Nasa is preparing to touch down on Mars for the first time in six years tonight in a mission designed to mine more information about the Red Planet.
The US space agency's latest probe, InSight, is scheduled to land on the planet at 3pm EST (8pm UK time), having travelled for six months and 300 million miles.
To land smoothly it must slow down from 12,300mph to 5mph, the equivalent of human jogging speed, in just seven minutes after hitting Mars's atmosphere. The mission is following in the footsteps of the Curiosity rover, which landed there in 2012, but the $1bn joint US-European mission will be breaking new ground, literally and metaphorically.
Just as there was a lot of hype around Curiosity, so too is there much anticipation about InSight, with parties expected to be held around the world to watch the landing. The Telegraph will be live streaming the action, taking in the the final plunge through the Martian atmosphere. Here's what you need to know about the landmark mission.
What will InSight do?
Curiosity has been moving around Mars, scouring different areas. InSight, however, will be staying in one place for its two-year mission once it lands.
InSight is short for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport. As its lengthy name suggests, its objective is to dig into the planet's interior.
Once it touches down, its 6-foot (1.8-meter) arm will remove the two main science experiments from the lander's deck and place them directly on the Martian surface. This is already uncharted territory in space exploration.
One experiment is intended to take Mars' temperature by drilling down 16 feet (5 meters) into the planet, using a self-hammering nail. That would be a new record for such an experiment, breaking the one set nearly a half-century ago by Apollo moonwalkers, who drilled down 8 feet (2 ½meters).
And just as those astronauts left behind instruments to measure moonquakes, InSight is bringing the first seismometers to monitor for marsquakes - if they exist.
Yet another experiment will calculate Mars' wobble, providing information about the core of the planet as the sun and its moons pull on Mars.
"It's got its own brain," said lead scientist Bruce Banerdt of Nasa's Jet Propulsion Laboratory. "It's got an arm that can manipulate things around. It can listen with its seismometer. It can feel things with the pressure sensors and the temperature sensors. It pulls its own power out of the sun."
With no life detectors on board, its primary objective is not to look for signs of life, past or present. But that's not to say it won't be able to provide such clues.
"When InSight drills down into the Martian soil, we'll learn more about how Mars and Earth formed. We'll know more about where we all came from, and why these two rocky worlds are so similar yet so different," Bill Nye, CEO of the nonprofit Planetary Society, said in a statement. "We may learn more about what kinds of planets can harbour life. InSight is more than a Mars mission -- it's a solar system mission."
Mars is much less geologically active than Earth, and so its interior is closer to being in its original state - a tantalizing time capsule.
InSight stands to "revolutionise the way we think about the inside of the planet," said Nasa's science mission chief, Thomas Zurbuchen.
The landing site
InSight is heading for a spot of land called Elysium Planitia, an area that astronomers have described as "the biggest parking lot on Mars".
A sizable equatorial plain, Tom Hoffman, InSight's project manager, hopes it's "like a Walmart parking lot in Kansas."
Nasa aimed for as flat an area as possible so the lander does not tip over and thereby kill the mission, and so the robotic arm can set the science instruments down.
"If Elysium Planitia were a salad, it would consist of romaine lettuce and kale - no dressing," Bruce Banerdt, InSight principal investigator of NASA's Jet Propulsion Laboratory, said. "If it were an ice cream, it would be vanilla."
The lander will stand close to the ground, its top deck barely a metre above the surface. Once its twin circular solar panels are open, it will take up the space of a large car.
Mr Hoffman said selecting a suitable good landing site was "a lot like picking a good home".
"It's all about location, location, location," he said. "And for the first time ever, the evaluation for a Mars landing site had to consider what lay below the surface of Mars. We needed not just a safe place to land, but also a workspace that's penetrable by our 16-foot-long (5-meter) heat-flow probe."
The landing - and the risks
Before it can start digging, it needs to land successfully - which is no mean feat. The success rate on the Red Planet is currently 40 percent, including planetary flybys dating back to the early 1960s, as well as orbiters and landers.
Two years ago, a European lander came in so fast, its descent system askew, that it carved out a crater on impact.
About seven minutes before it reaches the top of Mars' atmosphere, the lander will be released from the spacecraft that carried it to Mars.
The 800-pound (360-kilogram) vehicle, ensconced inside its heat-protecting “aeroshell” capsule, will be hurtling into Mars' atmosphere at a supersonic 12,300 mph (19,800 kph). Leaving a long flaming trail in its wake, temperatures are expected to reach about 1500C.
To slow down, it will be relying on its white nylon parachute and a series of engine firings.
A plethora of factors could spell disaster for the spacecraft: wind gusts could send it into a dangerous tumble during descent; the parachute could get tangled; a dust storm could hamper InSight's ability to generate solar power; a leg could buckle or an arm could jam.
The tensest time for flight controllers in Pasadena, California, will be the six minutes from the time the spacecraft hits Mars' atmosphere and touches down.
Nasa will be following the playbook of the 1976 twin Vikings and the 2008 Phoenix missions, which also were stationary and three-legged.
"But you never know what Mars is going to do," Tom Hoffman, InSight's project manager, said. "Just because we've done it before doesn't mean we're not nervous and excited about doing it again."
Communication from the Red Planet
Joining InSight for its extra-terrestrial flight are a pair of briefcase-size satellites, called MarCO.
It is hoped these experimental CubeSats, dubbed WALL-E and EVE from the 2008 animated movie, will provide near-live updates during the lander's descent. There's an eight-minute lag in communications between Earth and Mars.
The CubeSats will whizz past Mars and remain in perpetual orbit around the sun, their technology demonstration complete.
If they stay silent, news of InSight's landing will come from Nasa orbiters at Mars - albeit not as quickly.
Back on earth, people will have to be patient for results. While the first pictures of the landing site should start flowing shortly after touchdown, it will be at least 10 weeks before the science instruments are deployed.
Then it will be another several weeks for Martian thermometer to dig into Mars. In total, the mission is intended to last two years - or one full Martian year.