Why NASA is launching a spacecraft to Mars to feel the planet as it rumbles

On Saturday, NASA is launching its latest Mars explorer — a robot that will sit on the surface of the Red Planet and measure the world as it wobbles. This mission, InSight, is different from previous Mars vehicles, which studied the planet’s surface. Instead, InSight will be helping scientists to peer underneath the crust, to learn more about Mars’ insides, and that could tell us a whole lot about how this planet was born.

InSight is a lander, not a rover; once it touches down on Mars, it will stay put for the rest of its lifetime on the planet. From this stationary post, InSight will detect what are known as marsquakes. Like earthquakes, they’re rumblings in the planet’s crust — but they aren’t caused by the same forces. Earthquakes are often the result of our planet’s tectonic plates slipping past each other on the surface. Marsquakes are thought to happen when the planet cools and contracts, causing the crust to crinkle slightly.

Analyzing these Mars shakes can tell scientists what makes up the planet — the kinds of rocks that linger inside and how they’re layered. That’s crucial for understanding how Mars came to be. Earth has been churning and reshaping itself for billions of years, but Mars’ structure has stayed relatively constant. Scientists believe that soon after Mars formed, its development stopped. So figuring out the current layout of Mars’ insides means understanding what the planet’s interior look liked in its youth. “We believe that when we go to Mars, we’ll be able to use Mars as a window into the past,” William “Bruce” Banerdt, the principal investigator for the InSight mission, tells The Verge.

The way a planet’s interior forms also dictates what kind of planet it becomes. So InSight could answer a big question for scientists: why do some planets turn into habitable ones like Earth, and why do others turn into cold Mars-like worlds or super-hot Venuses? “To really understand why those processes happen at the surface, we have to know what’s going on in the inside,” Suzanne Smrekar, the deputy principal investigator for InSight, tells The Verge.“You have to look under the hood.”

Probing a marsquake

Though InSight is designed to measure marsquakes, scientists have never measured one on Mars before. NASA’s Viking landers tried to measure quakes on Mars in the 1970s, but their instruments weren’t sensitive enough to pick anything up. “All we ended up measuring was the wind blowing the lander around,” says Banerdt.

However, scientists are pretty sure these quakes do happen. In fact, they think most planetary objects wobble somehow. When Apollo astronauts went to the Moon, for instance, they brought a bunch of seismometers with them, which measured thousands of tiny lunar quakes throughout the ‘70s. Banerdt and his team think that since Mars is bigger, the Red Planet will have more quakes. They’re hoping to pick up somewhere between a couple dozen to many hundreds of quakes over the planned two years of InSight’s mission.

To do that, InSight has an extremely sensitive seismometer that can pick up a wide range of quakes — from those that vibrate super fast to ones that rumble soft and low. It’s so sensitive that the seismometer can only work if it’s in a complete vacuum. The slightest bit of air could mess up its measurements. This caused a big headache for the InSight mission two years ago. Just a few months before InSight was slated to launch in March of 2016, engineers found that the vacuum enclosure for the seismometer had sprung a leak. They didn’t have enough time to fix it before launch and had to push back the mission until this year — when Mars and Earth were aligned on their orbits again.

The seismometer has since been fixed and is ready to analyze every tiny vibration it can pick up — and not just from quakes. The seismometer is sensitive enough to detect rumblings caused by meteorites that slam into Mars’ surface. Whichever kind of wobble is detected, scientists will analyze every aspect of the vibration — such as its size and frequency, and how long it took to travel through the planet. These vibrations change depending on the kind of material they pass though. So a shake can hold a lot of information about what’s packed deep underground.

“It’s almost as if the wave traveling through the planet is picking up pieces of information as it goes along and putting them in its suitcase,” says Banerdt. “And at the other end, all we have to do is unpack the suitcase and figure out what that wave has traveled through.”

InSight is packing other key instruments to probe Mars’ depths, too. That includes radio antennas that will help scientists figure out the size of Mars’ core. And there’s even a nail-like device called the mole that will hammer itself deep under the ground to measure the planet’s internal temperature. Scientists are curious what fueled Mars’ volcanoes in the past, and how much heat is inside the planet could help answer that question. “The inside of the planet is kind of like an engine, and the heat flow tells us about the fuel source for that engine,” says Smrekar.

Onward to Mars

But before all that can happen, InSight needs to get off the Earth. The lander is slated to ride into space on top of an Atlas V rocket, made by the United Launch Alliance; the vehicle is taking off from Vandenberg Air Force Base in California on May 5th at 7:05AM ET. It’ll be the first interplanetary mission to ever launch from the West Coast. Before now, all US missions to other planets have lifted off out of Florida, where they get an extra speed boost. But InSight’s small size means it can launch from California without the need for that advantage.

Once in space, it’ll spend six and a half months en route to Mars, arriving on November 26th — the Monday after Thanksgiving. That’s when it will make the fateful plunge to the planet’s surface.

It’s a chore to land on Mars. Though it’s smaller than Earth, Mars still has a substantial amount of gravity to pull objects downward fast. But the planet’s atmosphere is thin — about 100 times thinner than Earth’s — so it provides little resistance to slow down incoming spacecraft. Yet there’s just enough atmosphere that descending vehicles still need some kind of heat shield to keep from burning up. Numerous robots have attempted to touch down on Mars before, and many didn’t make it in one piece.

To prevent that from happening, the InSight team has a very detailed landing process for their spacecraft. “Our job is to be paranoid and think about all that can go wrong with landing, to make sure we’re designing robustly,” Rob Grover, the InSight systems lead for entry, descent, and landing, tells The Verge. InSight will enter Mars’ atmosphere going about 13,000 miles per hour. As it falls, the lander slows to about twice the speed of sound in the atmosphere before deploying its parachutes. Those slow the vehicle down even further before breaking away when InSight is about three miles high still. That’s when 12 engines embedded in InSight’s belly fire up. They’ll control the vehicle’s landing all the way down to the surface, where InSight will (hopefully) touch down at a little more than five miles per hour.

It’s a landing that will last just six and a half minutes. And InSight has to do it all on its own, too. During the time of landing, getting a radio signal to Mars will take about eight minutes because the planet is so far away. There’s no time to send any corrective commands from Earth. It all has to be automated, and it all has to work perfectly.

As if that weren’t tricky enough, Insight will land on Mars during its dust storm season. And that could change how the landing is programmed. In the middle of a storm, the atmosphere on Mars tends to get thicker closer to the surface, so it will take longer for InSight to slow down. If that happens, engineers will need to adjust the timing of the parachute, so they don’t open up when the vehicle is going too fast. “We could have anything from just a clear regular atmosphere to a global dust storm when we land,” says Grover. “But the system is ready for that.”

Once it lands, InSight will deploy its solar panels, and then spend up to 10 weeks getting its instruments in position to collect data. And then the rest of InSight’s life will be mostly still. The 20-foot-long vehicle will sit there with its ear to the ground, listening for shakes. It will be just a tiny spec on the surface of Mars, but it should tell us a great deal about what’s lurking below. “All the exploration [of Mars] we’ve done so far in the last 50 years has looked at the surface, atmosphere, rocks,” Banerdt says. “The rest of the 99.99 percent of the planet is virgin territory for us to explore, and this little lander is going to do this exploration for us.”

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