If you're the Jet Propulsion Laboratory, you bring Mars down to Earth. In May, the Mars rover Spirit became embedded in a patch of fluffy Marian soil, the worst such incident in the more than five years that Spirit and its twin, Opportunity, have been exploring Mars' equatorial region. Since then, engineers have been trying to figure out the best way to extricate the rover, a project that has come to be known at the Pasadena, Calif., laboratory as the 'Free Spirit' program. T-shirts are being made to memorialize the effort. This week, scientists finished replicating the situation on Mars in a 30-foot-square work room, mixing 5,400 pounds of diatomaceous earth and clay to produce a powdery mixture the color of creme brulee and as fluffy and light as flour. Now comes trying to free the Earth Rover to figure out what might work for Spirit on Mars. 'This isn't the same as we have on Mars,' Paolo Bellutta, a rover team member, said of the powder. 'Diatomaceous earth is made of fossils, and we have no evidence of fossils on Mars.' But it is 'the closest thing' to the soil on Mars, said Rover project manager John Callas. The engineers then drove an Earth-bound sibling of the two Mars rovers, about 5 feet tall by 7 feet wide, into an 8-foot by 12-foot sandbox. By Wednesday, the rover was stuck -- its six wheels embedded in 5 inches of the Martian soil analog. After sloping the sand so that the test rover was pitched on its side to match Spirit's predicament, the engineering team pronounced itself satisfied that it had succeeded in marooning two rovers on two planets. The trick now, Callas said, is to put together a series of maneuvers on Earth that can be applied on Mars. The first technique, which engineers intend to apply next week, is to ask the rover to drive forward. Because it has a gimpy right front wheel, Spirit has been driving backward in recent years, dragging the wheel along. Commanding the rover forward would amount to backing out of the fluffy sand patch onto surer ground nearby. 'We think terrain we can drive on is just a few feet away,' Callas said. Callas said that although Spirit is embedded, he doesn't believe it is truly stuck. This might sound like a subtle difference, but Callas insists it's critical to the outcome of the Free Spirit effort. When last commanded to move, he said, 'the rover made a tiny bit of progress, which we intend to exploit to get the rover out.' Getting embedded has yielded some surprising science, Callas said. By digging so deeply into the soil in one spot, the rover has turned up evidence of ferric sulfate, calcium sulfate and silica, which Callas said could be evidence that snow or ice was present at Mars' equatorial regions in the fairly recent past. These days, water ice on the surface is believed to be only at the Martian poles. This discovery is more proof that, where the rovers are concerned, 'when Mars hands us lemons we make lemonade,' Callas said. While Spirit is parked, Opportunity is continuing to head for a crater called Endeavour. The twin rovers have far exceeded their expected lifetimes, and Callas declined to speculate how much longer they can last. 'These are phenomenal vehicles,' Callas said. 'They go through horrendous thermal cycles, about 150 degrees Fahrenheit each day. That's very stressing on a vehicle.' 