Astronomical Institute of the Czech Academy of Sciences

Institute Seminar

5 December 2022

13:15

The seminar will be held in the Seminar Room "Behind the 2m Telescope".
13:00 - 13:15 Seminar preparation
Programme Schedule
Speaker: Jaroslav Klokočník
Title: New findings about the gravity field of the Moon by means of the gravity aspects
Abstract:
The gravity aspects for the Moon (the gravity disturbance, the Marussi tensor, two gravity invariants, dimensionality ratio, the strike angles, and the virtual deformations), all combined with magnetic anomalies and detailed surface topography, allow new views of specific locations on the Moon. Using these new gravity quantities, we hypothesize the following for several features on the Moon. A dike-like intrusion (exceeding ~100 km in length) from inside to outside of the Clavius crater likely solidified at the time of the existence of lunar dynamo. Mare Crisium analyses show a specific distribution of faulting across the mare. The same size impacts, Crisium and Clavius, present the dilatational deformation that is smoother for Crisium, while Clavius is under variable concentric compression due to an uplift of denser rock. Mare Orientale deformation not only confirmed the prior finding of the near surface faults, but also reveals a nature of the faulting (expansion vs compression blocks). Magnetic analyses of related lunar anomalies constrain mascon extent under the Copernicus structure and outline contraction areas from cooling of the upwelled mantle material. Mare Imbrium impact event has demagnetized regolith along with the Copernicus crater using a novel mechanism of shock propagation while plasma demagnetization. For the first time, the application of the gravity aspects has been extended from the Earth to the Moon. This approach opens a new and inspiring field of planetary studies and point to otherwise hardly detectable phenomena. More detailed studies should follow.

Speaker: Raine Karjalainen
Title: Companions to Kepler giant stars
Abstract:
The discoveries of a substellar companion and a stellar companion around two intermediate-mass red giant branch stars are presented. Combining radial velocity measurements with Kepler photometric observations we found that KIC 3526061 b is a brown dwarf with minimum mass of ~18 Jupiter masses and HD 187878 B has a minimum mass of ~80 Jupiter masses. The latter has Gaia astrometric measurements and we could derive the orbital inclination of ~10 degrees, which gives it the mass of ~0.5 solar mass.

Speaker: Petr Pravec
Title: The DART mission to binary asteroid Didymos
Abstract:
On September 26, 2022, the NASA's spacecraft named DART impacted the secondary of the binary asteroid Didymos, called Dimorphos. It was a successful test of the Kinetic Impactor technique for deflecting dangerous asteroids. I will overview the DART mission, its preparation, the s/c flight and the impact. I will also present how we here at Ondrejov contributed to the mission, from the discovery of Dimorphos with the 0.65-m telescope and from collaborating stations in 2003, over acquiring additional photometric measurements of the mutual events between the two bodies of the binary system with 11 large (3.5-10 m) telescopes from 2015 to 2021, to accurate determination of the Dimorphos' orbit around the Didymos primary that allowed us to predict the relative position of the two bodies which NASA needed to set an optimal timing of the DART impact.

Speaker: Petr Hellinger
Title: Ion-scale transition of plasma turbulence: Pressure-strain effect
Abstract:
We analyze the ion-scale transition of plasma turbulence using direct numerical simulations in the hybrid (fluid electrons, kinetic ions) approximation. We apply a generalized Karman-Howarth-Monin equation to the simulation results to capture and quantify different turbulence processes. This analysis shows that the ion-scale transition results from a combination of the onset of Hall physics and dissipation. It also shows that the pressure-strain coupling may constitute an effective dissipation channel in collisionless plasmas