List of Past Planetary Astronomy Lunches (PALS) : 01-Sep-2014 to 31-Dec-2014

Date:   Tuesday 30-Sep-2014
Speaker:   Erika Nesvold (UMBC/GSFC)
Title:  Gaps, Warps, Rings and Collisions: How Planets Interact with Debris Disks

Observations of resolved debris disks show a spectacular variety of features and asymmetries, including inner cavities and gaps, inclined secondary disks or warps, and eccentric, sharp-edged rings. Embedded exoplanets could create many of these features via gravitational perturbations, which sculpt the disk directly and by generating planetesimal collisions.

We present the Superparticle-Method Algorithm for Collisions in Kuiper belts and debris disks (SMACK), the first code to simultaneously model the dynamical and collisional evolution of planetesimals in three dimensions. We use SMACK to investigate the effects of collisions on the morphology of a disk of planetesimals perturbed by a planet and apply our model to a number of resolved debris disks including Fomalhaut, beta Pictoris, and HR 4796. Including collisions can yield estimates for planet masses 5x smaller than collisionless models.

For further information contact PALS coordinator Dr. Michael Kelley at or 301-405-3796.

Date:   Tuesday 07-Oct-2014
Speaker:   Nicholas Schmerr (UMD Geology)
Title:  Planetary Seismology: Exploring the Interiors of the Moon, Mars, and Other Worlds

The structure of the crust, mantle, and core of bodies in the Solar System hold vital clues to understanding the formation and evolution of these objects. One way to access the detailed interiors of moons, planets, asteroids, and comets is the deployment of seismometers on their surface, either by robotic or manned missions, to monitor elastic waves that propagate through and interact with their interiors. In this talk, I will present how seismology has and is revolutionizing our understanding of planetary interiors. For example, seismometer measurements using source locations derived from high-resolution orbital images are capable of improving our constraints on the core, mantle, and crust of the Moon and Mars, as well as establishing the seismicity and recent tectonic activity of these objects. These new approaches are applicable to bodies across the Solar System, and hold the potential to revolutionize our understanding of planetary accretion, differentiation, and dynamics for a variety of seismically unexplored worlds.

For further information contact PALS coordinator Dr. Michael Kelley at or 301-405-3796.

Date:   Tuesday 14-Oct-2014
Speaker:   Scott Sheppard (Carnegie, DTM)
Title:  Beyond the Edge of the Kuiper Belt: The Inner Oort Cloud Population

The dynamical and physical properties of small bodies in our Solar System offer one of the few constraints on the formation, evolution and migration of the planets. The recent advent of sensitive, wide-field CCD detectors on large class telescopes are allowing us to complete the inventory of our Solar System and obtain detailed knowledge about the small bodies it contains. I will discuss the recent results we have obtained through our ongoing deep solar system survey with a focus on the discovery and characterization of the Inner Oort Cloud and Main Belt Comet populations.

For further information contact PALS coordinator Dr. Michael Kelley at or 301-405-3796.

Date:   Thursday 16-Oct-2014
Speaker:   Tom McCord (The Bear Fight Institute)
Title:  Ceres: Dawn visits a warm wet planet

*** Note special time and place ***

Ceres likely contains considerable water, has differentiated, and formed a hydrated silicate core and water mantle. There were major dimensional, thermal and chemical changes over its history, making it more a planet than an asteroid. These factors created the present day body, which the Dawn misson will visit next March. I will summarize our current understanding of Ceres and suggest what Dawn will find. A major uncertainty is how processes, such as aqueous mineralization, impact and cratering, infall of external material, mixing, and viscous relaxation of surface features have altered the formation materials and surface, hiding Ceres’ secrets. Ceres’ bulk density of 2100 kg/m3, suggest major water content. Modeling of Ceres’ thermodynamic evolution for different times of accretion, assuming several radioactive heating scenarios, produces results ranging from a dry Vestal-like object (earlier, hotter formation) to retention and melting of the ice and differentiation of silicates from liquid water. Mixing of liquid water and silicates leads to exothermic hydration reactions, formation of a core and a liquid mantle. Large dimensional changes are associated. A crust stays frozen but founders at times due to gravitational instability, dimensional changes and impacts. The liquid mantle freezes from top, down, but a layer of salty liquid water probably exists today near the core. Hydrated silicates from the initial differentiation would likely dehydrate near the core center due to temperature and pressure. From observations, only subdued spatial albedo and color variations are observed at UV and IR wavelengths on Ceres’ surface at the scale possible from Earth (~50-100 km) and an oblate spheroid shape is found, consistent with a differentiated body. Compositional evidence includes the long known similarity of Ceres’ albedo and visual-IR reflectance spectrum to those for carbonaceous chondrite meteorites. Thus, the surface is likely made of carbon-bearing, hydroxolated materials, with spectral evidence of OH and maybe H2O molecules, consistent with the results of both the evolutionary thermodynamic models and infill of carbonaceous chondrite-like materials. Two reports of OH and H2O in the exosphere, apparently originating from localized sources, suggest present day cryovolcanism.

For further information contact PALS coordinator Dr. Michael Kelley at or 301-405-3796.

Date:   Tuesday 28-Oct-2014
Speaker:   Karl Battams (Naval Research Lab.)
Title:  Roasting a Thanksgiving Comet: Piecing Together the Evidence for Comet ISON’s Destruction

One year ago, the astronomy community was gripped with anticipation as sungrazing comet C/2012 S1 (ISON) was just weeks away from an unprecedented close encounter with the Sun on November 28, 2013. Comet ISON held the potential of being a spectacular nighttime object - but its fate hinged on surviving a passage that would take it to within just 1.1-million kilometers of the solar surface. To the great disappointment of a global audience, the comet did not survive, fading rapidly in the hours surrounding perihelion and disappearing from sight in the following days. For the first half of the talk I will recap some of the background regarding ISON, and highlight the main points of interest during its well-observed final year of approach to the Sun. I will focus in particular on the final few days and hours of the comet’s passage, with images recorded by solar-observing spacecraft. The second half of the talk will focus on how, using numerous sources of observational and modeling evidence, we are now able to paint a coherent and very compelling picture of how, why, and when, comet ISON was catastrophically destroyed as it approached the Sun on Thanksgiving Day, 2013.

For further information contact PALS coordinator Dr. Michael Kelley at or 301-405-3796.

Date:   Tuesday 04-Nov-2014
Speaker:   Your Colleagues
Title:  DPS Preview

A special edition of PALS: preview talks for the upcoming AAS Division for Planetary Sciences in Tucson, AZ.

For further information contact PALS coordinator Dr. Michael Kelley at or 301-405-3796.

Date:   Tuesday 18-Nov-2014
Speaker:   Robert Tyler (GSFC/CREST)
Title:  Comparative estimates of the heat generated by ocean tides on icy satellites in the outer Solar System

This study illuminates scenarios whereby the heat produced by the dissipation of ocean tides is significant in the heat budgets maintaining liquid oceans on icy satellites in the outer Solar System. It has been shown in previous work that ocean tides, if resonantly forced, can supply heat at or exceeding the rates necessary for maintaining these oceans. It has also been shown that because of feedbacks these resonant configurations may be unavoidable under typical situations. This study extends from the previous work and seeks to examine the full set of dynamically-consistent ocean tidal solutions to describe the parameter dependencies that may cause one ocean to become trapped in such a vigorous ocean state while allowing another to freeze. Why do some of these satellites have oceans, and others do not? It is found that even with no other sources of heat, a liquid ocean on many of these satellites would be maintained by ocean tidal heat because the process of freezing (which changes the thickness of the remaining liquid ocean and thereby the eigenmodes) would push the ocean into a resonant configuration, with the asso- ciated increase in heat production preventing further freezing and stabilizing the configuration. An ocean on Io or Mimas would suffer extreme tides (with heat generated exceeding 1 W/m2) unless an implausibly large volume of water were present to lift the eigenmodes of the configuration out of resonance with the tidal forces. Europa can maintain a thick (~100 km) ocean due to an obliquity-forced tidal resonance, while parameters for most other satellites suggest eccentricity-driven resonance scenarios involving much thinner ocean thicknesses (1-10s km). But these thin ocean thickness in the latter scenarios will be altered by ice cover: as the ice cover damps the ocean tidal response, significant heat is still generated which would stall freezing but the ocean thicknesses are modified to larger values than would be expected without ice cover.

For further information contact PALS coordinator Dr. Michael Kelley at or 301-405-3796.

Date:   Tuesday 02-Dec-2014
Speaker:   Cancelled
Title:  Cancelled

No speaker for today.

For further information contact PALS coordinator Dr. Michael Kelley at or 301-405-3796.

Date:   Thursday 04-Dec-2014
Speaker:   Sebastien Besse (ESA RSSD)
Title:  67P, Rosetta, OSIRIS, and Gorgeous Images

Since August 2014, Rosetta has been in orbit around the comet 67P/Churyumov-Gerasimenko. The instruments on the orbiter have provided numerous observations of the comet and its environment, all leading to the successful landing of Philae on November 12th. All the data are helping to understand the nature of the comet nucleus, and images have particularly shown that the surface has a lot of similarities and differences with previous cometary nuclei. Additionally, we found a lot of evidence for processes that are commonly seen on Earth. In this presentation, I will review and present unique morphological data on this cometary nucleus that clearly show the awesomeness of comets!

For further information contact PALS coordinator Dr. Michael Kelley at or 301-405-3796.

Date:   Tuesday 09-Dec-2014
Speaker:   Dennis Bodewits (UMD)
Title:  A Glimpse into the Underworld: Active Pits on Comet 67P

Circular pits are common on cometary nuclei and are evidendence of structural heterogeneity deep below the surface. Produced by the collapse of sub-surface layers, pits trace comets’ thermal history and evolution.

For further information contact PALS coordinator Dr. Michael Kelley at or 301-405-3796.

Date:   Tuesday 16-Dec-2014
Speaker:   Basmah Riaz (Univ. Hertfordshire/UMD/MPE)
Title:  The radial distribution of dust species in young protoplanetary disks

Clues to planet-forming processes are provided by the properties of the dust grains in protoplanetary disks and in cometary nuclei in our own Solar System. I will present results from a compositional analysis of the 10-µm and 20-µm silicate emission features for young protoplanetary disks around FGKM stars, covering a wide range in stellar masses from ~1 Msun down to ~0.02 Msun. A notable trend is of an increase in the crystallinity levels towards larger radii, such that the median crystalline mass fraction is higher in the outer cold disk region compared to the inner warm parts of the disk. The median crystalline mass fraction in disks around late-type stars is found to be a factor of ~2 higher than the median for the higher mass FGK type stars. The relatively high abundance of crystalline silicates in the outer cold regions of protoplanetary disks provides an interesting analogy to comets. In this context, I will discuss the applicability of the mechanisms that have been proposed for comets on the formation and the outward transport of high-temperature material. A (weak) anti-correlation between the X-ray emission strength and the extent of crystallinity in the disk is observed, suggesting X-rays to be an important dust amorphization agent in these disks. This work has highlighted the ubiquity of Solar System like chemical signatures in young protoplanetary disks, and suggests that disks around very low-mass stars/brown dwarfs undergo a higher level of crystallization and grain growth compared to solar-type stars.

For further information contact PALS coordinator Dr. Michael Kelley at or 301-405-3796.

Date:   Wednesday 17-Dec-2014
Speaker:   Dimitri Veras (Univ. of Warwick, UK)
Title:  The Growing Importance of Asteroids, Comets, Dust and Planets in Post-Main-Sequence Systems

Robust observational evidence indicates that between 25%-50% of all white dwarfs host currently dynamically-active planetary systems. Over 35 of these white dwarfs harbour gaseous and dusty debris discs which are thought to arise from the tidal disruption of asteroids and comets. Here I provide a review of our current knowledge of these systems and related theoretical explorations. I show how this field incorporates several facets of planetary science, including dynamics, interiors, and atmospheres. I outline the fundamental outstanding questions which remain about the origin and evolution of these fascinating systems.

For further information contact PALS coordinator Dr. Michael Kelley at or 301-405-3796.

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