PASADENA, Calif. - When it came to pinpointing a touchdown spot for the Mars Polar Lander, the team at mission control hemmed and hawed for a full eight months into the spacecraft's journey before announcing its final destination.
One reason for the delay was the team's uncertainty about what would await the Lander when it alights on Mars this Friday.
Scientists expect smooth, rolling terrain that will make landing a cinch.
The region should be uncluttered as the rocks and boulders that marked Mars Pathfinder's landing site two years earlier could topple the Polar Lander, which rests on spindly legs.
Yet over the last 28 years, the various spacecraft which have surveyed Mars have sent back contradictory messages, revealing a planet that is sometimes beguiling, playful, yet seemingly loathe to reveal its true nature to admirers from afar.
Case in point is what scientists call the Martian paradox.
Simply put, if terrain imaged at low resolutions by Mariner 9 (1971) or the twin Viking Orbiters (1976) appears rugged, then it will appear smooth at high resolutions in images acquired by the Mars Global Surveyor over the last 18 months.
On the flip side, if terrain appears smooth in the Mariner 9 or Viking images, then it will appear rough in the higher-resolution Global Surveyor images.
"If you were a mystic, youd say Mars is getting even," said Michael Malin of Malin Space Science Systems, the San Diego builder of cameras on the Polar Lander and Global Surveyor.
Malin said he first noticed the paradox about 18 months ago. He now chalks it up to scientists bringing to Mars expectations about the planet grounded in observations they have made far closer to home.
"We bring to any planet our geological prejudices from the Earth and moon," Malin said.
Malin said the apparent paradox shows that Mars is its own place, often without terrestrial or lunar analog.
"There is some process that roughens the surface at a scale weve never seen before and that was not anticipated," said Malin, referring to terrain marked with ridges and groves, similar to the wavy surface of a corrugated tin roof.
The paradox is now treated as a rule. Using Mariner or Viking images, Malin said he can predict with at least 75 percent accuracy whether the same swath of territory will be smooth, rough or rugged when viewed by the Global Surveyors camera.
Best guesses aside, the Mars Polar Lander site had remained covered with seasonal frost until just months ago, forcing mission members to await the Martian spring to get detailed and conclusive images of the region.
NASA will release more updated images from the targeted landing zone on Thursday, which could lead to a final trajectory correction maneuver on Friday just hours before the spacecraft lands.
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