What is the interior of Mars like? What is the structure and dynamics of the Red Planet? Planetary researchers only had a rough idea about this. They have only been able to use one of their most efficient methods of analysing ground vibrations for the past year or so, thanks to ETH Zurich.

The seismometer as a 1:2 model. Photo: Basil Stücheli

Mars Seismological Service. The name conjures up a lot of images: a dome somewhere in the red dust, a pioneering project to explore and colonise the desert planet? It might sound like the stuff of science fiction, but it is real. Domenico Giardini, professor of seismology and geodynamics, would be happy to help on that. Three young researchers are sitting in front of a bank of screens in an office at ETH Zurich, analysing and characterising the data received. The Mars Seismological Service is operated in collaboration with seismologists from the Swiss Seismological Service. A number of groups at ETH Zurich are ultimately responsible for the data acquisition and control electronics. The highly sensitive electronics of the seismometer were developed at the Aerospace Electronics and Instruments Laboratory at ETH Zurich.

The analogy to the regular seismological service is no coincidence. There is a competitive edge to NASA's Discovery programs – whoever presents the best scientific idea is invited to join the flight. The proposal put forward by ETH Zurich went down well, and so the InSight mission brought the seismometer developed by the European consortium to the Red Planet. The proposal explicitly stated: “We will do everything in the Mars Seismological Service exactly as we do on Earth,” said Giardini. This means using tried and tested infrastructure, existing knowledge and an institution with a reputation for a stable research environment.

But there is one difference. “The InSight instrument is more sensitive than any other instrument used on Earth.” And it had to withstand a long voyage through space, not to mention a tricky landing. It was set down on the surface of Mars on 19 December 2018 as the only seismometer to detect vibrations. The first recording of a quake on Mars was made on 6 April 2019. The researchers use sophisticated methodologies to accurately pinpoint some of the one or two quakes that are recorded each day. To do this, Giardini and his team combine methods from the early days of seismology with modern analytical techniques. What they discover will not only help to answer unsolved questions about the geological structure of Mars, but more generally about the formation of Earth-like planets in the inner solar system.

“You only get one chance. Everything has to work right as the mission is unmanned", knows Domenico Giardini, ETH Zurich professor of seismology and geodynamics

“We already knew a lot about the surface of Mars,” says Giardini, “but we could only speculate about the inner life of the planet.” This is now being scrutinised for the first time with hard facts – a series of assumptions have been refuted. After just over half a year of InSight measurements, almost three quarters of the 2,000 or so models on the structure of Mars have already been discarded. And he adds with a smile: “There is quite a lot of discussion going on in the Mars research community right now. One thing is certain, quakes on Mars must have different triggers than those on Earth. They are mostly caused by shifts in the tectonic plates here, whereas Mars only consists of a single tectonic plate.”

Because a completely new chapter has been started in planetary research, the InSight mission was a flight into the unknown. “We had no idea what kind of quakes to expect.” So the scientists designed a broad amplitude spectrum. Giardini says that he would send up “much simpler sensors” next time. But there's one big problem that's hard to ignore - the wind on Mars. It has literally blown away all the seismographic measurement experiments on Mars up to now. And the InSight instrument also only transmits storm noise during the day on Mars. Things only calm down on the Red Planet at night. The seismometer listens all the more closely then.

Giardini knows that a mission like this can also go wrong. “You only get one chance. Everything has to work right as the mission is unmanned, and there is no astronaut on board to keep an eye on things.” It takes a little bit of luck, too. ETH Zurich has specialists for the complicated data from smaller quakes, which are common on Mars, as has now been shown. But what they “hear” is also puzzling. The first seismic signals from the Mars quakes were easy for the researchers to classify, but the ensuing signals produced stronger echoes than expected. Some quakes lasted 10 to 20 minutes. In the meantime, many of our international colleagues are waiting impatiently for major tremors on the surface of Mars; such as a meteorite strike or a volcanic eruption. This would produce signals that would provide completely different insights into the structure of Mars. The Mars Seismological Service benefits them too.