The autonomously-guided procedure was completed more than 11 minutes earlier, which is how long it takes for radio signals to return to Earth.

This NASA photo was taken as Perseverance rover landed on the surface of Mars on February 18, 2021.
This NASA photo was taken as Perseverance rover landed on the surface of Mars on February 18, 2021. (AFP)

NASA has said that the Perseverance rover has touched down on the surface of Mars after successfully overcoming a risky landing phase known as the "seven minutes of terror."

"Touchdown confirmed," said operations lead Swati Mohan on Thursday at around 2055 GMT (3:55 pm local Eastern Time) as mission control at NASA's Jet Propulsion Laboratory headquarters erupted in cheers.

The autonomously-guided procedure was completed more than 11 minutes earlier, which is how long it takes for radio signals to return to Earth.

"WOW!!" tweeted NASA Associate Administrator Thomas Zurburchen as he posted the Perseverance's first black and white image from the Jezero Crater in Mars' northern hemisphere.

Perseverance now embarks on a multi-year mission to search for the biosignatures of microbes that might have existed the re billions of years ago, when conditions were warmer and wetter than they are today.

Starting from summer, it will attempt to collect 30 rock and soil samples in sealed tubes, to be eventually sent back to Earth sometime in the 2030s for lab analysis.

Nail-biting moment

Ground controllers at the space agency's JPL in Pasadena, California, settled in nervously on Thursday for the descent of Perseverance to the surface of Mars, long a deathtrap for incoming spacecraft. 

It takes a nail-biting 11 1/2 minutes for a signal that would confirm success to reach Earth.

The landing of the six-wheeled vehicle would mark the third visit to Mars in just over a week. 

Two spacecraft from the United Arab Emirates and China swung into orbit around the planet on successive days last week.

All three missions lifted off in July to take advantage of the close alignment of Earth and Mars, traveling some 300 million miles in nearly seven months.

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Percy's mission

Perseverance, the biggest, most advanced rover ever sent by NASA, stood to become the ninth spacecraft to successfully land on Mars, every one of them from the US, beginning in the 1970s.

The car-size, plutonium-powered rover was aiming for NASA’s smallest and trickiest target yet: a 5-by-4-mile strip on an ancient river delta full of pits, cliffs and fields of rock. 

Scientists believe that if life ever flourished on Mars, it would have happened 3 billion to 4 billion years ago, when water still flowed on the planet.

Percy, as it is nicknamed, was designed to drill down with its 2-metre (7-foot) arm and collect rock samples that might hold signs of bygone microscopic life. 

The plan called for three to four dozen chalk-size samples to be sealed in tubes and set aside on Mars to be retrieved by a fetch rover and brought homeward by another rocket ship, with the goal of getting them back to Earth as early as 2031.

Mars has proved a treacherous place: In the span of less than three months in 1999, a US spacecraft was destroyed upon entering orbit because engineers had mixed up metric and English units, and an American lander crashed on Mars after its engines cut out prematurely.

NASA is teaming up with the European Space Agency to bring the rocks home. Perseverance’s mission alone costs nearly $3 billion.

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Signs of life

Scientists hope to answer one of the central questions of theology, philosophy and space exploration.

“Are we alone in this sort of vast cosmic desert, just flying through space, or is life much more common? Does it just emerge whenever and wherever the conditions are ripe?” said deputy project scientist Ken Williford. 

“Big, basic questions, and we don’t know the answers yet. So we’re really on the verge of being able to potentially answer these enormous questions.”

China’s spacecraft includes a smaller rover that also will be seeking evidence of life – if it makes it safely down from orbit in May or June.

The only way to confirm – or rule out – signs of past life is to analyse the samples in the world’s best labs. 

Instruments small enough to be sent to Mars wouldn’t have the necessary precision.

“The Mars sample return project is probably the most challenging thing we’ve ever attempted within NASA,” said planetary science director Lori Glaze, “and we don’t do any of these things alone.”

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'Seven minutes of terror'

Perseverance's descent has been described by NASA as “seven minutes of terror," in which flight controllers can only watch helplessly. 

The preprogrammed spacecraft was designed to hit the thin Martian atmosphere at 19,500 kph (12,100 mph), then use a parachute to slow it down and a rocket-steered platform known as a sky crane to lower the rover the rest of the way to the surface.

Touchdown on the Jezero Crater is scheduled for 2055 GMT but it will take about 11 minutes to get a radio signal back from Mars and know it happened.

Weather conditions so far appear favourable in the Martian northern hemisphere spring, but nothing is taken for granted.

"This is one of the most difficult manoeuvres that we do in this business, and almost 50 percent of the spacecraft that had been sent to the surface of Mars have failed," Matt Wallace, the mission's deputy project manager said.

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Atmospheric entry

Ten minutes before entering the Martian atmosphere, the spacecraft sheds its cruise stage that supplied the fuel tanks, radios and solar panels on the voyage.

It's left with just a protective aeroshell, carrying the rover and descent stage, and it fires thrusters to make sure its heat shield is forward facing.

At about 130 kilometres (80 miles) altitude, it careens into the atmosphere and things start to get hot: peak heating occurs about 80 seconds in when the heat shield surface reaches about 1,300 degrees Celsius (2,370 degrees Fahrenheit).

Perseverance is tucked away safely in the aeroshell, only experiencing room temperature.

The craft might need to fire thrusters to stay on course as it hits air pockets.

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Parachute deployment

Once the spacecraft has slowed down to 1,600 kilometres (less than 1,000 miles) an hour, it's time to deploy the 21.5 metres (70.5 feet) wide supersonic parachute at an altitude of 11 kilometres (seven miles).

Perseverance is deploying a new technology called Range Trigger that decides the precise moment to deploy, based on the craft's position relative to the landing site.

Asked to name the single most critical event, NASA's EDL lead Allen Chen said: "Obviously there's a lot of concentrated risk in supersonic parachute opening."

To try out its new design, NASA had to carry out extensive supersonic parachute testing from high altitudes here on Earth, a field of research that had been dormant since the 1970s.

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Heat shield separation

Next, the spacecraft jettisons its heat shield, around 20 seconds after the parachute has been deployed. The rover is exposed to the atmosphere for the first time, and uses a landing radar to bounce signals off the surface and calculate its precise altitude.

The mission will also see another technology deployed for the first time: the "Terrain Relative Navigation" (TRN) system that uses a special camera to identify surface features and compare them to an onboard map where engineers pre-programmed the safest landing sites.

"That gives our vehicle eyes, and the ability to really see where she's going and figure out where she is," said Chen.

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Powered descent

In the thin atmosphere of Mars, the parachute will only get the vehicle down to 300 kilometres (200 miles) per hour – so Perseverance has to cut the chute loose, dispense with its back shell, and use rocket thrusters to ease itself down.

It does this using an eight-engine jetpack that's installed directly above the rover and fires up at around 2,100 metres (6,900 feet) above the surface.

The vehicle has to tilt right away in order to avoid the falling parachute and back shell, then uses its sophisticated systems to continue its descent.

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Skycrane

With 12 seconds to go, at a height of 20 metres (66 feet), the rocket-powered descent stage lowers the rover down to the ground using long cables in a manoeuvre called "skycrane."

The rover locks its legs and wheels into a landing position and touches the ground at 1.2 kilometres (a little less than two miles) an hour, as the descent stage flies off and makes its own controlled landing.

Perseverance is now set for its mission as Earth's fifth rover on Mars.

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Source: TRTWorld and agencies