we are saving ourselves and not changing a near miss to a hit, we need to make the course change big enough to push the body outside the possible range of orbit prediction errors.

This is not easy, but there is an incentive, just ask the dinosaurs.

May this Christmas season bring us all lots of good cheer and no encounters with asteroids.

•••

• On Dec. 21, the Sun reaches the southernmost point in its yearly travels—the winter solstice. From here on it will start moving north again. The sunrise and sunset points on the horizon will start moving northward, and the days will start getting longer.

• Mars lies low in the dawn twilight.

• After sunset, Venus lies close to the southwest horizon, with Saturn to its left and then Jupiter. Venus shines brightest and Saturn the faintest. • The Moon will reach last quarter on the Dec. 26.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.



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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]



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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