Martian seismology begins to reveal the planet’s structure
In a series of 6 articles published this Monday February 24 in Nature Geoscience and Nature Communication, the scientific team behind NASA's InSight mission begins to lift the veil on the mysteries of the planet Mars.
Publication date: 14/02/2020
Observatories, Press, Research
Related observatories : InSight Observatory
Related themes : Earth and Planetary Interiors
The numerous geophysical data collected during the first 6 months of the mission shed light on the structure of the first few kilometres of the Martian subsoil and provide a new understanding of atmospheric phenomena on the planet’s surface.
Researchers from the Institut de Physique du Globe de Paris (IPGP, CNRS, Université de Paris, Université de la Réunion, IGN) have been particularly interested in the seismicity of Mars and the first Martian seismo-tectonic analyses, the internal crustal structures imaged by these first data, and the interaction of the Martian atmosphere with the Martian subsurface.
A dozen researchers, post-docs and doctoral students from the IPGP’s Planetology and Space Sciences and Seismology teams took part in these analyses, in close collaboration with their French, European and American colleagues. The data was also distributed to the international community by the IPGP Data Centre, while SEIS operations, carried out at the CNES Toulouse Centre, always involve several IPGP engineers.
In mid-February, by analysing the recordings of the SEIS seismometer, deployed on the Martian surface since December 2018, the seismologists of the Mars Quake Service, coordinated by ETH Zurich and to which IPGP contributes, identified nearly 460 seismic events. 40 of these are low-frequency signals, corresponding to relatively deep earthquakes, while the vast majority are high-frequency events, much more superficial and nearby, the origin of which is still unclear: small surface earthquakes, landslides and micro-shaking of cliffs are candidate sources.
Seismic waves from earthquakes, which are sensitive to the materials they pass through, offer planetary scientists a way of studying the composition of the planet’s internal structure. By combining them with other sources of vibrations (from the lander and its instruments or from the dust devils that criss-cross the Elysium plain), researchers from the Mars Structure Service, coordinated by the IPGP and the Jet Propulsion Laboratory, have been able to distinguish 3 distinct layers in the subsurface: the duricrust, an indurated layer just a few centimetres thick; the regolith, a superficial stratum made up of material crushed by countless impacts over billions of years; and finally a layer around ten kilometres thick that has been altered over billions of years. Beneath these ten kilometres is a consolidated deep crust, where the observed scattering and attenuation of seismic waves is similar to that observed in the Earth’s crystalline massifs.
A final group of IPGP researchers focused on the seismo-tectonic analysis of the largest events. Two earthquakes, of magnitude 3.6, were located 1600 kilometres to the east of InSight, in a sector called Cerberus Fossae, a vast region criss-crossed by immense faults where scientists had already noticed, in the very high-resolution images from Mars Reconnaissance Orbiter, blocks of rock that may have been shaken by earthquakes and precipitated along the abrupt slopes. In this region, ancient earthquakes have carved out canyons almost 1,300 kilometres long. Lava flows have infiltrated these canyons over the last 10 million years, and some of these recent lava flows (on the geological time scale) show signs of fractures caused by earthquakes less than 2 million years ago. If the analysis of these earthquakes is confirmed, Cerberus Fossae would be the first active seismic zone ever discovered on the Red Planet.
While the Martian crust is beginning to reveal its secrets, the earthquakes detected so far have not yet shed any light on the interior of Mars, or on the mantle and core.
However, the initial results provided by the SEIS seismometer during its first year of operations on Mars are very encouraging, and the data, made public as it comes in by the IPGP data centre, is being studied intensively not only by numerous international teams but also by a worldwide network of secondary school pupils, as part of the Sismo à l’Ecole project run by the GéoAzur laboratory in Nice. And Martian seismology is already stimulating new lines of research, ultimately leading to a better understanding of the formation of all rocky planets, including the Earth and its Moon.
Find out more:
- the InSight SEIS instrument website
- the joint press release on the CNRS/CNES/IPGP website
- the mission portal on the NASA website
Ref:
- Banerdt, Smrekar et al. (2020) Initial results from the InSight mission on Mars, Nature Geoscience, (doi.org/10.1038/s41561-020-0544-y) – open access article
- Lognonné et al (2020) Constraints on the shallow elastic and anelastic structure of Mars from InSight seismic data, Nature Geoscience, (doi.org/10.1038/s41561-020-0536-y) – open access article
- Giardini et al (2020) The seismicity of Mars, Nature Geoscience, https://doi.org/10.1038/s41561-020-0539-8
- Banfield, Spiga et al.(2020) The atmosphere of Mars as observed by InSight, Nature Geoscience, (doi.org/10.1038/s41561-020-0534-0) – open access article
- Johnson et al. (2020) Crustal and time-varying magnetic fields at the InSight landing site on Mars, Nature Geoscience, https://doi.org/10.1038/s41561-020-0537-x
- Golombek et al. (2020) Geology of the InSight Landing Site on Mars, Nature Communications, open access: https: //doi.org/10.1038/s41467-020-14679-1
