After decades of dreaming and preparation, scientists have finally put the Rosetta spacecraft into orbit around a comet. And now the Rosetta is about to land!
To the previous commenter - it would not work to use comets as modes of transport for the following reason: To land on the comet, you need to use the energy to get into the comet's orbit - i.e. to "pull up along side it". At that point, anything in that orbit is just falling around the sun through the vacuum of space - all of that is free motion. So you'd have already done all the work you need to go everywhere the comet is going, whether or not the comet is actually there. Another way to think of this: the comet is just falling; it isn't actually expending any of its own energy to propel itself, so there's no "engine" to hitch onto there.
