NASA's newest mission to Mars will attempt to touch down on the red planet on Monday – but the agency has warned only 40% of missions ever sent there have been successful.
The InSight mission successfully launched from California in May on a powerful Atlas V-401 rocket, but while going up was a success the landing is going to be particularly tricky.
Mars is a difficult planet to investigate. Its thin atmosphere makes landing a challenge and its extreme temperature swings make it very tough for missions to be conducted on the surface.
Talking ahead of the landing, NASA's chief engineer at the jet propulsion laboratory, Rob Manning, said: "Although we've done it before, landing on Mars is hard, and this mission is no different.
"It takes thousands of steps to go from the top of the atmosphere to the surface, and each one of them has to work perfectly [for InSight] to be a successful mission."
InSight, which stands for Interior Exploration Using Seismic Investigations, Geodesy and Heat Transport, hopes to place a single lander spacecraft on Mars.
NASA says the mission will help scientists understand what is happening around the planet's core.
It will also help explain how all rocky planets, including the Earth, evolved. There are significant mysteries here, because while both Mars and the Earth were formed from the same stuff more than 4.5 billion years ago, they are now very different planets.
The first large, stable mass of liquid water was detected on Mars in July, boosting the probability that life similar to that on Earth, or at least traces of it, may one day be found on the planet.
NASA's scientists have seen a lot of evidence that Mars has quakes – known as marsquakes. Unlike Earth, where quakes are caused by tectonic plates, Mars has very quiet tectonic processes.
This means marsquakes are more likely to be caused by other forms of tectonic activity, including volcanism and cracks forming in the planet's crust.
NASA said: "Each marsquake would be like a flashbulb that illuminates the structure of the planet's interior.
"By studying how seismic waves pass through the different layers of the planet (the crust, mantle and core), scientists can deduce the depths of these layers and what they're made of.
"In this way, seismology is like taking an X-ray of the interior of Mars."
Earth and Venus have tectonic systems which have destroyed most evidence of their early history, but Mars (which is just one third the size of those planets), contains less energy to power these tectonic processes.
NASA said this makes Mars a fossil planet in many ways because it has remained static for more than three billion years.
The mission launched from Vandenberg Air Force Base in California.
Usually, missions to other planets launch from the Kennedy Space Centre in Florida and fly east, over the water of the Atlantic Ocean.
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Flying towards the east adds the momentum of Earth's eastward rotation to the launch vehicle's own thrust – but the Atlas V-401 rocket is powerful enough to fly south towards the sea from Vandenberg.
It has taken InSight about six months to travel the 301 million miles (485 million kilometres) to Mars, and it is expected to arrive at Mars exactly on schedule on 26 November 2018.