Mars InSight: NASA’s Journey Into the Red Planet’s Deepest Mysteries
Posted April 30, 2018 5:12 p.m. EDT
NASA’s Mars InSight spacecraft, scheduled to launch on Saturday, is headed to one of the most boring places on the red planet.
Its landing spot will be Elysium Planitia, an idyllically named expanse that will most likely be flat as far as the spacecraft’s eyes can see — no mountains in the distance, probably not even many large rocks nearby.
“We picked something as close to a 100-kilometer-long parking lot as we could find anywhere,” said Bruce Banerdt, the mission’s principal investigator.
He said that one of his colleagues described it as “Kansas without the corn.”
Which is exactly what the scientists want.
InSight — the name is a compression of the mission’s full name, Interior Exploration Using Seismic Investigations, Geodesy and Heat Transport — is in many ways a diversion from “follow the water,” the mantra that has kept NASA focused on the possibility that the sun’s fourth planet may have once been hospitable for life.
This mission will instead probe the mysteries of Mars’ deep interior and help answer geophysical questions about the planet’s structure, composition and how it formed.
Since there was not much interest in what InSight will find at the surface, a safe — that is, flat — landing spot was selected.
Mars is, like Earth, largely rock. But it is considerably smaller — half as wide as Earth and one-ninth the mass. A cubic foot of Mars weighs, on average, 245 pounds, making it almost 30 percent less dense than Earth. (Because Mars is smaller, the gravity is weaker, and the center is not squeezed as tightly.)
It was only in 2003 that scientists, delving into tiny variations in Mars’ gravitational pull on one of NASA’s orbiting spacecraft, concluded that the core must still be at least partly molten.
Many other details remain unknown. How often does the ground shake with marsquakes? Just how big is the core? How thick is the crust? How much heat is flowing out?
“We know some, but we don’t know a lot,” Banerdt said. The new mission aims to provide “foundational information of the planet’s history and its activity,” he added. “I’m looking forward to making the first map of the inside of the planet.”
— Red Planet Redo
The 1,380-pound spacecraft is currently sitting on top of an Atlas 5 rocket at Vandenberg Air Force Base in California. Launch is scheduled at 4:05 a.m. local time on Saturday, and the southward trajectory could offer a predawn light show for early risers in Los Angeles and San Diego.
Tagging along for the ride is Mars Cube One — two briefcase-size satellites that are to test communications technologies for relaying signals from InSight to Earth. This will be the first time such small satellites, known as CubeSats, have been sent on an interplanetary journey.
If weather or other issues prevent a Saturday launch, NASA has additional opportunities over the next five weeks to get InSight off the ground before Mars and Earth move too far out of alignment. Even if the launch slips, InSight’s arrival date at Mars remains the same: Nov. 26.
After landing, InSight will take a few months to deploy two instruments: a dome-shaped package containing seismometers and a heat probe that will hammer itself about 16 feet into the Martian soil.
The $814 million mission hinges on detecting something that has never been definitively detected before: Marsquakes.
That is not for lack of trying. NASA’s two Viking landers in the 1970s carried seismometers. Only the one aboard Viking 2 was successfully deployed. But it was mounted on the spacecraft, and not placed on the ground, so it ended up measuring the buffeting of wind gusts rather than marsquakes. Only one event, which occurred at night when winds are generally calmer, may have been seismic. But the weather station was turned off at the time, so the possibility that it was just another gust could not be ruled out.
“It was ambiguous and not particularly useful,” Banerdt said.
Russia’s Mars 96 mission, launched in November 1996, was also slated to make seismic measurements, but because of a rocket malfunction, it fell back to Earth.
InSight itself missed its initial launch date two years ago. Leaks in the vacuum enclosure around the seismometers would have rendered them useless. Rather than risk failure, NASA postponed the mission. Banerdt said a redesigned vacuum enclosure has passed all the tests.
The spacecraft is, in large part, a copy of a two-decade-old design that has experienced failure and success at Mars.
The failure occurred in December 1999, when the Mars Polar Lander spacecraft, descending to the surface, vanished. An investigation concluded that the spacecraft may have plunged to its demise when its computer misinterpreted vibrations from its unfolding landing legs and shut off its engines too early.
NASA had already built another almost identical lander for another mission, Surveyor 2001. It canceled those plans, and put the spacecraft in storage. After fixing the spacecraft’s shortcomings, most of the Surveyor 2001 lander was recycled into a new craft, Phoenix Mars, which landed successfully in 2008.
InSight looks almost the same on the outside, but has been outfitted with improved electronics and modestly larger solar arrays. It is all newly built — except for one piece of vintage spacecraft hardware. The robotic arm that will place the seismometer dome and heat probe onto Mars is the one left over from Surveyor 2001. It did not fit the needs of the Phoenix mission and remained stored away until it might find another use.
— Marsquakes, Not Earthquakes
They may not have observed any Martian tremors yet, and there is nothing like the San Andreas fault or the sliding of tectonic plates on Mars, but scientists are confident that temblors course around and through the planet.
The planet is cooling and shrinking, and its crust most likely occasionally cracks, setting off a marsquake up to magnitude 6.0 or maybe even 7.0.
Similar rumblings are known to occur on Earth’s moon, which is smaller than Mars. Moonquakes were recorded by seismometers placed on the surface by NASA astronauts during the Apollo moon landings.
The hope is that InSight will record enough marsquakes to generate what is essentially a sonogram of the planet. The instrument can measure surface movements less than the width of a hydrogen atom. Not only can it detect the vibrations of a distant marsquake, it can also detect the even fainter vibrations of waves circling Mars the second time around.
That sensitivity and multiple measurements are needed to figure out where the marsquake occurred, within a few tens of kilometers.
Scientists expect at least 10 to 12 marsquakes over two years, the length of the spacecraft’s primary mission. Additional seismic events could be generated by meteors slamming into the surface.
By piecing together a three-dimensional image of the planet’s interior, the researchers expect they will finally know how thick the outer crust of Mars is. From gravity measurements of orbiting spacecraft, scientists can discern which parts are relatively thicker and thinner, but they have no ruler to put a precise thickness at any particular location.
The average crust thickness could be as little as 20 miles or as much as 50 miles. (The Earth’s crust along ocean bottoms is, by contrast, 3 to 5 miles thick.)
— Probes, Pulses and Flexes
InSight’s second instrument, a heat probe, is about 1 1/2-feet long and an inch wide. It needs to burrow deep enough to be insulated from the temperature variations of Mars’ days and seasons. Behind it is a tether that remains connected to the spacecraft, and sensors along the tether will measure how the temperature changes with depth.
The probe will also send out brief pulses of warmth that will be detected by the temperature sensors. That will indicate how well heat flows through Martian soil. All that will help tell how much heat is welling up from the interior of Mars, and the Elysium Planitia location is believed to be typical of the planet, said Tilman Spohn of the German Aerospace Center’s Institute of Planetary Research, the instrument’s principal investigator.
“We think it would be a very average, boring, but characteristic location on Mars,” he said, “and therefore good for us.”
A third experiment takes advantage of the onboard radio communications system to measure within a few inches the distance from a radio antenna on Earth to the spacecraft on Mars, tens of millions of miles away. “It’s really excellent precision,” said Suzanne Smrekar, the deputy principal investigator for the mission.
With that precision, scientists can track the wobbling in Mars’ spin. The sloshing of liquid deep inside the planet affects the pace and magnitude of the wobble. The measurements will help pin down the diameter of the core, currently estimated at 2,200 miles. Although the emphasis of InSight is on geophysics and not the possibilities of life, its data could help fill in some important blanks. For example, scientists could learn more about early eruptions from Mars’ now dormant volcanoes, the largest in the solar system, and how much gas bubbled out of the magma to fill the atmosphere.
“Those are all things the people who are concerned about habitability would like to know,” Banerdt said.