Another near miss

Publisher’s version / Version de l'éditeur:

Skygazing: Astronomy through the seasons, 2018-05-22

READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. https://nrc-publications.canada.ca/eng/copyright

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la

première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.

Questions? Contact the NRC Publications Archive team at

PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.

NRC Publications Archive

Archives des publications du CNRC

This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. / La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur.

For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous.

https://doi.org/10.4224/23003364

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at

Another near miss

Tapping, Ken

https://publications-cnrc.canada.ca/fra/droits

L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.

NRC Publications Record / Notice d'Archives des publications de CNRC:

https://nrc-publications.canada.ca/eng/view/object/?id=1bcf61ba-2840-4069-b2d6-9bfd558a1225 https://publications-cnrc.canada.ca/fra/voir/objet/?id=1bcf61ba-2840-4069-b2d6-9bfd558a1225

ANOTHER NEAR MISS

By the time you read this, asteroid 2010 WC9 will have passed the Earth at around 12.8 kilometres a second (46,000 kilometres an hour), at a distance of roughly 200,000 kilometres, about half the distance between the Earth and Moon. The

asteroid is roughly 70 metres in diameter, although it could be a bit larger. If it is made of basalt, the most common rock in the Solar System, it would weigh about half a million tonnes. Being hit by it would have been a disaster, although we as a species would probably survive. Since there are many such objects, some smaller, some larger, in orbits crossing the Earth’s path around the Sun, and almost certainly many more we have not yet detected, there is a definite risk of being hit. The Earth has been hit many times over its 4.5 billion year history. We see a record of this in the oldest rocks, such as those of the Canadian Shield. For example, the mineral riches of

Sudbury, Ontario are due to the impact some 1.98 billion years ago of an object 10-15 kilometres in diameter. Another large object hit us some 65 million years ago. It was a major cause of the extinction of about 75% of animal species. If we were hit by a similar object today, it would be a disaster. With people inhabiting most of the Earth’s surface, and our lives depending on a world-wide infrastructure of trade and communications, we are now highly vulnerable. What can we do to avoid being hit by an asteroid? Basically, at least for the immediately foreseeable future, not very much. Our problem is reliably predicting the collision in time to prevent it. An asteroid made of basalt, a dark coloured rock, almost certainly covered by a layer of basalt dust, would be extremely hard to see. Unless very lucky, we normally only see the small ones when they are very close, just in time to see them whizz past.

If we want to deflect an asteroid like 2010 WC9, coming towards us at 12.8 kilometres a second, and already quite close, we would have to attach a very large rocket motor to it. This would involve

transporting it to the asteroid, matching speeds and then soft-landing it on its surface. To do a last minute change to half a million tonnes of rock will need an extremely powerful rocket. Even if we had such a rocket, it is unlikely we would be able to deliver it to the asteroid in time. In movies we have the heroes blowing up the threatening asteroid with a very large bomb. This would not be the greatest idea. Blasting one object, which would have impacted one part of the world, into many, impacting all over the world, would be far worse. If we could detect threatening asteroids years before the predicted collision, we could soft-land a low-power rocket motor on them, possibly using the asteroid’s own material as fuel. Given enough time, even a low thrust rocket motor could slowly change the asteroid’s orbit into a less threatening one. However, it is very hard to predict impacts with any certainty years in advance. The problem is that the asteroids’ orbits are being continually tweaked by the gravitational attractions of the other planets, mainly the giant planet Jupiter. The result is that our predictions contain

uncertainties. We can only guarantee that at the forecast encounter time, an asteroid will pass through a volume of space with the Earth lying in it. To avoid disaster, the uncertainties in our prediction have to be much smaller than any change our low-power rocket can make to the asteroid’s orbit, so that we can be sure we are making the right correction. This requires better position measurements, over more of the asteroid’s orbit. People are working hard on this. After sunset Venus is spectacular in the west and Jupiter almost as spectacular in the southeast. Saturn rises around midnight and Mars around 2 am. The Moon will reach First Quarter on the 22nd and will be Full on the 29th_.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9.

Tel (250) 497-2300, Fax (250) 497-2355 E-mail: ken.tapping@nrc-cnrc.gc.ca