Seminars Temps-Espace-Société

My group at UNLV has developed several new tools for the study of exoplanet science.  These include modules for the REBOUND n-body integrator that incorporate stellar evolution, tides, the Yarkovsky effect, and collisions and fragmentation between uniform and differentiated bodies.  In addition, our group has a new, fast interior structure code, MAGRATHEA, to model the internal properties of planets.  I will describe these different tools and show some of the interesting results that have come from their application.

The ground-based optical observations of near-Earth asteroids (NEAs) remain the primary tool for accumulating data on their physical properties. Since 1995, regular photometric observations of NEAs at Kharkiv and Simeiz Observatories were carried out using 70-cm and 1-m telescopes respectively, while it was stopped on February 22, 2022. At present, the observations continue in cooperation with colleagues at telescopes/observatories: 0.7-m telescope at Abastumani (Georgia), 0.6 and 2-m at Rozhen Observatory (Bulgaria), 0.6 and 1.5-m at Maidanak (Uzbekistan), 1-m at Tien-Shan (Kazakhstan), and 0.4 and 0.8-m at CTIO (Chile, USA).

The observations are aimed at determining the absolute magnitudes, rotation periods, colour indices, albedos, taxonomic types, sizes and shapes of the NEAs, and finding and investigating binary systems between them. The main objects are: newly discovered NEAs during its close approach to the Earth; potentially hazardous asteroids (PHA); asteroids for which the YORP effect is expected to be detected, the well-known binary NEAs to investigate the BYORP effect; asteroids that are objects of research by radar or/and a space mission. The obtained results will be presented.

The Earth's atmosphere acts as a filter that modifies the population of meteoroids reaching the surface. In this seminar, I will present an analysis comparing the meteoroid flux at the top of the atmosphere with the meteorite flux, using data from the FRIPON and 18 similar networks encompassing observations from over 39 countries. Our findings reveal statistically significant differences between these populations, suggesting that atmospheric entry processes and thermal disintegration in near-Earth space affect meteoroid survival. We also examine cosmic ray exposure ages of carbonaceous chondrites and assess orbital clustering amongst impact and near-Earth object populations to better understand meteoroid sources and evolutionary pathways. These insights have implications for refining meteoroid production, delivery, and meteorite source region models.

Studies of micrometeorites in mid-Ordovician limestones and Earth’s impact craters reveal that our planet experienced a massive infall of ordinary L chondrite material approximately 466 million years ago. This event is believed to have triggered the mid-Ordovician ice age, sea level fall, and major faunal turnovers (Schmitz et al. 2019). The breakup of a large asteroid in the main belt is the likely cause of this massive infall. In modern times, material originating from this breakup still dominates meteorite falls (37% of all falls). I will present spec- troscopic observations and dynamical evidence showing that we have identified the only plausible source of this remarkable event and the most abundant class of meteorites falling on Earth today.

Earth-based radar speckle tracking observations in 2006–2020 improved the
knowledge of the spin axis orientation of Venus by a factor of 5-15 compared to Magellan estimates. They also enabled the first measurement of the spin precession rate and moment of inertia of Venus. I will describe prospects for improving the estimates and other geodesy aspects at Venus. Radar speckle tracking observations of Europa and Ganymede in 2011-2023 yielded estimates of their spin axis orientations to 0.01 degrees. These measurements conform to the expected 30-year precessional cycle and provide insights into the moons’ Cassini States. I will discuss new scientific prospects associated with these observations. First, the spin state can reveal the presence of a subsurface ocean: a decoupling between the icy shell and the interior results in a different obliquity than that of a solid body. Second, an angular deviation from the strict Cassini state enables estimates of energy dissipation. Third, a measurement of librations, if detectable, would enable the first measurement of the shell’s moment of inertia and bounds on the rheology and thickness of the shell. Fourth, the obliquity may explain remarkable surface features, such as the distribution and orientation of cycloids, strike-slip faults, and lineaments on Europa. Fifth, knowledge of the obliquity is required to enable tidal heating calculations. Finally, these measurements are expected to facilitate Clipper and JUICE operations and prevent initial, large mapping errors in spacecraft data products.