NASA will begin a new chapter in decoding the evolution of our solar system on Nov. 26, when its InSight lander performs the first Mars landing in six years and provides our first in-depth look at the Martian interior—with the help of a one-of-a-kind underground probe.
En route since May, InSight is targeting a 3 p.m. EST touchdown on Elysium Planitia, a flat expanse on the Martian equator. It’s the first surface mission since the Curiosity rover, and roughly 373 miles from its landing site. NASA will cover the event live from Jet Propulsion Laboratory in Pasadena, CA, which is managing the $814 million mission. (You can also watch the event with other humans at landing parties worldwide.)
Unlike Curiosity, however, the solar-powered InSight will remain in place, using three instruments to study the planet’s seismic activity, rotational wobble, and underground temperatures to determine the planet’s interior structure and geothermal activity, and a liquid or solid core. (The next Mars landing after InSight, the Mars 2020 Rover mission–which announced its landing site Monday–will search for the potential of ancient life by collecting and caching samples for return to Earth for further study.)
What’s InSight doing on Mars?
The data InSight collects may help explain how all terrestrial (rocky) planets formed, including Mercury, Venus, Earth, and Mars, and why Earth and Mars began evolving the same way, but diverged so that only one presently sustains life on its surface. Unlike Mars, Earth’s geological churning has erased structural evidence of its first several tens of millions of years after forming 4.5 billion years ago.
“We have a presumption about our solar system history, at least based on how the Earth developed,” says Michael Meyer, lead scientist for the Mars Exploration Program. “We have models and good data from Earth deducing how our planet formed and evolved. Now we need data from other planets letting us know that those models are correct.”
A comparative example is the Kepler mission close-ups of other solar systems, prompting scientists to readjust assumptions about our own. “We had models on how the solar system formed and everyone was happy with them until Kepler found large [gaseous] Jupiter-sized planets closely orbiting other stars,” instead of farther away, says Meyer. “We realized the models worked for our solar system, but didn’t necessarily explain what was going on in others.”
The mission has been a dream of InSight principal investigator Bruce Banerdt. After a rejected 2006 attempt, his revamped proposal was accepted in 2010, and beat two competitors in 2012 for funding. InSight is part of NASA’s Discovery Program, cost-capped science missions overseen by the Marshall Space Flight Center in Huntsville, AL.
“Bruce has been trying to get a seismometer to Mars for decades,” says Troy Hudson, an InSight instrument systems engineer at JPL, who walked Fast Company through portions of the science. (Hudson’s talk on InSight science can be found here.)
InSight–or, Interior Exploration using Seismic Investigations, Geodesy and Heat Transport–will use seismometers and timing of the Martian rotation to ascertain the constitution of its mantle and core, and current geothermal activity. While that technology has been around for decades on Earth, enabling an intact landing and functioning on Mars took an international mindset. Research institutes in France, Germany, Switzerland, and the United Kingdom helped design parts of the instruments, while Lockheed Martin Space in Denver designed the spacecraft.
U.S. investment in InSight is $813.8 million, including over $163 million for the launch vehicle/services, spacecraft, and operations. France and Germany–the major European participants–have invested another $180 million, primarily for the seismometer and heat flow instruments. JPL and NASA are investing over $18 million in the Mars Cube One technology, a separate but complementary mission.
A carefully choreographed landing
Even without a sky crane, the Insight landing will be as harrowing as Curiosity’s nail-biter in its series of exquisitely timed movements.
They include the lander and back shell separating from the cruise stage, turning the heat shield toward the atmosphere, which it will hit at a 12-degree angle that will prevent its burning up or bouncing off. Seventy miles above the surface, the temperatures will exceed 1800 ºF, and InSight will face 12 g’s as it rapidly descends from 13,000 mph to 1000 mph. At 10 miles, InSight will deploy a supersonic parachute, jettison its heat shield, release the landing legs, and transmit radar toward the surface to gauge its distance and speed.
At a mile from the surface, the lander portion will detach from the back shell and parachute. Its back thrusters will ignite, rotating the lander away from the back shell, bringing it to a soft landing on the surface, and turning off the moment it hits ground, so as to not tip the lander over. Scientists chose the site for its sunny exposure, dearth of rocks, and a low-enough elevation to ensure sufficient atmosphere for a safe landing, including in a dust storm.
“When you’ve worked on something this complex and challenging for a decade, and it all hinges on that eponymous ‘7 minutes of terror,’ for those of us involved in the mission, it will be the most harrowing experience of our lives,” says Hudson.
To relay data from its entry, descent, and landing, InSight will pair with a separate flyby mission, Mars Cube One (MarCO), the two first deep-space CubeSats, which have accompanied InSight along for the ride to Mars. Once on the surface, the craft will unfold its solar panels to power up, but will take up to two months before the instruments get to work. Specifically, two days before the robotic arm unlatches from the deck; 10-15 days of site reconnaissance with onboard cameras, and another 30-40 days of methodically placing the seismometer and heat flow instruments on the ground.
“This is the part of the mission that will involve the greatest number of people working simultaneously and it’s one of the many things on InSight we’ve never done before,” says Hudson. “We’ve never deployed instruments this sophisticated for ‘remote’ operation to be physically separated from the lander.”
The RISE instrument will measure Mars’s wobble
As Mars spins on its axis and orbits the sun, it wobbles like a top as the sun pushes and pulls it in its orbit (as does Earth). We know that Mars wobbles every Martian year, but we don’t know by how much. That variation will help scientists determine the size and composition of Mars’s core. A liquid core will create a greater wobble.
RISE (Rotation and Interior Structure Experiment) comprises two X-band antennas atop the craft that will send radio signals to a receiving station on Earth for scientists to track and measure. As InSight rotates with the planet, their apparent frequencies will shift. That change in frequency, caused by the Doppler effect, allows the RISE team to measure the distance between the InSight spacecraft and the receiving station on Earth to within tens of centimeters–better than one part in a billion.
Observing those frequency changes and measuring the degree of wobble over InSight’s Mars-year-long mission (roughly two Earth years) will suggest whether Mars’s core is liquid or solid.
It will also be a step toward explaining the planet’s weak magnetic field. A stronger magnetic field, like Earth’s, is thought to be beneficial for life because it deflects much of the sun’s solar wind, reducing the sun’s ability to strip away a planet’s atmosphere. Swirling convection currents within Earth’s liquid iron outer core create this planetary dynamo. Mars’s lack of a strong magnetic field, possibly due to a thinner or absent liquid outer core, is a likely culprit in Mars having lost much of its early atmosphere to stripping from solar wind.
SEIS will measure Marsquakes
SEIS (Seismic Experiment for Interior Structure) will measure Mars’s internal activity and structure via seismic waves from marsquakes, meteorite strikes, landslides, dust storms, and tidal bulges in the crust from the pull of Mars’s two moons. As the seismic energy moves through Mars, the waves reflect at layer boundaries and bend in response to changes in the properties of the material through which they travel.
“Seismology is analogous to using ultrasound to see inside your body,” says Hudson. “Different seismic sources, like quakes or impacts, generate waves with unique characteristics, like the different timbres of musical instruments.”
Seismometers detect vertical ground movements through springs and weights, whose motion generates an electrical voltage that is recorded digitally. Greatly improved from the 40-year-old seismometers in the Viking landers, SEIS is sensitive enough to detect vibrations smaller than the width of a hydrogen atom.
Such sensitivity requires protection. On Earth, scientists bury seismometers in the ground, which they don’t have the ability yet to do on Mars. After landing, InSight’s robotic arm will place SEIS on the ground, then place over it a dome-shaped cover, the Wind and Thermal Shield. This “portable hole” will protect SEIS from Mars’s 100º F-temperature swings and features a Mylar-and-chainmail skirt that conforms to the ground surface to keep out vibrations from wind.
Related: Will the humans kill Mars?
Although Mars has calmer tectonics than Earth, scientists expect it to experience considerably more detectable meteorite hits, thanks to a thinner atmosphere and no ocean. If SEIS detects any, it will coordinate with the Mars Reconnaissance Orbiter for visual confirmation.
“If InSight hears something and we think it’s in a certain area of Mars, we can see if there were fresh impactors,” says Hudson. Scientists expect to detect five to 10 meteor impacts during InSight’s two-year mission.
In addition to these high-energy seismic events, SEIS will sense much slower changes. “We’ll also see how Mars flexes and bulges under tides,” he adds. “Just as the gravity of Earth’s moon creates tides, Mars’s moons (much smaller than Earth’s, but much closer to their parent planet) cause its crust to rise and fall. This tidal motion of the land is very small; on the scale of a millimeter. The seismometer will pick up how fast it rises and falls, and from that we can construe how thick the crust is. A thicker crust moves less.”
It was SEIS’s design that proved the most challenging, leading to the delayed launch, says Hudson. Because of their sensitivity, its instruments needed to be encased in a vacuum. But the engineering team kept detecting a slow leak. It turned out to be the connection between the instrument components on both sides of the vacuum, requiring a complete design and manufacturing overhaul.
The delay resulted in about $150 million in cost overruns and caused the mission to miss the 2016 launch window, requiring waiting another 26 months for the next Mars launch opportunity. But the extra time also allowed for Hudson’s team to make improvements to the mission’s one-of-a-kind heat flow instrument.
HP3 will take Mars temperature: “No one before has created a device like this”
Last to deploy will be the HP3 (Heat Flow and Physical Properties Package), which will gauge the heat coming from the interior of the planet, left over from the planet’s formation and from the decay of radioactive elements. This is the same heat that helped shaped the surface of Mars, with some of the tallest mountains in the solar system and a volcano three times the height of Mount Everest. Foremost, constraining the heat flow will help resolve whether Mars, Earth, and the Moon sprang from the same material, as scientists believe, and how geologically active Mars is today.
But HP3‘s specific data-taking needs to happen well below the surface. In order to avoid surface temperature swings, readings must be taken three to five meters (some 10 to 16 feet) underground. To that end, engineers devised a self-burrowing cylindrical probe, or mole, attached to a long tether embedded with temperature sensors capable of measurements accurate to a hundredth of a degree. A mechanism inside the probe will hammer it down as much as five meters–deeper than humans have dug on any other planet, moon, or asteroid–pulling the tether behind it.
“As the mole penetrates, it stops periodically to measure the thermal conductivity of the ground,” says Hudson. “Once it has reached its final depth, the embedded sensors report the change in subsurface temperatures with depth: the geothermal gradient. The increase we expect to see over five meters is only one or two degrees. That’s tiny, but it’s enough for HP3‘s temperature sensors. Going deep is challenging, but the further we get below those first two meters, the cleaner the data will be.”
The mole design faced challenging requirements: it had to be a self-contained drilling mechanism less than 1-kg (2.2 lbs.), able to function on 10 watts of available power, strong enough to penetrate a variety of planetary soil types, and robust enough to survive the self-imposed and violent accelerations of the hammering. All while containing some delicate temperature and orientation sensors.
“No one before has created a device like this–capable of self-propelled penetration into a planetary subsurface while using so few resources,” says Hudson. “The HP3 mole can simultaneously produce intense hammer strikes of over 10,000 g’s, can survive tens of thousands of those violent shocks, uses less power than a Wi-Fi router, and weighs barely more than a pair of shoes.”
The drilling will also offer a batch of extra data.
“There will a 30-day period where the mole will be hammering for a couple of hours a day every four days, creating vibrations the SEIS will be able pick up,” he adds. “We’ll be able to use that information to characterize the subsurface near the lander, such as the depth to the bedrock layer. Doing so is not one of the mission requirements; it’s an example of us trying to squeeze every last drop of science from this mission.”