The US space agency's Perseverance robot has left Earth on a mission to try to detect life on Mars.
The one-tonne, six-wheeled rover was launched out of Florida by an Atlas rocket on a path to intercept the Red Planet in February next year.
When it lands, the Nasa robot will also gather rock and soil samples to be sent home later this decade.
Perseverance is the third mission despatched to Mars inside 11 days, after launches by the UAE and China.
Nasa made this mission one of its absolute priorities when the coronavirus crisis struck, establishing special work practices to ensure Perseverance met its launch deadline.
"I'm not going to lie, it's a challenge, it's very stressful, but look - the teams made it happen and I'll tell you, we could not be more proud of what this integrated team was able to pull off here, so it's very, very exciting," Administrator Jim Bridenstine told reporters.
Perseverance is being targeted at a more-than 40km-wide, near-equatorial bowl called Jezero Crater.
Satellite images suggest this held a lake billions of years ago.
Scientists say the rocks that formed in this environment stand a good chance of retaining evidence of past microbial activity - if ever that existed on the planet.
Perseverance will spend at least one Martian year (equivalent to roughly two Earth years) investigating the possibility.
Unlike the previous four rovers Nasa has sent to Mars, its new machine is equipped to directly detect life - either current or in fossilised form.
But any evidence it uncovers will almost certainly have its sceptics, which is why researchers want to bring whatever Perseverance finds back home for the deeper analysis only sophisticated laboratories on Earth can perform.
The rover will therefore package its most interesting rock discoveries in small tubes. An elaborate mix of future missions will then launch later this decade to try to retrieve these samples.
How does Perseverance fit into wider Mars goals?
We know from the search for the earliest life on Earth that the evidence can sometimes be controversial.
So, even if Perseverance stumbles across rocks that appear to have been fashioned by some ancient Martian biology, it will almost certainly require confirmation by analytical instruments on Earth that are far superior to the miniaturised versions carried on the rover.
That's why a key task for Perseverance will be to package its most interesting rocks in small metal canisters and leave them on the Jezero Crater floor.
Nasa and the European Space Agency (Esa) intend to go fetch these tubes with two more missions that are scheduled to leave Earth in 2026.
It's a remarkable endeavour involving a second rover, a Mars rocket and a huge satellite to ship the sample tubes home, getting them here in 2031. "You can argue that what we'll be trying to do is as complicated as the Apollo Moon landings - when you think of the complexity of the robotics involved," David Parker, director of human and robotic exploration at Esa, told BBC News.
"And it will also be a step on the way to sending humans to Mars because the architecture of this Mars Sample Return project is really a scale model of a human mission with its multiple vehicles that have to launch, land, launch again, rendezvous in orbit and return to Earth."
Nasa and Esa estimate the total cost of getting samples back to Earth, including the $2.7bn (€2.3bn; £2bn) cost of Perseverance, will come to at least $7bn (€6bn; £5.4bn).