24. February 2020
First results of the InSight mission and a new plan for the Mars 'Mole'

Seismic activity on Mars resembles that found in the Swabian Jura

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Cerberus Fossae – shaped by volcanism and tectonics
Cerberus Fossae – shaped by volcanism and tectonics
Image 1/8, Credit: ESA/DLR/FU Berlin

Cerberus Fossae – shaped by volcanism and tectonics

The landscape in the Cerberus Fossae region appears as if cut by a knife. The tectonic fracture structures were formed less than 100 million years ago, perhaps even only 10 million years ago. This can also be seen in the profiles of the fossae, which are bound by extremely steep walls that are almost vertical in places and more than 500 metres high in some areas. The SEIS seismometer on NASA’s InSight lander was able to localise two quakes here, about 1700 kilometres east of the landing site, quite accurately, and another one with somewhat greater uncertainty. The image was created from data acquired on 27 January 2018 by the High Resolution Stereo Camera (HRSC) on board the European Mars Express spacecraft.
InSight locates marsquakes in the Cerberus Fossae region
InSight locates marsquakes in the Cerberus Fossae region
Image 2/8, Credit: NASA/USGS/MOLA; DLR (nach Giardini et al., 2020)

InSight locates marsquakes in the Cerberus Fossae region

The SEIS seismometer on NASA’s InSight lander recorded a total of 174 low-intensity marsquakes between February and the end of September 2019. With the help of models of the propagation of seismic waves in the Martian subsurface, the probable source of two larger quakes (s0235b and s0173a) could be determined quite accurately, and of that another quake (s0183a), which produced fewer clear signals, with somewhat reduced accuracy. The marsquakes occurred in the Cerberus Fossae region, a young volcanic area about 1700 kilometres east of the InSight landing site located in Elysium Planitia. Red lines show known fault zones. The topographical map is based on laser altitude measurements performed by NASA’s Mars Global Surveyor spacecraft (1999-2006) and shows height differences from approximately minus 3000 metres (blue-green) to plus 7000 metres (summit of Elysium Mons), related to a reference surface referred to as an areoid. This is a modelled elliptical surface of equal gravitational attraction, which is used on Mars as a ‘zero’ level in the absence of sea level.
Model of the subsoil conditions
Model of the subsoil conditions
Image 3/8, Credit: ©IPGP/Nicolas Sarter

Model of the subsoil conditions

The ground at the InSight landing site consists of three different layers and materials with different properties. A model of the soil properties has been developed using the propagation times of marsquake waves and the signals generated by the 'Mole' when it was hammering into the ground with the Heat Flow and Physical Properties Package (HP3) geothermal measurement system, as well as the many measurements performed with the Auxiliary Payload Sensor Suite (APSS) – consisting of a barometer, an anemometer, a magnetometer and two cameras), the HP3 radiometer and the Rotation and Interior Structure Experiment (RISE). Beneath what is referred to as the 'duricrust' (from Latin 'durus', meaning hard, and 'crusta', meaning shell or crust), there is a comparatively firm crust consisting of a kind of 'cemented' sand and roughly comparable to the firm, caramelised sugar crust of a crème brûlée. Further down, there is a several-metre-thick regolith of finely fragmented crustal rock and finally fragmented bedrock reaching deep underground.
Quake measurements at night-time
Quake measurements at night-time
Image 4/8, Credit: DLR (CC-BY 3.0)

Quake measurements at night-time

A day on Mars, a 'sol', lasts 24 hours and 37 minutes, almost the same length as a day on Earth. The graphic shows a 24-hour clock with Martian hours, which are therefore slightly longer than terrestrial hours. Midnight is at the top, followed clockwise by morning with sunrise, noon and evening with sunset. The slightly curved orange line indicates the times of sunrise and sunset, which vary slightly throughout the year. The distance from the centre indicates the number of sols since InSight's landing. The innermost circle is Sol 72, when the seismometer began to record continuously. The different symbols show the various types of marsquakes, which have different signal frequencies. Since the weather becomes noticeably calmer after sunset, the first half of the night is the best time window for recording distant marsquakes, because practically no wind interferes with the measurements being performed by the ultra-sensitive experiment.
SEIS experiment for recording marsquakes
SEIS experiment for recording marsquakes
Image 5/8, Credit: NASA/JPL-Caltech/CNES/IPGP

SEIS experiment for recording marsquakes

The Seismic Experiment for Interior Structure (SEIS) instrument is a seismometer for measuring movements in the Martian soil at different frequencies and consists of a total of six sensors. The instrument was developed under the leadership of the French space agency CNES. The heart of the SEIS experiment consists of two sets of three extremely sensitive pendulums that register even the smallest movements of the Martian surface. The biggest problem for reliable measurements on Mars is the large temperature differences between day and night and between summer and winter. Because materials expand when warm and contract when cold, SEIS is equipped with a sophisticated thermal protection system in the form of several insulated shells – comparable to a ‘Matryoshka doll’. These covers compensate for the temperature differences so that the instrument has stable measurement conditions. SEIS is protected from the effects of the Martian wind and the dust transported with it by a hemispherical dome consisting of several separate layers.
Next activity with the DLR HP³ geothermal sensor system
Next activity with the DLR HP³ geothermal sensor system
Image 6/8, Credit: NASA/JPL-Caltech

Next activity with the DLR HP³ geothermal sensor system

So far, it has not been possible to use the self-hammering 'Mole', the main component of the DLR Heat Flow and Physical Properties Package (HP3), to penetrate deeper than 38 centimetres into the Martian soil, which has unusual properties, even for Mars. After the Mole was almost completely in the Martian soil, it backed out a short distance. Subsequently, with repeated lateral pressure from the robotic arm, it has moved a little deeper into the ground, again with a recent slight backward movement. In the coming weeks, pressure from above with the robotic arm should help.
Daily temperature variations at the InSight landing site
Daily temperature variations at the InSight landing site
Image 7/8, Credit: DLR

Daily temperature variations at the InSight landing site

The temperature variations on Mars are much greater than on Earth. InSight measures the thermal radiation at the landing site from the ground and from the layer of air above using the RAD radiometer, part of the DLR HP3 experiment. Located near the equator, the high-elevation Sun heats the fine sand on the surface to above zero degrees Celsius on most days, while the thin atmosphere remains 10 to 20 degrees Celsius colder. At night, however, temperatures drop to minus 90 degrees Celsius or even lower. The gaps in the temperature curves are due to the fact that, because the operating modes are tailored to the experiment and optimised for the measurement of large temperature variations, it is not possible to measure during the switch from high to low temperature mode.
NASA's InSight lander on Mars
NASA's InSight lander on Mars
Image 8/8, Credit: NASA/JPL-Caltech

NASA's InSight lander on Mars

After its launch on 5 May 2018, NASA's InSight spacecraft landed on 26 November of the same year in Elysium Planum, four-and-a-half degrees north of the equator and 2613 metres below the reference level on Mars. InSight, a NASA Discovery Class mission, is the first purely geophysical observatory on another celestial body. In addition to the French Seismic Experiment for Interior Structure SEIS (lower left) and the geothermal probe HP3 (Heat Flow and Physical Properties Package, lower right) provided by DLR, a collection of supporting instruments are installed on the lander platform (the Auxiliary Payload Sensor Suite (APSS) – consisting of a barometer, an anemometer, a magnetometer and two cameras), the HP3 radiometer and the Rotation and Interior Structure Experiment (RISE).
  • The SEIS experiment on board NASA's InSight geophysical station recorded 174 seismic events up to the end of September 2019.
  • Weak earthquakes – magnitude less than three to four.
  • Accompanying measurements provide information about the local weather conditions.
  • In the coming weeks, the Mars 'Mole' is to be assisted more effectively by pressure from above applied with the robotic arm.
  • Focus: Space, exploration, planetary geophysics

Mars is a seismically active planet – quakes occur several times a day. Although they are not particularly strong, they are easily measurable during the quiet evening hours. This is one of many results of the evaluation of measurement data from the NASA InSight lander, which has been operating as a geophysical observatory on the surface of Mars since 2019. A series of six papers have now been published in the scientific journals Nature Geoscience and Nature Communications. Eight scientists from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) have made contributions to these. The papers describe the weather and atmospheric dynamics at the landing site, its geological environment, the structure of the Martian crust and the nature and properties of the planetary surface.

The Seismic Experiment for Interior Structure (SEIS) instrument – a seismometer developed by an international consortium under the leadership of the French space agency CNES – recorded a total of 174 seismic events between February and September 2019. Twenty of these marsquakes had a magnitude of between three and four. Quakes of this intensity correspond to weak seismic activity of the kind that occurs repeatedly on Earth in the middle of continental plates, for example in Germany on the southern edge of the Swabian Jura hills. Although only one measurement station is available, models of wave propagation in the Martian soil have been used to determine the probable source of two of these quakes. It is located in the Cerberus Fossae region, a young volcanic area approximately 1700 kilometres east of the landing site.

"Due to the higher gravity, SEIS could only be tested to a limited extent on Earth. We are all very excited about how sensitive it actually is," says Martin Knapmeyer, a geophysicist at the DLR Institute of Planetary Research, who is involved in SEIS data evaluation. "The seismic activity observed on Mars so far is significantly stronger than that found on the Moon – which is what we expected. How much stronger it actually is and whether there are more powerful marsquakes than those of magnitude four will become clear as the mission continues." However, even now, important and fundamentally new conclusions can be drawn about the planet's internal structure: "Similar to the Moon, the crust seems to be heavily disrupted down to a depth of several kilometres. Nevertheless, the seismic signals are more similar to Earth than to the Moon, but we do not yet understand why. For example, much of the time we cannot identify the cause of the marsquakes. Here, we are breaking new scientific ground." The mission will continue at least until the end of 2020 and will continuously provide further data. "We have not detected any meteorite impacts yet. However, it was clear early on that only expect a very small number of impacts would be expected during the mission."

InSight takes the 'pulse' of the Red Planet

This is the first time that an experiment to record marsquakes has provided such data on a larger scale and over a longer period of time. After the Moon, Mars is only the second celestial body other than Earth on which natural quakes have been recorded. It is true that instruments for performing seismic measurements were also installed on the first landers to visit Mars – the legendary Viking 1 and 2 missions – which arrived there in July 1976. However, these instruments were located on the lander platforms and only provided 'noisy' results, which were not particularly meaningful due to the presence of interfering signals, particularly those caused by the wind.

Following its launch on 5 May 2018, InSight landed on 26 November of the same year in Elysium Planum, four-and-a-half degrees north of the equator and 2613 metres below the reference level on Mars. The InSight team named the landing site ‘Homestead hollow’. More precisely, the landing site is located in an old, shallow crater that is approximately 25 metres across. The crater is heavily eroded and filled with sand and dust. The more distant surroundings of InSight are not very interesting geologically, but that was exactly one of the most important criteria for the selection of the landing site. It needed to be flat and level – and have as few rocks and stones as possible. The entire region consists of lava flows that solidified two-and-a-half billion years ago and were subsequently broken down by meteorite impacts and weathering into what is referred to as 'regolith'. It is thought that there are no large boulders down to a depth of at least three metres.

Magnetic field surprise

InSight, a NASA Discovery-class mission, is the first purely geophysical observatory on another celestial body in the Solar System. Its primary objective is to study the composition and structure of Mars, its thermal evolution and current internal state, and current seismic activity. Forces and energies inside a planetary body 'control', to some extent, geological processes – the results of which are visible on the surface – such as volcanism and tectonic fractures in the rigid crust, over billions of years.

With SEIS and the DLR Heat Flow and Physical Properties Package (HP3) geothermal sensor system, together with a collection of supporting instruments (the Auxiliary Payload Sensor Suite (APSS) – consisting of a barometer, an anemometer, a magnetometer, and two cameras), the HP3 radiometer and the Rotation and Interior Structure Experiment (RISE), InSight takes the 'pulse' of the Red Planet, measuring irregularities in its daily rotation and recording atmospheric parameters and weather at the landing site. One surprising result has been the local detection of a magnetic field that is 10 times stronger than predicted using the results of observations from Mars' orbit. This magnetic field is generated by magnetised minerals in the rock. The magnetisation ultimately came from a planet-wide magnetic field from Mars' early history.

The 'moving' day of a seismometer on Mars

Before the turn of the year 2018/2019, the SEIS experiment was set down on the surface of Mars and, protected from wind and weather by its characteristic dome (resembling a 'Cheese Bell') and perfectly horizontally aligned by a levelling system developed at the Max Planck Institute for Solar System Research in Göttingen, started routine measurement operations in February 2019. The experiment is so sensitive that almost any small change at the landing site is recorded as a signal: Movements of the robot arm, gusts of wind, thermal 'stress' in the lander caused by temperature differences, or of course the vibrations of the hammering Mars Mole right beside it. For this reason, the daily weather patterns, in particular the activity of the wind and the extreme fluctuations in temperature in the day and night rhythm, as well as the vibrations caused by the hammering mechanism of the DLR experiment HP3 were analysed.

"We are dealing with much greater temperature differences at the landing site than those that occur on Earth," explains Nils Müller from the DLR Institute of Planetary Research, who has analysed thermal radiation from the surface using the HP3 radiometer experiment. "At midday, the Sun heats the fine sand on the surface to above zero degrees Celsius on most days, while the thin atmosphere remains 10 to 20 degrees Celsius colder. At night, however, temperature drops to minus 90 degrees Celsius or even lower."

During the day, the increase in temperature always results in a very characteristic weather pattern, with winds first freshening and then easing in the afternoon. The scientists have even identified traces of small tornadoes or 'dust devils', frequent phenomena in the Martian weather pattern, on the ground after their course was recorded from orbit by NASA's Mars Atmosphere and Volatile Evolution (MAVEN) orbiter. These dust devils can even raise the Martian soil a little, which is registered by the seismometer. This allows conclusions to be drawn about the properties of the upper layer of the surface material. At night, the weather calms down noticeably, so the best time window for recording distant marsquakes is in the first half of the night, because almost no atmosphere-induced noise interferes with the experiment.

HP3 delivers results and the Mars mole gets help from above

Measurements and observations performed by DLR's HP3 experiment have also been incorporated into the scientific inventory, including the radiometer data and the soil properties derived from the course of the experiment to date, with the hammering of the Mars Mole serving, among other things, as a seismic source for analysing the upper layer of the soil. However, it has not yet been possible to use the self-hammering thermal probe to penetrate deeper than 38 centimetres into the Martian soil there, with its unusual properties, even for Mars. In autumn 2019, the experiment seemed to be well on its way – the 'Mole' was given lateral support by the scoop on the robotic arm, which provided the friction necessary for driving into the subsurface. "After the Mole was almost completely in the Martian soil, it backed out again a small distance. Subsequently, with repeated lateral pressure from the robotic arm, it has moved a little deeper into the ground again with a recent slight backward movement," explains the Principal Investigator of the HP3 experiment – Tilman Spohn from the DLR Institute of Planetary Research. "In the coming weeks we want to help more effectively by applying pressure from above with the scoop on the robotic arm." For months, DLR researchers and numerous technicians and engineers at the Jet Propulsion Laboratory (JPL) have been working meticulously with the Mole on Mars and with simulations, models and tests on Earth to find a solution. In his P.I. blog, Tilman Spohn explains the current situation and the possibilities for moving deeper into the soil with the Mars Mole.

The publications

  • Banerdt, Smrekar et al. (2020) Initial results from the InSight mission on Mars, Nature Geoscience, in press, DOI : 10.1038/s41561-020-0544-y
  • Lognonné et al. (2020) Constraints on the shallow elastic and anelastic structure of Mars from InSight seismic data, Nature Geoscience, in press, DOI : 10.1038/s41561-020-0536-y
  • Giardini et al. (2020) The seismicity of Mars, Nature Geoscience, in press, DOI : 10.1038/s41561-020-0539-8
  • Banfield, Spiga et al. (2020) The atmosphere of Mars as observed by InSight, Nature Geoscience, in press, DOI : 10.1038/s41561-020-0534-0
  • Johnson et al. (2020) Crustal and time-varying magnetic fields at the InSight landing site on Mars, Nature Geoscience, in press, DOI : 10.1038/s41561-020-0537-x
  • Golombek et al. (2020) Geology of the InSight Landing Site on Mars, Nature Communications, in press, DOI : 10.1038/s41467-020-14679-1

The HP3 instrument on NASA's InSight mission

The InSight mission is being carried out by NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, on behalf of the agency's Science Mission Directorate. InSight is part of NASA's Discovery Program. DLR is contributing the Heat Flow and Physical Properties Package (HP3) experiment to the mission. The scientific leadership lies with the DLR Institute of Planetary Research, which was also in charge of developing and implementing the experiment in collaboration with the DLR Institutes of Space Systems, Optical Sensor Systems, Space Operations and Astronaut Training, Composite Structures and Adaptive Systems, and System Dynamics and Control, as well as the Institute of Robotics and Mechatronics. Participating industrial partners are Astronika and the CBK Space Research Centre, Magson GmbH and Sonaca SA, the Leibniz Institute of Photonic Technology (IPHT) as well as Astro- und Feinwerktechnik Adlershof GmbH. Scientific partners are the ÖAW Space Research Institute at the Austrian Academy of Sciences and the University of Kaiserslautern. The DLR Microgravity User Support Center (MUSC) in Cologne is responsible for HP3 operations. In addition, the DLR Space Administration, with funding from the German Federal Ministry for Economic Affairs and Energy, supported a contribution by the Max Planck Institute for Solar System Research to the French main instrument SEIS (Seismic Experiment for Interior Structure).

Detailed information on the InSight mission and the HP3 experiment is available on DLR's dedicated mission site, with extensive background articles. Information can also be found in the animation and brochure about the mission or via the hashtag #MarsMaulwurf on the DLR Twitter channel. Tilman Spohn, the Principal Investigator for the HP3 experiment, is also providing updates in the DLR Blog portal about the activities of the Mars Mole.

Contact
  • Falk Dambowsky
    Editor
    German Aerospace Center (DLR)
    Media Relations
    Telephone: +49 2203 601-3959
    Fax: +49 2203 601-3249
    Linder Höhe
    51147 Cologne
    Contact
  • Prof.Dr. Tilman Spohn
    HP³ Principal Investigator
    German Aerospace Center (DLR)

    DLR Institute of Planetary Research
    Telephone: +49 30 67055-300
    Fax: +49 30 67055-303
    Linder Höhe
    51147 Köln
    Contact
  • Matthias Grott
    German Aerospace Center (DLR)
    DLR Institute of Planetary Research, Planetary Geodesy
    Telephone: +49 30 67055-419

    Contact
  • Martin Knapmeyer
    German Aerospace Center (DLR)
    Institute of Planetary Research
    Telephone: +49 30 67055-394
    Rutherfordstraße 2
    12489 Berlin
    Contact
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