On May 5, NASA's "InSight" plane departed on its trip to Mars. This is the first mission dedicated to investigating the internal structure of the red planet and answering some key questions such as: Why did Earth and Mars evolve so differently even though their original structure and chemical composition seem so similar? How large, thick and dense are the core, the mantle and the crust? What is its structure? Scientists hope to obtain fundamental knowledge about the general formation of rocky planets such as Mars, Earth, Mercury and Venus.
Seismometer for extreme conditions
The landing module is equipped with geophysical instruments, in particular a special seismometer; After landing in late November 2018, this device will record the seismic vibrations and transfer the data to Earth.
Researchers from ETH Zurich and the Swiss Seismological Service, who participated in the development of the seismometer electronics (see ETH News from May 5, 2018), will be among the first to badyze and interpret the data.
Scientists from the Geophysics Institute have already begun to prepare these badyzes. In the supercomputer "Piz Daint" of the National Supercomputing Center of Switzerland (CSCS), the researchers calculated the propagation of seismic waves for around 30 different models of Mars.
For their model catalog, the researchers consolidated all available knowledge about the planet and used it to calculate the synthetic seismic data that could be received from Mars. The scientists then used this data to perform a blind test, in which they published the data and invited experts from around the world to interpret it to exchange knowledge and experiences in this area.
Universal code to simulate waves
To investigate the influence of the 3D structure of the Martian cortex in more detail, Martin van Driel, principal investigator at ETH Zurich, simulated seismic waves on Mars with Salvus, a code that he developed at ETH together with his colleagues Michael Afanasiev, Lion Krischer and Christian Böhm. This code is flexible and can be used universally for questions about the propagation of waves in different media at different scales.
Mars simulations run on "Piz Daint" in real time in 7,200 computing cores, which means that calculations last as long as seismic waves need to travel through Mars. Depending on the internal structure of the planet, the waves travel at different speeds and take different routes from the source to the seismometer. The time it takes for the waves to travel through the interior of Mars will help scientists better understand the structure and rocky properties of the planet.
With around 10 billion degrees of freedom and 300,000 steps of time, scientists managed to solve a big problem. "Without a supercomputer like" Piz Daint, "the simulation of a single model on a laptop would have taken more than two years, four times longer than the module's trip to Mars," says Böhm.
Visualization of the mission in launch
The researchers visualized one of the numerical simulations in a video. This was shown at the NASA press conference for the rocket launch of the Mars mission. The visualization shows how waves travel along the surface of Mars, orbiting around the planet and pbading the lander three times. Van Driel explains that it is essential to measure the waves in each of the three steps, as this will allow scientists to gather information about the planet, identify the timing and location of the Mars earthquake, and calculate its approximate structure, all with only a seismic station However, the amplitude of the third wave is less by a factor of ten; The seismometer must be sensitive and sophisticated enough to measure this and the earthquake must have a magnitude of at least 4.5.
On Earth, earthquakes of this magnitude are generated primarily by plate tectonic processes in which continental or oceanic plates collide or slip past each other. Scientists currently believe that plate tectonics is not active on Mars. However, over the course of the two years they expect meteor impacts or contractions caused by the cooling of Mars to produce seismic events that are strong enough to be observed by the seismometer.
Previous simulations allow data evaluation
Since seismic waves on Mars have never been registered with such a sensitive seismometer, numerical simulations are the only way to prepare for the data evaluation of the InSight mission. of NASA.
"We are using the calculated models to check how certain structures, such as the thickness of the crust, influence the measurements," says Böhm. The models thus help researchers to verify their methods and better understand seismograms on Mars. Although the seismic data generated by the models appear similar to the terrestrial data at first sight, the subtle differences are important. Scientists must, therefore, become familiar with these new data and learn to interpret them.
To finally understand the Martian structure, the ETH researchers will compare the real measurements with the simulated data. For this, they will use the model catalog of Mars to see if the measurement changes and how it does it, taking into account the models, the structures and what all the simulations have in common.
NASA's newest Mars lander to study earthquakes on the Red Planet
J. F. Clinton et al. Preparation for InSight: an invitation to participate in a blindness test for Martian seismicity, Letters of seismological research (2017). DOI: 10.1785 / 0220170094
Ebru Bozdağ et al. Simulations of Seismic Wave Propagation on Mars, Reviews of Space Sciences (2017). DOI: 10.1007 / s11214-017-0350-z