Planetary Science Seminar - winter-2014

Jan. 9, 2014
noon - 1 p.m.
3853 Slichter

Presented By:

• Aurelien Hees - JPL

In this presentation, I will briefly review the principles upon which General Relativity (GR) is built. I will also review the main effects produced by GR in the Solar System. Motivations for considering alternative theories of gravitation will be given. The main tests of GR at Solar System scales will be presented. In particular, I will present the current constraints in the two main formalisms used so far: the Parametrized Post-Newtonian formalism and the fifth force formalism. Then, some motivations for considering alternative theories of gravitation beyond the PPN and fifth force formalism will be presented. A very recent analysis of Cassini tracking data in a Modified Newtonian Dynamics (MOND) formalism will be presented. After this, I will speak about a recent tool to simulate radioscience observations in very general alternative theories of gravitation. This tool computes everything (orbit of planets/spacecraft, propagation of electromagnetic signal, clock behaviour) directly from the space-time metric. As an illustration, some simulations within the Standard Model Extension (SME) and some sensitivity analyses will be presented.

Jan. 16, 2014
noon - 1 p.m.
Slichter 3853

Presented By:

• Davide Farnocchia - JPL

Orbit determination for Near-Earth Asteroids presents unique technical challenges due to the imperative of early detection and careful assessment of the risk posed by specific Earth close approaches. The occurrence of an Earth impact can be decisively driven by the Yarkovsky effect, which is the most important nongravitational perturbation as it causes asteroids to undergo a secular variation in semimajor axis resulting in a quadratic effect in anomaly. We discuss the cases of (99942) Apophis and (29075) 1950 DA. The relevance of the Yarkovsky effect for Apophis is due to a scattering close approach in 2029 with minimum geocentric distance ~38000 km. For 1950 DA the influence of the Yarkovsky effect in 2880 is due to the long time interval preceding the impact. We use the available information on the asteroids' physical models as a starting point for a Monte Carlo method that allow us to measure how the Yarkovsky effect affects orbital predictions. For Apophis we map onto the 2029 close approach b-plane and analyze the keyholes corresponding to resonant close approaches. For 1950 DA we use the b-plane corresponding to the possible impact in 2880. We finally compute the impact probability from the mapped probability density function on the considered b-plane.

Feb. 4, 2014
noon - 1 p.m.
Slichter 3853

Presented By:

• Elizabeth Carey - JPL

Seminar Description coming soon.

Feb. 13, 2014
noon - 1 p.m.
Slichter 3853

Presented By:

• Sarah Nymeyer - UCLA
• Elizabeth Palmer - UCLA

Seminar Description coming soon.

Feb. 27, 2014
noon - 1 p.m.
Slichter 3853

Presented By:

• Jack Wisdom - MIT

The isotopic similarity of the Earth and Moon has motivated a recent investigation (Cuk and Stewart, 2012) of the formation of the Moon with a fast-spinning Earth. Angular momentum was found to be drained from the system through the evection resonance, a resonance between the pericenter of the Moon and motion of the Earth about the Sun. However, tidal heating within the Moon was neglected. Here we explore the coupled thermal-orbital evolution of the early Earth-Moon system, taking account of tidal heating within the Moon. Large tidal heating in the Moon significantly changes the tidal parameters in the Moon, with consequent early escape from the evection resonance. Insufficient angular momentum is withdrawn from the system to be consistent with the current configuration of the Earth-Moon system.

March 6, 2014
noon - 1 p.m.
Slichter 3853

Presented By:

• Jessica Watkins - UCLA
• Sean Faulk - UCLA

Jessica Watkins (UCLA) "Structurally controlled subsurface fluid flow as a mechanism for the formation of Recurring Slope Lineae" Sean Faulk (UCLA) "The structure of the Intertropical Convergence Zone (ITCZ) on terrestrial planets"

March 14, 2014
noon - 1 p.m.
Slichter 3853

Presented By:

• Jennifer Scully - UCLA

Seminar Description coming soon.