Comet seen from planet Earth - BBC science

Scientists explain the reason why so few probes have been launched to monitor the trail of a comet. As nobody can truly predict the appearance of comets, scientists might only get 2 - 6 months notice. Clip taken from BBC documentary ' A Comet's Tale'. Watch more Comet's Tale clips with BBC Worldwide here: http://www.youtube.com/view_play_list?p=0E69828D29AD416B