The National Aeronautics and Space Administration (NASA) issued the caution as its Mars Exploration Rover hurtles towards Mars.
"Spirit" is the first of two rovers due to touchdown on the planet in Janaury.
"I don't know what else humans could have done to make these two rovers successful," said Ed Weiler, NASA's associate administrator for space science.
NASA launched its two Mars rovers into space on June 10 and July 7 respectively. The craft -- which form a 800 million dollar mission -- will follow in the tracks of the "Sojourner" rover that touched down on Mars in 1997 in a bid to establish if conditions for life exist.
"The risk is real but so is the potential reward," Weiler told reporters at a press conference.
More than half of the 30 missions launched to Mars have failed. Both rovers will have to make textbook landings on the planet's rock-strewn surface.
The slightest bout of misfortune like a malfunction of the landers' retro rockets or a sharp rock bursting one of the landers' airbags could easily turn the rovers' lights out.
"We've cleared two of the big hurdles, building both spacecraft and launching them, now we're coming up on a third, getting them safely onto the ground," stressed Peter Theisinger, project manager for the Mars Exploration Rover project.
NASA is upbeat the landings will go well and that it will reap the rewards.
"Think of Spirit and Opportunity as robotic field geologists. They look around with a color camera and with an infrared instrument that can classify rock types from a distance," explained Steve Squyres of Cornell University, one of the project's scientific heads.
NASA expects "Spirit" to touch down on January 3, "Opportunity" is due to land on January 24.
Each robot rover, once it has driven off its respective lander, has six wheels and is about the size of a golf cart.
The rovers are scheduled to explore Mars for three months. All being well, the first pictures should be transmitted back to earth shortly after touchdown, and the rovers will begin exploring Mars' surface within eight days of landing.
The craft will unfold their solar panels a few hours after landing and then deploy panoramic cameras to send back the first images, which will be 360 degress and in color
The rovers will be dropped into Mars' atmosphere by parachute, the parachutes will then be jetisoned and retro rockets will guide the rovers to the surface. Their undercarriages will be cushioned by airbags.
Despite these precautions, the landers could still bounce and roll a kilometer (0.6 mile) from where they initially land. If the spacecraft do not fulfill each task at precisely the right second during the descent, the mission could be over before it has fully begun.
The rovers should be able to travel some 40 meters a day, according to NASA.
NASA employees are keeping their fingers crossed that the missions will be a success in the wake of the February 1 Columbia shuttle disaster that killed seven astronauts returning to earth.