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Karakostas, Foivos

Publications and source records attributed to Karakostas, Foivos.

5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Listening for the Landing: Seismic Detections of Perseverance's Arrival at Mars With InSight

The entry, descent, and landing (EDL) sequence of NASA's Mars 2020 Perseverance Rover will act as a seismic source of known temporal and spatial localization. We evaluate whether the signals produced by this event will be detectable by the InSight lander (3,452 km away), comparing expected signal amplitudes to noise levels at the instrument. Modeling is undertaken to predict the propagation of the acoustic signal (purely in the atmosphere), the seismoacoustic signal (atmosphere-to-ground coupled), and the elastodynamic seismic signal (in the ground only). Our results suggest that the acoustic and seismoacoustic signals, produced by the atmospheric shock wave from the EDL, are unlikely to be detectable due to the pattern of winds in the martian atmosphere and the weak air-to-ground coupling, respectively. However, the elastodynamic seismic signal produced by the impact of the spacecraft's cruise balance masses on the surface may be detected by InSight. The upper and lower bounds on predicted ground velocity at InSight are 2.0 × 10 -14 and 1.3 × 10 -10 m s -1 . The upper value is above the noise floor at the time of landing 40% of the time on average. The large range of possible values reflects uncertainties in the current understanding of impact-generated seismic waves and their subsequent propagation and attenuation through Mars. Uncertainty in the detectability also stems from the indeterminate instrument noise level at the time of this future event. A positive detection would be of enormous value in constraining the seismic properties of Mars, and in improving our understanding of impact-generated seismic waves.

58 GEOSCIENCES↗
DOE OSTI2020

A New Crater Near InSight: Implications for Seismic Impact Detectability on Mars

A new 1.5 m diameter impact crater was discovered on Mars only ~40 km from the InSight lander. Context camera images constrained its formation between 21 February and 6 April 2019; follow-up High Resolution Imaging Science Experiment images resolved the crater. During this time period, three seismic events were identified in InSight data. In this paper, we derive expected seismic signal characteristics and use them to evaluate each of the seismic events. However, none of them can definitively be associated with this source. Atmospheric perturbations are generally expected to be generated during impacts; however, in this case, no signal could be identified as related to the known impact. Using scaling relationships based on the terrestrial and lunar analogs and numerical modeling, we predict the amplitude, peak frequency, and duration of the seismic signal that would have emanated from this impact. The predicted amplitude falls near the lowest levels of the measured seismometer noise for the predicted frequency. Hence, it is not surprising this impact event was not positively identified in the seismic data. Finding this crater was a lucky event as its formation this close to InSight has a probability of only ~0.2, and the odds of capturing it in before and after images are extremely low. We revisit impact-seismic discriminators in light of real experience with a seismometer on the Martian surface. Using measured noise of the instrument, we revise our previous prediction of seismic impact detections downward, from ~a few to tens, to just ~2 per Earth year, still with an order of magnitude uncertainty.

58 GEOSCIENCES↗
DOE OSTI2019

InSight, 3D modeling CTX impact [Slides]

This technical report contains a set of slides intended for the Insight Impact Working Group. It discusses how the project is working on benchmarking between SPECFEM3D and AXISEM, how a hypothesis is needed in relation to the data on the thickness of the regolith layer, and the need to develop a 3D model of scattering.

58 GEOSCIENCES↗
DOE OSTI2018

Inversion of Meteor Rayleigh Waves on Earth and Modeling of Air Coupled Rayleigh Waves on Mars

Meteor impacts and/or meteor events generate body and surface seismic waves on the surface of a planet. When meteoroids burst in the atmosphere, they generate shock waves that subsequently convert into acoustic waves in the atmosphere and seismic waves in the ground. This effect can be modeled as the amplitude of Rayleigh and other Spheroidal modes excitation, due to atmospheric/ground coupling effects. First, an inversion of the seismic source of Chelyabinsk superbolide is performed. We develop an approach in order to model a line source in the atmosphere, corresponding to the consecutive generation of shock waves by the interaction with the atmosphere. The model is based on the known trajectory. We calculate the synthetic seismograms of Rayleigh waves associated with the event by the summation of normal modes of a model of the solid part and the atmosphere of the planet. Through an inversion technique based on singular value decomposition, we perform a full Rayleigh wave inversion and we provide solutions for the moment magnitude. SEIS will likely detect seismic waves generated by impacts and the later might be further located by remote sensing differential processing. In the case of Mars, we use the same method to obtain waveforms associated with impacts on the planetary surface or in low altitudes in the Martian atmosphere. We show that the contribution of the fundamental spheroidal solid mode is dominating the waveforms, compared to that of the first two overtones. We perform an amplitude comparison and we show that small impactors (diameter of 0.5 to 2 m), can be detected by the SEIS VBB seismometer of InSight mission, even in short epicentral distances, in the higher frequencies of the Rayleigh waves. We perform an analysis based on impact rate estimations and we calculate the number of detectable events of 1 meter diameter meteor impacts to be 6.7 to 13.4 per 1 Martian year for a Q=500 .

79 ASTRONOMY AND ASTROPHYSICS↗