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We have analyzed 14 impact melt glass samples, covering the compositional range from highly felsic to mafic/basaltic, as part of our effort to provide mid-infrared spectra (7–14 µm) for MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer), an instrument onboard of the ESA/JAXA BepiColombo mission. Since Mercury was exposed to many impacts in its history, and impact glasses are also common on other bodies, powders of tektites (Irghizite, Libyan Desert Glass, Moldavite, Muong Nong, Thailandite) and impact glasses (from the Dellen, El'gygytgyn, Lonar, Mien, Mistastin, and Popigai impact structures) were analyzed in four size fractions of (0–25, 25–63, 93–125 and 125–250 µm) from 2.5 to 19 µm in bi-directional reflectance. The characteristic Christiansen Feature (CF) is identified between 7.3 µm (Libyan Desert Glass) and 8.2 µm (Dellen). Most samples show mid-infrared spectra typical of highly amorphous material, dominated by a strong Reststrahlen Band (RB) between 8.9 µm (Libyan Desert Glass) and 10.3 µm (Dellen). Even substantial amounts of mineral fragments hardly affect this general band shape. Comparisons of the SiO2 content representing the felsic/mafic composition of the samples with the CF shows felsic/intermediate glass and tektites forming a big group, and comparatively mafic samples a second one. An additional sign of a highly amorphous state is the lack of features at wavelengths longer than ∼15 µm. The tektites and two impact glasses, Irghizite and El'gygytgyn respectively, have much weaker water features than most of the other impact glasses. For the application in remote sensing, spectral features have to be correlated with compositional characteristics of the materials. The dominating RB in the 7–14 µm range correlates well with the SiO2 content, the Christiansen Feature shows similar dependencies. To distinguish between glass and crystalline phases of the same chemical composition, a comparison between CF the SCFM index (SiO2/(SiO2 + CaO + FeO + MgO)) ( Walter and Salisbury [1989 ] J. Geophys. Res., 94, 9203–9213) is useful, if chemical compositional data are also available.

Feldspars are major components of terrestrial planetary surfaces. For future space application and the setup of a comprehensive reference database, Na- and K-rich alkali feldspars, NaAlSi3O8 – KAlSi3O8, have been investigated by infrared reflectance spectroscopy. We related the feldspar spectra to the chemical composition and state of Al,Si order/disorder. The infrared measurements were analyzed with respect to band shifts and peak shapes using the autocorrelation function. Natural samples served as starting materials. Some samples were treated by the alkali exchange method to produce pure end-members, which were then heated to generate various states of Al,Si disorder. X-ray diffraction (XRD) methods served to determine the Al,Si distribution. Our autocorrelation allowed to differentiate between the compositional and the order/disorder influences seen in the spectra in the wavelength range between 7 μm up to 14 μm (1429 cm− 1 to 714 cm− 1). Space missions often analyze the surfaces of planetary bodies using remote sensing. Therefore, our results are essential to characterize and distinguish alkali feldspars on the surfaces of terrestrial planetary bodies like Mercury., Deutsches Zentrum für Luft- und Raumfahrt https://doi.org/10.13039/501100002946

The imaging spectrometer MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) is part of the payload of ESA/JAXA’s BepiColombo mission, launched in 2018 [1,2]. The instrument consists of an IR-spectrometer and radiometer, which will observe the surface in the wavelength range of 7–14µm and 7–40μm, respectively. In preparation of the mission, we are investigating Mercury analog minerals at the IRIS (Infrared and Raman for Interplanetary Spectroscopy) laboratory of the Institut für Planetologie at the Westfälische Wilhelms-Universität Münster. We study typical rock-forming minerals, e.g., pyroxenes, olivines, and feldspars, as well as mineral mixtures.Here we present results of a deconvolution model used to quantify mineral specific abundances of mineral mixtures [4,5]. Planetary surfaces are composed of a variety of different minerals, therefore the obtained spectral data reflects a mixture of these minerals. In order to quantify the mineral abundances a non-linear unmixing model is necessary. Our model is based on the Hapke reflectance theory [6-8] and is applied to data obtained at the IRIS laboratory [9]. Results of olivine and pyroxene mixtures, as well as grain size mixtures, will be presented at the meeting.We used olivine (Fo91) from Dreiser Weiher, Germany, and pyroxene (En87) from Bamble, Norway and a range of mineral mixtures for IR measurements. Samples are sieved in grain size fractions of The pure pyroxene and olivine spectra clearly show characteristic Christiansen features and Reststrahlen bands for all applied geometries and increasing phase angles result in decreased intensities. The reflectance increases from pyroxene and pyroxene-rich mixtures to olivine and olivine-rich mixtures. Moreover, the olivine-rich mixtures exhibit more olivine reflectance features, compared to pyroxene-rich mixtures [11].Our studies of pyroxene grain size analysis focus on pyroxene mixtures of 50%fine/50%coarse and 30%fine/70%coarse material. Generally, the intensities increase with increasing grain sizes. The transparency feature is evident for small grain sizes and the 50%fine/50%coarse mixture.At IRIS laboratory, we will further investigate planetary analog material and their mineral mixtures applying various analytical techniques. With these data we are establishing a database that will enable the correct interpretation of MERTIS results. This work has been funded by DLR grant 50 QW 1701 in the framework of the BepiColombo mission. [1] Hiesinger H. et al. (2010) PSS58, 144-165. [2] Benkhoff J. et al. (2010) PSS58, 2-20. [3] Grumpe A. et al (2017) Icarus299, 1-14. [4] Rommel D. et al. (2017) Icarus284, 126-149. [5] Hapke B. (1981), JGR86(B4), 3039-3054. [6] Hapke B. (2002), Icarus157, 523-534. [7] Hapke B. (2012), 2ndCambr. Univ. Press., NY. [8] Bauch, K.E. et al. (2019) LPSC L, Abstract#2521. [9] Weber I. et al. (2019) LPSC L, Abstract#2326. [10] Weber, I. et al. (2020) LPSC LI, Abstract#1889.

In this thesis, methods are developed and studied for radar and laser altimetry to measure radial tidal deformations of planets and satellites. The thesis investigates further how the tidal measurement allows constraining the interior structure and rheologic properties of the bodies. A semi-analytical performance model for laser altimetry has been developed to predict probability of false detection and ranging accuracy. At cross-over locations of the ground tracks, which canbe derived from the spacecraft trajectory, the tidal deformation can be retrieved by a differential height measurement. With a known tidal potential at the time of the passes and a sufficient number of cross-over points, it is possible to solve for the tidal Love number h2. On this basis, the geodetic inversion of h2 is simulated for Mercury and the BepiColombo mission, with its BepiColombo Laser Altimeter (BELA). The measurement is affected by the high eccentricity of the spacecraft orbit and BELA's limited shot frequency (10 Hz), which leads to a large spot-to-spot distance and associated interpolation errors at the cross-over locations. The measurement of h2 is further complicated by only small variations of the tidal potential and by Mercury's slow rotation rate. The accuracy of h2 is predicted to be 0.14 (1-sigma) after two years in orbit. A comparable simulation has been performed for Ganymede, where significant higher radial amplitudes are expected. For the Ganymede Laser Altimeter (GALA), on board the Jupiter Icy Moons Explorer (JUICE), the predicted absolute accuracy for Ganymede's tidal Love number h2 is around 0.03 (1-sigma) after 132 days in a polar 500 km orbit. This result can be explained by higher tidal amplitudes, GALA's higher shot frequency (30 Hz), and by a more favorable distribution pattern of the measurable cross-over points. For radar, an equivalent method has been developed, analyzed, and applied to the Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON) on board the Europa Clipper mission. The measurement accuracy of the radar is estimated to be between 3 and 15 m. The main drivers are the signal to-noise ratio, which is heavily dependent on Europa's surface roughness, and Europa's dynamic ionosphere. As the Europa mission only involves a set of fast ybys limiting the orbit determination, a method has been conceived to solve for the spacecraft trajectory simultaneously with the tidal deformation. The expected h2 accuracy is between 0.04 and 0.17 (1-sigma). Further, it has been investigated how the h2 measurement allows constraining the interior structure of the bodies, eventually together with the tidal Love number k2. For Mercury, it has been shown that the h2/k2 ratio may set an upper bound on the inner core size. The ratio of both Love numbers allows for a stronger constraint on Mercury's core than other geodetic measurements, e.g., the libration amplitude. For Ganymede and Europa, the h2 measurement can confirm the existence of a global, subsurface ocean beneath the ice shell. Combined with k2, a constraint on the ice shell thickness to around 20 km can be provided via the linearcombination 1 + k2 - h2. The largest ambiguity in this measurement is the rheology of the ice., Die vorgelegte Dissertation entwickelt und untersucht Methoden der Radar- und Laseraltimetrie für die Messung radialer Gezeitendeformationen von Planeten und Monden. Sie untersucht außerdem, inwieweit die Gezeitenmessungen dazu beitragen, den inneren Aufbau und die rheologischen Eigenschaften der Körper zu bestimmen. Für die Laser Altimeter wurde ein semi-analytisches Modell entwickelt, welches für gegebene Kenngrößen des Instruments, die Detektionswahrscheinlichkeit und Messgenauigkeit von Einzelschüssen ermittelt. Unter Berücksichtigung der Bahn der Raumsonde im Orbit lassen sich Kreuzungspunkte errechnen, an denen, durch Interpolation zwischen den Einzelschüssen, eine differenzielle Höhenmessung erfolgen kann. Mit dem bekannten Gezeitenpotential zu den jeweiligen Zeitpunkten einer Vielzahl von Messungen, lässt sich so die Lovesche Zahl h2 bestimmen. Auf dieser Grundlage wurde die geodätische Bestimmung von h2 für den Merkur und die Mission BepiColombo mit dem BepiColombo Laser Altimeter (BELA) simuliert. Zu berücksichtigen sind die hohe Bahn-Exzentrizität der Raumsonde und die begrenzte Schussfrequenz von BELA (10 Hz), wodurch die Abstände zwischen den Einzelschüssen und Interpolationsfehler an den Kreuzungspunkten groß werden. Messungen von h2 auf dem Merkur werden zudem erschwert durch die nur geringen Schwankungen der Gezeitenverformung im erzeugenden Potential, sowie die langsame Rotation des Planeten. Die erwartete Genauigkeit der h2 Messung mit BELA, nach einer zweijährigen Mission, ist mit 0.14 (1-sigma) abgeschätzt. Zum Vergleich wurde eine ähnliche Simulation für Ganymed erstellt, für den eine deutlich höhere Gezeitenamplitude erwartet wird. Für das Ganymede Laser Altimeter (GALA), auf der Mission Jupiter Icy Moons Explorer (JUICE), liegt die erwartete Genauigkeit für h2 bei ca. 0.03 (1-sigma) nach 132 Tagen in einem polaren 500 km Orbit. Dieser Wert gründet zum einen auf den höheren Gezeitenamplituden, zum anderen aber auch auf der höheren Schussfrequenz von GALA (30 Hz) und der vorteilhafteren Verteilung der messbaren Kreuzungspunkte. Für das Radaraltimeter wurde ebenfalls ein Modell für die Abschätzung der Messgenauigkeit und ein Verfahren zur Gezeitenmessung entwickelt, speziell zugeschnitten auf das "Radar for Europa Assessment and Sounding: Ocean to Near-surface" (REASON) auf der Europa Clipper Mission. Der Messfehler des Radars wird auf 3 bis 15 m (1-sigma) bestimmt, in Abhängigkeit von Signalstärke und Rauschen, wobei beide Terme stark von der Rauhigkeit der Oberflächen abhängen. Ein limitierender Faktor der Messungen ist weiterhin der Einfluss von Europas dynamischer Ionosphäre. Da sich die Mission auf schnelle Vorbeiflüge am Jupitermond beschränkt und nach jetziger Planung Bahninfromationen nur mit relativ großen Ungenauigkeiten vorliegen werden, wurde ein Verfahren entwickelt, bei dem - gleichzeitig zu den Gezeitendeformationen - Bahnmodelle unter Zuhilfenahme von Kreuzungspunkten der Bodenspuren des Radars bestimmt wurden. Die zu erwartende, absolute Genauigkeit für h2 liegt zwischen 0.04 und 0.17 (1-sigma). Außerdem wurde untersucht, inwieweit die h2 Bestimmung, ggf. zusammen mit der Messung der Gezitenpotential Love-Zahl k2, zu Modellen des inneren Aufbaus der Körper beitragen kann. Für Merkur wurde gezeigt, dass das Verhältnis h2/k2 Auskunft über den Radius des festen, inneren Kerns geben kann. Das Verhältnis beider Lovescher Zahlen stellt eine stärkere Randbedingung für den Aufbau des Merkurkerns dar als andere geodätische Messungen, wie zum Beispiel die Messung der Librationsamplitude. Für Ganymed und Europa kann die h2 Messung einen Beweis für die Existenz eines globalen Ozeans unter der äußeren Eisdecke liefern. Zusammen mit der k2 Messung kann mittels der Linearkombination 1+k2 - h2 die Mächtigkeit der Eisdecke auf ca. 20 km bestimmt werden. Die größte Unsicherheit in der Eisdickenbestimmung ist auf die Eisrheologie zurück zu führen.