Nasa satellites around Mars will provide updates.
It is Nasa's eighth successful Mars landing since the 1976 Vikings.
The thee-legged, one-armed InSight will operate from the same spot for the next two years. It landed less than 600km from Nasa's Curiosity rover, which until today was the youngest working robot in town.
The spacecraft InSight - designed to explore Mars' insides, surface to core - has been travelling for six months and 482 million km.
The robotic geologist went from 19,800 km/h to zero as it pierced the Martian atmosphere, popped out a parachute, fired its descent engines and, landed on three legs.
Nasa's top science mission official, Thomas Zurbuchen, confided yesterday that his stomach was already churning over the landing.
"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.
It was 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, InSight is placing a mechanical self-hammering mole and seismometer on the ground.
The 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 centimetres, 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 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 ($1.48b), two-year operation could even spill over to rocky worlds beyond our solar system, Banerdt believes. The Mars findings 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.
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 the public.
The real action, at least on Earth, will unfold at Nasa's Jet Propulsion Laboratory in Pasadena, California, home to InSight's flight control team.
Nasa is providing a special 360-degree online broadcast from inside the control centre. Confirmation of touchdown could take minutes - or hours. At the minimum, there's an eight-minute communication lag between Mars and Earth.
- AP
