Nasa has landed its Curiosity rover, a one-tonne robot the size of a Mini Cooper, on Mars, in one of the most daring and difficult interplanetary operations attempted.
President Obama said the landing "will stand as a point of national pride far into the future."
Scientists at the Nasa control room reacted with whoops of jubilation early Monday morning as the £1.6 billion one-ton robot was lowered to the Martian surface on three nylon tethers suspended from a hovering "sky crane" kept airborne with retro rockets.
An expected signal confirming that the robot had landed was received on Earth at 6.31am UK time.
The craft has already sent its first pictures from the planet.
This is the first picture from Mars, sent by the Curiosity rover
Curiosity can now start its 98 week mission - the length of one Martian year - exploring a Martian crater that billions of years ago may have been filled with water.
Dr John Bridges, from the University of Leicester, one of two British scientists leading teams on the mission, wrote in a live blog from mission control: "It's down - landed!
"The first images are already being sent back via Odyssey. They are Hazcam images, showing a shadow cast by Curiosity on the Gale surface.
"Lots of very happy and excited people in this room! What an opportunity we have now to explore this fascinating planet."
Professor Sanjeev Gupta, from Imperial College London, who is also in the US leading a rover team, said: "Now that the MSL has landed we can get to grips with some remarkable science.
"The area the rover will be exploring, with its large areas of exposed rock and variety of landforms, will take us on a journey through geological time.
"With the extraordinary volume of data MSL can produce, we will be able to reconstruct how the rocks and climate of this region have changed through time."
Two thirds of Mars missions to date have failed, including Britain's ill-fated Beagle 2 lander which was lost on Christmas Day 2003.
No previous mission have been as complex and daring as the Mars Science Laboratory (MSL) mission, which is twice as long and five times as heavy as the twin rovers Spirit and Opportunity which landed there in 2004. Because of its size and weight, getting the vehicle on to the Martian surface presented a major challenge to scientists at the American space agency Nasa.
Curiosity's target is Gale Crater, near the Martian equator, where billions of years ago there may have been a large lake.
The craft bristles with sophisticated instruments designed to discover if Gale Crater could ever have supported simple life.
For one Martian year - 98 Earth weeks - the rover will explore its surroundings using a robot arm to scoop up soil and drill into rock.
It also carries its own laser gun for "zapping" rocks up to 30 feet away. The laser will vaporise tiny amounts of material in a flash of light that can be analysed to reveal chemical data.
As well as carrying a stereo camera for panoramic shots, Curiosity has a magnifying imager that can reveal details smaller than the width of a human hair.
Nasa is expecting to see more pictures from the rover later today
Samples will be analysed using a state-of-the-art onboard laboratory.
The landing site bears geological signs of past water, including what appears to be a lake bed on the floor of the crater. Channels that may have been carved by flowing water have also been identified.
An Atlas V rocket carrying Curiosity blasted off from Cape Canaveral, Florida, last November. The journey to Mars crossed 352 million miles of space.
Nasa Administrator Charles Bolden said the agency was now looking towards future missions to Mars, including manned exploration.
"Earlier this year, I directed Nasa's science mission director, along with the head of human exploration, Chief Technologist, and Chief Scientist to develop a more integrated strategy to ensure that the next steps for Mars exploration will support the nation’s planetary science objectives as well as our human exploration goals," he said.
"They are looking at many options, including another robotic mission to land on Mars in this decade."