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Potential Pitfalls in the Analysis and Structural Interpretation of Seismic Data from the Mars InSight Mission.

ABSTRACT: The Seismic Experiment for Interior Structure (SEIS) of the InSight mission to Mars, has been providing direct information on Martian interior structure and dynamics of that planet since it landed. Compared to seismic recordings on Earth, ground motion measurements acquired by SEIS on Mars are made under dramatically different ambient noise conditions, but include idiosyncratic signals that arise from coupling between different InSight sensors and spacecraft components. This work is to synthesize what is known about these signal types, illustrate how they can manifest in waveforms and noise correlations, and present pitfalls in structural interpretations based on standard seismic analysis methods. We show that glitches, a type of prominent transient signal, can produce artifacts in ambient noise correlations. Sustained signals that vary in frequency, such as lander modes which are affected by variations in temperature and wind conditions over the course of the Martian Sol, can also contaminate ambient noise results. Therefore, both types of signals have the potential to bias interpretation in terms of subsurface layering. We illustrate that signal processing in the presence of identified nonseismic signals must be informed by an understanding of the underlying physical processes in order for high fidelity waveforms of ground motion to be extracted. While the origins of most idiosyncratic signals are well understood, the 2.4 Hz resonance remains debated and the literature does not contain an explanation of its fine spectral structure. Even though the selection of idiosyncratic signal types discussed in this paper may not be exhaustive, we provide guidance on best practices for enhancing the robustness of structural interpretations.

SUBMITTER: Kim D

PROVIDER: S-EPMC8739436 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:By the end of 2018, 42 years after the landing of the two Viking seismometers on Mars, InSight will deploy onto Mars' surface the SEIS (Seismic Experiment for Internal Structure) instrument; a six-axes seismometer equipped with both a long-period three-axes Very Broad Band (VBB) instrument and a three-axes short-period (SP) instrument. These six sensors will cover a broad range of the seismic bandwidth, from 0.01 Hz to 50 Hz, with possible extension to longer periods. Data will be transmitted in the form of three continuous VBB components at 2 sample per second (sps), an estimation of the short period energy content from the SP at 1 sps and a continuous compound VBB/SP vertical axis at 10 sps. The continuous streams will be augmented by requested event data with sample rates from 20 to 100 sps. SEIS will improve upon the existing resolution of Viking's Mars seismic monitoring by a factor of ?2500 at 1 Hz and ?200000 at 0.1 Hz. An additional major improvement is that, contrary to Viking, the seismometers will be deployed via a robotic arm directly onto Mars' surface and will be protected against temperature and wind by highly efficient thermal and wind shielding. Based on existing knowledge of Mars, it is reasonable to infer a moment magnitude detection threshold of Mw?3 at 40? epicentral distance and a potential to detect several tens of quakes and about five impacts per year. In this paper, we first describe the science goals of the experiment and the rationale used to define its requirements. We then provide a detailed description of the hardware, from the sensors to the deployment system and associated performance, including transfer functions of the seismic sensors and temperature sensors. We conclude by describing the experiment ground segment, including data processing services, outreach and education networks and provide a description of the format to be used for future data distribution. Electronic Supplementary Material:The online version of this article (10.1007/s11214-018-0574-6) contains supplementary material, which is available to authorized users.

Project description:Interplanetary human spaceflight represents a formidable medical challenge, but also provides a unique platform for investigating human adaptation to extreme environmental changes. Understanding the long-term effects of isolation has relevance in a range of scenarios and it is well recognized that a better understanding of the relationship between environmental exposure and the epigenome can lead to more effective preventive measures. Here we conduct a longitudinal epigenetic, mood state and biochemical profiling of 6 crew members in an experiment simulating a 520-day mission to Mars. Illumina HumanMethylation450 BeadChip was used to obtain DNA methylation profiles. Firstly, we found that long-term isolation can induce global DNA methylation remodeling, and this change seems to be an active adaptation (rather than a random process or a by-product of the isolation). This study is the first to demonstrate the dynamic relationship between global epigenetic remodeling and isolation-induced mood state and biochemical changes. Secondly, by considering the location of methylation sites within the genome and using gene-pathway annotation, we were able to identify pathways that were significantly enriched in methylation events and consider their association with specific function and the timeline of the mission. Thirdly, via our definition of epi-entropy, a measure of entropy adapted to methylation events, we observed that the methylation remodeling produced a marked reduction in epi-entropy. Results suggest that DNA methylation change is an indicator of change rather than its by-product, i.e., there is a psychology-epigenome-metabolism model of long-term depression; DNA methylation programs the environment signal into the epigenome, which is subsequently transformed into the biochemical output and health outcome. Thus, longitudinal epigenetic profiling could code the effect of isolation and act as early indicators of latent health outcome. A longitudinal epigenetic, mood state and biochemical profiling of 6 crew members in an experiment simulating a 520-day mission to Mars. 36 samples of blood cell DNA methylation profiling were obtained by Illumina HumanMethylation450 BeadChip, across 6 sampling points during the 520 days mission for all of the 6 crew members.

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Potential Pitfalls in the Analysis and Structural Interpretation of Seismic Data from the Mars InSight Mission.

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