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.'' ||||| That landing is scheduled for 1:31 a.m., and officials said they could know almost immediately if the rover was safely on the ground. That tracking would come from the Odyssey orbiter circling Mars, if the spacecraft is able to get to the right location at the right time. 
 
 If not, the waiting time for a final answer on whether the rover was safely on the surface could range from two to eight hours. If no signal arrives from Curiosity via three Mars orbiters and the Deep Space Network after 18 hours, NASA officials said, then they would start to worry about its safety. 
 
 The final descent has been pre-programmed and the army of engineers and scientists at the Jet Propulsion Lab’s Mission Control have no control over it. “Our position will be identical to anyone at home,” said Adam Steltzner, lead of the Entry, Descent and Landing (EDL) team. “We’re all along for the ride.” 
 
 Speaking for the team as a whole, Steltzner said they were “Rationally confident, emotionally terrified and ready for EDL.” 
 
 Because the rover is so much larger, more complicated and more ambitious than earlier models, it has to land in a new and far more hazardous way. The landing, which could never be tested in full on Earth, includes a hovering rocket stage, a kind of sky crane, to lower it to the ground. NASA’s chief scientist John Grunsfeld has said that because of that heightened landing difficulty, in addition to the unprecedented sophistication of the instruments on board, Curiosity is “the most important NASA mission of the decade.” 
 
 Worldwide spectacle 
 
 The Curiosity landing is shaping up to be an international spectacle. Formal “landing” parties have been scheduled from South Australia to Rome, from Israel to Crete; and in the United States from Atlanta to Seattle, Milwaukee to Honolulu. 
 
 NASA also has helped organize a landing gathering in New York’s Times Square, which will feature a large screen that will beam the streaming news from atop a building and high above the crowd. 
 
 Reaching, orbiting and landing on Mars is notoriously hard. In addition to the European Space Agency, nations including the United States, the former Soviet Union, Russia, the European Space Agency, China and Japan have sent missions to Mars since the late 1960s, but only about one-third of them have succeeded. 
 
 The United States is the only nation to land a vehicle on Mars and complete its mission, having done it six out of seven tries.
– 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.