The Martian space robot family had a new addition on Monday, Nov. 26, after NASA's InSight mission made a dramatic entrance into the red planet's atmosphere and stuck a picture-perfect landing on a flat plain near the equator.
After cruising through interplanetary space for nearly seven months and over 300 million miles (483 million kilometers) inside its protective aeroshell, the $850 million robotic mission entered the wispy upper atmosphere like a speeding bullet. It was protected by its heatshield, which skyrocketed to temperatures of nearly 3,000 degrees Fahrenheit (1,649 degrees Celsius) – heated by the extreme friction between atmospheric gases and invading spacecraft.
Cozy inside its protective shell, the lander prepared for the next step of its descent onto Mars: deployment of its hypervelocity parachute, which slowed the robot before explosive bolts jettisoned the spent heatshield. Then, rapidly, the lander cut free of its aeroshell and dropped – in freefall for a few seconds – before its retrorockets fired, with its onboard radar guiding the lander to the ground at a pedestrian pace of only 5 miles per hour (8 kilometers per hour).
At precisely 11:52:59 a.m. PST (2:52:59 p.m. EST), InSight's three legs planted themselves into the dusty surface of Elysium Planitia – its new "forever home" near the Mars equator and north of NASA's Mars rover Curiosity, which is currently exploring Gale Crater.
"We hit the Martian atmosphere at 12,300 miles per hour, and the whole sequence to touching down on the surface took only six-and-a-half minutes," said Tom Hoffman, InSight project manager at Jet Propulsion Laboratory, during a post-landing press conference. "During that short span of time, InSight had to autonomously perform dozens of operations and do them flawlessly, and by all indications that is exactly what our spacecraft did."
Although the lander accomplished the fiery re-entry by itself, it did have a little help from two small cubesats that were flying in tandem with the mission during its cruise phase.
To communicate with Earth, Martian surface missions use orbiting satellites (such as NASA's Mars Odyssey orbiter) to relay data across interplanetary space. But at the time of InSight's landing, no orbiters were flying overhead to relay the valuable data streaming from the mission's entry, descent and landing (EDL). Anticipating this problem, a pair of cubesats, called Mars Cube One (or MarCO-A and MarCO-B), launched with InSight to watch over the lander as it entered the Martian atmosphere to beam the EDL telemetry data back to Earth in near real time.
Although the MarCO cubesats weren't vital to the survival of the mission, they provided NASA with invaluable observations of InSight's EDL – while limiting the agonizing wait for news of a successful landing. They also were able to snap images during their time in space, the last was from nearly 5,000 miles (8,000 kilometers) from Mars just as InSight was approaching the Martian atmosphere.
"MarCO is a technology demonstration and, as a secondary payload on the mission, our primary goal is to do no harm to the primary payload," said Brian Clement, MarCO engineer at JPL. "Performing as the communications relay during EDL is a proof of this concept." Now that this concept has been proven, Clement added that future robotic missions may be inspired to use cubesats in this fashion.
Going Deeper Underground
InSight is the eighth mission to successfully land on Mars, but it's not so interested in studying the planet's surface or atmosphere; the stationary lander is designed to look deep underground to understand what its interior is made of and how the planet evolved to be the cold, dry place it is today. By studying Mars' evolution, we also may learn a little about how Earth came to be — our planet is alive with tectonic activity that continually erases evidence of our planet's past, whereas Mars does not have tectonics and is therefore more willing to give up its secrets.
Key to InSight's mission are three primary experiments. Over the coming weeks, mission controllers will send commands to the lander to use its robotic arm to grab two instruments from its upper deck – the Seismic Experiment for Interior Structure, or SEIS, experiment and Heat Flow and Physical Properties Package, or HP3, experiment. Once in hand, SEIS and HP3will be lowered onto the surface just in front of the lander.
The seismometer will be trying to detect extremely faint seismic waves traveling through the planet's interior. Triggered by "marsquakes" and meteorite impacts, these waves can be used to reveal compositional changes as they bounce around inside Mars. Never before have we glimpsed the subsurface of Mars, but now we have a mission that's going to take a 3-D "ultrasound" of its interior, revealing some of Mars's deepest secrets, mission scientists said.
The heat flow probe will slowly drill its way underground to a depth of up to 16 feet (5 meters). Once below the surface, the probe (aptly nicknamed "the mole") will gauge how much heat is propagating through the crust from the planet's mantle. All planets slowly release heat since they formed, and the amount of heat is directly related to what the planet is made of. One mystery surrounding Mars's interior focuses on the type of asteroids that accreted over 4 billion years ago to form the mass of the planet we see today. According to Suzanne Smrekar, InSight's deputy principal investigator, the HP3 probe will fill an important gap in our understanding of how Mars evolved.
"We have all these models about the thermal evolution of planets, but we have very little way of validating them," she explained. "It's super important for understanding all that's going on with the surface and what's going on with the interior of Mars now."
By measuring the heat flow at this one location, argued Smrekar, planetary scientists can extrapolate that number for the rest of the planet, finally revealing what the planet's primitive building blocks are.
Finally, with a little help from InSight's onboard X-band radio, mission scientists will also be able to measure Mars' "wobble" – a measurement that complements the science investigations of SEIS and HP3. They plan on sending radio signals from the Earth-based Deep Space Network (DSN), which is used to communicate with our robotic missions throughout the solar system, and then measure the Doppler shift of the returned radio signal over the course of InSight's two-year primary mission. This signal can then be used to gauge how fast the lander is moving, relative to Earth, and will therefore reveal how much the entire planet wobbles on its axis. The amount of planetary wobble relates to the size and composition of the Martian core, another piece of the Martian puzzle that we don't yet know.
InSight may be an immobile lander (in contrast to its roving six-wheeled cousin Curiosity), but that won't affect the scope of the science that the mission hopes to achieve. One neat study that could use the lander's unique data-collection methods focuses on an atmospheric phenomenon that is very common on the red planet: dust devils. Though usually fairly small on Earth, Martian dust devils are king, sometimes rising miles high into the atmosphere — and they can cause quite a rumble.
"Several people on our science team have been doing a bunch of studies on dust devils in the Mojave Desert," said Bruce Banerdt, InSight principal investigator at JPL. Using a system of seismometers, wind sensors and pressure sensors, the team set out to see what kind of signal InSight might measure should a Mars dust devil sweeps through the lander's landing site.
"We can actually watch the pressure drop, it's like a mini-hurricane, the pressure in the center of a dust devil is very low when compared to the ambient pressure," Banerdt noted. "So, as it goes by, even if it doesn't go right over the lander, we can see a pressure signature, and that pressure slightly pulls up ground and the seismometer can detect the minuscule tilt of the ground as the devil goes by."
With that information in hand, Banerdt is confident that they will be able to not only detect these dust devils as they swirl over InSight, they will also be able to decipher their size and direction of travel, while also learning about the elasticity of the soil beneath the seismometer.
Now that InSight has landed on Mars and even returned its first images of the "parking lot" plain, mission scientists are looking forward to the Mars mysteries they hope their mission will elucidate. And, who knows, we might learn a little about the origins of our own planet along the way.