The Lunar Geophysical Network Mission

The National Academy’s current Planetary Decadal Survey (NRC, 2011) prioritizes a future Lunar Geophysical Network (LGN) mission to gather new information that will permit us to better determine how the overall composition and structure of the Moon inform us about the initial differentiation and subsequent evolution of terrestrial planets

The InSight HP3 Penetrator (Mole) on Mars: Soil Properties Derived from the Penetration Attempts and Related Activities

The NASA InSight Lander on Mars includes the Heat Flow and Physical Properties Package HP3 to measure the surface heat flow of the planet. The package uses temperature sensors that would have been brought to the target depth of 3–5 m by a small penetrator, nicknamed the mole. The mole requiring friction on its hull to balance remaining recoil from its hammer mechanism did not penetrate to the targeted depth. Instead, by precessing about a point midway along its hull, it carved a 7 cm deep and 5–6 cm wide pit and reached a depth of initially 31 cm. The root cause of the failure – as was determined through an extensive, almost two years long campaign – was a lack of friction in an unexpectedly thick cohesive duricrust. During the campaign – described in detail in this paper – the mole penetrated further aided by friction applied using the scoop at the end of the robotic Instrument Deployment Arm and by direct support by the latter. The mole tip finally reached a depth of about 37 cm, bringing the mole back-end 1–2 cm below the surface. It reversed its downward motion twice during attempts to provide friction through pressure on the regolith instead of directly with the scoop to the mole hull. The penetration record of the mole was used to infer mechanical soil parameters such as the penetration resistance of the duricrust of 0.3–0.7 MPa and a penetration resistance of a deeper layer (> 30 cm depth) of 4.9±0.4 MPa. Using the mole’s thermal sensors, thermal conductivity and diffusivity were measured. Applying cone penetration theory, the resistance of the duricrust was used to estimate a cohesion of the latter of 2–15 kPa depending on the internal friction angle of the duricrust. Pushing the scoop with its blade into the surface and chopping off a piece of duricrust provided another estimate of the cohesion of 5.8 kPa. The hammerings of the mole were recorded by the seismometer SEIS and the signals were used to derive P-wave and S-wave velocities representative of the topmost tens of cm of the regolith. Together with the density provided by a thermal conductivity and diffusivity measurement using the mole’s thermal sensors, the elastic moduli were calculated from the seismic velocities. Using empirical correlations from terrestrial soil studies between the shear modulus and cohesion, the previous cohesion estimates were found to be consistent with the elastic moduli. The combined data were used to derive a model of the regolith that has an about 20 cm thick duricrust underneath a 1 cm thick unconsolidated layer of sand mixed with dust and above another 10 cm of unconsolidated sand. Underneath the latter, a layer more resistant to penetration and possibly containing debris from a small impact crater is inferred. The thermal conductivity increases from 14 mW/m K to 34 mW/m K through the 1 cm sand/dust layer, keeps the latter value in the duricrust and the sand layer underneath and then increases to 64 mW/m K in the sand/gravel layer below

Lithological Interpretation of Martian Crustal Seismic Velocities from InSight

Analysis of data from the seismometer SEIS [1] on NASA’s InSight mission [2] has provided a wealth of information on the crustal structure of Mars, both beneath the lander [3-11] and for other locations on the planet [12-16]. Here, we collect all P- and S-wave velocity information for kilometer-scale crustal layers available and compare it with parameters predicted by rock physics models to guide the interpretation in terms of crustal lithology. A similar approach has previously only been attempted for crustal SV-wave velocities below the lander [17,18] and P- and SV-wave velocities in the shallowest 200 meters of the subsurface beneath InSight [19]

Obtaining Average Crustal and Uppermost Mantle Properties for Planetary Models of Mars

After more than 4 Earth years (∼1450 sols) of operations on the martian surface monitoring the planet’s ground vibrations, the InSight’s seismometer is now retired. Throughout the mission, analyses of body waves from marsquakes and impacts have led to important discoveries about the planet’s interior structure of the crust, mantle, and core [1-5]. Recent detection of surface waves, together with gravimetric modeling enabled the characterization of crustal structure variations away from the InSight landing site and showed that average crustal velocity and density structure is similar between the northern lowlands and the southern highlands [6-7]. These new constraints obtained by surface wave measurements provide an important opportunity to refine and verify our previous radially symmetric models of the planet’s interior structure. As part of this effort, we obtain the average crustal and uppermost mantle velocities of Mars using Rayleigh waves orbiting the planet multiple times. These higher-orbit Rayleigh wave observables independently constrain the average crustal and uppermost mantle velocities, and crustal thickness, which are found to be consistent with previous InSight studies. Successful incorporating of these velocity constraints into the existing joint inversion framework used for modeling body wave travel times [8], geophysical [9], and geodynamic parameters [10] will improve the current reference 1D interior models of Mars

Geophysics in Elysium Planitia - First Year Results from the InSight Mars Mission

On November 26, 2018, NASA's InSight mission landed in Elysium Planitia, Mars, and installed the first geophysical station on the planet. InSight's primary payload consists of a seismometer, a heat flow probe, and a radio tracking experiment to determine the planet's rotational state. In addition, the lander is equipped with a robotic arm that has been used to deploy the seismometer and heat flow probe, two cameras, a radiometer, and an atmospheric and magnetic field package. InSight's primary objectives are to determine the interior structure, composition, and thermal state of Mars, as well as constrain present-day seismicity and impact cratering rates. While the heat flow probe was able to emplace sensors to a depth of 0.37 m only, the seismometer has been successfully installed. Here we will provide a mission overview and report on results obtained during the first year of operations on Mars

Hindsight from InSight: what science coud have been don with a simpler mission?

The InSight mission was very successful at producing high quality seismic data to investigate the deep interior of Mars, delivering new estimates of the core size, the first value of the seismicity level and many other results. At the same time, the deployment of a high quality seismometer (very broadband, VBB) shaped the mission profile and required a dedicated robot arm. Future missions to Mars may want to carry a more robust short period seismometer (SP) to monitor the seismicity of the planet or investigate specific questions without shaping the whole mission around the instrument. We therefore investigated, which science results of the InSight mission could have been obtained with a significantly reduced effort