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The SEIS seismometer on the InSight mission detects the first marsquake!

Le 19 décembre 2018, l’atterrisseur de la NASA, InSight, déposait le sismomètre français, SEIS sur la surface de Mars. Le 6 avril 2019, 128ème jour martien de la mission, un signal sismique faible mais distinct a été détecté, semblable aux signaux sismiques captés à la surface de la Lune lors des missions Apollo.

The SEIS seismometer on the InSight mission detects the first marsquake!

Publication date: 20/04/2019

General public, Observatories, Press, Research

Related observatories : InSight Observatory

The “Sol 128” event (128th Martian day), detected by SEIS, is the first Martian tremor whose origin is thought to come from the interior of the planet – as opposed to a movement caused by the wind – although scientists are still not entirely sure. The seismic event is too weak to provide useful data on the interior of Mars, one of the main objectives of the mission. Such a tremor would not have been detectable on Earth, but the extremely stable Martian surface allowed the seismometer’s highly sensitive sensors to pick up this weak signal.

Several characteristics of “Sol 128” correspond to the profile of moonquakes detected on the lunar surface. NASA astronauts measured thousands of moonquakes while exploring the Moon between 1969 and 1972, revealing that it was still geologically active. The reflection of seismic waves or the modification of their propagation speed depending on the materials they pass through have given scientists information about the Moon’s internal structure, as well as the size of its core. This has led to a better understanding of the impact process between the Earth and the proto-Moon, as well as the formation of the Moon from orbiting debris. With the SEIS seismometer, similar data can be collected on Mars, providing a better understanding of the formation of such a telluric planet.

“The first data collected by InSight will enable us to continue the scientific advances that began with the Apollo missions,” notes Bruce Banerdt, chief scientist on the Insight mission, from NASA’s Jet Propulsion Laboratory (JPL) based in Pasadena, California. “Until now, we have collected background noise, but this first marsquake marks the official birth of a new discipline: Martian seismology.

The SEIS seismometer under its wind and heat shield on April 7th, 2019 (sol 128), as seen by the InSight probe's ICC camera (NASA/JPL-Caltech).

Three other signals that could also be of seismic origin were detected on March 14th (“Sol 105”), April  10th (“Sol 132”) and April 11th (“Sol 133”). The interpretation of these signals is still ambiguous for the InSight team, but for at least two of them, they do not appear to be due to the effect of wind or other sources of parasitic noise. In practice, these signals are much weaker than that of ‘Sol 128’, and have only been detected by the ultra-sensitive VBB sensors on the SEIS instrument. The team is working hard to pinpoint the origin of these new signals.

The InSight mission is piloted by JPL. Called the Seismic Experiment for Interior Structure (SEIS), the seismometer installed on the space lander was delivered by CNES, which acted as prime contractor. Philippe Lognonné, Professor at the University of Paris Diderot and geophysicist at the IPGP, is scientific director of SEIS in association with teams from the CNRS.

“We’ve been waiting for our first marsquake for months,” explains Philippe Lognonné. “It’s great to finally have a sign that seismic activity still exists on Mars. We look forward to reporting detailed results as soon as we have studied and modelled our data more closely.”

Mars has no tectonic plates, which are responsible for most of the quakes on Earth. But the two planets and the Moon share another type of quake, caused by faults or fractures in their crust. When the crust undergoes excessive stress due to weight or slow cooling, it ruptures and releases energy.

Detecting these earthquakes is a real technological feat. On our planet, high-performance seismometers are often placed underground to protect them from temperature variations and bad weather. But the SEIS seismometer cannot be buried on Mars, so several ingenious devices have been put in place to protect it from temperature variations, which are extremely high on Mars, and from other sources of noise. A protective shield built by JPL called the “Wind and Thermal Shield” helps to attenuate environmental noise by protecting SEIS from wind, dust and temperature variations. As a result, the sensitivity of SEIS to date exceeds all the team’s expectations.

CNES is the prime contractor for SEIS, and IPGP (Institut de Physique du Globe de Paris, CNRS, Université de Paris) has scientific responsibility for the project. CNES is funding the French contributions, coordinating the international consortium (*) and has been responsible for the integration, testing and supply of the complete instrument to NASA. IPGP designed the VBB (Very Broad Band) sensors, then tested them before delivery to CNES. Several CNRS laboratories, the LMD (CNRS/ENS Paris/Ecole Polytechnique/Sorbonne University) and the LPG in Nantes (CNRS/Université de Nantes/Université d’Angers) and ISAE-SUPAERO are also involved in analysing data from the InSight mission.

(*) in collaboration with SODERN for the production of the VBBs, JPL, the Swiss Federal Institute of Technology Zurich (ETHZ, Switzerland), the Max Planck Institute for Solar System Research (MPS, Göttingen, Germany), Imperial College London and Oxford University provided the SEIS subsystems and are participating in the scientific exploitation of SEIS.

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