On Saturday, NASA plans to launch a robot designed to peek into the mysterious interior of Mars from California’s Vandenberg Air Force Base. Named InSight (Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport), the lander is scheduled for liftoff at 4:05 AM local time. If all goes to plan, it will become the first interplanetary mission in history to lift off from the West Coast.
But that’s not the only thing that distinguishes InSight from the diverse squad of orbiters, landers, and rovers that already populates the red planet. Provided it completes its six-month voyage to Mars, and successfully touches down at its target site in the equatorial Elysium Planitia region, this lander will also make history by digging a full five meters (16 feet) into the Martian terrain, exponentially deeper than any previous Mars mission.
InSight will accomplish this feat with its Heat Flow and Physical Properties Package (HP3), nicknamed “the mole” because it can burrow through regolith (the loose rocky surface layer on Mars and many other terrestrial planets). The instrument consists of a tube with a spring-loaded mechanism that will hammer out a hole in half-meter increments. Every 50 centimeters, it will stop for several hours or days to take thermal measurements and cool down from the frictional and operational heat generated by the dig process.
According to HP3 instrument co-investigator Paul Morgan, a senior geothermal geologist at the Colorado School of Mines, five meters is the target depth because it is the estimated distance that the mole should be able to descend before hitting tougher bedrock.
“The regolith is the broken-up layer, and as you get deeper, it tends to compact and get harder to penetrate,” Morgan told me in a phone call. “There’s an outcrop not too far from the landing site where we think we can see the base of the regolith, so five meters is an estimate of what we should be able to penetrate.”
HP3 will help study Mars’s interior in tandem with another major instrument called the Seismic Experiment for Interior Structure (SEIS), which will be placed on the Martian surface by InSight’s robotic arm. The instrument’s mushroom-cap dome will shield a sensitive seismometer as it records the first ever measurements of “Marsquakes,” which are vibrations in Mars landscape similar to earthquakes.
These quakes could be set off by asteroid impacts or by old fault lines in the planet’s crust. SEIS is so sensitive that it can detect vibrations on the scale of a hydrogen atom’s diameter, and this precision will help it capture snapshots of Mars’ insides through seismic waves.
“We can use the information about how long it has taken the energy to travel from the quake to the seismometer to figure out something about the interior structure,” SEIS co-investigator Catherine Johnson, a planetary scientist at the University of British Columbia, told me over the phone. “This is how we build what we call ‘images’ of the interior structure. It’s basically indirect information that comes from ground motion that is caused by quakes.”
InSight is led by NASA but carries many instruments developed in part by the French and German space agencies, international research centers, and the aerospace company Lockheed Martin. These devices include the Rotation and Interior Structure Experiment (RISE), Temperature and Winds for InSight (TWINS), the Laser RetroReflector for InSight (LaRRI), two cameras, and two small CubeSat spacecraft which will separate from InSight shortly after launch.
Still, SEIS and HP3 are the two main components of the mission, and they will work together to develop a better portrait of Mars’ inner dynamics and evolution, much of which is still poorly understood. “There are a number of models of how Mars works on the interior,” Morgan said. “We’ve only got one point on Mars [with InSight], but one is better than none. Hopefully, if this experiment is successful, future landers will make similar measurements.”
This never-before-tapped data about Mars interior has the potential to clarify some of the most tantalizing questions about the planet. For instance, SEIS is equipped with a magnetometer that will measure the electrical conductivity of rocks beneath the surface, and that in turn can help scientists piece together its interior composition—including how much water remains locked up in the subsurface layers of the planet.
“From all these landed and satellite missions over the last decade, we know Mars had a lot more water in the atmosphere and the surface at least on short timescales in its early history,” Johnson told me. “Understanding the water content of the interior is a really key part of understanding Mars today, and particularly that early history when there was a lot more water around.”
This information could shed light on the origins of terrestrial planets in general, because Mars happens to be in “a sweet spot” in terms of size, Johnson said. It’s big enough that it likely evolved similarly to larger worlds like Earth or Venus, but it’s too small to have sustained long-term geological processes, like plate tectonics or volcanism, that tend to erase evidence of infant planetary history.
That’s why the InSight team is so eager to bid farewell to the lander this weekend, and watch it embark on its scientific journey to the center of Mars. “I’m really excited about what we’re going to find that we didn’t even know enough to ask questions about,” Johnson said.
“Everywhere we go in the solar system, every mission we do, we discover things that we never expected,” she added. “Those really always end up revolutionizing our thinking because we didn’t think of the question ahead of time, but then we have the observation [that makes us say] ‘whoa, what’s that?’”
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