The Mars Pathfinder has found that like Earth, Mars has a crust, a mantle and an iron core. But while the iron core implies there was once heat there, scientists are still chasing that other elusive ingredient necessary for life: water.
During a news briefing Wednesday, scientists at NASA's Jet Propulsion Laboratory offered little interpretation of the iron core find. However, having enough heat to create the distinct inner layers some 4 billion years ago adds weight to theories that the planet once may have been warm and wet enough for life to form.Scientists also found past signs that the surface teemed with flowing streams that carried rocks from place to place. Such flowing water could have created newly observed little cementings of rocks and pebbles called conglomerations.
The evidence that the planet is not merely a solid ball of rock comes by measuring the changes in radio signals from Pathfinder as Mars spins on its axis, and comparing signals measured from the Viking spacecraft that landed in the 1970s.
Scientist William Folkner said they estimate the iron core is somewhere between 800 miles and 1,247 miles in radius, compared with Mars' full radius of about 2,113 miles. But he said they don't know whether the iron core is solid or molten.
Molten cores are rare. Earth and Mercury are the only planets known to have one. The movement of liquid metal within the Earth's core is what creates the magnetic field around the planet.
So far, the orbiting Mars Global Surveyor has found evidence of a weak magnetic field at the red planet. Pathfinder project scientist Matthew Golombek said those observations are not necessarily evidence that the magnetic field was generated by the interior or that the core is liquid today.
In other results, Henry Moore of the U.S. Geological Survey showed images taken by the Pathfinder rover of rock conglomerations. The close-ups show small depressions called sockets and small round spheres, probably pebbles smoothed by water.
They would have been produced in "long eras of liquid water rolling those rocks," Moore said.
Wes Ward, another Geological Survey scientist, said he's seen the first signs of true sand on Mars, with grains about 1 millimeter in size. A product of weathering and erosion, they lie in dunes and in fluted patterns like desert sands on Earth.
Pathfinder is still mired in some technical problems. Scientists resumed communicating with it Tuesday after nine days of quiet.
Both rover and lander have outlived their primary missions since landing July 4. But mission scientists saw no reason that both couldn't function for months more once glitches are resolved.