NASA Mars Curiosity rover: Five years on the red planet

Updated

Five years of roaming on the surface of Mars.

It has been five years since NASA's Curiosity rover touched down on Mars, lowered to the surface of the planet by a rocket-powered crane in a sequence scientists dubbed the "seven minutes of terror".

Terror, because of the risk of it all going wrong when you drop a $2.5 billion rover on an alien planet.

And seven minutes, because that is how long it would take the car-sized Curiosity to go from the top of Mars' atmosphere to the surface.

After approaching the planet at 21,000 kilometres per hour, the heat shield separated and a parachute — then reverse rockets — fired in succession, slowing the craft down until it hovered metres from the ground.

Then using a mothership called the Sky Crane, suspended in the air by rocket thrusters, Curiosity was slowly brought down to the surface using a never-before tested tethered crane system.

Sorry, this video has expired Video: Curiosity Rover lands on Mars (ABC News)

On August 6, 2012, the world waited…

Success came seven minutes later and soon Curiosity began sending its first data and photos back to Earth from its new home.

Location: Gale Crater, base of Mt Sharp

Temperature: -60 degrees Celsius (average)

Atmosphere: 100 times thinner than Earth's

Length of day: 24hr 37min

The real mission begins

"We spent so many years being so nervous about whether the choice of Gale Crater was right, and whether the mission would land successfully, and whether it would find anything related to habitability," chief scientist for the mission Ashwin Vasavada said.

Curiosity's task: determine Mars' habitability using its 11 different scientific instruments, including three cameras to take detailed images of the landscape, and sensors to analyse rock samples, sniff the atmosphere for organic molecules and detect radiation levels on the planet's surface.

Since August 2012, the rover has been exploring what lies above and below the surface of the red planet, looking for evidence of the chemical building blocks needed for life, including traces left behind by water.

Travelling at a glacial speed of about 30 metres per hour, Curiosity has ventured 17 kilometres from its landing site in its search.

Dr Vasavada said so much of what NASA had hoped for had come to fruition.

From the flat landing site, Curiosity began its meandering trip past landmarks on a trek towards Mount Sharp, where the layers of rocks and material change with altitude.

Mount Sharp rises 5.5 kilometres high from the centre of the crater. The mountain's base was formed from sedimentary layers rich in clay and sulphur that were deposited there long ago by flowing water.

The water may be long gone, but evidence of the three-billion-year-old lake bed remains.

Drilling into the past

It did not take long for the rover to mine scientific gold.

Methane and elements such as nitrogen, hydrogen and carbon — all crucial to the creation of simple microbes — were found after the rover drilled into rocks and sniffed the planet's atmosphere.

Samples also revealed that Yellowknife Bay, near the landing site, was once part of an ancient river system.

In the years since, Curiosity has collected key evidence from 3.5 billion-year-old rocks that life could have once existed on Mars.

These sediment samples are also reshaping our understanding of how long liquid water persisted on Mars.

The lakes and streams could have existed on the planet's surface for millions of years, Dr Vasavada said.

"The mountain itself, the base of the mountain, is lake sediment, layer after layer after layer for about 200 vertical metres," he said.

"[It would take] about a million years or more for lakes to be able to deposit that much sediment."

That timescale is key to the viability of the environment for supporting life.

The sediment layers show habitability was present not for an instant, but at a timescale where you can start to imagine life originating and evolving, Dr Vasavada said.

"The timescale of the habitability and water is the most ground-breaking new result for Mars."

But finding out that Mars had flowing water for such a long time has upturned what we used to think about the red planet's climate. Had Mars actually been warm?

Climate debate

A common theory had been that Mars was cold, and any liquid water on the planet's surface only flowed when a meteorite struck or a volcano erupted.

However, Curiosity's evidence about the length of time water existed on the surface of Mars "throws a wrench" in that theory, Dr Vasavada said.

"The evidence from Curiosity … suggests the lakes were present and open to the atmosphere, they weren't protected by an ice cover for millions of years," he said.

But if the planet used to be wet that presents scientists with another conundrum.

For there to be flowing water, you would expect the atmosphere was once much thicker than it is today and had large amounts of carbon dioxide to trap heat and warm the planet.

Analysis of gases in Mars' atmosphere by Curiosity and another spacecraft called MAVEN indicate much of the carbon dioxide was blown away by the solar wind.

However, rock samples have not turned up much in the way of carbonate minerals, which you would expect to find if that was the case.

Dr Vasavada said it was an ongoing area of investigation for NASA.

"Curiosity's data really re-opens the idea that we haven't figured out how yet, but Mars maybe actually was warm in its climate," he said.

Curiosity's nuclear power source will eventually wear down, but Dr Vasavada hopes the rover will continue talking to him for at least another five years, likely longer.

The rover is currently about 250 metres up Mount Sharp, but making it to the top was never the goal.

"Most of the really good stuff is in the bottom several hundred metres," Dr Vasavada said.

It has still got a trek ahead to reach the endgame of its mission — a "treasure trove of ancient habitability" in a layer of clay minerals a few hundred metres farther up.

2020 and beyond

Despite its achievements, Curiosity is only the middle chapter of NASA's Mars exploration program.

It started with orbiters mapping the planet, then twin rovers Spirit and Opportunity arriving to search for evidence of sustained water.

Curiosity has built on their work in showing that Mars could have been habitable at some stage of its life.

And next? Scientists want to look for more sophisticated evidence that ancient life once existed, such as finding amino acids — the building blocks of proteins.

That will be the task of the 2020 rover.

In that way, each subsequent mission builds off the findings of the one before it, Dr Vasavada said.

"If Curiosity hadn't discovered that Mars was habitable, that would have been a real problem for 2020," he said.

But it did. And it found traces of organic molecules that once existed on Mars.

"It makes us confident other more complex ancient evidence of life, that 2020 could discover, would also survive 3 to 4 billion years and not be lost," he said.

Topics: space-exploration, science-and-technology, astronomy-space, planets-and-asteroids, spacecraft, australia, united-states

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