Showing papers in "Earth Moon and Planets in 2021"

The Mechanical Properties of Chelyabinsk LL5 Chondrite Under Compression and Tension

Abstract: The mechanical properties of Chelyabinsk LL5 chondrite (Chelyabinsk meteorite) were studied by uniaxial compression and diametral compression/indirect tension test. Twenty cylindrical samples, 10 for compression and 10 for tension, with the diameter 3.3 mm and 1.65 mm in height have been prepared for testing. It was shown that the strength of the tested samples under compression almost 45 times greater than it is at tension: 372 ± 10 MPa and 8.2 ± 0.7 MPa, respectively. Fracture behaviour under compression and tension was similar and can be characterised as brittle. The obtained compression strength of the Chelyabinsk meteorite lies close to the maximal values of strength for many other chondrites, whereas its tensile strength magnitude resides in the bottom quarter of the range of similar measurements. It may be caused by the small sizes of the investigated samples together with a large number of tiny cracks between the grains in the Chelyabinsk chondrite. Our estimations have shown that if one assumes that the initial shape of the Chelyabinsk fireball was spherical or ellipsoidal, then its fragmentation stress is close to the experimental tensile strength and much lower than the compression strength. Hence, a stress state equivalent to one appearing at the indirect tension test could occur in the Chelyabinsk fireball during its fall in the Earth atmosphere.

The EURONEAR Lightcurve Survey of Near Earth Asteroids—Teide Observatory, Tenerife, 2015

Abstract: One meter class telescopes could bring important contributions in the acquisition of lightcurves of near earth asteroids (NEAs), based on which rotations and other physical properties could be derived or constrained. Part of a collaboration between IAC, ESA and the EURONEAR during the semester 2015A, the IAC80 and OGS telescopes at Teide Observatory in Tenerife were allocated for a photometric project during 64 nights spread in a few observing runs. The main funding for this long observing mission was raised by the student observer Radu Cornea from private sponsors based in his natal city of Sibiu, Romania, mentioned in the Acknowledgements. We observed 33 lightcurves of NEAs not published before, including 10 potentially hazardous asteroids (PHAs). Based on the quality of the Fourier period fits, we sorted the results in four groups which include 7 secured periods, 9 candidate periods, 10 tentative periods and 7 objects not solved. We resolved periods or suggested constraints for 13 NEAs having no other rotation knowledge (including 3 PHAs), confirming periods for other 6 targets published by other authors (mainly by Brian Warner). We suggested tumbling or binary nature for 6 targets (probing one of them) recommended for future dedicated campaigns. We derived ellipsoid shape ratios for 21 NEAs (including 4 PHAs) not known before.

Depths of Copernican Craters on Lunar Maria and Highlands

Abstract: We present a study on the relationship between the ratio of the depth of a crater to its diameter and the diameter for lunar craters both on the maria and on the highlands. We consider craters younger than 1.1 billion years in age, i.e. of Copernican period. The aim of this work is to improve our understanding of such relationships based on our new estimates of the craters’s depth and diameter. Previous studies considered similar relationships for much older craters (up to 3.2 billion years). We calculated the depths of craters with diameters from 10 to 100 km based on the altitude profiles derived from data obtained by the Lunar Orbiter Laser Altimeter (LOLA) onboard the Lunar Reconnaissance Orbiter (LRO). The obtained ratios h/D of the depths h of the craters to their diameters D can differ by up to a factor of two for craters with almost the same values of diameters. The linear and power approximations (regressions) of the dependence of h/D on D were made for simple and complex Copernican craters selected from the data from Mazrouei et al. (Science 363:253–255, 2019) and Losiak et al. (Lunar Impact Crater Database, 2015). For the separation of highland craters into two groups based only on their dependences of h/D on D, at D 18 km are in a better agreement with the approximation curve of h/D versus D for complex craters than for simple craters. At the same diameter, mare craters are deeper than highland craters at a diameter smaller than 30–40 km. For greater diameters, highland craters are deeper. The values of h/D for our approximation curves are mainly smaller than the values of the curve by Pike (in: Roddy, Pepin, Merrill (eds) Impact and explosion cratering: planetary and terrestrial implications, University of Arizona Press, Tucson, 1977) at D 53 km for highland craters, and at D < 80 km for mare craters.

Test of the Hypothesis for an Unknown Distant Massive Planet in the Solar System Applying Tisserand’s Criterion to a System of Long-Period Comets

Abstract: This article presents the results of an analysis of Tisserand’s constant for 1389 long-period comets in relation to a hypothetical planet. A mechanism is proposed to apply Tisserand’s criterion for a relatively trans-Neptunian planet with a notable inclination and orbit eccentricity. In particular, the algorithm considers the planet’s heliocentric distance in the era of a clearly-defined transformational change in the cometary orbit. Thus, we carried out the corresponding calculations by simulating the planet motion plane. This study allows a comparative analysis of Tisserand constant values for proposed hypothetical planet parameters. The most notable result is for a planet at a proposed distance of 340 AU.

Migration of Water Molecules in the Permanently Shaded Areas of Polar Areas of Mercury

Abstract: Radar observations of the surface of Mercury had revealed areas with bright reflective properties in both polar regions of the planet. It was suggested that such areas contain depositions of volatile compounds, including water. In this paper, we investigated migration of water molecules to the permanently shaded areas, located in the impact crater in the polar regions of Mercury. To simulate the migration of water molecules in the exosphere of Mercury, we used the Monte Carlo method. To estimate the proportion of water molecules falling into cold traps in the polar regions of Mercury, we estimated the area of such regions. We found that the area of permanently shaded areas near the north pole of the planet reaches 23,300 km2, and in the area of the south pole—45,500 km2. Most of the water molecules (~ 92%) will be destroyed as a result of photolysis, and ~ 7.5% of them will be destroyed while they are on the planet's surface between hops. The fraction of water molecules that left the planet's exosphere as a result of reaching the escape velocity is only 0.3%. The fraction of water molecules trapped in permanently shaded areas in the polar regions of Mercury reaches 7.8% of the total number of particles participating in the simulation. Only 2.2% of them can be trapped in cold traps in the North Pole region and 5.6% in the South Pole region.