Characterizing the Dielectric Properties of Geologic and Asteroid Regolith Analogue Material for Improved Planetary Radar Interpretation

Planetary radar has provided an increasingly growing number of datasets on the inner terrestrial planets and near-Earth and main-belt asteroid populations in our solar system. Physical interpretation of radar data for inference of surface properties requires constraints on the constitutive parameters of the material making up a given surface. For many planetary surfaces, the response to electromagnetic radiation is described by the complex permittivity. In this thesis, the dielectric response of several geologic materials as a function of frequency and porosity was characterized to supplement radar data interpretation. Using the coaxial transmission line method, the complex permittivity of seven powdered mineral samples was measured. The samples were characterized for their composition and structure using a variety of laboratory techniques. A detailed review of the theory and use of electromagnetic mixing equations was presented to introduce the range of models available to describe the experimental permittivity measurements. A thorough analysis of the experiments was performed which showed that the Looyenga-Landau-Lifshitz and Bruggeman (Symmetric) mixing models described the experimental results with the highest accuracy. Measurement bias in the coaxial transmission line method highlighted in previous research due to inhomogeneities at the sample/conductor interface was modelled using these mixing theories, providing a way to correct for these effects post-measurement. The variation in the permittivity of the solid mineral grains between different minerals was characterized based on the grain density of the minerals, as well as the chemical composition. The experimentally verified mixing models were incorporated into an existing asteroid radar model and were used to calculate the porosity in the near-surface of seven asteroids visited by robotic spacecraft. Comparing with bulk porosity estimates, the asteroid radar model indicated the presence of a porous regolith covering on each asteroid that is similar in porosity to the upper 30 cm of the Moon. The results from this research are important for future radar studies, and the model predictions for asteroid surface properties will be tested with results from upcoming space missions visiting asteroids, such as NASAs OSIRIS-REx and JAXAs Hayabusa2 missions

Laboratory analysis of returned samples from the AMADEE-18 Mars analog mission

Between 01-28. February 2018, the Austrian Space Forum, in cooperation with the Oman Astronomical Society and research teams from 25 nations conducted the AMADEE-18 mission, a human-robotic Mars expedition simulation in the Dhofar region in the Sultanate of Oman As a part of the AMADEE-18 simulated Mars human exploration mission, the Remote Science Support team performed analysis of the Dhofar area, (Oman) in order to characterize it as a potential Mars analog site. The main motivation of this research was to study and register selected samples collected by the analog astronauts during the AMADEE-18 mission with laboratory analytical methods and techniques comparable to the techniques that will be used on Mars in the future. The 25 samples representing unconsolidated sediments obtained during the simulated mission were studied by using optical microscopy, Raman spectroscopy, X-ray diffraction, laser-induced breakdown spectroscopy, and laser-induced fluorescence. The principal results showed the existence of minerals and the detection of alteration processes related to volcanism, hydrothermalism, and weathering. The analogy between the Dhofar region and the Eridana Basin region of Mars is clearly noticeable, particularly as an analog for secondary minerals formed in a hydrothermal seafloor volcanic-sedimentary environment. The synergy between the techniques used in the present work provides a solid basis for the geochemical analyses and organic detection in the context of future human-robotic Mars expeditions. AMADEE-18 has been a prime test bed for geoscientific workflows with astrobiological relevance and has provided valuable insights for future space missions

Asteroids Inside Out: Radar Tomography

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Arecibon planetaarisen tutkan Maan lähiasteroidihavainnot: 2017 joulukuu - 2019 joulukuu

We successfully observed 191 near-Earth asteroids using the Arecibo Observatory's S-band planetary radar system from 2017 December through 2019 December. We present radar cross sections for 167 asteroids; circular-polarization ratios for 112 asteroids based on Doppler-echo-power spectra measurements; and radar albedos, constraints on size and spin periods, and surface-feature and shape evaluation for 37 selected asteroids using delay-Doppler radar images with a range resolution of 75 m or finer. Out of 33 asteroids with an estimated effective diameter of at least 200 m and sufficient image quality to give clues of the shape, at least 4 (∼12%) are binary asteroids, including 1 equal-mass binary asteroid, 2017 YE5, and at least 10 (∼30%) are contact-binary asteroids. For 5 out of 112 asteroids with reliable measurements in both circular polarizations, we measured circular-polarization ratios greater than 1.0, which could indicate that they are E-type asteroids, while the mean and the 1σ standard deviation were 0.37 ± 0.23. Further, we find a mean opposite-sense circular-polarization radar albedo of 0.21 ± 0.11 for 41 asteroids (0.19 ± 0.06 for 11 S-complex asteroids). We identified two asteroids, 2011 WN15 and (505657) 2014 SR339, as possible metal-rich objects based on their unusually high radar albedos, and discuss possible evidence of water ice in 2017 YE5.Peer reviewe

Planetary Radar—State-of-the-Art Review

Planetary radar observations have provided invaluable information on the solar system through both ground-based and space-based observations. In this overview article, we summarize how radar observations have contributed in planetary science, how the radar technology as a remote-sensing method for planetary exploration and the methods to interpret the radar data have advanced in the eight decades of increasing use, where the field stands in the early 2020s, and what are the future prospects of the ground-based facilities conducting planetary radar observations and the planned spacecraft missions equipped with radar instruments. The focus of the paper is on radar as a remote-sensing technique using radar instruments in spacecraft orbiting planetary objects and in Earth-based radio telescopes, whereas ground-penetrating radar systems on landers are mentioned only briefly. The key scientific developments are focused on the search for water ice in the subsurface of the Moon, which could be an invaluable in situ resource for crewed missions, dynamical and physical characterization of near-Earth asteroids, which is also crucial for effective planetary defense, and a better understanding of planetary geology

Planetary Radar—State-of-the-Art Review

Planetary radar observations have provided invaluable information on the solar system through both ground-based and space-based observations. In this overview article, we summarize how radar observations have contributed in planetary science, how the radar technology as a remote-sensing method for planetary exploration and the methods to interpret the radar data have advanced in the eight decades of increasing use, where the field stands in the early 2020s, and what are the future prospects of the ground-based facilities conducting planetary radar observations and the planned spacecraft missions equipped with radar instruments. The focus of the paper is on radar as a remote-sensing technique using radar instruments in spacecraft orbiting planetary objects and in Earth-based radio telescopes, whereas ground-penetrating radar systems on landers are mentioned only briefly. The key scientific developments are focused on the search for water ice in the subsurface of the Moon, which could be an invaluable in situ resource for crewed missions, dynamical and physical characterization of near-Earth asteroids, which is also crucial for effective planetary defense, and a better understanding of planetary geology

FBH1 disrupts RAD51 filaments in vitro and modulates homologous recombination in mammalian cells

Efficient repair of DNA double-strand breaks and inter-strand cross-links requires the homologous recombination (HR) pathway, a potentially error-free process that utilizes a homologous sequence as a repair template. A key player in HR is RAD51, the eukaryotic ortholog of bacterial RecA protein. RAD51 can polymerize on DNA to form a nucleoprotein filament that facilitates both the search for the homologous DNA sequences and the subsequent DNA strand invasion required to initiate HR. Because of its pivotal role in HR, RAD51 is subject to numerous positive and negative regulatory influences. Using a combination of molecular genetic, biochemical and single molecule biophysical techniques, we provide mechanistic insight into the mode of action of the FBH1 helicase as a regulator of RAD51-dependent HR in mammalian cells. We show that FBH1 binds directly to RAD51 and is able to disrupt RAD51 filaments on DNA through its ssDNA translocase function. Consistent with this, a mutant mouse embryonic stem cell line with a deletion in the FBH1 helicase domain fails to limit RAD51 chromatin association and shows hyper-recombination. Our data are consistent with FBH1 restraining RAD51 DNA binding under unperturbed growth conditions to prevent unwanted or unscheduled DNA recombination

Near-Earth Objects

International audienc

Surface Heterogeneity, Physical, and Shape Model of Near-Earth Asteroid (52768) 1998 OR2

peer reviewedOn 2020 April 29, the near-Earth object (52768) 1998 OR2 experienced a close approach to Earth at a distance of 16.4 lunar distances (LD). 1998 OR2 is a potentially hazardous asteroid of absolute magnitude H = 16.04 that can currently come as close to Earth as 3.4 LD. We report here observations of this object in polarimetry, photometry, and radar. Our observations show that the physical characteristics of 1998 OR2 are similar to those of both M- and S-type asteroids. Arecibo's radar observations provide a high radar albedo of sigma _OC = 0.29 ± 0.08, suggesting that metals are present in 1998 OR2 near-surface. We find a circular polarization ratio of μc = 0.291 ± 0.012, and the delay-Doppler images show that the surface of 1998 OR2 is a top-shape asteroid with large-scale structures such as large craters and concavities. The polarimetric observations display a consistent variation of the polarimetric response as a function of the rotational phase, suggesting that the surface of 1998 OR2 is heterogeneous. Color observations suggest an X-complex taxonomy in the Bus–DeMeo classification. Combining optical polarization, radar, and two epochs from the NEOWISE satellite observations, we derived an equivalent diameter of D = 1.80 ± 0.1 km and a visual albedo pv = 0.21 ± 0.02. Photometric and radar data provide a sidereal rotation period of P = 4.10872 ± 0.00001 hr, a pole orientation of (332.°3 ± 5°, 20.°7 ± 5°), and a shape model with dimensions of ({2.08}_{-0.10}^{+0.10}, {1.93}_{-0.10}^{+0.10},{1.60}_{-0.05}^{+0.05}) km