How to stop an asteroid using nothing but "pebbles"

<div><br /></div><div><a href="http://io9.com/5908066/how-to-stop-an-asteroid-using-nothing-but-pebble…;
</div><div><br /></div><div><b>snip</b></div><div><span style="color: #333333; font-family: Georgia, Times, 'Liberation Serif', serif; font-size: 15px; line-height: 22px; text-align: -webkit-auto">According to </span><i style="border-style: initial; border-color: initial; border-image: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 15px; font-family: Georgia, Times, 'Liberation Serif', serif; vertical-align: baseline; color: #333333; line-height: 22px; text-align: -webkit-auto; border-width: 0px; padding: 0px; margin: 0px">New Scientist</i><span style="color: #333333; font-family: Georgia, Times, 'Liberation Serif', serif; font-size: 15px; line-height: 22px; text-align: -webkit-auto">, 500 kilograms worth of these spacecraft could push a 250-meter wide asteroid at least 35,000 kilometers off course, which would be more than enough to remove pretty much any chance of a collision with Earth.</span>
</div><div><div><b>snip</b></div><br class="Apple-interchange-newline" /></div>