The one ton, $2.5 billion Curiosity is the most scientifically equipped probe ever sent to another planet. And when the robot rover touches down on Sunday, it will begin an intensive search for signs that Mars may have once hosted life. WSJ takes an inside look at NASA's ambitious Mars mission. 
 
 NASA's Curiosity rover was flying under the influence of Martian gravity today, on course and on schedule, as the control room crew in Pasadena got ready for Sunday night's nail-biting landing. 
 
 At midmorning today, Curiosity was approaching Mars at 8,000 miles per hour, and is accelerating under the planet's gravity to an eventual speed of 13,200 mph. A heat shield and very-complicated landing system will slow it down to a virtual stop as it hovers with jet power, and the actual rover vehicle is lowered to the surface by three nylon tethers. 
 
 Scientists at the Jet Propulsion Laboratory said today that a worrisome dust storm on the red planet was dissipating. "Mars is cooperating by providing good weather for landing,'' said the JPL's Ashwin Vasavada, deputy project scientist for the NASA effort. 
 
 A Martian dust storm would have been a serious problem for the one-ton, car-size rover that is billed by NASA and JPL as the most scientifically advanced robotic vehicle ever dispatched. The jet-powered descent vehicle cannot be steered away from its planned landing site, and NASA has one chance to land it. 
 
 The rover carries 10 science instruments, including a mast that extends to seven feet above ground for cameras and a laser-firing apparatus to study objects from a distance. The rover also includes analytical instruments to determine the composition of rock and soil samples collected with the rover arm's drill and scoop. 
 
 The rover also has instruments to study the planet's environment, including the weather and natural radiation. 
 
 But before all of those instruments can be put to work, Curiosity needs to land intact. The rover is scheduled to touch down on Mars at 10:31 p.m. California time. 
 
 That landing will come after a knuckle-whitening seven minutes at JPL in Pasadena, where scientists will be monitoring the novel method of delivering the rover to the planet's surface. 
 
 Enlarge Image Close Zuma Press An artist's concept depicts the rover Curiosity as it investigates the composition of a rock surface. 
 
 Previous Mars rovers such as Spirit and Opportunity plunged through Mars' atmosphere in protective air-bag-like structures, allowing them to literally bounce onto the planet's surface. 
 
 Curiosity is far too large for that type of landing, so mission planners had to come up with something different. What they came up with was a "sky-crane'' system, during which the Mars Science Laboratory spacecraft carrying the rover will wing through the planet's upper atmosphere. 
 
 During what JPL controllers have been calling "the seven minutes of terror,'' the spacecraft will have to decelerate through the Martian atmosphere from a speed of about 13,200 mph to about 1.7 mph, with the help of a high-tech supersonic parachute. 
 
 In the final seconds, Curiosity will be lowered on three nylon tethers, and retro rockets will be fired to control its descent onto the surface on its wheels. 
 
 "Those seven minutes are the most challenging part of this entire mission,'' said Pete Theisinger, the $2.5 billion Curiosity mission's project manager at JPL. "For the landing to succeed, hundreds of events will need to go right, many with split-second timing and all controlled autonomously by the spacecraft. We've done all we can think of to succeed. We expect to get Curiosity safely onto the ground, but there is no guarantee. The risks are real.'' ||||| As big as a car and as well-equipped as a laboratory, NASA's newest Mars rover blows away its predecessors in size and skill. 
 
 In this 2011 artist's rendering provided by NASA/JPL-Caltech, a "sky crane" lowers the Mars Science Laboratory Curiosity rover onto the surface of Mars. The mobile robot is designed to investigate Mars'... (Associated Press) 
 
 In this 2011 artist's rendering provided by NASA/JPL-Caltech, the Mars Science Laboratory Curiosity rover examines a rock on Mars with a set of tools at the end of its arm, which extends about 2 meters... (Associated Press) 
 
 Nicknamed Curiosity and scheduled for launch on Saturday, the rover has a 7-foot arm tipped with a jackhammer and a laser to break through the Martian red rock. What really makes it stand out: It can analyze rocks and soil with unprecedented accuracy. 
 
 "This is a Mars scientist's dream machine," said NASA Jet Propulsion Laboratory's Ashwin Vasavada, the deputy project scientist. 
 
 Once on the red planet, Curiosity will be on the lookout for organic, carbon-containing compounds. While the rover can't actually detect the presence of living organisms, scientists hope to learn from the $2.5 billion, nuclear-powered mission whether Mars has _ or ever had _ what it takes to nurture microbial life. 
 
 Curiosity will be "the largest and most complex piece of equipment ever placed on the surface of another planet," said Doug McCuistion, director of NASA's Mars exploration program. 
 
 Ten feet long, 9 feet wide and 7 feet tall at its mast, Curiosity is about twice the size of previous rovers Spirit and Opportunity, weighs 1 ton and is loaded with 10 science instruments. Its formal name: Mars Science Laboratory, or MSL. 
 
 In a spacecraft first, Curiosity will be lowered to Mars' surface via a jet pack and a tether system similar to the sky cranes used by helicopters to insert heavy equipment in inaccessible spots on Earth. No bouncing air bags like those used for the Mars Pathfinder lander and rover in 1997 and for Spirit and Opportunity in 2004 _ Curiosity is too heavy for that. 
 
 It is the kind of precision landing that officials said will benefit future human explorers on Mars. 
 
 The rover is scheduled to arrive at the mineral-rich Gale Crater next August, 8 1/2 months after embarking on the 354-million-mile voyage aboard an Atlas V rocket. 
 
 It's a treacherous journey to Mars, and the road is littered with failures. In all, more than three dozen missions have aimed over the decades at the most Earth-like planet known, and fewer than half have succeeded. Of this flotilla, only one lander is still working on the dry, barren, cold surface _ Opportunity _ and only three craft still are observing the planet from orbit. 
 
 In fact, Russia's latest Mars probe remains stuck in orbit around Earth two weeks after its botched launch. NASA has had better luck at Mars, although it has lost a few spacecraft there. 
 
 "Mars is difficult, and so many things have to go right for a mission to work," said Michael Meyer, lead scientist for NASA's Mars exploration program. 
 
 Curiosity is the capstone of what NASA calls the year of the solar system. A spacecraft is en route to Jupiter after lifting off last August from Cape Canaveral, and twin lunar probes launched in September will arrive at the moon New Year's weekend. 
 
 A huge crowd _ 13,500 invited guests _ is expected for Curiosity's Thanksgiving weekend send-off. 
 
 There will be more anxiety than usual over the launch. Curiosity holds 10.6 pounds of plutonium, more than enough to power the rover on the Martian surface for two years. A nuclear generator won out over solar energy because it allows for a bigger workload and more flexibility. The plutonium is encased in several protective layers in case of a launch accident. 
 
 Once safely down on Mars, the rover will survey the landscape with high-definition and laser cameras mounted like eyes atop its mast. The laser will aim at soil and rocks as far as 23 feet away to gauge their chemical composition. 
 
 The rover also has a weather station for updates on Martian temperature, humidity and wind, as well as a radiation detector that will be especially useful for planning human expeditions. 
 
 Despite all its fancy upgrades, Curiosity will go no faster than the one-tenth-mile-per-hour logged by past Martian rovers. But it is expected to venture more than 12 miles during its two-year mission. If it's still working after that, it will keep on trucking, possibly all the way up the crater's 3-mile peak. 
 
 This mountain is composed of geologic layers similar to what one might find in the Grand Canyon, said project scientist John Grotzinger, a geologist at the California Institute of Technology. 
 
 "Our rover is going to be like John Wesley Powell going down the Grand Canyon," Grotzinger said, referring to the 19th-century explorer who led an expedition down the Colorado River. 
 
 The next logical step in Mars exploration, said Cornell University's Steve Squyres, who led the science team for Spirit and Opportunity, would be a robotic mission to deliver Mars samples to Earth for analysis. NASA hopes to pull that off later this decade, but the project is on Congress' chopping block. 
 
 Squyres warned that without such missions, U.S. leadership in science won't just be challenged _ "it's going to go away." 
 
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 Online: 
 
 NASA: http://marsprogram.jpl.nasa.gov/msl/
– The Curiosity rover landed safely on Mars early this morning, prompting whoops of joy and relief in NASA's mission control center, reports the New York Times. The rover quickly beamed back a picture of its own shadow cast on the surface of the Red Planet. "Touchdown confirmed. We are safe on the surface of Mars!" the team read out after receiving signals from the rover. After a journey of 354 million miles, the rover, which is much bigger and more complex than previous models, had to land in a new way that could never be fully tested on Earth, leading to what control room staff described as "seven minutes of terror" before confirmation was received, notes the Washington Post. As earlier reported, the spacecraft ferrying it had to rely on a supersonic parachute to slow it from 13,200mph to about 1.7mph; with seconds to go, the rover was then lowered to the surface using three nylon tethers and retro rockets.