Then help your son fill the water bowl as well.

On first blush, you might think not: the planet where the comet or comets came to grief is farther out than Mars, in an orbit where water would be permanently frozen.

Recently, scientist have also discovered comets in the main asteroid belt - these main-belt comets might be a key source of water for the inner terrestrial planets.

Their observations rewrote the history of water on Mars.

You' ve been seated, they' ve given you water and bread, and you decide - because the place is a bit grimy or too expensive, or nothing on its menu is appealing - that you want to leave.