With just a day to go, Nasa's InSight spacecraft aimed for a bull's-eye touchdown on Mars, zooming in like an arrow with no turning back.
InSight's journey of six months and 482 million km comes to a precarious grand finale tomorrow at 9am NZT.
The robotic geologist — designed to explore Mars' insides, surface to core — must go from 19,800 km/h to zero in six minutes flat as it pierces the Martian atmosphere, pops out a parachute, fires its descent engines and, hopefully, lands on three legs.
Nasa says the overall landing sequence will begin at 8.40am NZT.
It is Nasa's first attempt to land on Mars in six years, and all those involved are understandably anxious.
Nasa's top science mission official, Thomas Zurbuchen, confided today that his stomach is already churning. The hardest thing is sitting on his hands and doing nothing, he said, except hoping and praying everything goes perfectly for InSight.
"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."
Earth's success rate at Mars is 40 per cent, counting every attempted flyby, orbital flight and landing by the US, Russia and other countries dating all the way back to 1960.
But the US has pulled off seven successful Mars landings in the past three decades. With only one failed touchdown, it's an enviable record.
No other country has managed to set and operate a spacecraft on the dusty red surface.
InSight is shooting for Elysium Planitia, a plain near the Martian equator that the InSight team hopes is as flat as a parking lot with few, if any, rocks.
This is no rock-collecting expedition. Instead, the stationary 360kg lander will use its 1.8m robotic arm to place a mechanical mole and seismometer on the ground.
The self-hammering mole will burrow 5m down to measure the planet's internal heat, while the ultra-high-tech seismometer listens for possible marsquakes.
Nothing like this has been attempted before at our smaller next-door neighbour, nearly 160 million km away.
No experiments have ever been moved robotically from the spacecraft to the actual Martian surface.
No lander has dug deeper than several cm, 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 differently.
One of the big questions is what made Earth so hospitable to life.
Mars once 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 US$1 billion, 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 at these so-called exoplanets "and how they fit into the story that we're trying to figure out for how planets form," 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.
FOLLOWING THE LANDING
Because it's been so long since Nasa's last Martian landfall — the Curiosity rover in 2012 — Mars mania is gripping not only the space and science communities, but everyday folks.
Viewing parties are planned in the US coast to coast at museums, planetariums and libraries, as well as in France, where InSight's seismometer was designed and built.
The giant NASDAQ screen in New York's Times Square will start broadcasting NASA Television an hour before InSight's scheduled touchdown; so will the National Air and Space Museum's Udvar-Hazy Centre in Chantilly, Virginia, and the Denver Museum of Nature and Science.
Nasa is providing a special 360-degree online broadcast.
Confirmation of touchdown could take minutes — or hours.
At the minimum, there's an eight-minute communication lag between Mars and Earth.
A pair of briefcase-size satellites trailing InSight since liftoff in May will try to relay its radio signals to Earth, with a potential lag time of under nine minutes.
These experimental CubeSats will fly right past the red planet without stopping. Signals also could travel straight from InSight to radio telescopes in West Virginia and Germany. It will take longer to hear from Nasa's Mars orbiters.