arXiv subjects

Simon C. Stähler

Publications and source records attributed to Simon C. Stähler.

13 recordsLinked to original sources

arXiv2026

Lava Tube Exploration with LunarLeaper

Lunar pits, some of which are interpreted as collapse features into underlying lava tubes, expose otherwise inaccessible stratigraphy and may provide entry points to subsurface voids that preserve records of lunar volcanism and offer potential sites for future human exploration. We synthesize the current state of knowledge on lunar pits and lava tubes, covering their morphological characteristics, classification, proposed formation mechanisms, mechanical stability, and detection from orbit. We then review the open science questions that pit and pit-wall investigation is uniquely placed to address, spanning the volcanic stratigraphy of the lunar maria, the structure and lateral variability of the regolith, and the dimensions and accessibility of subsurface conduits. To evaluate how these questions can be tackled in situ, we assess the feasibility and expected performance of geophysical and remote-sensing investigations for subsurface voids and surface exposures, mainly focusing on gravity measurements, ground-penetrating radar, high-resolution imaging, and spectroscopy. Building on this, we present LunarLeaper, a small legged robot mission concept combining a gravimeter, ground-penetrating radar, high-resolution imager, spectrometer, and leg-based geomechanical experiments to deliver the first in situ investigation of a mare pit. The concept targets the Marius Hills Pit and its associated rille, with a mobility architecture optimized for the rugged terrain encountered at pit edges and funnel slopes.

astro-ph.EP↗

arXiv2026

Discrimination of Tectonic, Swarm and Impact-related Marsquakes using Spectral Characteristics

The NASA InSight mission observed over 2000 marsquakes in the course of its three year mission. These quakes varied in magnitude between 1.5 and 4.5, as well as in spectral content. We present a simple framework to describe the spectral characteristics of all observed marsquakes, based on source process; propagation through the mantle or crust; and local, receiver-side amplification. We assign to each quake an objective measure of its amplitude, as well as the spectral decay created by the duration of the rupture and the dampening of high frequencies due to visco-elastic attenuation. Together, this allows us to obtain characteristic patterns of the whole marsquake dataset, e.g. in terms of event magnitudes, source size, and - for quakes caused by meteoritic impacts - crater size. We show that a significant fraction of all marsquakes - the high-frequency quakes - form a swarm that is likely not caused by tectonic processes in rocks. Our analysis allows separation of the whole marsquake catalogue into three event classes, of tectonic quakes, meteoritic impacts, and swarm events. We finally conclude that the largest marsquake, S1222a, most likely belongs to the group of meteoritic impacts.

astro-ph.EP↗

arXiv2024

Global Analysis of LISA Data with Galactic Binaries and Massive Black Hole Binaries

The Laser Interferometer Space Antenna (LISA) is a planned space-based observatory to measure gravitational waves in the millihertz frequency band. This frequency band is expected to be dominated by signals from millions of Galactic binaries and tens of merging massive black hole binaries. The LISA Data Challenge 2a is focused on robust signal extraction from a blend of these two types of gravitational wave signals. Here, we introduce a novel high performance and cost-effective global fit pipeline extracting and characterizing galactic binary and massive black hole binary signals and estimate the noise of the residual. We perform the pipeline in a time-evolving weekly analysis starting with an observation time of 1 week until we reach a full year. As expected we detect more galactic binaries and massive black hole binaries bringing the noise estimate of the residual closer to the instrument noise with each week of additional observation time. Furthermore, we present a novel maximum likelihood estimate-based algorithm for extracting multiple massive black hole binaries. Additionally, we demonstrate a massive black hole binary signal extraction with a more accurate LISA response, considering higher harmonic modes, in a noisy data set.

gr-qc↗

arXiv2023

Accelerating global parameter estimation of gravitational waves from Galactic binaries using a genetic algorithm and GPUs

The Laser Interferometer Space Antenna (LISA) is a planned space-based gravitational wave telescope with the goal of measuring gravitational waves in the milli-Hertz frequency band, which is dominated by millions of Galactic binaries. While some of these binaries produce signals that are loud enough to stand out and be extracted, most of them blur into a confusion foreground. Current methods for analyzing the full frequency band recorded by LISA to extract as many Galactic binaries as possible and to obtain Bayesian posterior distributions for each of the signals are computationally expensive. We introduce a new approach to accelerate the extraction of the best fitting solutions for Galactic binaries across the entire frequency band from data with multiple overlapping signals. Furthermore, we use these best fitting solutions to omit the burn-in stage of a Markov chain Monte Carlo method and to take full advantage of GPU-accelerated signal simulation, allowing us to compute posterior distributions in 2 seconds per signal on a laptop-grade GPU.

astro-ph.IM↗

arXiv2022

Locating the Nordstream explosions without a velocity model using polarization analysis

The seismic events that preceded the leaks in the Nordstream pipelines in the Baltic Sea have been interpreted as explosions on the seabed, most likely man-made. We use a polarization-based location method initially developed for marsquakes to locate the source region without a subsurface velocity model. We show that the 2 largest seismic events can be unambiguously attributed to the methane plumes observed on the sea surface. The two largest events can be located with this method, using 4 and 5 stations located around the source, with location uncertainties of 30km and 10x60km. We can further show that both events emitted seismic energy for at least ten minutes after the initial explosion, indicative of resonances in the water column or the depressurizing pipeline.

physics.geo-ph↗

arXiv2022

Bayesian parameter-estimation of Galactic binaries in LISA data with Gaussian Process Regression

The Laser Interferometer Space Antenna (LISA), which is currently under construction, is designed to measure gravitational wave signals in the milli-Hertz frequency band. It is expected that tens of millions of Galactic binaries will be the dominant sources of observed gravitational waves. The Galactic binaries producing signals at mHz frequency range emit quasi monochromatic gravitational waves, which will be constantly measured by LISA. To resolve as many Galactic binaries as possible is a central challenge of the upcoming LISA data set analysis. Although it is estimated that tens of thousands of these overlapping gravitational wave signals are resolvable, and the rest blurs into a galactic foreground noise; extracting tens of thousands of signals using Bayesian approaches is still computationally expensive. We developed a new end-to-end pipeline using Gaussian Process Regression to model the log-likelihood function in order to rapidly compute Bayesian posterior distributions. Using the pipeline we are able to solve the Lisa Data Challenge (LDC) 1-3 consisting of noisy data as well as additional challenges with overlapping signals and particularly faint signals.

astro-ph.IM↗

arXiv2022

Tectonics of Cerberus Fossae unveiled by marsquakes

The InSight mission has measured Mars' seismicity since February 2018 and has allowed to investigate tectonics on another planet. Seismic data shows that most of the widely distributed surface faults are not seismically active, and that seismicity is mostly originating from a single graben structure, the Cerberus Fossae. We show that both major families of marsquakes characterized by low and high frequency content, LF and HF events respectively, are located on central and eastern parts of this graben system. LF hypocenters are located at 15-50 km depth and the spectral character suggests a structurally weak, potentially warm source region consistent with recent volcanic activity at those depths. HF marsquakes occur in the brittle, shallow part of the crust and might originate in fault planes associated with the graben flanks. Estimated magnitudes are between 2.8 and 3.8, resulting in a total seismic moment release within Cerberus Fossae of 1.4-5.6 $\times10^{15}$ Nm/yr, or at least half of the observed value of the entire planet. Our findings confirm that Cerberus Fossae represents a unique tectonic setting shaped by current day volcanic processes, with implications for minimum local heat flow.

astro-ph.EP↗

arXiv2022

Seismology in the Solar System

The NASA InSight mission has helped to measure the deep interior of Mars using observations of seismic waves excited by marsquakes. Currently, installation of seismometers on the moon is foreseen. We review the case for seismic experiments on all major planetary bodies of the solar system. We discuss scientific goals in accordance with the Decadal survey for planetary science and astrobiology and the ESA Voyage 2050 program as well as technical challenges and potential mission concepts, to answer the question: Where could we do seismology on other planets and why should we do it?

astro-ph.EP↗

arXiv2022

Low Frequency Marsquakes and Where to Find Them: Back Azimuth Determination Using a Polarization Analysis Approach

NASA's InSight mission on Mars continues to record seismic data over 3 years after landing, and to date, over a thousand marsquakes have been identified. With only a single seismic station, the determination of the epicentral location is far more challenging than on Earth. The Marsquake Service (MQS) produces seismicity catalogues from data collected by InSight and provides distance and back azimuth estimates when these can be reliably determined - when both are available these are combined to provide a location. Currently, MQS do not assign a back azimuth to the vast majority of marsquakes. In this work we develop and apply a polarization analysis method to determine the back azimuth of seismic events from the polarization of observed P and S-wave arrivals. The method is first applied to synthetic marsquakes, and then calibrated using a set of well-located earthquakes that have been recorded in Tennant Creek, Australia. We find that the back azimuth is estimated reliably using our polarization method. The same approach is then used for a set of high quality marsquakes recorded up to October 2021. We are able to estimate back azimuths for 24 marsquakes, 16 of these without MQS back azimuths. We locate most events to the east of InSight, in the general region of Cerberus Fossae.

physics.geo-ph↗

arXiv2020

On-deck seismology: Lessons from InSight for future planetary seismology

Before deploying to the surface of Mars, the short-period (SP) seismometer of the InSight mission operated on deck for a total of 48 hours. This dataset can be used to understand how deck-mounted seismometers can be used in future landed missions to Mars, Europa, and other planetary bodies. While operating on deck, the SP seismometer showed signals comparable to the Viking-2 seismometer near 3 Hz where the sensitivity of the Viking instrument peaked. Wind sensitivity showed similar patterns to the Viking instrument, although amplitudes on InSight were ~80% larger for a given wind velocity. However, during the low wind evening hours the instrument noise levels at frequencies between 0.1 and 1 Hz were comparable to quiet stations on Earth, although deployment to the surface below the Wind and Thermal Shield lowered installation noise by roughly 40 dB in acceleration power. With the observed noise levels and estimated seismicity rates for Mars, detection probability for quakes for a deck-mounted instrument are low enough that up to years of on-deck recordings may be necessary to observe an event. Because the noise is dominated by wind acting on the lander, though, deck-mounted seismometers may be more practical for deployment on airless bodies, and it is important to evaluate the seismicity of the target body and the specific design of the lander. Detection probabilities for operation on Europa reach over 99% for some proposed seismicity models for a similar duration of operation if noise levels are comparable to low-wind time periods on Mars.

physics.geo-ph↗

arXiv2019

Seismic Signals from Waves on Titan's Seas

Seismology is the main tool for inferring the deep interior structures of Earth and potentially also of other planetary bodies in the solar system. Terrestrial seismology is influenced by the presence of the ocean-generated microseismic signal, which sets a lower limit on the earthquake detection capabilities but also provides a strong energy source to infer the interior structure on scales from local to continental. Titan is the only other place in the solar system with permanent surface liquids and future lander missions there might carry a seismic package. Therefore, the presence of microseisms would be of great benefit for interior studies, but also for detecting storm-generated waves on the lakes remotely. We estimated the strength of microseismic signals on Titan, based on wind speeds predicted from modeled global circulation models interior structure. We find that storms of more than 2 m/s wind speed, would create a signal that is globally observable with a high-quality broadband sensor and observable to a thousand kilometer distance with a space-ready seismometer, such as the InSight instruments currently operating on the surface of Mars.

astro-ph.EP↗

arXiv2017

Seismic wave propagation in icy ocean worlds

Seismology was developed on Earth and shaped our model of the Earth's interior over the 20th century. With the exception of the Philae lander, all in situ extraterrestrial seismological effort to date was limited to other terrestrial planets. All have in common a rigid crust above a solid mantle. The coming years may see the installation of seismometers on Europa, Titan and Enceladus, so it is necessary to adapt seismological concepts to the setting of worlds with global oceans covered in ice. Here we use waveform analyses to identify and classify wave types, developing a lexicon for icy ocean world seismology intended to be useful to both seismologists and planetary scientists. We use results from spectral-element simulations of broadband seismic wavefields to adapt seismological concepts to icy ocean worlds. We present a concise naming scheme for seismic waves and an overview of the features of the seismic wavefield on Europa, Titan, Ganymede and Enceladus. In close connection with geophysical interior models, we analyze simulated seismic measurements of Europa and Titan that might be used to constrain geochemical parameters governing the habitability of a sub-ice ocean.

physics.geo-ph↗

arXiv2017

Expected seismicity and the seismic noise environment of Europa

Seismic data will be a vital geophysical constraint on internal structure of Europa if we land instruments on the surface. Quantifying expected seismic activity on Europa both in terms of large, recognizable signals and ambient background noise is important for understanding dynamics of the moon, as well as interpretation of potential future data. Seismic energy sources will likely include cracking in the ice shell and turbulent motion in the oceans. We define a range of models of seismic activity in Europa's ice shell by assuming each model follows a Gutenberg-Richter relationship with varying parameters. A range of cumulative seismic moment release between $10^{16}$ and $10^{18}$ Nm/yr is defined by scaling tidal dissipation energy to tectonic events on the Earth's moon. Random catalogs are generated and used to create synthetic continuous noise records through numerical wave propagation in thermodynamically self-consistent models of the interior structure of Europa. Spectral characteristics of the noise are calculated by determining probabilistic power spectral densities of the synthetic records. While the range of seismicity models predicts noise levels that vary by 80 dB, we show that most noise estimates are below the self-noise floor of high-frequency geophones, but may be recorded by more sensitive instruments. The largest expected signals exceed background noise by $\sim$50 dB. Noise records may allow for constraints on interior structure through autocorrelation. Models of seismic noise generated by pressure variations at the base of the ice shell due to turbulent motions in the subsurface ocean may also generate observable seismic noise.

astro-ph.EP↗