List of Past Planetary Astronomy Lunches (PALS) : 01-Sep-2015 to 31-Dec-2015

Date:   Thursday 01-Oct-2015
Speaker:   Dr. Ottaviano Ruesch (NASA Goddard Space Flight Center)
Title:  "Looking back at Vesta and spiraling down into Ceres"

Asteroid Vesta is a survivor protoplanet and the knowledge it yields is essential to understand the early stages of planet formation. New insights about the interior structure of Vesta have been obtained with the unprecedented observations of the Dawn mission coupled to new near infrared measurements of the HED meteorites. Olivine enriched locations have been mapped and their geological context characterized. These results partly contradicts many pre-Dawn concepts of Vesta differentiation. As an alternative to the HED parent body model, few scenarios exist for the early evolution of Vesta, and none provide consistent explanation for the entire range of observations by Dawn. This reveals that protoplanets experienced a complex differentiation process, which is only partly understood. Preliminary results about the very recent discoveries at Ceres will be given, in particular about the peculiar topographic rises.

For further information contact PALS coordinator Dr. Silvia Protopapa at or (301)-405-2579.

Date:   Thursday 15-Oct-2015
Speaker:   Dr. Tony Farnham (UMD)
Title:  "Comet Siding Spring's close approach to Mars"

On Oct 19, 2014, comet Siding Spring made an historic close approach to Mars, passing within 138,000 km of the planet. Many of the spacecraft orbiting Mars, including MRO, MAVEN and MEX, took this opportunity to measure the comet's effect on Mars’ atmosphere, and MRO directly observed Siding Spring before, during and after the encounter. I will discuss the results from the atmospheric observations along with their interpretation and implications, and will also present the preliminary results from our analyses of the MRO observations of the comet itself.

For further information contact PALS coordinator Dr. Silvia Protopapa at or (301)-405-2579.

Date:   Thursday 22-Oct-2015
Speaker:   Dr. Michael A Disanti (NASA Goddard Space Flight Center)
Title:  "IR Spectroscopy of Comet D/2012 S1 (ISON) from Keck and IRTF: Unique perspective and compositional context"

The apparition of dynamically new, sun-grazing C/2012 S1 (ISON) in the fall of 2013 generated great excitement and stimulated a solar system-wide observing campaign, providing the rare opportunity to conduct compositional and morphological studies to heliocentric distances (Rh) well within 1 AU. Production rates and molecular abundances were obtained using first NIRSPEC at Keck 2 and then CSHELL at the NASA-IRTF. Both instruments operate in the 1 – 5 micron wavelength range, where molecular quantum vibrational modes are concentrated. The high spectral resolution (λ/Δλ ~ 2.5 x 104) afforded by these spectrographs permitted line-by-line studies in the coma, and measurement of volatile abundances over a wide range of heliocentric distances (Rh = 1.2 – 0.35 AU).

A suite of molecules (H2O, CO, H2CO, CH3OH, C2H6, C2H2, CH4, HCN, NH3) and radicals (OH, NH2) were targeted and detected. Our serial measurements allowed a search for potential changes in molecular abundances relative to H2O. Those of some species remained relatively constant with Rh, while others increased in abundance with decreasing Rh. I will present an overview of our methodology for analyzing long slit IR spectra together with our Comet ISON results, and place these in the context of the overall taxonomy of comets based on parent volatile composition.

For further information contact PALS coordinator Dr. Silvia Protopapa at or (301)-405-2579.

Date:   Thursday 29-Oct-2015
Speaker:   Dr. Jian-Yang Li (Planetary Science Institute)
Title:  "Bright Spots on Ceres and Search for Dust Around Ceres"

In this presentation, I will discuss two pieces of work with Dawn data collected during its approach to and early rendezvous with Ceres. The first part is about the mysterious bright spots on Ceres, most notably the concentration of brightest spots in Occator crater that is at least 4-5 times brighter than the average Ceres. Based on the photometric properties and color, the comparison with other objects in the solar system, as well as the associated geological setting of the bright spots, we suggest that they are likely endogenic and associated with water activities on Ceres’ surface. The second part of this talk is about a search of dust around Ceres, motivated by the active water sublimation revealed by the previous detection of water vapor around Ceres. No active dust plume or envelope is detected. The negative search results and the characteristics of Ceres activity suggest that either water sublimation is inactive during Dawn’s approach, or the dust environment around Ceres is dominated by nm-sized grains.

For further information contact PALS coordinator Dr. Silvia Protopapa at or (301)-405-2579.

Date:   Thursday 05-Nov-2015
Speakers:   Mark J. Moretto,Maggie McAdam,Michael Kelley,Matthew M. Knight
Title:  "DPS practice"

Title: Volatile Abundance and Distribution in the Tempel 1 Ejecta Cloud Speaker: Mark J. Moretto

Title: SOFIA observations of dark asteroids: Evidence for hydrated minerals on asteroidal surfaces? Speaker: Maggie McAdam

Title: Lightcurves and revised masses of the large particles at comet 103P/Hartley 2 Speaker: Michael Kelley

Title: 322P/SOHO 1: Sunskirting Comet or Asteroid? Speaker: Matthew M. Knight

For further information contact PALS coordinator Dr. Silvia Protopapa at or (301)-405-2579.

Date:   Thursday 19-Nov-2015
Speaker:   Dr. Jean-Baptiste Vincent/Max Planck Institute for Solar System Research
Title:  "Cometary activity and nucleus erosion"

Dust jets, i.e. fuzzy collimated streams of cometary material arising from the nucleus, have been observed in-situ on all comets since the Giotto mission 30 years ago. Yet their formation mechanism remains unknown. Several solutions have been proposed, from localized physical mechanisms on the surface/subsurface to purely dynamical processes involving the focusing of gas flows by the local topography. While the latter seems to be responsible for the larger features, high resolution imagery has shown that broad streams are composed of many smaller features (a few meters wide) that connect directly to the nucleus surface.

The OSIRIS cameras on board ESA’s Rosetta give us for the first time the possibility to image these features at a spatial scale better than 30 cm/px, and to monitor their evolution over many months. I will present here observational evidence that jets of comet 67P arise from fractured cliffs. These active walls show similar morphology independently of their location on the nucleus. They are fractured and present signs of ongoing erosion. Large debris fields can be observed below the cliffs, interpreted as blocks falling down from the wall. Cliffs upper edges display mass wasting features, with the upper dust layer seemingly flowing down as the edge of the cliff collapses.

My talk will review these observations and describe the physical processes involved, which may explain the resurfacing and erosion of most comets.

For further information contact PALS coordinator Dr. Silvia Protopapa at or (301)-405-2579.

Date:   Thursday 03-Dec-2015
Speaker:   Dr. Conor A. Nixon (NASA Goddard Space Flight Center)

Titan, largest satellite of Saturn, is the only moon in the solar system to possess a dense atmosphere, primarily composed of the gases nitrogen (98%) and methane (2%). These molecules are broken apart by sunlight and Saturn's magnetospheric electrons, and recombined through a photochemical cascade to produce ever larger and more complex species, mainly hydrocarbons (CxHy) and nitriles (CxHyCN). The largest molecule confirmed by remote sensing spectroscopy is benzene (C6H6). However in situ mass spectrometry of the upper atmosphere has shown a continuous mass distribution of particles up to and beyond 10,000 u. Cassini's remote sensing instruments, especially mid and far IR spectroscopy, have mapped the global and vertical abundances of some ~15 molecular species, provided direct insights into the global circulation, and constraints on photochemical models. Sub-millimeter spectroscopy has filled in some gaps, with the CH3CN species being detected in the 1993 by IRAM array, and HNC in 2011 using the Herschel space observatory. The advent of the ALMA array has provided a powerful new tool to probe Titan's atmosphere, already yielding two new molecular detections (C2H5CN and C2H3CN) with integration times of only a few minutes. In this talk I will begin by describing the current picture that we have of Titan's atmospheric chemistry, based mainly on the past 11 years of Cassini data in tandem with chemical modeling, and highlighting prominent gaps in our knowledge. I will then move on to discuss the remarkable potential of ALMA to fill in many of these gaps in the coming decade, giving examples of recent discoveries. I will conclude by mentioning the questions that even ALMA cannot address, that will await a future dedicated mission to Titan to be answered.

For further information contact PALS coordinator Dr. Silvia Protopapa at or (301)-405-2579.

Date:   Thursday 10-Dec-2015
Speaker:   Dr. Stefanie N. Milam (NASA Goddard Space Flight Center)
Title:  “Solar System science with JWST”

The James Webb Space Telescope (JWST) is optimized for observations in the near and mid infrared and will provide essential observations for targets that cannot be conducted from the ground or other missions. The state-of-the-art science instruments, along with the telescope’s moving target capabilities, will enable the infrared study, with unprecedented detail, for nearly every object (Mars and beyond) in the solar system. This presentation features highlights for planetary science applications, extracted from the recent articles recently accepted to PASP as a special edition. The goals of this special issue are to stimulate discussion and encourage participation in JWST planning among members of the planetary science community. Key science goals for various targets, observing strategies for JWST, and the latest status of the project will be presented.

For further information contact PALS coordinator Dr. Silvia Protopapa at or (301)-405-2579.

Date:   Thursday 17-Dec-2015
Speaker:   Canceled
Title:  Canceled

The talk has been postponed to spring 2016.

For further information contact PALS coordinator Dr. Silvia Protopapa at or (301)-405-2579.

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