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Digging deep into Mars

Although dozens of spacecraft have explored Mars’ surface, InSight is the first to target the planet’s interior.
RELATED TOPICS: MARS | INSIGHT
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InSight took this selfie December 6, 2018, with its Instrument Deployment Camera. The probe’s two solar panels dominate the scene, with the deck and its science instruments, weather sensor booms, and UHF antenna between them. The camera, which resides on the elbow of the spacecraft’s robotic arm, took 11 images that scientists on Earth stitched together to create this mosaic.
All photos by NASA/JPL-Caltech unless otherwise noted
Is Mars a dead world like the Moon, or an active, living terrestrial planet like Earth? That’s the $830 million question that an international team of scientists and engineers are trying to answer with the latest robotic inhabitant of the Red Planet. NASA selected the InSight mission in 2012 from a pool of nearly 30 proposals for exploring the solar system that had been submitted to the space agency’s Discovery program competition two years earlier. InSight — short for “Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport” — is, as the name implies, a mission designed to study the deep interior of Mars from the vantage point of a single station on the surface.
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An Atlas V rocket carrying NASA’s InSight spacecraft rises above a fog bank shortly after launch from Vandenberg Air Force Base in California the morning of May 4, 2018. 
NASA/Cory Huston
Dreaming deep

Planetary scientist Bruce Banerdt, the mission’s principal investigator, has been studying the formation and evolution of Mars and other planets at Caltech’s Jet Propulsion Laboratory (JPL) since 1983. For decades, he and scores of other planetary geophysicists from around the world have been thinking about ways to learn whether Mars is dead or alive.



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They knew that seismology — the study of earthquakes and related phenomena — was the key to understanding Earth’s interior. But to do similar research on Mars meant that they’d have to figure out how to build and deploy seismometers and other geophysical sensors that could handle the stresses of a launch from Earth and the harsh environment of Mars’ surface. And they knew that it wouldn’t be possible to deploy a global network of thousands of seismometers like we have on our planet. At best, they could contemplate setting up a small network of at least a few seismometers and other instruments, like the Apollo astronauts had done at six landing sites on the Moon, using spacecraft similar to those that had already successfully landed on Mars. At worst, they could deploy only one.

And indeed, one it would have to be. The costs, complexity, and risks of attempting multiple landings on Mars simply didn’t fit within the constraints of NASA’s “faster, better, cheaper” Discovery program line, and no larger-class missions to study martian geophysics were scheduled for the foreseeable future. So, Banerdt began lining up a team to make the best possible pitch to NASA for a mission to study Mars’ interior.

InSight
To reduce risk, the team proposed to leverage JPL’s experience in designing and operating Mars surface missions, and to use essentially the same Lockheed Martin lander that had successfully carried the Phoenix mission’s experiments to the surface in 2008. And to reduce cost, the team relied on space agencies from other countries to contribute a major percentage of the instruments. This rather gutsy decision would come back to haunt — but fortunately not kill — the mission.

Is Mars alive?

Prior to InSight, planetary scientists had a rudimentary understanding of what the interior of Mars was probably like, and some crude hypotheses about its level of activity. Based on general similarities among our solar system’s terrestrial planets, and on basic physical, compositional, geologic, and other information about Mars provided by previous missions, researchers also deduced that Mars was differentiated — with an interior segregated into a core, mantle, and crust like Earth’s.

NASA’s Mars Global Surveyor orbital mission in the mid-1990s provided a key piece of information supporting this hypothesis. The spacecraft’s magnetometer measured strong magnetic fields in the rocks on certain parts of the planet’s surface. Scientists presume these signatures are remnants of what was once a global magnetic field, perhaps similar in some ways to Earth’s. Our planet’s magnetic field arises in the core. This partially melted, spinning ball of highly conductive iron creates a strong magnetic field that extends from the core well out into space. The field helps shield the surface from harmful radiation and allowed life to emerge and thrive here. Did Mars once have a partially molten core that gave rise to a similarly beneficial global magnetic field?

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InSight flipped open the lens cover on its ICC on November 30. Although some dust still clings to the lens, this much clearer view reveals a nearby rock at bottom center as well as one of the spacecraft’s footpads at bottom right. The camera’s fisheye lens creates the curved horizon.
Another key piece of evidence suggesting that Mars is differentiated comes from tracking the radio signals Mars Pathfinder and subsequent missions sent from the surface. Landers and rovers transmit their radio signals from a spinning planet that wobbles slightly. Those tiny wobbles stem from the fact that Mars is not a uniform sphere, but instead has internal variations in mass and density. By modeling the minuscule changes in radio signal frequency associated with those wobbles, planetary geophysicists can deduce the nature of the interior variations. Scientists tracking the Pathfinder radio signals, for example, inferred that Mars has a denser, and presumably iron-rich, core that extends from the center of the world out to somewhere between 40 and 60 percent of the planet’s radius.

But is that core still at least partially molten? Does Mars have enormous quantities of internal heat — high heat flow, in geophysical terms — like Earth, and does that heat drive contemporary geologic processes? Mars has no global magnetic field today, which is one argument that the core has solidified and the interior is no longer active.

Other arguments against high heat flow include the absence of any proof for recently active volcanoes or hotspots, as well as no convincing evidence for past or present plate tectonics. Earth’s crust is divided into a dozen or so large tectonic plates. These plates move relative to one another, causing most of our planet’s earthquakes and volcanoes, and play a role in helping our planet release its internal heat. But from orbit, Mars appears to be a one-plate planet with no obvious internal geologic activity. Could surface observations verify this supposition?

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InSight’s deck bristles with science instruments December 4, 2018, before controllers on Earth had the robotic arm deploy the devices. The copper-colored hexagonal structure in the foreground is a cover to protect the seismometer. The gray dome behind it is the Wind and Thermal Shield, which would be placed over the seismometer February 2.
The view from Elysium

The InSight mission team worked frantically for four years to design, build, and test the lander and its instruments in time to meet the planned 2016 launch. The task proved challenging because a number of technical and management problems cropped up along the way. The most serious of these was a small leak in the housing for the seismometer, which needs to operate in a vacuum to achieve its required sensitivity, discovered several months before the scheduled launch.

The instrument, built by a European consortium led by the French Space Agency (CNES), could not be repaired in time and the launch was delayed for two years. NASA estimated the cost of this delay at around $150 million, canceling out the hoped-for savings from relying on a heavily international science payload.

The delay also had ramifications within NASA. The space agency realized that highly technical international collaborations can be exceedingly difficult to manage and decided to tighten the rules on how much outside countries could contribute to instruments on future missions. The new limit is now one-third the total cost of all instruments.

The delay did give JPL, Lockheed, and their international partners time to diagnose and repair the problems, and to test the full system in a giant, Mars-simulating vacuum chamber at Lockheed’s facility in Colorado. Technicians then packaged the spacecraft into its protective cruise-stage aeroshell and heat shield and shipped it to Vandenberg Air Force Base in California, where it would become the first interplanetary mission launched from the U.S. West Coast. NASA chose Vandenberg over the usual Cape Canaveral Air Force Base launch facility in Florida because it could better handle the spacecraft’s large mass and gave more flexibility in timing the launch. In the wee hours of May 5, 2018, an Atlas V rocket lit up the skies north of Los Angeles and set InSight on its way to Mars.

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InSight’s robotic arm places its copper-colored seismometer onto Mars’ surface December 19, 2018. The seismometer records seismic rumbles caused by marsquakes and nearby meteorite strikes.
Doing the dirty work

The InSight lander carries two cameras — one mounted below the deck and the other on the robotic arm — three main sets of geophysical experiments, and one set of meteorological instruments. The geophysical experiments include the CNES-led seismometer package called the Seismic Experiment for Interior Structure (SEIS). The science team designed it to detect potential marsquakes with up to 300 times the sensitivity of typical terrestrial seismometers, and to measure the strength of the magnetic field at Mars’ surface.

The German Aerospace Center built the Heat Flow and Physical Properties Package (HP3), which will measure the planet’s heat flow and conductivity by hammering a small probe nicknamed “the mole” as deep as 16 feet (5 meters) into the subsurface. The JPL-led radio transmitter experiment, called the Rotation and Interior Structure Experiment (RISE), will improve upon the experiments on previous landers that helped deduce the nature of the planet’s interior, including the size of the core. The Temperature and Winds for InSight (TWINS) meteorology package consists of several temperature, pressure, wind speed, and wind direction sensors placed at various heights on the lander.

In addition, the lander carries a passive retroreflector that will allow future Mars orbiters to shoot laser beams at the device and accurately track their range to the surface. Apollo astronauts left similar devices on the Moon that let scientists precisely monitor the distance between Earth and its satellite. Finally, the probe carries two tiny silicon wafer chips upon which NASA microscopically etched the names of more than 2.4 million people who signed up to have their names sent to Mars.

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In June 28, InSight’s robotic arm moved the HP3 instrument’s support structure (far left) to give scientists a better look at its digging tool, informally known as the “mole,” to see why it couldn’t burrow deeper. Controllers lifted the structure in three small steps to make sure they didn’t pull the mole out of the soil.
During the years prior to launch, the InSight science and engineering team worked to identify the perfect landing site for the mission. This team’s idea of perfection differed greatly from that of most previous mission teams, however. The InSight seismometers and other geophysical instruments need to be in good contact with the planet’s solid surface to sense seismic waves and to measure heat flow accurately. This meant avoiding rocks, loose sand, and piles of dust.

In addition, the heat shield-parachute-retrorocket landing system, inherited from the Phoenix lander, did not have the sophisticated obstacle-avoidance systems that have allowed other missions to target specific small areas. In fact, the mission’s landing ellipse — the region of uncertainty where the spacecraft was most likely to set down — stretched a robust 81 by 17 miles (130 by 27 kilometers). Compare that with the Curiosity rover’s landing ellipse, which spanned just 12 by 4 miles (20 by 7 km).

Thus, the InSight team wanted the spacecraft to land in a big, flat, rock-free, sand-free, low-dust parking lot. Indeed, it was almost the exact opposite of what most planetary geologists seek — exotic minerals, sedimentary layers, hills, valleys, water-related landforms — when they want to land on Mars. Luckily for the InSight team, Mars has an abundance of flat, relatively boring places. One particular site — in Elysium Planitia near 4.5° north latitude and 135.0° east longitude — also satisfied the mission’s additional requirements: a low elevation for the parachute to work well and an equatorial region so the mission could operate under solar power.

After a speedy and relatively uneventful six-and-a-half-month cruise to Mars, InSight team members and millions following online experienced their own “seven minutes of terror” as the spacecraft autonomously executed its carefully choreographed set of entry, descent, and landing activities November 26, 2018.

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The multiple footprints seen around the HP3 instrument’s support structure reveal that it was moving slightly as the instrument attempted to hammer its “mole” into Mars’ subsurface. Scientists think soil properties or a rock are preventing the mole from going deeper, and are working on ways to get it operating.
Scientists on the ground monitored many of these activities in near-real time, delayed only by the eight-minute light travel time from Mars, as the lander relayed its radio signals back to Earth through two CubeSats. These small satellites, each about the size of a cereal box, had been launched with the main spacecraft back in May. Called Mars Cube One (MarCO) A and B and nicknamed Eve and Wall-E by their JPL engineering creators, the satellites did their job perfectly. They relayed telemetry and eventually the first dusty InSight photos from the surface as they sped past Mars, performing flawlessly as the world’s first deep-space interplanetary CubeSats.

Unpacking for a long stay

Although the cameras started taking pictures and TWINS began collecting Mars weather data soon after landing, it took more than three months to truly complete the landing process. That’s because many of InSight’s key geophysics instruments were packed on the lander’s deck during the journey to Mars. To work properly, the Instrument Deployment Arm (IDA) had to carefully unpack and then set them in contact with the rocky surface.

The InSight team deployed SEIS first, on December 18, or sol 22. (Mars scientists typically express time on the planet’s surface in sols. One sol is the length of a martian day, and equals 24 hours 39 minutes 35 seconds.) It would take until sol 66 (early February 2019) to complete the adjustments of the seismometer’s tether back to the rover and to cover the instrument with its protective Wind and Thermal Shield (WTS) designed to lower background noise that the sensitive instrument would otherwise pick up.

HP3 was deployed to the surface on sol 76 (February 12), and it began hammering the mole into the subsurface on sol 92 (February 28). After a long wait, the mission team could finally begin to collect all the different kinds of measurements it had set out to make.

In a sense, then, the InSight mission has only just started. The SEIS team detected its first probable marsquake on sol 128 (April 6), but as of early July, it has yet to pick up a second. The quake had a magnitude between 2.0 and 2.5 — a quiver, really, that a human would not have felt if it had occurred on Earth. Despite the apparent calm on Mars, the seismometers are operating beautifully, detecting ground motions on the scale of 25 picometers — just 20 percent the diameter of a hydrogen atom! SEIS’s high sensitivity has also recorded the effect of what team members presume to be numerous dust devils as well as other kinds of low-frequency atmospheric turbulence, known as infrasound, passing over the seismometer.

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InSight captured this panorama of its landing site December 9, 2018, the 14th martian day (sol) of its planned two-year mission. This 290°-wide field of view comprises 30 individual images and shows the rim of the degraded crater the spacecraft landed in, nicknamed Homestead Hollow.
The scarcity of detected marsquakes in SEIS’s first few months of operations already rules out the possibility that Mars’ interior is as seismically active as Earth’s. Although not unexpected, the team is eager to see if continued monitoring will reveal Mars to have as little activity as the Moon, or whether it slots in somewhere between Earth and the Moon. InSight should have plenty of time to sort this out — its primary mission lasts a full martian year, or just over two Earth years.
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InSight’s Instrument Deployment Camera captured the rising Sun on April 24 (sol 145). The camera took this image around 5:30 a.m. local Mars time.
HP3’s mole hasn’t fared as well. Shortly after hammering began, the mole became stuck some 12 inches (30 centimeters) below the surface, perhaps because the soil is not providing enough friction or because the instrument encountered one or more rocks. The team continues to diagnose the problem and hopes to devise a strategy that will allow the instrument to do its work. The mole needs to move deeper to make higher-quality heat-flow measurements.

Meanwhile, TWINS has been generating outstanding daily Mars weather reports. It discovered a small dust storm starting around sol 42 and has detected dozens of smaller atmospheric disturbances passing over the lander every sol.

The instrument’s pressure sensors have observed many of the same infrasound-producing small-scale atmospheric vortices that the seismometer has detected. Most of these atmospheric vortices have not produced visible dust devils in camera images, however, indicating that a whole new class of atmospheric disturbances — “dustless devils” — apparently exists, and InSight’s instruments will be able to study them for the first time.
Scientists have even taken simultaneous weather measurements and images when Mars’ larger moon, Phobos, eclipses the Sun. The moon’s shadow produces tiny drops in temperature and light levels during these events, which last less than 30 seconds.

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InSight also caught sunset on sol 145, when earthly calendars had flipped to April 25. The same camera took this image around 6:30 p.m. local Mars time.

And, of course, the lander and IDA cameras continue their imaging to monitor the instruments as well as to understand the geologic context of the Elysium site. The rocky rims of several small, distant impact craters dot the landscape, and dusty material fills smaller nearby craters that scientists have dubbed hollows. The team got the pretty flat and rock-free site they were hoping for — rocks cover less than 4 percent of the surface.

Even though InSight carries no mineralogy or geochemistry instruments, the images alone are consistent with a bedrock surface of volcanic origin fractured and pulverized to depths of many tens to hundreds of meters by eons of countless impacts. This material is probably basaltic, like most of Mars and the typical lava flows seen in Hawaii and Iceland. Geologically, InSight’s landing site in Elysium Planitia turns out to have a lot in common not only with the Spirit rover’s landing site in Gusev Crater but also with the Phoenix mission’s landing site in the high-latitude northern plains.

A legacy in the making

Although InSight’s full payload became operational only a few months ago, the mission is already making important meteorological discoveries about the current martian climate. And with the successful deployments of all the main instruments except for the mole, the stage is now set for the mission to make historical geophysical discoveries as well. Now, it’s time for Mars to cooperate.

With the first marsquake now in the books, how many more will be found? And will these turn out to be the results of nearby impacts, some deep, internal churning of a still-active mantle or core, or both? Is Mars as dead as the Moon, or does it still experience some internal activity? Over the coming years, scientists expect to record many seismic events. What will they reveal about the planet’s internal structure, and what can scientists glean from this about the timescale over which the planet’s once-abundant volcanism and strong magnetic field waned?

And ultimately, what other new insights will come from InSight? Stay tuned — the latest round of excitement and discovery on the Red Planet has only just begun.

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