Mars mission got lucky: NASA lander touched down in a sand-filled crater, easing study of planet’s interior

PASADENA, CALIFORNIA—In a laboratory on Earth, the marsforming had already begun.

On 27 November, the day after the successful touchdown of NASA’s InSight lander on Mars, after the television crews had departed, technicians here at the Jet Propulsion Laboratory (JPL) were already at work, simulating Mars for a full-size model of the lander, which they call ForeSight. Scientists don’t yet know exactly where on Mars InSight is. But the first few images sent back to Earth have established its immediate environment—and that the lander is slightly tilted, by 4°. So yesterday, NASA engineers were playing in the sand, moving fake Mars rocks into position. They heaved ForeSight up on their shoulders while shoving small blocks underneath a lander leg to get it listing just right.

Looking on from a gallery above ForeSight was Matt Golombek, the JPL geologist who will lead the placement of two of InSight’s instruments, a heat probe and seismometer. From the few photos returned so far, he says, much has been learned about its location, which closely resembles martian terrains previously scouted by the Spirit rover.

For example, InSight landed in what’s called a hollow, a crater that has been filled in with soil and leveled flat. In images taken from the elbow of the lander’s stowed robotic arm, the edge of the crater is visible. Once the team determines the diameter of the crater—it could be meters, maybe tens of meters—researchers can infer its depth and the amount of sand blown into it. Either way, this bodes well for the heat probe instrument, called HP3, which should penetrate the material with ease. “This is about as good news for HP3 as you could possibly hope,” he says.

Landing in the hollow was fortunate for another reason. InSight didn’t quite hit the bull’s-eye of its target landing zone, and ended up in terrain that, overall, is rockier than desired. But the hollow is mostly devoid of rocks. One, about 20 centimeters across, sits close to the lander’s feet, whereas three smaller ones lie farther away—but none poses a threat to placing the instruments. The hollow is flat and lacks sand dunes, and small pebbles indicate a surface dense enough to support the weight of the instruments. “We won’t have any trouble whatsoever,” Golombek says.

The biggest mystery for the lander team right now is figuring out exactly where it is. A Mars orbiter set to image the center of the landing zone on Thursday will miss the lander, because it missed the center slightly. An instrument on InSight called the inertial measurement unit has pinned the location to within a 5-kilometer-wide circle. InSight’s entry, descent, and landing team will refine that estimate down to a kilometer or less. “But they haven’t done that yet because they were so happy to have landed safely that we don’t know what they did last night,” Golombek says with a smile. “And they have not yet shown up today.”

There is one more technique that could help: InSight’s third primary experiment, called the Rotation and Interior Structure Experiment (RISE). The main purpose of RISE’s two sensitive listening antennas is to detect wobbles in the martian core. But the InSight team can also use them to map the lander’s latitude and longitude by using the radio signals of passing orbiters. That has given the geologists a location to within about 100 meters or so.

Now, a friendly competition is on. Golombek and his peers hope to beat the satellites to fixing InSight’s location. They should have until 6 December, when an orbiter will likely capture it. Right now, they’re stretching out the scant imagery, trying to compare their hollow to existing high-resolution maps. Their job will get much easier next week, when the camera on the robotic arm’s elbow will be extended to photograph the lander’s terrain in detail. For now, the arm is stowed—Tuesday was about simple steps, like firing off the small charges that secure the arm to the deck. But later this week, after the camera caps come off and the arm is released, the detailed reconnaissance will begin.