With rover poised to land, Mars continues to fascinate.(Knight Ridder Newspapers)

Byline: Faye Flam

PHILADELPHIA _ With mountains that rise to three times the height of Everest and Grand Canyon-like gorges long enough to connect Philadelphia to Los Angeles, Mars and its dramatic landscape inspires a certain awe.

For as long as they have spied it through a telescope, scientists have been drawn to the story behind the red planet, which Carl Sagan has described as a billion years past its prime. In its youth did rivers carve these gorges? Did lakes fill the craters? Did life take hold?

And so despite a string of costly failures, earthlings keep hurling new spacecraft toward the more hospitable of our two neighboring planets in the solar system. Last June NASA launched twin rovers, one of which is poised to land on Mars late Saturday night, the other three weeks later.

Scientists designed the rovers to trundle over the Martian surface, taking measurements and pictures to help fill in the blanks in the planet's tantalizing four and a half billion-year history.

Meanwhile, mission control has not abandoned hope ...