Colloquium

The Curious Case of Planet 9

Speaker: Jihad Touma (American University of Beirut, Beirut, Lebanon)

Date and time

Abstract

Astronomers have argued for a distant, massive, eccentric and inclined planet to explain elongated and apparently clustered orbits of extreme Trans-Neptunian Objects. The so-called Planet 9 Hypothesis has  generated a flurry of both theoretical and observational works: most constraining Planet 9 properties and its location on the sky, some proposing alternative clustering mechanisms, and others dismissing the signal as observational bias, thus obviating the need for a shepherding mechanism in the first place.

I shall start this overview of the Planet 9 Hypothesis by highlighting the stunning precedent of the prediction and detection of Neptune, then proceed to a blow by blow account of the evidence for and current predicament of Planet 9. I will then briefly review an alternative we proposed, and conclude with recent work which provides a clean scaffolding for Planet 9 dynamics, as it points to applications in hierarchical systems, exo-planetary debris disks included. The whole will make for a leisurely guided tour of the Trans-Neptunian realm and the beautiful bits of celestial mechanics that were ushered by a most seductive idea, whose time is yet to come (if at all). 

Jihad Touma

Short Biography
Jihad Touma is a Professor of Physics at the American University of Beirut. His work in astrophysical dynamics has brought to light the chaotic rotation of Mars (with dramatic implications for the evolution of climate, and life on the red planet), potential episodes of large scale volcanism on Earth and Venus (touching on mass extinction on Earth, and resurfacing of Venus), the early resonant forcing of the lunar orbit (a significant step towards a solution of a then thirty-year-old puzzle ), the chaotic orbital architecture of extrasolar planets, and a generic dynamical process for the doubling of stellar black hole nuclei. More recently, he helped bring to light disruptive instabilities in multi-planet systems in binaries, proposed a novel mechanism for shepherding Trans-Neptunian Objects, and argued for the metastability of spherical stellar clusters around black holes, identifying a generic phase transition to lopsidedness with loss cone dynamics.