Almost 4 billion years ago, an asteroid slammed into the southern hemisphere of Mars. Even today, the scar of that primordial impact remains the largest crater in the solar system.
But not until NASA's Mars Global Surveyor completed the first detailed topographical map of the planet's surface earlier this spring were scientists able to appreciate the true dimensions of that ancient collision.
The Hellas crater on Mars is so deep it could easily swallow Mt. Everest. The spray of debris radiating from the impact covers an area the size of the continental United States with a blanket of material two miles thick, stretching 2,500 miles across.
The topographical particulars of the crater itself--6 miles deep and 1,300 miles across--are among many surprising revelations from a new, highly accurate surface map of Mars. The panorama is based on 27 million elevation measurements gathered in March and April from the Mars Orbiter Laser Altimeter aboard the Global Surveyor spacecraft, which is orbiting 229 miles above the red planet.
"Probably the most unexpected finding was how much the Hellas impact basin dominates the topography of the southern hemisphere," said Maria Zuber, a planetary scientist at the Massachusetts Institute of Technology and one of the 20 scientists who created the global grid of Mars.
In creating a high-resolution, three-dimensional map of the Martian terrain, the researchers--working with NASA's Goddard Space Flight Center in Greenbelt, Md., and the Jet Propulsion Laboratory in Pasadena--scaled the heights of the tallest mountains and plumbed the depths of the deepest craters on any planet in the solar system.
Indeed, the new map reveals that Mars has the highest, lowest and smoothest land forms anywhere in the solar system.
Between the loftiest and the lowest points on Mars, there is 19 to 20 miles difference in elevation--1 1/2 times the range of elevation seen on Earth. It is a testament to the strength of the underlying crust of Mars that it can support such weight.
The Olympus Mons volcano, for example, rises nearly 17 miles above the average elevation of Mars, making it the tallest known volcano in the solar system.
The broad outlines of such Martian geography have long been known but never before has the planet's surface been revealed in such precise detail.
