Seminars

List of seminars in Ile-de-France: January-February 2023

17 January 2023, 15:00

The interior of Venus as seen from gravity and topography data
Julia Maia (Observatoire de la Côte d’Azur)
IPGP Planetary and Space Sciences, Bâtiment Lamarck B, 35 rue Hélène Brion, Paris

Summary
Although Venus and the Earth are commonly called “twin planets” for their many similarities, they have been through very different evolutionary paths, as indicated by the absence of an active magnetic field and plate tectonics on Venus. Understanding the interior structure of Venus is essential to interpret why these two planets turned out so different and constrain its geodynamic evolution. Yet, the interior of the planet is essentially unknown. Our studies aim to improve the interior structure constraints for Venus, including new estimations of crustal thickness, elastic lithosphere thickness and mantle viscosity structure. To do so, we investigate Venus gravity and topography data, obtained during the Magellan mission (1990-1994), using modern analysis techniques, inversion methods and geophysical models.

Directions
The IPGP Planetary and Space Sciences seminar series is held in the building Lamarck B that is part of the Université Paris Cité - Campus des Grands Moulins near the BnF (Bibliothèque Nationale de France). We are not at the main IPGP campus near the Jardin des Plantes and the Jussieu metro station. You do not need a badge to enter this building. You only need to go to 35 rue Hélène Brion, and once in the lobby of the main entrance, take the elevators on the right to the 5th floor. Exit the elevator and take the corridor to the right. The seminar room is number 522.

24 January 2023, 15:00

The thermodynamic state of the protolunar disk after the giant impact
Razvan Caracas (Insitut de Physique du Globe de Paris)
IPGP Planetary and Space Sciences, Bâtiment Lamarck B, 35 rue Hélène Brion, Paris

Summary
We study the behavior of a multi-component silicate fluid with bulk silicate Earth composition at conditions typical for the giant impact that generated the protolunar disk. We find that the Earth’s protolunar disk reached the supercritical state of the silicate mantle. As such, the Earth, and most rocky planets, will traverse a temporary state that lacks a surface defined by a magma ocean-atmosphere boundary. The atomic structure of the silicate fluid varies with the radius within the disk due to strong pressure and temperature gradients. Fluffy short-lived chemical species dominate the outer parts of the disk, and long-lasting dense polymers abound in the deeper parts. During cooling, when the temperature and density profile of the disk intersect the liquid-vapor dome, liquid and vapor start to separate, the disk evolves as a two-phase system, and the central body starts to condense. The composition of the post-impact atmosphere is dominated by species along the mantle vapor curve.

31 January 2023, 15:00

Moon Evaporation during its formation
Sébastien Charnoz (Institut de Physique du Globe de Paris)
IPGP Planetary and Space Sciences, Bâtiment Lamarck B, 35 rue Hélène Brion, Paris

Summary
Prevailing models for the formation of the Moon invoke a giant impact between a planetary embryo and the proto-Earth. Despite similarities in the isotopic and chemical abundances of refractory elements compared to Earth’s mantle, the Moon is depleted in volatiles. Current models favour devolatilisation via incomplete condensation of the proto-Moon in an Earth-Moon debris-disk. However the physics of this protolunar disk is poorly understood and thermal escape of gas is inhibited by the Earth’s strong gravitational field. Here we propose the Earth’s tidal pull promotes intense hydrodynamic escape from the liquid surface of a molten proto-Moon assembling at 3–6 Earth radii. Such tidally-driven atmospheric escape persisting for less than 1 Kyr at temperatures ~1600 − 1700 K reproduces the measured lunar depletion in K and Na, assuming the escape starts just above the liquid surface.

7 February 2023, 15:00

Turbulence in the atmosphere of Mars and Titan
Aymeric Spiga (Laboratoire de Météorologie Dynamique, Sorbonne Université)
IPGP Planetary and Space Sciences, Bâtiment Lamarck B, 35 rue Hélène Brion, Paris

Summary
Mars and Titan have both vastly distinct environments from the Earth’s, yet they exhibit atmospheric turbulent phenomena akin to the ones we experience at the surface of our planet. What is particularly interesting on Mars and Titan is that turbulence is somewhat a distant exotic cousin of Earth’s atmospheric turbulence, with many different aspects that allows for a rich comparative study. This study can be placed in a context of planetary exploration and multi-disciplinary planetary science.

21 February 2023, 15:00

Nudging virtual planets
Nicolas Coltice (Ecole Normale Supérieure, Paris)
IPGP Planetary and Space Sciences, Bâtiment Lamarck B, 35 rue Hélène Brion, Paris

Summary
Tectonics, climate, and landscapes are symptoms of underlying intrinsic properties of planets. Looking at the Earth in recent times, I will propose ways to nudge virtual planets towards real ones.