No Need for Planet 9, by Dr Ann Marie Madigan - 2021-11-08
Channel: Cork Astronomy Club
Date: 2022-03-09

Dr Ann-Marie Madigan is Assistant Professor of Astrophysics and JILA Fellow at the Department of Astrophysical and Planetary Sciences in the University of Colorado, Boulder.

Born in Dublin, as an undergraduate she studied Physics & Astronomy at the National University of Ireland, Galway, then received her Masters and PhD in Astronomy at Leiden Observatory in the Netherlands. She became a NASA Einstein & Theoretical Astrophysics Center Postdoctoral Fellow at University of California, Berkeley, then, in 2016, she joined the Department of Astrophysical and Planetary Sciences (APS) at CU Boulder. She leads a group that studies relativistic stellar and gas dynamics near massive black holes, with applications to the centre of our Milky Way galaxy, the Andromeda Galaxy (M31) nucleus, and post-starburst galaxies. The group studies the dynamics of dark matter in disk galaxies and rotating globular clusters. They also investigate the orbits of icy bodies in the outer solar system, and exoplanet dynamics.

In this Lockdown Lecture to Cork Astronomy Club via Zoom, Dr Madigan discusses the orbits of the icy minor planets beyond Neptune, which are regarded as doing something very strange: they all tilt and pitch in similar ways, and maybe even cluster together. One explanation for this is the Planet 9 hypothesis of Batygin and Brown (2016)*. But, also in 2016 Dr Madigan and co-investigator Mike McCourt showed that when gravitational forces between minor planets on eccentric orbits are modeled in N-body simulations, the orbits incline rapidly off the disk plane, and tilt and pitch in exactly the same way (https://academic.oup.com/mnrasl/article/457/1/L89/2589679). This gravitational instability is something that a disk of eccentric orbits does on its own - there is no need to invoke an external reason (like a Planet 9). This research predicts many more minor planets in the outer Solar System, a "new Kuiper Belt" but with an order of magnitude more mass to prevent the precessing effects of the gravity of the giant planets from disrupting the orbital clustering. Subsequently, Dr Madigan and her research team have provided an explanation of the dynamics behind the collective gravity mechanism, and the discovery of eccentricity oscillations when a spectrum of minor planet masses is included.
(Sources: https://www.colorado.edu/aps/ann-marie-madigan; https://jila.colorado.edu/~madigan/)

Future tests of this research will use synoptic data provided by the Vera C Rubin Observatory, currently under construction in Chile. For the Rubin Observatory, see a previous Lockdown Lecture to Cork Astronomy Club by Dr Amanda Bauer: https://www.youtube.com/watch?v=rULMAV61EaM&list=PLgwJkghoj_XjitRT2RZZHlOsSeG_V6X0Q&index=5&ab_channel=CorkAstronomyClub

* Batygin, Konstantin; Brown, Michael E. (2016). "Evidence for a Distant Giant Planet in the Solar System". The Astronomical Journal. 151 (2): 22. arXiv:1601.05438. Bibcode:2016AJ....151...22B. doi:10.3847/0004-6256/151/2/22. S2CID 2701020