Journey to the centre of the red planet
Meet the lander to peel off the face of Mars and tell us what is really going on underneath its surface
With InSight due for launch,
All About Space speaks to the mission's scientists
Mars is the second-most studied planet – only behind our own – but we know virtually nothing about its interior. All astronomers have to go by is models and theories, but no concrete evidence. NASA’s Interior Exploration using Seismic Investigations, Geodesy and Heat Transport, or ‘InSight’, mission will look beneath the surface of Mars to reveal the secrets within the Red Planet. With its launch just on the horizon, scientists around the world eagerly anticipate the arrival of the lander that will reveal the intricacies of our neighbouring planet.
About 4.5 billion years ago, the eight planets of our Solar System were formed. All eight planets were formed from a clumpy disc of rock, ice and debris orbiting the young Sun. Fast-forward to the present and we now see a distinct difference between the inner and outer planets. The terrestrial planets (Mercury, Venus, Earth and Mars) all have a dense, rocky structure, with only one able to support life. The Jovian planets (Jupiter, Saturn, Uranus and Neptune) are all primarily gas and swollen up to enormous sizes. The question that astronomers still can’t answer, though, is how did these terrestrial planets form and evolve?
Thanks to modern technology and perseverance, astronomers have tried to answer this question in a period of extensive exploration of one of our closest neighbours, Mars. However, previous missions have only been able to scratch the surface. Where landers, rovers and orbiters before it have been in the hot pursuit of water on the dry, sandy surface, or designed to study the planet’s tiny atmosphere, InSight is delving deeper into the unknown. By putting an ear to the ground, astronomers will get a more comprehensive understanding of the Red Planet’s core, mantle and crust.
“The objectives of the mission are to map the structure and thermal state of the deep interior of Mars for the first time, and to use this information to better understand the early formation processes of terrestrial planets, including the Earth,” Dr Bruce Banerdt, principal investigator of the InSight mission, tells all about Space.
Originally due to launch in March 2016, InSight suffered a major setback when a vacuum leak was found in one of the lander’s key instruments in December 2015. Now the time is finally here. On 5 May 2018, InSight is scheduled to launch from the Vandenberg Air Force Base in California, United States on board an Atlas V-401 rocket. This will be the first interplanetary mission to take off from the United States' West Coast.
After its launch, the InSight payload and its first two CubeSats, which will provide a more efficient data relay back to Earth, will endure a six-month (or so) journey before their arrival at a planet redder, drier and roughly half the size of Earth. From here, InSight can finally join its NASA predecessors as it finds unequivocally important and revolutionary results. When NASA sent their first successful orbiter in 1971, the Mariner 9, it became the first spacecraft to orbit another planet, sending back over 7,300 images of the Martian surface and its two moons. Since then, humans have maintained an impressive number of satellites in orbit and probes on the surface, including the late and great missions such as the Mars Global Surveyor orbiter, the Viking 1 and 2 missions and the Spirit rover. There are also many functioning visitors still at Mars, including the Curiosity and Opportunity rovers and the Mars Reconnaissance Orbiter (MRO) and Mars Atmosphere and Volatile Evolution Mission (MAVEN). The Phoenix lander, which was launched on 4 August 2007 and laid stationary on the surface for 157 Martian days (also known as a sol, which is roughly 40 minutes longer than an Earth day), is the mission that InSight’s design is based on. “InSight will use the same lander design as the 2007 Phoenix mission, which gives us a proven landing and surface system without the cost of developing them from scratch,” Banerdt explains. “Plus, we will be using several orbiters at Mars to relay back to Earth our precious data. It’s hard to overstate the extent that knowledge from earlier missions informs InSight science.”
The InSight lander will stand at a height between 83 to 108 centimetres (33 to 43 inches) above the Martian surface, and once InSight's solar panels are deployed, its total span will be six metres (19.7 feet). This is roughly equivalent to two-thirds of the length of a London bus. Overall the whole lander will weigh 360 kilograms (794 pounds), which is about 88 per cent of the mass of the Phoenix lander. Packed within this bundle are some of the finest and most sensitive instruments to ever grace the planet’s soil, and they are required to function for at least one Martian year, which is roughly equivalent to two Earth years.
Before these instruments can blossom, the InSight rover needs to survive what is commonly referred to as the ‘seven minutes of terror’. In these seven minutes, the lander has to go from travelling at 22,692 kilometres (14,100 miles) per hour through the atmosphere of Mars, to a dead stop on the surface. As Mars’ atmosphere is 100 times thinner than Earth’s, slowing down the spacecraft is a much more difficult task. To succeed, a heat shield will cause as much friction with as little atmosphere as possible, causing the shield to reach extreme temperatures. The spacecraft will then deploy its
“The objectives are to map the structure and thermal state of the deep interior of Mars for the first time” Dr Bruce Banerdt
parachute, jettison its heat shield and extend its legs. After bringing the lander to a reasonable descending speed, the parachute is shed and 12 boosters at the bottom of the lander begin firing. This provides the final cushion before it lands in Elysium Planitia.
When asked about why Elysium Planitia was selected as the designated home for the duration of InSight’s mission, Dr Matthew Golombek, InSight’s landing site lead, told all about Space it’s because “it meets all the engineering constraints for landing and surviving for a Mars year. It is low in elevation, near the equator and smooth, flat and relatively rock free over the landing ellipse.”
Once landing is complete and InSight has reached its destination, its solar panels and instruments can be prepared. The blooming of the solar panels is the most essential part of the whole mission, as the lander will be powered by the less intense rays of a further away Sun. The Sun shines roughly half as bright on Mars than Earth, meaning InSight’s solar panels need to be able to squeeze as much solar juice out of those rays as possible.
Once its solar wings are spread the instruments can be deployed, and the mysteries of Mars’ mischievous mantle and core can be unveiled. The Instrument Deployment Arm (IDA) will place the seismometer, the Seismic Experiment for Interior Structure (SEIS) and the heat flow probe, the Heat Flow and Physical Properties Probe (HP3), on the
ground. Along with the radio science instrument, the Rotation and Interior Structure Experiment (RISE), this tactical trio will be at the forefront of the interior investigations.
Each instrument has been carefully planned and created to perform a very specific task. SEIS will be the first seismometer to Mars in 40 years, and will listen out for tremors that could come from marsquakes, meteorite impacts or even possibly magma churning deep underneath the Red Planet's surface. In fact, this Martian stethoscope is so sensitive it can pick up vibrations smaller than a hydrogen atom.
“SEIS will be placed on the ground by a robotic arm and will ‘listen’ for the small (fractions of a nanometre) ground vibrations due to seismic waves that have travelled through the planet from distant marsquakes,” says Banerdt. “Analysis of these waves will allow us to create a 3D picture of the inside of the planet.”
The InSight team also have plans to collaborate with the Mars Reconnaissance Orbiter (MRO), which will be on the lookout for meteorite impacts. When the seismometer detects a meteoritic impact, the MRO and its meticulous High Resolution Imaging Science Experiment (HiRISE) camera will scout out the fresh crater.
Alongside SEIS is a drill that will take the planet’s temperature. HP3 will make its way five metres (16 feet) down into the Martian crust. This is just 10 per cent of Mars’ overall crust, but it is a good enough depth to allow astronomers to analyse the heat that comes from deep within the planet. The heat flowing underneath the surface reveals how active the planet is. On Earth, we are well aware of a region of magma churning beneath our crust which drives our tectonic plates and heats up our planet. The heat flow within Mars could be compared to Earth’s and reveal that both were formed from the same substances, and if they aren't, then why not. "We're essentially doing the same thing anyone would do on a campout, but we're putting our stake down on Mars,” says Dr Suzanne Smrekar, InSight’s deputy principal investigator.
"Getting well below the surface gets us away from the Sun's influence and allows us to measure heat coming from the interior," says Smrekar. "InSight is going take the heartbeat and vital signs of the Red Planet for an entire Martian year, two Earth years. We are really going to have an opportunity to understand the processes that control the early planetary formation."
“Getting well below the surface… allows us to measure heat coming from the interior” Dr Suzanne Smrekar
Not detached from the lander, but equally important, is RISE. With two antennae fitted on the lander deck, highly detailed X-band radio signals will be sent between InSight and the Deep Space Network dishes on Earth, allowing us to confine InSight’s position to within a couple of centimetres every day. “This is enough to determine the direction of Mars’ rotation pole and any wobble that it exhibits. This wobble is connected to the properties of the core, and will yield its size and density [which is related to its elemental composition],” explains Banerdt.
The way that InSight and the Deep Space Network determine the wobble of Mars is the same way a person’s ears perceive the change of a siren’s sound as it travels either towards or away from them. For example, if a police car has its siren on and it is speeding away from you, you will hear a relatively low-pitched sound. Then, when it’s speeding towards you, the pitch is much higher. This is known as the ‘Doppler Effect’. As the police car moves away, the siren’s sound waves are stretched into a longer wavelength, and therefore a lower pitch. As the police car narrows the distance between the siren and you, it causes the sound’s wavelength to shrink and creates a higher pitch.
This technique has been carefully developed to improve the accuracy of InSight’s position and tell us if there is a metal core or a liquid molten core causing a planetary wobble. Also, RISE will be able to see how this wobble changes over time due to seasonal changes at the poles of the Red Planet. As the season changes from winter to spring, the frozen carbon dioxide at the poles sublimates – changes from solid to gas – affecting the rotation of the planet and therefore changing the length of a sol. RISE can track these changes throughout the course of its mission.
The data collected will not only have longstanding and fruitful benefits for our understanding of Mars, it will also provide astronomers with valuable resources for future missions. As Banerdt explains, “Our meteorological data will be important in characterising the Martian environment for future human visits. More indirectly, the scientific understanding of the planet that InSight supplies will serve as a foundation for whatever research that people will carry out on the surface of Mars.”
As for how long this mission will last? Who knows! Although the primary mission is only scheduled for one Martian year, we have seen many Mars missions function way beyond their primary mission lifetimes. The best example would have to be the Opportunity rover. The rover was only built for a 90-sol mission in 2004, and at the time of writing it is still operational, thus completing the first ever ‘Martian Marathon’ with a finish time of about 11 years and two months. It has now travelled over 45 kilometres (28 miles) travelled in that time, which is a remarkable achievement. And with over 2.4 million names placed on a microchip attached to the InSight lander, people worldwide will have their boarding pass ready as this historic expedition aims to change our cosmic understanding.