Seminars Temps-Espace-Société

Unless otherwise stated: Monday at 2 pm – Jean-François Denisse room/Observatoire de Paris, 77 Avenue Denfert-Rochereau, F-75014 PARIS

For people outside the Observatoire de Paris: please contact the organizers in advance.

Upcoming Seminars

MASSED – Mapping Arrival times in the Solar System for Extraterrestrial Debris

Patrick Shober

  • Observatoire de Paris. Site de Paris. Salle Denisse.

(rescheduled) - Over the previous century, scientists have collected >60,000 meteorites. These meteorites originally come from asteroids, primarily in the main asteroid belt between Jupiter and Mars. However, that is where things become unclear. Despite this vast collection, we still struggle to identify the asteroids or regions where these meteorites are derived. Current modeling and meteorite recovery networks have significantly helped us piece together the story of meteorites and, consequently, our solar system. Nevertheless, these models rely on rare cases where meteorites were precisely observed and orbital information was collected. Currently, only ~40 meteorites have been recovered in this manner. Instead, this project aims to create a novel numerical model of solar system debris that could be calibrated with data from tens of thousands of meteorites. Scientists can infer how long ago any meteorite was ejected from its parent asteroid by analyzing isotopic variations  - referred to as the cosmic-ray exposure age (CRE). Concurrently, our new model would be able to predict the transfer times from different regions of the main asteroid belt, enabling us to compare to the CRE ages found in meteorites and draw important conclusions about meteorite source regions.

Collapse and Ejection in the N-body problem and the Formation of Rubble Pile Asteroids

Dan Scheeres, Univ. Colorado

  • Observatoire de Paris, salle du Conseil .

Rubble pile asteroids are thought to form in the aftermath of cataclysmic collisions between proto-planets. The details of how the detritus from such collisions reaccumulate to form these bodies are not well understood, yet can play a fundamental role in the subsequent evolution of these bodies in the solar system. Simple items such as how particle sizes and porosity is distributed within a body can have a significant influence on how they subsequently evolve. Current space missions are just starting to gain limited insight into these fundamental questions, but require a better theoretical understanding to fully explain their observations.

To that end, this work studies how the initial energy and angular momentum of a random collection of gravitating bodies is partitioned and redistributed between escaping components and bound multiple body systems. A generic initial distribution of N bodies will naturally lose many components due to multi-body dynamical interactions. If the bodies have finite density, some components will also form condensed distributions. We find and apply rigorous results from the Full N-body problem to place limits and constraints on how the energy and angular momentum of such systems can evolve, which may control the formation of stable rubble pile asteroids.

We are able to establish some of our constraints analytically, providing unique insight into this process. Ultimately, however, we require numerical simulations to elucidate certain aspects of the ejection process. As will be shown, these gravitational ejections will always reduce the system energy yet can cause significant fluctuations in the total angular momentum of the remaining bodies. Some possible implications of these trends will be discussed.


Science Accessible via GPU-accelerated Planetary Dynamics Integrators

Brett Gladman

  • Observatoire de Paris, Salle Denisse.77 avenue Denfert-Rochereau, 75014 Paris..

The hardware characterstics of Graphical Processing Units (GPUs) have advanced to the point that two order of magnitude performance improvements can be obtained in problems that are of general utility. 
I will describe high-level design of the code GLISSE (GPU Longterm Integrator in Solar System Evolution), and use it to illustrate scientific exploration of the stability of orbits (1) between Uranus and Neptune, and (2) in Kuiper Belt resonances. 
For these applications GLISSE is 300-1000 times faster than a CPU core, and thus the hardware cost makes it vastly more financially effective  to use GPU based hardware rather than clusters of nodes.
We are extending the integrator's capabilities to handle small bodies encountering planets, handling such relatively rare encouters on CPU  cores while the GPU deals with huge numbers of test particles.  
I will discuss the application of this GLISSER code (the R standing for 'regularized') the the orbital evolution of the Kuiper Belt region under the existence of additional planets in the early Solar System.