Many scientists who study the tectonic inventory of planetary bodies were initially trained as Earth-based structural geologists. In this context, a comparative approach of methodology in planetary and terrestrial tectonics is helpful with regards to what works and what does not. The methodological approaches are subdivided into (i) nature, (ii) experiment, (iii) modeling.

(i) Acquisition of data in the field, which provides the ground truth for the Earth geologist, is still largely impossible on planetary bodies, at least nowadays, or limited to small regions with the help of rovers. Likewise, microstructural analysis – an important branch in structural geology - is not possible, or is limited to meteorites and the few mission return samples. Those deficits are compensated by remote sensing data. Their quality, spatial resolution and coverage varies greatly, but is steadily improving, and sometimes reaches decimeter resolution (Mars). Most data are sufficient for tectonic work, and sometimes allow the measurement of strike and dip of layers and faults and even enable the construction of cross-sections. The outcrop conditions are usually better on planetary surfaces and the context between geomorphology and tectonics is apparent and similar to neotectonics on Earth due to lower resurfacing rates. Determination of surface ages using crater size-frequency-distributions also allows dating of tectonic processes, although this approach is much less sensitive than Earth-based methods. The exploration of the subsurface by drilling and geophysical surveying is strongly limited in planetary tectonics (e.g., GPR). Detailed seismic surveys cannot be performed yet. However, geophysical measurements (gravity and magnetic field) are often available, which at least allow to decipher crustal-scale processes.

(ii) Rock-mechanical experiments are key for determining the rheology of crustal rocks in planetary and terrestrial tectonics. However, some of the physical boundary conditions to be considered in planetary tectonics are less well constrained and cover a larger range of temperatures. In planetary tectonics, basalts and various types of ices play a central role, which receive little attention in terrestrial structural geology. In tectonic analogue modeling, the parameter gravity poses a challenge. Gravity affects the scaling relationships of faults (displacement–length–width) but gravity can only be modified in centrifuges, space, or parabola flights.

(iii) The mathematical simulation of deformation processes on planetary bodies works in the same way as for terrestrial processes by discretization of the continuum. It is easily adaptable but the systems to be modeled are sometimes underdetermined with regard to the parameter space.

To conclude the methodological tools in planetary tectonics are somewhat limited compared to those applied in terrestrial structural geology. Analogue field studies in specific terrestrial environments (e.g., Svalbard, Iceland) are aimed to compensate the missing field acquisition in planetary tectonics. Despite these limitations, planetary tectonics is a fascinating endeavor that allows us to better understand the dynamic geological processes and narrow down the physical boundary conditions of planetary bodies. With the ever improving remote sensing data by recent and upcoming missions (e.g., BepiColombo, EnVision, Veritas, Juice) the field of planetary tectonics will continue to gain importance.

How to cite: Kenkmann, T.: Planetary tectonics versus Earth tectonics: a comparative approach of working principles, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11631, https://doi.org/10.5194/egusphere-egu23-11631, 2023.

The InSight mission collected an astounding seismic dataset from Mars during more than four years (1450 sols) of operation until it was retired on 21 December 2022.

The Marsquake Service MQS detected more than 1300 events of seismic origins. Two of these events (S1000a and S1094b) were later confirmed as distant impacts (Figure 1), with magnitudes of M_W^Ma=4.0 and 4.2 and crater diameters of 130 and 150 m, respectively. Finally, the largest marsquake (S1222a, M_W^Ma=4.6) that occurred during InSight's lifetime was recorded on May 4, 2022.

Here, we present the current understanding of the Martian seismicity and the different types of events we observed on Mars, based on the data collected over the whole mission.

Low-frequency (LF) and broadband (BB)
The LF family of events include energy predominantly below 1 Hz. They are similar to teleseismic events observed on Earth, and clear P and S waves are often identified. The hypocenter is known for about half of the recorded LF-BB events, owing to the difficulty of determining back-azimuth and in some cases also distance for the smaller events. The following elements are now understood:

• Seismicity appears to be located only in few spots around Mars (Figure 2) and no tectonic events were located within 25° from the InSight station.
• A large number of LF-BB events are located 26–30° from the station, interpreted to be associated with the active dynamics of the volcanic Cerberus Fossae area.
• A group of events show only a weak S-wave energy and are aligned using the P-wave and length of its coda to around 46°. Their tectonic origin is yet unknown.
• A few events are located around 60° with relatively emergent P- and S-wave energy.
• Two large events (S0976a and S1000a) lie beyond the core shadow and have PP and SS phases; S0976a in the Valles Marineris region 146° away from InSight, and S1000a as the result of a meteoritic impact.
• A number of events of uncertain location are clustered in the same distance, around 100-120° distance.
• LF events have the largest magnitudes with S1222a reaching M_W^Ma=4.6 and a few others at or above M_W^Ma=3.5.

High-frequency (HF)
The HF family of events are predominantly at and above the 2.4 Hz, local subsurface resonance. The HF events have magnitudes below M_W^Ma 2.5 and originate from a distance range of 25–30°, likely a single area in the central Cerberus Fossae region, as very shallow events associated to active volcanic dykes. 

Very high frequency (VF):
A small number of HF events are characterized by higher frequency content, up to 20–30 Hz with a notable amplification on the horizontal components at very high frequency, and are termed VF events. The amplification is plausibly explained by the local subsurface structure. These events are observed only close to the lander. Remote imaging of recent craters and the presence of a distinctive acoustic signal confirmed that the closest events were produced by meteoric impacts. Investigations are being conducted to understand if other VF events can be confirmed as impacts, too.

How to cite: Stähler, S. C., Ceylan, S., Giardini, D., Clinton, J., Kim, D., Khan, A., Zenhäusern, G., Dahmen, N., Duran, C., Horleston, A., Kawamura, T., Charalambous, C., Knapmeyer, M., Garcia, R., Lognonné, P., Panning, M., Pike, W. T., and Banerdt, W. B.: Review of the seismicity on Mars, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7383, https://doi.org/10.5194/egusphere-egu23-7383, 2023.

After more than 4 Earth years of operation 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 martian interior structure of the crust, mantle, and core. 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. Especially for the observed overtones and multi-orbiting surface waves in S1222a, we find the depth sensitivity expands down to the uppermost mantle close to 90 km. Furthermore, our 3D wavefield simulations show significantly broadened volumetric sensitivity of the higher-orbit surface waves. These new constraints obtained by our surface wave analyses provide an important opportunity not only to refine and verify our previous radially symmetric models of the planet’s interior structure but also to improve understanding of seismo-tectonic environments on Mars. Here, we summarize our recent effort in the analyses of surface waves on Mars and discuss the inferred crustal property and its global implications.

How to cite: Kim, D., Stähler, S., Boehm, C., Lekic, V., Giardini, D., Ceylan, S., Clinton, J., Davis, P., Duran, C., Khan, A., Knapmeyer-Endrun, B., Maguire, R., Panning, M., Plesa, A.-C., Schmerr, N., Wieczorek, M., Zenhäusern, G., Lognonné, P., and Banerdt, W.: Crustal structure observed by the InSight mission to Mars, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12524, https://doi.org/10.5194/egusphere-egu23-12524, 2023.

Analysis of data from the seismometer SEIS on NASA’s InSight mission has by now provided a wealth of information on the crustal structure of Mars, both beneath the lander and at other locations on the planet. Here, we collect the P- and S-wave velocity information for kilometer-scale crustal layers available up to now and compare it to predictions by rock physics models to guide the interpretation in terms of crustal lithology.

Modeling is performed based on the Hertz-Mindlin model for un- or poorly consolidated sediments, Dvorkin and Nur’s cemented-sand model for consolidated sediments and Berryman’s self-consistent approximation to simulate cracked rocks. Considered lithologies include basalt, andesite, dacite, kaolinite, and plagioclase, and cementation due to calcite, gypsum, halite and ice. We use Gassmann fluid substitution to study the effect of liquid water instead of atmosphere filling the pores or cracks.

Below the lander, available constraints are based on Ps-receiver functions and vertical component autocorrelations for SV- and P-wave velocities, whereas SH-reflections and SsPp phases provide additional information on SH- and P-wave velocities in the uppermost 8-10 km, respectively. SS and PP precursors at the bouncing point of the most distant marsquake contain information on crustal velocities at a near-equatorial location far from InSight. Surface wave observations from two large impacts as well as the largest marsquake recorded by InSight provide average crustal velocities along their raypaths, which are distinct from the body wave results.

The subsurface structure beneath the lander can be explained by 2 km of either unconsolidated basaltic sands, clay with a low amount (2%) of cementation, or cracked rocks (e.g. basalts with at least 12% porosity). Within the range of lithologies considered, the seismic velocities can neither be explained by intact rocks, nor rocks with completely filled pores, e.g. by ice, nor by fluid-saturated rocks. Below, down to a depth of about 10 km beneath InSight, both P- and SV-wave velocities are consistent with fractured basaltic rocks or plagioclase of at least 5% porosity, depending on crack aspect ratios. About 10% of that porosity needs to have a preferred orientation to explain the observed anisotropy. For porosities exceeding 12%, the measured velocities would also be consistent with water-saturated rocks. The transition to higher velocities at about 10 km depth beneath InSight can be modeled by more intact material, i.e. a porosity reduction by 50% compared to the layer above, which can be achieved by either cementation or a lower initial porosity.

The SV-velocities derived by surface waves down to 25-30 km depth, averaging over a large part of Mars, are consistent with basalts of a porosity of less than 5% or nearly intact plagioclase. They could also be explained by rocks with a higher porosity if pores are filled by ice, but that is unlikely for the whole depth range considered. The velocities at larger depth, i.e. below about 20 km beneath InSight and 25-30 km along the surface wave paths, are consistent with intact basalt.

How to cite: Knapmeyer-Endrun, B., Li, J., Kim, D., Plesa, A.-C., McLennan, S., Hauber, E., Joshi, R., Shi, J., Beghein, C., Wieczorek, M., Panning, M. P., Lognonne, P., and Banerdt, W. B.: Constraints on Martian Crustal Lithology from Seismic Velocities by InSight, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15069, https://doi.org/10.5194/egusphere-egu23-15069, 2023.

Geological cartography and structural analysis are essential for understanding Mercury’s geological history and tectonic processes. This work focuses on the Michelangelo quadrangle (H-12), located at latitudes 22.5°S-65°S and longitudes 180°E-270°E. We present the preliminary results derived from the photointerpretation of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Mercury Dual Imaging System (MDIS) imagery. The first geological map of this quadrangle was produced by [1] at 1:5M scale using Mariner 10 data. The Authors identified and mapped five classes of craters and four main plain units. The present study is a contribution to the 1:3M geological map series, planned to identify targets to be observed at high resolution during the ESA-JAXA BepiColombo mission [2]. Geologic contacts and linear features were drawn at a mapping scale between 1:300,000 and 1:600,000.

We mapped tectonic structures and geological contacts using the MDIS derived basemaps, with an average resolution of 166 m/pixel. Linear features are subdivided into large craters (crater rim diameter > 20 km), small craters (5 km < crater rim diameter < 20 km), subdued or buried craters, certain or uncertain thrusts, certain or uncertain faults, wrinkle ridges and irregular pits. Geological contacts, mapped as certain or approximate, delimit the geological units grouped into three classes of crater materials (c1-c3) based on degradation degree, and plains (smooth, intermediate and intercrater plains).

We identified two main regional thrust systems with a NW-SE strike. The presence of old impact basins influenced the arrangement of faults because of the frequent reactivation of crater rims. Beethoven basin (20.8°S–236.1°E) and Vincente-Yakovlev basin (52.6°S–197.9°E) represent clear examples of tectonic inversion. The reactivation structures [3] are the result of previous impact-related normal faults that were reactivated due to the compressive tectonic regime deriving from the global contraction. Similarly to the Victoria quadrangle (H-02) [4], in the Michelangelo quadrangle the NW-SE system borders the southwestern edge of the high-Mg region, although the accuracy of XRS data at these latitudes is much lower than the accuracy of data acquired in the Northern hemisphere. We noted the frequent interaction between volcanic vents and thrusts, as already suggested by [5]. These vents are often located along lobate scarps or in soft-linkage zones between thrust segments. Indeed, as also observed on Earth, curved thrust surfaces or linkage areas between fault segments represent weakness zones acting as preferential pathways for magma uprising.

Acknowledgements: We gratefully acknowledge funding from the Italian Space Agency (ASI) under ASI-INAF agreement 2017-47-H.0.

References:

[1] Spudis P. D. and Prosser J. G., (1984). U.S. Geological Survey, IMAP 1659.

[2] Galluzzi et al. (2021). LPI Contrib., 2610.

[3] Fegan E. R. et al., (2017). Icarus, 288, 226-234.

[4] Galluzzi et al. (2019). Journal of Geophysical Research Planets, 124, 2543-2562.

[5] Thomas R. J. et al., (2014). Journal of Geophysical Research Planets, 119, 2239-2254.

How to cite: Buoninfante, S., Galluzzi, V., Ferranti, L., Milano, M., and Palumbo, P.: Geological mapping and structural analysis of the Michelangelo (H-12) quadrangle of Mercury, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5378, https://doi.org/10.5194/egusphere-egu23-5378, 2023.

Meteorite impact is recognized as a fundamental geological process of the solar system. Although mechanisms of large impact cratering have been studied intensely, mostly by numerical modelling, an outstanding problem concerns long-term crater modification, which operates on time scales of tens of thousands of years after impact. Localized deformation in the form of radial and concentric floor fractures (FFCs) are known from large craters on all terrestrial planets. On Earth, we can observe the occurrence of radial and concentric impact melt rock dikes in the eroded basement of large impact structures, such as Sudbury (Canada) and Vredefort (South Africa). Two mechanisms were proposed in the past to explain the formation of FFCs: the intrusion and inflation of igneous bodies below the crater floor and long-term isostatic re-equilibration of impacted target rocks. Using two-layer analogue experiments scaled to physical conditions on Earth, we explore to what extent isostatic re-equilibration of crust may account for the observed dike and fracture patterns of FFCs.

The structural evolution of model upper crust was examined for a variety of initial depths and diameters of crater floors. The crater diameter-to-depth ratio was scaled according to numerical models for average continental crust. Specifically, a tank, 80cm by 80cm in size, was filled with PDMS, representing the viscous middle and lower crust and granular material, simulating the brittle upper crust. Moreover, we introduce a method, which allowed us to generate any shapes of model impact crater floors.

The experiment surfaces were monitored with a 3D digital image correlation system allowing us to quantify key parameters, such as surface motion as well as the distribution and evolution of surface strain. The results of our scale models enabled us to quantify the duration, geometry and distribution of brittle deformation of upper crust. Most importantly, the analogue experiments provided, for the first time, a quantitative relationship between diameter, depth and fracture geometry of crater floors.

Our results indicate that FFCs are caused by long-term uplift of the crater floor, compensated by crustal flow toward the crater center. Such radial convergent flow generated radial and concentric dilation fractures. Crater floor uplift is accompanied by long-wavelength subsidence of the crater periphery on the order of 50 minutes, amounting to some 3000 years in nature. The formation of radial versus concentric fractures depends on the ratio between crater diameter and crater depth and, hence, is controlled by isostacy and crustal strength. The geometry and distribution of fractures in analogue experiments are strikingly similar to the geometry of impact melt rock dikes at Sudbury and Vredefort.

How to cite: Eisermann, J. O. and Riller, U.: Long-term crustal modification of large terrestrial meteorite impact structures: insights from scaled analogue experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1295, https://doi.org/10.5194/egusphere-egu23-1295, 2023.

On terrestrial bodies other than Earth, volcanism and magmatism are often related to impact craters. On Venus, RADAR observations of the surface have revealed two categories of craters: bright-floored and dark-floored craters, the latter being interpreted as partial filling of the crater by lava. On the Moon, volcanic deposits and evidence of pyroclastic activities are also frequently located within impact craters, especially within floor-fractured craters. These craters are characterized by uplifted, fractured floors resulting from underlying shallow magmatic intrusions. 

The elastic stress induced within the crust by a crater excavation indeed has two competitive effects. It induces a depressurization of the encasing elastic medium, which provides a driving pressure to the magma. This allows its ascent through the crust despite the magma’s negative buoyancy and explains why the magma tends to erupt preferentially within impact craters (Michaut and Pinel, 2018). However, the state of stress below the unloading is such that the minimum compressive stress is vertical at the unloading axis, which tends to horizontalize the dyke intrusion, therefore favoring magma storage below a crater at the expense of eruption.

We calculated the stress fields generated by surface unloadings of different radius on top of a semi-infinite half-space and use them in numerical mechanical models of magma ascent (Maccaferri et al, 2011) to evaluate the path followed by a dyke below a crater. We identify several types of behavior (ascent to the crater floor, horizontalization of the intrusion, storage at depth, ascent to the planet surface) depending on the physical properties of the magma and crust, as well as on the dyke and crater unloading characteristics. We draw a regime diagram for magma ascent below craters as a function of two characteristic dimensionless numbers depending on these different physical parameters.

Our results show that magma ascent to the crater interior requires relatively small density contrasts between the crust and magma and rather small crustal thicknesses as opposed to dyke horizontalization that results from larger crust-magma density contrasts and crustal thicknesses. Furthermore, on the Moon, craters are considerably deeper than on Venus, leading to a larger dimensionless deviatoric stress below a crater of a given radius, favoring dyke horizontalization and storage. This well explains why the magma tends to store as horizontal intrusions below floor-fractured craters on the Moon while it tends to erupt on the floor of dark-floored craters on Venus.

ACKNOWLEDGMENT: This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No. 101001689).

How to cite: Le Contellec, A., Michaut, C., Maccaferri, F., and Pinel, V.: A comparative study of magma ascent and storage below impact craters on terrestrial planets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3108, https://doi.org/10.5194/egusphere-egu23-3108, 2023.

Floors of impact craters on rocky planetary bodies in our Solar System are often fractured and bulged. Such deformation features are thought to form by the ascent of impact-generated magma and the inflation of laccolith-shaped magma bodies at a shallow depth below the crater floor. Only the final surface deformation features can be observed from space, and so modeling is the only manner to understand controls on magma emplacement depth and volume, and deformation of the overlying rock. The existing models of crater floor fracturing mostly assume linearly elastic deformation of the shallow planetary crust and are not capable of simulating dynamic opening and propagation of fractures. In contrast, magma-induced deformation on Earth often displays non-elastic deformation features. This mismatch between the realistic mechanical response of planetary crust to magma intrusion and the one assumed by numerical models leads to significant inaccuracies in the modeled magma intrusion characteristics. This has important consequences for volcanic unrest monitoring on Earth and our understanding of structural deformation generated by volcanism throughout the Solar System.

We propose a new two-dimensional (2D) Discrete Element Method (DEM) approach to model dynamic fracturing and displacement in a particle-based host medium during the simulated inflation of a laccolith intrusion. The model indicates highly discontinuous deformation and dynamic fracturing and visualizes the localization of subsurface strain. We explored the effect of different gravitational conditions on the Moon, Mars and Earth on the spatial distribution of strain, stress, and fracturing above an inflating laccolith. Moreover, by systematically exploring a range of numerical parameters that govern host rock strength (bond cohesion, bond tensile strength, bond elastic modulus), and intrusion depth, we find complex controls of mechanical properties of planetary crust on the magma intrusion characteristics. Our models help understand fracture distribution patterns above laccolith intrusions in the shallow crust of rocky planetary bodies. We demonstrate that considering dynamic deformation and fracturing mechanisms in numerical models of magma-induced deformation is essential to better understand the formation of floor-fractured craters and the magmatic intrusions that lie beneath.

How to cite: Poppe, S., Morand, A., Cornillon, A., and Harnett, C.: Modeling of surface displacement and dynamic fracturing during magma emplacement at floor-fractured craters on the Moon and Mars, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16365, https://doi.org/10.5194/egusphere-egu23-16365, 2023.

Exploration of the Solar System has revealed that the surfaces of many icy bodies have been resurfaced by cryovolcanism: a process during which liquid and vapour are released from the surface into extremely cold and low pressure conditions. Water is one of the most commonly released liquids, and its stability and behavior under such conditions are thus of special interest. When exposed to low pressure, water boils, but it may also start freezing at the phase boundary due to evaporative cooling, as indicated by previous studies. There is only limited insight into how exactly the multiple phase transitions interact and what parameters control the dynamics of the system. To overcome this knowledge gap, we performed experiments in which we simulated the release of water at low pressure and low temperatures, such as could be encountered at local conditions at the  surface of an icy moon.

We used the Mars Simulation Chamber at The Open University (UK), in which a 60 x 40 cm container containing 5 and 17 litres of water was exposed to a reduced atmospheric pressure of ~4.5 mbar. Deionised water was mixed with a small amount of NaCl to achieve a salinity of 0.5% and was precooled to ~3.8°C to be close to the freezing point. Experiments were documented by video cameras situated around the container and the temperature inside the chamber and of the water was recorded by thermocouples.

At the beginning of each experiment, the atmospheric pressure was gradually reduced from ambient, which triggered boiling within the entire volume of water and evaporative cooling in its uppermost layer. This caused a gradual drop in the water temperature down to the freezing point, forming pieces of floating ice. The area where ice was present slowly grew and within timescales of a few minutes the entire surface of the container was covered with ice. However, the ice layer was broken into blocks with uneven surfaces. This was due to active boiling below the freezing layer of the water, with the intense formation of vapour bubbles which were capable of breaking and/or uplifting the ice. Once the fracture(s) developed, trapped vapour was released and deflation followed. Experimental results show that the process was more intense when larger amounts of water were used within the container, which significantly disrupted the freezing of water in those experiments and affected the final topography of the ice layer.

Our experiments show that water phase transition during effusive cryovolcanic eruptions are likely to be a highly complex process due to boiling causing major ice fracturing and the formation of topographical anomalies on the frozen surface.

How to cite: Brož, P., Patočka, V., Běhounková, M., Sylvest, M., and Patel, M.: The complexity of water freezing under reduced atmospheric pressure – insights on effusive cryovolcanism from laboratory experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6827, https://doi.org/10.5194/egusphere-egu23-6827, 2023.

During late spring 2022, using JWST aperture masking interferometry (ERS program #1373) and ground-based adaptive optics at the Keck telescope, we detected a new emission feature in Io’s Bosphorus Regio.  To pinpoint the location more accurately we followed up with the Large Binocular Telescope (LBT).  An accurate location will help determine if this feature is part of the Emakong Patera, is part of the Seth Patera, or is an independent volcano emitting lava from its own magma source.  Here we report on the LBT observation and data analysis.

On UT November 8th, 2022, we observed Io with the Large Binocular Telescope Interferometer (LBTI).  We acquired over 30,000 14ms frames over a period of 4 hours and parallactic angle coverage of approximately 70 degrees.  Data were acquired at both M-band (4.8 microns) and a wide band-pass spanning 2.2 to 5.0 microns.  As in past LBTI observations of Io (Conrad et al., 2015), we employed lucky fringing and frame selection to assemble a data set in which all frames are co-phased.  From these data (taken with a 23-meter baseline), we expect to determine the location of the feature to a degree of accuracy approximately three times greater than is possible with adaptive optics on 8-10 meter ground-based telescopes.

Image reconstruction is the preferred method for combining interferometer data for most science programs.  However, for science programs that a) require only accurate astrometry of point sources (all volcanoes in our data are unresolved at the observed wavelengths) and b) utilize data taken with a Fizeau interferometer like LBTI, we have developed a simpler method.  This method has two advantages.  First, the method preserves the spatial information available in the raw data.  Image reconstruction can sometimes shift the location of a measured source.  Second, with our method data taken at different wavelengths can still be combined to yield a single measurement.  Image reconstruction methods can only combine images which were all taken with the same filter.

The method is quite simple.  Because a Fizeau interferometer like LBTI provides complete images (i.e., the image is not reconstructed from visibilities and closure phases), we can take a one-dimensional cut through each fringe pattern as it appears in the raw data.  From each cut we compute a one-dimensional centroid to get a sub-pixel location along that baseline.  These results, taken at different baseline angles (the LBTI baseline rotates with parallactic angle) are statistically combined to produce a single location measurement.  This location is then mapped from detector space to a latitude and longitude on the sphere of Io.  The uncertainty in the measurement is reflected as two orthogonal error bars, one for latitude and one for longitude, computed by statistically combining the individual uncertainties of each cut.

This same method can be used to locate other volcanoes visible in our data set, which will be the subject of a future work.

How to cite: Conrad, A., Ertel, S., de Pater, I., Molter, N., Thatte, D., Sanchez-Bermudez, J., Sivaramakrishnan, A., Shields, J., de Kleer, K., Cooper, R., and Leisenring, J.: Locating a new emission source in Io’s Bosphorus Regio, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3625, https://doi.org/10.5194/egusphere-egu23-3625, 2023.