It's notoriously hard to land on Mars, yet Nasa managed just that with its recent InSight lander. From childhood, I've loved watching landings and other spacecraft maneuvers on TV – always feeling a bit of that edge-of-the-seat excitement. But it didn't prepare me for the feeling of watching a mission I've worked on. Each period of silence during the seven-minute descent of InSight felt like an eternity, with a time-out and only active call-outs from systems engineer Christine Szalai. I will never forget the joy of the moment when she finally announced "touchdown confirmed".
The InSight mission has been over 10 years in planning. Among planetary missions, it's a bit of an oddball. While most people are designed to look at the surface or atmosphere of planetary bodies, InSight's goal is to look at the beneath the surface – and the other rockets formed.
The lander carries a number of instruments, including seismometers, a heat flow probe, magnetometer and a radio transmitter. The Heat Flow and Physical Properties Probe (HP3) will be a depth of five meters below Mars' surface, almost as far as the handheld drills of the lunar missions. Its measurements will tell us how quickly heat is being lost from the planet's interior – helping us understand how Mars cools over time.
The Rotation and Interior Structure Experiment (RISE) will essentially bounce a radio signal sent from Earth back to us. The difference between the original signal and the return signal can be used to work out the velocity of the lander relative to Earth, rather like the pitch of a siren telling us whether it is moving toward or away from us. We're specifically interested in using the velocity to tell us how Mars's axis of rotation wobbles over time. The size of these wobbles is dependent on the structure of the interior, and especially its dense metallic core. Just like a raw egg wobbles, more than a hard-boiled one when spinning on a flat surface, Mars will wobble more if its core is liquid.
I work on the Seismic Experiment for Interior Structure (SEIS), which consists of two seismometers, mounted on a leveling system that will sit about 15cm above the surface of Mars. This experiment is designed to tell us the amount of seismic activity on Mars. We will also use the time it takes to reach the seismic waves to tell us about the temperature and composition of the interior, rather like a doctor using a CT scanner.
We now have about three months during which the instruments will be deployed and activated. Over the next few days, the health of the systems will be checked, and the lander and surrounding areas will be thoroughly so that the operations team can decide where to place heat flow probes and seismometers. The first image taken from the surface suggests that we have landed on a shallow sand-filled crater almost free of rocks, so it looks like there will be multiple options.
Around mid-December, a robotic arm will lift the tripod-mounted seismometers off the deck of the landers and lower them to the surface. After detailed checks, the leveling system will be used to make sure the seismometers are perfectly horizontal. By mid-January, a shield should be placed on top of seismometers to protect them from the elements. Then they can be turned on, and the heat flow probes will be deployed.
The heat flow probe will start returning as soon as it starts to hammer the way beneath the surface, so we will have results in the first half of 2019. The radio experiment will take somewhat longer. It just happens that, over the next year, we will not be in the best position to see the wobble of Mars' pole. That changes in mid-2020, when we should ideally situated to uncover the secrets of its core.
As for the SEIS experiment, when we see something exciting it will depend on how often seismic energy is generated. We don't currently know this. What we do is know that there are two potential sources of seismic activity: meteorite impacts and "marsquakes" created by movement along faults near the surface.
While we know that meteorites often hit Mars, the rate of fault motion is a mystery. Unlike the Earth, Mars has no moving tectonic plates, so it is estimated that the fault movement happens as the planet's interior cools. However, some of the youngest faults on Mars, but by the movement of molten rock beneath the surface. Discovering the frequency and nature of the matrix will help us work out the exact causes.
Through its three main experiments, InSight will provide a "snapshot" of the present state and composition of Mars. But that isn't where the scientific discoveries will end. Ultimately, the company will place over 4.5 billion years ago, when the solar system was very young.
Here’s why. The composition of the planet is set when it is formed, which is only a few million years after the sun is ignited. We think that as a result of its greater distance from the sun, Mars is formed from different, more volatile-rich material than Earth. However, until Mars’s composition is known, this idea is very hard to test and develop. The data returned to form a fundamental key to understanding how the solar system is formed – and perhaps those around other stars.
The composition, temperature and magnetic fields of our planet are also vital to sustaining life on our planet. So even though InSight is not looking for life, it will give us a new primed for life over four billion years ago.
InSight has already been a huge engineering success, and the science team now gets the incredible opportunity to use it to reveal Mars' secrets. We hope you’re as excited as we are.
- Written by Bob Myhill, UK Space Agency postdoctoral fellow, University of Bristol
- This article is published from The Conversation under a Creative Commons license