The US space agency's Spirit rover on Mars has made its first significant communications with Earth since a major fault cut off its stream of data.
Engineers knew the probe was alive
Nasa said two signals were captured on Friday shortly after the Martian dawn by an antenna of the international Deep Space Network near Madrid, Spain.
Spirit had been refusing to speak to Earth, transmitting only short beeps to indicate it was powered up and alive.
The vehicle was about to drill into a rock when the breakdown occurred.
The encouraging news was released as the European Space Agency unveiled its first results from the Mars Express probe now in orbit around the Red Planet.
The spacecraft has sent back a series of astonishing pictures of Mars and new details about its water-ice coverage.
The US space agency said the first communication with Spirit occurred at 1234 GMT and lasted for 10 minutes. The data rate was weak at 10 bits per second.
The second contact came at 1326 GMT and lasted 20 minutes. On this occasion, the data was fed at a rate of 120 bits per second.
"The spacecraft sent limited data in a proper response to a ground command, and we're planning for commanding further communication sessions later today," said Mars Exploration Rover project manager Pete Theisinger.
Nasa has not said what was in the feeds. But engineers are keen to get any information from the rover that might help them diagnose and correct the problems it has been experiencing.
Since Wednesday, Spirit has returned only "noise" and a few beeps in response to ground contact.
The rover landed on Mars on 3 January, for a planned three-month mission to explore the geological history of the planet. Its aim was to tour Gusev Crater, studying its rocks and soil for signs of water, past or present.
Soon to land
When its troubles began on Wednesday, the six-wheeled robotic geologist was parked in front of a football-sized rock, its tool-laden arm extended and prepared to grind the rock's surface.
Commands were being fed via a radio telescope in Canberra, Australia, but a thunderstorm over the facility interrupted the transmission.
Scientists were asked whether the Australian-fed commands being cut short could have caused the rover's current problems. They consider this unlikely, however.
"We believe the architecture does not allow this to happen," said Theisinger.
Meanwhile, the rover Opportunity is still on course to land on Mars on Sunday, at 0505 GMT.
The vehicle is aimed at Meridiani Planum, a plain which is near the Martian equator. It will be halfway around the planet from Gusev Crater.
The US landers are identical. Nasa will want, therefore, to trace the source of Spirit's problems because it could have implications for the way Opportunity is deployed.
After the failure in 1999 of Nasa's Mars Polar Lander and Mars Climate Orbiter, the agency opened the rover project to independent scrutiny.
Outside auditors have studied every detail in the plans, looking for any flaws which might scupper a successful mission for the vehicles.
Nasa says everything was done that was humanly possible to send the vehicles to Mars in good working order.