Meet InSight: The Mission To Measure Marsquakes and Unlock Red Planet

Emily Lakdawalla is senior editor and planetary evangelist at The Planetary Society.

Even while tucked away in a testing lab in Colorado, the instrument picks up the sloshing of the oceans thousands of miles away. That's the kind of sensitive equipment that's about to go to Mars, where NASA's next mission will dig into the mysterious history of the Red Planet and find out how active our neighboring world still is.

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On May 5, NASA will launch InSight, which stands for Interior exploration using Seismic Investigations, Geodesy, and Heat Transport. Over the course of two Earth years, the lander will try to answer fundamental questions about Mars' deep interior, including the thicknesses of its onion-like layers, and how rapidly Mars is cooling. It will bring new insights into the hidden history and mysterious present of this planet.

The Long Journey

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When the Mars InSight mission lift offs atop an Atlas V rocket from Vandenberg Air Force Base in California, it will mark the United States' first interplanetary launch from the West Coast. NASA prefers to blast off its biggest missions from Florida, where they can zoom out over the ocean and take advantage of Earth's eastward rotation for a boost to low-Earth orbit. That strategy conserves fuel the mission will need later.

From the West Coast, it's unsafe to launch east; Vandenberg launches typically head southward into orbits that go pole-to-pole. It costs more fuel to achieve Earth orbit from Vandenberg than it does from Florida, but the InSight's Atlas-Centaur rocket combination is overpowered relative to its needs. So even after going into a costlier polar orbit, it will have plenty of fuel left to deliver the relatively small spacecraft on to its interplanetary cruise.

NASA’s InSight to Mars undergoes final preparations at Vandenberg Air Force Base in Central California, ahead of its launch, expected as early as May 5, 2018.

NASA

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Launching with InSight will be a pair of CubeSats, the first of these tiny satellites to go on a mission to another planet. MarCO, or Mars Cube One, comprises two identical spacecraft. If successful, they will relay telemetry in real time from InSight to Earth as the lander experiences its "seven minutes of terror" of entry, descent, and landing on Mars on November 26, 2018.

To transmit across the 150 million kilometers that will separate Earth and Mars on landing day, the MarCO satellites will use an innovative "reflect array" system. This is a flat X-band radio antenna that operates at a lower power than traditional dish antennas. If neither MarCO survives the trip to Mars, we'll still receive "tones" on Earth from the spacecraft's low-gain antenna to indicate the success of critical moments in its landing. The Mars Reconnaissance Orbiter, a different mission that's been orbiting Mars since 2006, will record everything broadcast by InSight for later replay, just in case anything goes wrong.

Marsquake!

NASA

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This is not a plucky little rover. InSight will not roam the Martian countryside like NASA's charismatic Opportunity and Curiosity bots. The mission's landing site is deliberately chosen to be as bland as possible in terms of both geology and weather. InSight will spend about four months carefully and deliberately setting up its scientific experiments, and then it will sit there.

And sit.

For two whole Earth years.

One reason for InSight's stationary nature is that its sophisticated tools need to remain quiet and still. The heart of the mission is the Seismic Experiment for Interior Structure (SEIS), the exquisitely sensitive seismometer that can hear ocean noise from Colorado. After landing, InSight will lift SEIS from its deck and place the tool on a flat spot on the ground. Direct contact with the ground will dramatically increase SEIS' ability to detect tiny ground motions, and it will reduce the temperature swings it experiences between day and night.

InSight will also place a lid over SEIS to further insulate it from temperature variation and to provide a shield against wind. A suite of environmental sensors, provided by many of the same people who run Curiosity's weather experiments, will help the SEIS remove noise in the data caused by weather, temperature, and even magnetic-field variations.

SEIS will be able to detect marsquakes. One of the fundamental questions it will answer is just how much seismic activity there is on Mars. Mars doesn't have plate tectonics like Earth, so its seismicity is expected to be much more like the Moon's: relatively small shudders and creaks caused by the planet's very slow cooling and shrinking. It will also detect asteroid impacts or airbursts, thereby determining the modern rate of impacts on Mars. SEIS can even detect minute signals from nearby dust devils and from Mars' moon Phobos passing overhead.

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By measuring the arrival times of different types of earthquake waves—including compression (P) waves, which travel quicker, and shear (S) waves, which travel slower—seismologists can figure out the distance to seismic events. By studying the arrival times of other waves, which have reflected off of discontinuities in the subsurface such as the boundary between crust and mantle, they can measure crustal thickness, another of InSight's scientific objectives.

Update the Textbooks

In addition to SEIS, InSight carries a second instrument, the Heat Flow and Physical Properties Probe (HP³, pronounced “H-P cubed”). HP³ has a 40-centimeter-long "mole" that will drive itself into the ground. Inside its cylinder is a spring-loaded tungsten block that will hammer thousands of times to slowly drive the mole to a depth of 3 meters, or about 10 feet.

The mole will trail a cable that contains temperature sensors and heaters. It will use the heaters and sensors to measure how fast the Martian regolith conducts heat, then will use the temperature sensors to measure the thermal gradient (how much and how fast the temperature changes with depth). Heat flow is a fundamental quantity that influences the physics of a planet's interior. InSight's heat flow measurements will dramatically improve geophysicists' understanding of Mars.

A final experiment will use the radio transmitter to broadcast a signal to Earth-based antennas. Over the course of a full Martian year, radio scientists will measure InSight's position on the sky and use that information to measure Mars' rotation. Why? Mars' rotation axis shifts very slightly over time, in a way that's sensitive to how large its core is and how much of it is molten, so studying its rotation in detail tells you something about its interior.

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InSight must stay quiet and motionless for two Earth years for its experiments to succeed, and so the mission can build up statistics and study changes over a full Mars year. The three experiments depend on incredibly precise measurements of tiny ground motions and minute temperature gradients.

While there could be some exciting results early on, like the detection of an asteroid impact through its seismic waves, the real scientific payoff won't come until the experiment has run to completion and the science team has removed all spurious contributions to the signals measured by the instruments. Then it will be time to update the textbooks.

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