InSight registers seismic signal on Mars

The faint event could indicate a “marsquake” that occurred on 6 April.

April 24, 2019

The seismometer SEIS on board NASA's InSight lander may have recorded the first “marsquake”. The event occurred about two and a half weeks ago on 6 April and was significantly weaker than typical earthquakes. Insight landed on our neighboring planet on 26 November last year. The main objective of the SEIS team, which includes researchers from the Max Planck Institute for Solar System Research in Göttingen (Germany), is to deduce the planet’s inner structure from the propagation of seismic waves. No previous Mars mission has succeeded in collecting meaningful seismic data.

Mars’ seismic activity is tiny compared to that of our home planet. On Earth, most earthquakes originate in the Earth's crust: tectonic plates shift against each other and thus build up tension that discharges into quakes. Mars, on the other hand, consists of a single tectonic plate. Scientists suspect that the cooling of the planet triggers the few weak “marsquakes”. The sensitivity requirements for InSight’s seismometer SEIS are therefore enormous: the instrument is capable of recording vibrations that move the Martian surface by only the thickness of a hydrogen atom.

SEIS has recorded a total of four seismic events since its commissioning in February: on 14 March (on the 105th day of the mission, also called sol 105), on 6 April (sol 128), on 10 April (sol 132), and on 11 April (sol 133). While the cause of the first signal and the last two is still unclear, it appears likely that the event on 6 April originated inside the planet. "The marsquake was nevertheless so weak that one would not have noticed it on Earth", explains Ulrich Christensen, director at the Max Planck Institute for Solar System Research and member of the SEIS team. On Earth, oceans, human activity, and weather provide a constant seismic background noise. This would have completely covered an earthquake of the order of magnitude of the now registered Martian vibration.

Earthquakes can reveal details of Mars' internal structure

In the coming weeks, the researchers intend to continue investigating the exact cause of the Martian quake. "It is to be feared that the quake was too faint to derive reliable information about the internal structure of Mars", says John-Robert Scholz, SEIS scientist at the Max Planck Institute for Solar System Research. While it is considered certain that Mars, like Earth, has an inner layered structure consisting of core, mantle, and crust, the exact composition and thickness of these layers are still unclear. "The InSight mission is still at its beginning. We are hopeful, that we will witness stronger marsquakes in the coming weeks and months," says Christensen.

InSight is the first Mars mission to carry out meaningful seismological measurements on Mars. The first two Mars landing units, Viking 1 and 2, which landed on the Red Planet in 1976, were already equipped with seismometers. However, as they did not have direct contact to the ground, they recorded vibrations especially when the wind shook the landing units. SEIS, on the other hand, has been standing on the Martian surface since December 2018. 

InSight is a NASA mission led by the Jet Propulsion Laboratory (JPL). The InSight seismometer was provided by a team led by the French space agency CNES. The Göttingen based Max Planck Researchers developed and built the instrument's levelling system, which aligned the instrument exactly horizontally on the Martian surface. This is a decisive prerequisite for high-precision seismological measurements.  

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