NASA's spacecraft's six-month trip to Mars is nearing its dramatic grand finale.
The InSight lander is targeted for touchdown within hours, as anxiety builds among those involved in the $ 1 billion international effort.
InSight's perilous descent through the Martian atmosphere has churning stomachs and nerves stretched to the max. Although an old pro at this, NASA has not attempted a landing at Mars for six years.
InSight is scheduled for landing at 7am on Tuesday (AEDT).
The robotic geologist – designed to explore Mars' mysterious insides – must go from 19,800 kph) to zero in six minutes flat as it pierces the Martian atmosphere, pops out a parachute, shows its descent engines and lands on three legs.
It's aiming for flat red plains, hopefully low on rocks.
"Landing on Mars is one of the hardest single jobs that people have to do in planetary exploration," noted InSight's lead scientist, Bruce Banerdt. "It's such a difficult thing, it's such a dangerous thing that there's always a fairly uncomfortably large chance that something could go wrong."
The overall rate of success for landings on Mars is 40 percent.
The landing is notoriously difficult, Don Lincoln a senior scientist at the Fermi National Accelerator Laboratory told CNN, because of the Martian atmosphere.
The lander must hit the atmosphere at an angle of exactly 12 degrees. Any shallower, and the probe will bounce off into deep space, "Mr Lincoln said.
"Any steeper, and the probe will burn itself up in a spectacular and fiery death. The probe will first touch the atmosphere six minutes and 45 seconds before landing. "
Soon after the probe hits the atmosphere, a parachute will deploy, slowing it down further.
Seconds later, explosives will blow the heat shield off, exposing the InSight probe hidden inside.
Ten seconds after the heat shield falls away, the probe will extend its legs, much like an airplane extends its wheels before touching down.
This is no rock-collecting expedition. Instead, the stationary 360-kilogram lander will use its 1.8-meter robotic arm to place a mechanical mole and seismometer on the ground.
The self-hammering mole will burrow 5 meters down to measure the planet's internal heat, while the ultra-high-tech seismometer listens to possible marsquakes. Nothing like this has been tried before on Mars. No experiments have ever been moved robotically from the spacecraft to the current Martian surface. No lander has dug more than several inches deep, and no seismometer has ever worked on Mars.
By examining the deepest, darkest interior of Mars – still preserved from its earliest days – scientists hope to create 3D images that could reveal how our solar system's rocky planets formed 4.5 billion years ago and why they turned out so different. One of the big questions is what made Earth so hospitable to life.
Mars had flowing rivers and lakes; the deltas and lakebeds are now dry, and the planet cold. Venus is a furnace because of its thick, heat-trapping atmosphere. Mercury, closest to the sun, has a surface that's positively baked. The planetary know-how gained from InSight's two-year operation could even spill over to rocky worlds beyond our solar system, according to Banerdt. The findings on Mars could help explain the type of conditions in these so-called exoplanets "and how they fit into the story that we are trying to figure out how they form the planets," he said.
Concentrating on planetary building blocks, InSight has no life-detecting capability. That will be left for future rovers. NASA's Mars 2020 mission, for instance, will collect rocks for eventual return that could hold evidence of ancient life.