Seismic constraints from a Mars impact experiment using InSight and Perseverance

NASA’s InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission has operated a sophisticated suite of seismology and geophysics instruments on the surface of Mars since its arrival in 2018. On 18 February 2021, we attempted to detect the seismic and acoustic waves produced by the entry, descent and landing of the Perseverance rover using the sensors onboard the InSight lander. Similar observations have been made on Earth using data from both crewed1,2 and uncrewed3,4 spacecraft, and on the Moon during the Apollo era5, but never before on Mars or another planet. This was the only seismic event to occur on Mars since InSight began operations that had an a priori known and independently constrained timing and location. It therefore had the potential to be used as a calibration for other marsquakes recorded by InSight. Here we report that no signal from Perseverance’s entry, descent and landing is identifiable in the InSight data. Nonetheless, measurements made during the landing window enable us to place constraints on the distance–amplitude relationships used to predict the amplitude of seismic waves produced by planetary impacts and place in situ constraints on Martian impact seismic efficiency (the fraction of the impactor kinetic energy converted into seismic energy)

The interior of Mars as seen by InSight (Invited)

InSight is the first planetary mission dedicated to exploring the whole interior of a planet using geophysical methods, specifically seismology and geodesy. To this end, we observed seismic waves of distant marsquakes and inverted for interior models using differential travel times of phases reflected at the surface (PP, SS...) or the core mantle-boundary (ScS), as well as those converted at crustal interfaces. Compared to previous orbital observations1-3, the seismic data added decisive new insights with consequences for the formation of Mars: The global average crustal thickness of 24-75 km is at the low end of pre-mission estimates5. Together with the the thick lithosphere of 450-600 km5, this requires an enrichment of heat-producing elements in the crust by a factor of 13-20, compared to the primitive mantle. The iron-rich liquid core is 1790-1870 km in radius6, which rules out the existence of an insulating bridgmanite-dominated lower mantle on Mars. The large, and therefore low-density core needs a high amount of light elements. Given the geochemical boundary conditions, Sulfur alone cannot explain the estimated density of ~6 g/cm3 and volatile elements, such as oxygen, carbon or hydrogen are needed in significant amounts. This observation is difficult to reconcile with classical models of late formation from the same material as Earth. We also give an overview of open questions after three years of InSight operation on the surface of Mars, such as the potential existence of an inner core or compositional layers above the CM

Clock errors in land and ocean bottom seismograms: High-accuracy estimates from multiple-component noise cross-correlations

Many applications in seismology rely on the accurate absolute timing of seismograms. However, both seismological land stations and ocean bottom seismometers (OBSs) can be affected by clock errors, which cause the absolute timing of seismograms to deviate from a highly accurate reference time signal, usually provided by GPS satellites. Timing problems can occur in land stations when synchronization with a GPS signal is temporarily or permanently lost. This can give rise to complicated, time-dependent clock drifts relative to GPS time, due to varying environmental conditions. Seismometers at the ocean bottom cannot receive GPS satellite signals, but operate in more stable ambient conditions than land stations. The standard protocol is to synchronize an OBS with a GPS signal immediately before deployment and after recovery. The measured timing deviation, called “skew”, is assumed to have accumulated linearly over the deployment interval, an assumption that is plausible but usually not verifiable. In recent years, cross-correlations of ambient microseismic noise have been put to use for correcting timing errors, but have been limited to interstation distances of at most a few tens of kilometres without reducing the temporal resolution. We apply noise cross-correlations to the evaluation of clock errors in four broadband land stations and 53 wideband and broadband OBSs, which were installed on and around the island of La Réunion in the western Indian Ocean during the RHUM-RUM (Réunion Hotspot and Upper Mantle - Réunions Unterer Mantel) experiment. We correlate all three seismic components, plus a hydrophone channel in OBS stations. Daily cross-correlation functions are derived for intermediate distances (∼20 km) for land-to-land station pairs; stable, 10-day stacks are obtained for very large interstation distances up to >300 km for land-to-OBS, and OBS-to-OBS configurations. Averaging over multiple station pairs, and up to 16 component pairs per station, improves the accuracy of the method by a factor of four compared to the single-channel approaches of prior studies. The timing accuracy of our method is estimated to be ∼20 ms standard deviation, or one sample at a sampling rate of 50 Hz. In land stations, non-linear clock drifts and clock jumps of up to six minutes are detected and successfully corrected. For 52 out of 53 OBSs, we successfully obtain drift functions over time, which validate the common assumption of linear clock drift. Skew values that were available for 29 of these OBSs are consistent with our independent estimates within their observational error bars. For 23 OBSs that lacked skew measurements, linear OBS clock drifts range between 0.2 ms/day and 8.8 ms/day. In addition to linear drift, three OBSs are affected by clock jumps of ∼1 s, probably indicating a missing sample problem that would otherwise have gone undetected. Thus we demonstrate the routine feasibility of high-accuracy clock corrections in land and ocean bottom seismometers over a wide range of interstation distances

The Mars Structure Service for InSight:Single-Station Marsquake Inversions for Structure

AGU Fall Meeting in San Francisco, 9-13 December 2019The SEIS seismometer package was successfully deployed on Mars by February 2019. Routine operations are split into two services: the Mars Structure Service (MSS) and the Marsquake Service (MQS), which are responsible for defining interior structure models and seismicity catalogs, respectively. Initial model delivery from MSS is based on a limited dataset of two Marsquakes with a clear P and S arrivals. Different inversion algorithms were developed by the MSS team in order to retrieve the first 1D averaged model of Mars. Two complementary approaches are considered. One set of models (called M1) is parameterized in seismic velocity and density as a function of depth. A second set of models (called M2) is obtained by parameterizing with geodynamical constraints like temperature and composition. We use Bayesian inversion techniques to obtain robust probability density functions of seismic velocity profiles. Different types of data are considered for these inversions including body waves, surface waves and receiver functions. To characterize what we could learn about Mars¿ interior structure with only one station and with the first seismic event, we performed inversions of synthetic data following a blind test process, where the interior model and the Marsquake parameters (location, depth, origin time, and moment tensor) were unknown to all team members carrying out data analysis and inversion. In this presentation we will discuss the results of this blind test in terms of structure and compare different methods developed by the MSS. We will then show results from investigations of the first, real seismic data due to quakes on Mars recorded by SEIS in terms of the structure and quake locations. We will especially focus our investigation on joint inversions made not only with the arrival time, but also with secondary seismic data extracted from the detected events, including apparent attenuation rate and with receiver functions. Of course, much more detailed analysis will be made if Mars seismicity provide us in the near future larger quakes with body wave phases and first orbit surface wave dispersion, and/or one event large enough to record multiple orbit surface waves, and will augment future interiors models of Mars

New seismological constraints on the crustal structure of Mars and the Moon

Planetary crusts are the results of mantle differentiation, so their thickness provides important constraints on the thermochemical evolution of a planet, including its heat budget and mantle rheology. Information on crustal layering and seismic velocities can also provide important constraints on porosity and geochemistry of the crust. Here, we use data from the InSight mission, which landed in November 2018, to provide seismological constraints on the crustal layering and thickness of Mars for the first time. Results are mainly based on Ps-receiver functions from three events with magnitudes between 3.1 and 3.6 at distances between 27.5° and 47° (±10°) from the lander, originating in the Cerberus Fossae region, the only events, so far, with clear, impulsive P-wave onsets and known epicenter. Ps-receiver functions use converted phases in the P-wave coda to derive information on discontinuities beneath the seismometer. Due to the limited number of events and the small epicentral distance range covered, inversions of the data are still ambiguous. Two sets of models can explain the waveforms, one consisting of a two-layer crust of about 20 to 23 km thickness, the other having a three-layer crust of about 40 to 45 km thickness. By excluding crustal thicknesses in excess of 45 km at the landing site, we can constrain the global average crustal thickness of Mars to be less than 70 km. Both model types also agree with S-receiver functions for two events and seismic P-waves reflected in the crust and extracted from autocorrelations using the coda of different types of marsquakes as well as the background wavefield. Furthermore, the results are compatible with independently conducted moment tensor inversions for a limited number of events as well as modeling of the wave-propagation of high-frequency events. We find low seismic P-wave velocities below 3.4 km/s within the upper approximately 10 km, likely indicating a high porosity. For the Moon, we present Sp-receiver functions for three Apollo landing sites, including the first application of this method to Apollo 15 and 16 data. Data are compatible with a two-layer crust beneath a thin, low-velocity regolith layer and a crustal thickness of 35 to 45 km, with an increased thickness at the Apollo 15 and 16 sites compared to the Apollo12 location

Elderly patients diagnosed with idiopathic pulmonary arterial hypertension: Results from the COMPERA registry

BACKGROUND: Originally reported to occur predominantly in younger women, idiopathic pulmonary arterial hypertension (IPAH) is increasingly diagnosed in elderly patients. We aimed to describe the characteristics of such patients and their survival under clinical practice conditions. METHODS: Prospective registry in 28 centers in 6 European countries. Demographics, clinical characteristics, hemodynamics, treatment patterns and outcomes of younger (18-65years) and elderly (>65years) patients with newly diagnosed IPAH (incident cases only) were compared. RESULTS: A total of 587 patients were eligible for analysis. The median (interquartile, [IQR]) age at diagnosis was 71 (16) years. Younger patients (n=209; median age, 54 [16] years) showed a female-to-male ratio of 2.3:1 whereas the gender ratio in elderly patients (n=378; median age, 75 [8] years) was almost even (1.2:1). Combinations of PAH drugs were widely used in both populations, albeit less frequently in older patients. Elderly patients were less likely to reach current treatment targets (6min walking distance>400m, functional class I or II). The survival rates 1, 2, and 3years after the diagnosis of IPAH were lower in elderly patients, even when adjusted for age- and gender-matched survival tables of the general population (p=0.006 by log-rank analysis). CONCLUSIONS: In countries with an aging population, IPAH is now frequently diagnosed in elderly patients. Compared to younger patients, elderly patients present with a balanced gender ratio and different clinical features, respond less well to medical therapy and have a higher age-adjusted mortality. Further characterization of these patients is required. Clinical trials registration: NCT01347216

InSight seismic data from Mars: Effect and treatment of transient data disturbances.

The instrument package SEIS (Seismic Experiment for Internal Structure) with the two co-located seismometers VBB and SP is installed on the surface of Mars as part of NASA's InSight mission. When compared to terrestrial installations, SEIS is deployed in a very harsh wind and temperature environment that leads to inevitable degradation of the quality of the recorded data. The daily atmospheric temperature variations of approx. 80K are attenuated by different insulation layers to approx. 15K peak-to-peak at the sensor level. Typical wind speeds vary between 0 and 5 m/s leading to a diurnal variation in the broad-band rms noise level by two orders of magnitude. One ubiquitous artifact in the raw broad-band data is an abundance of one-sided, transient pulses often accompanied by high-frequency spikes. We show that these pulses, which we term "glitches", can be modeled as the response of the instrument to a step in acceleration, while the spikes can be modeled as the response to a simultaneous step in displacement. We attribute the glitches primarily to intermittent stress relaxation events internal to SEIS caused by the large diurnal temperature variations to which the instrument is exposed during a Martian sol. Only a small fraction of glitches correspond to a motion of the SEIS package as a whole caused by minuscule tilts of the instrument. Whilst such kind of data disturbances are typically discarded when occurring in terrestrial data, this is no option for the data returned from the Red Planet. We therefore do not only demonstrate their effects on the seismic data and analyze their origins, but also propose algorithms that are able to detect and remove many of these (mostly) non-seismic signals. We further published our codes (both Python and MATLAB) so that interested researchers can make their own choices on how to treat the data and to which extent

SEIS first year: nm/s^2 (and less) broadband seismology on Mars and first steps in Mars-Earth-Moon comparative seismology. (Invited)

AGU Fall Meeting 2019 in San Francisco , 9-13 December 2019EIS/InSIght teamInSight is the first planetary mission with a seismometer package, SEIS, since the Apollo Lunar Surface Experiments Package. SEIS is complimented by APSS, which has as a goal to document the atmospheric source of seismic noise and signals. Since June 2019, SEIS has been delivering 6 axis 20 sps continuous seismic data, a rate one order of magnitude larger originally planned. More than 50 events have been detected by the end of July 2019 but only three have amplitudes significantly above the SEIS instrument requirement. Two have clear and coherent arrivals of P and S waves, enabling location, diffusion/attenuation characterization and receiver function analysis. The event¿s magnitudes are likely ¿ 3 and no clear surface waves nor deep interior phases have been identified. This suggests deep events with scattering along their final propagation paths and with large propagation differences as compared to Earth and Moon quakes. Most of the event¿s detections are made possible due to the very low noise achieved by the instrument installation strategy and the very low VBB self-noise. Most of the SEIS signals have amplitudes of spectral densities in the 0.03-5Hz frequency bandwidth ranging from 10-10 m/s2/Hz1/2 to 5 10-9 m/s2/Hz1/2. The smallest noise levels occurs during the early night, with angstrom displacements or nano-radian tilts. This monitors the elastic and seismic interaction of a planetary surface with its atmosphere, illustrated not only by a wide range of SEIS signals correlated with pressure vortexes, dust devils or wind activity but also by modulation of resonances above 1 Hz, amplified by ultra-low velocity surface layers. After about one half of a Martian year, clear seasonal changes appear also in the noise, which will be discussed. One year after landing, the seismic noise is therefore better and better understood, and noise correction techniques begun to be implemented, either thanks to the APSS wind and pressure sensors, or by SEIS only data processing techniques. These data processing techniques open not only the possibility of better signal to noise ratio of the events, but are also used for various noise auto-correlation techniques as well as searches of long period signals. Noise and seismic signals on Mars are therefore completely different from what seismology encountered previously on Earth and Moon