The very broad band seismometer, which is currently deployed on the Martian surface as a part of the INSIGHT mission, recently detected the first known Mars-quake.
In an interview with RFI’s Dhananjay Khadilkar, IPGP researcher and principal investigator of the probe, Philippe Lognonné, talks about the importance of measuring Martian quakes and the information they can reveal.
Why do you believe the signal you detected on the seismometer indicates a Mars-quake?
This is based on the two and a half months of data in which we have seen a lot of events. We have seen activities associated with wind and what we call ‘dust devils’. There is also activity associated with small thermal signals. In all this, we noticed a signal which wasn’t the same as the others. It was a new signal. After comparison with observations on the earth and the moon, we reached the conclusion that it was looking similar to a moon-quake signal.
The signal from Mars had very high frequency, something never seen in the past. So after ruling out any origin associated with Martian weather and wind, we are almost certain that this signal is associated with ground vibrations on Mars and that it is most likely a quake.
What information can we get about Mars by measuring quakes?
The quake we measured was of a small intensity but it tells us that we will have larger quakes in the future. There is an important relationship in seismology between frequency and magnitude. These small quakes tell us something about the number of big quakes we might expect over the course of the mission, which would be something between 10 and 20.
In a way, quakes are like light. Each time there is a quake, waves are propagated into the planet. With small quakes, we mostly see superficial characteristics. So with the quake we recorded, we will get some information about the Martian upper crust.
But the larger the quake is, the deeper the waves go. Bigger quakes can reveal information from the bottom of the crust and the upper part of the mantle. If the quakes are even more powerful, we can get information about the core.
Will measuring quakes tell us about the presence of bodies of water on Mars?
We already know there is water on Mars in the form of ice. What we do not know is the depth at which liquid water is present at the equator. It turns out that liquid water dampens seismic waves.
At this time, the signal we have detected indicates dryness of the material where the waves propagated. In the near future, we could expect a different quake with a larger epicentre distance. This quake might go to the part of Mars where there is liquid water.
The seismometer that you and your team developed is a remarkable instrument. How sensitive is it and how does it work?
The seismometer measures the ground vibrations associated with acceleration. Each time the ground vibrates, there is an extremely small change in gravity. The quake we measured was changing the gravity of the planet by less than 1 billionth of its value.
The seismometer consists of three pendulums that detect the gravity change due to vibrations in three directions. Each pendulum consists of a mass that is supported by a spring. When the ground shakes, the mass moves. We are able to detect very small mass displacement to the order of 1/50th of the size of a hydrogen atom, which is really small.
Since the seismometer is detecting such small displacements, it has to be shielded from temperature variations, pressure variations and wind. The Wind and Thermal shield, developed by the Jet Propulsion Laboratory, achieves this.
Other parts of the Seismic Experiment for Interior Structure mission were provided by researchers in Zurich, the Max Planck Institute of Goettingen and by the Imperial College of London. The overall management of the mission was handled by the French space agency.