List of Past Planetary Astronomy Lunches (PALS) : 01-Jan-2014 to 01-Jun-2014

Date:   Tuesday 04-Feb-2014
Speaker:   Brian Jackson (DTM)
Title:  On the Edge: Exoplanets with Orbital Periods Shorter Than a Peter Jackson Movie

The vast majority of gas giant exoplanets with close-in orbits is unstable against tidal decay and may spiral into their host stars in only a few billion years. Moreover, rocky planets with orbital periods of only a few hours would induce stellar radial velocity (RV) signals measurable by current facilities. Motivated by these considerations, I recently led a search for very short-period transiting planets using Kepler data. We found four planetary candidates, with periods as short as four hours, and one candidate was independently discovered and confirmed by follow-up RV observations. This planet, Kepler-78 b, has an Earth-like density but an orbital period of only 8.5-hours and a surface temperature approaching 3,000 K. These potentially rocky planets in orbital periods of only a few hours have opened an exciting, new avenue for exoplanet study but pose severe challenges to theories of planet formation and evolution. In this presentation, I'll discuss our search for very short-period planets and their observational and theoretical implications. I'll describe why the usual origin scenarios for close-in planets may not apply to these candidates and the possibility that they are remnant fossil cores of disrupted close-in gas giants. Whatever their origins, such planets would be particularly amenable to discovery by the planned TESS mission and detailed follow-up.

Brian Jackson -- Carnegie Dept. of Terrestrial Magnetism, Washington DC --

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

Date:   Tuesday 18-Feb-2014
Speaker:   Tim McClanahan (GSFC)
Title:  Evidence for upper latitude hydration of the Moon's poleward-facing slopes

Over 60 years ago the great geochemist Harold Urey postulated the possibility that volatiles, including hydrogen, may be sequestered in the cryogenic conditions of permanent shadowed regions near the lunar poles. Any sustained human presence on the lunar surface will require hydrogen as an exploitable resource and in more recent years a multi-national armada of scientific missions and instruments was deployed to understand the distributions of hydrogen on the lunar surface. In July 2009 the Lunar Reconnaissance Orbiter (LRO)'s, Lunar Exploration Neutron Detector (LEND) began observations of the lunar surface using its specialized collimated epithermal detector system to measure the surface emission flux of epithermal neutrons. Now, over 4.5 years later we review evidence that LEND finds a pervasive hydration of the Moon's poleward-facing slopes above 60 degrees latitude. Perhaps, more importantly sloped hydration appears to be occurring in a continuum of spatial-scales, perhaps to meter-scales, where contrasts in surface illumination and temperature conditions can be at least temporarily maintained. We also review corroborating evidence from the LEND's uncollimated Sensor for EpiThermal Neutrons (SETN) and the Lunar Prospector Neutron Spectrometer (LPNS).

Dr. Tim McClanahan is a computer and planetary scientist at the NASA Goddard Space Flight Center. He currently is a participating scientist with the LEND science team and an LRO associate project scientist in charge of specialized instrument operations.

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

Date:   Tuesday 25-Feb-2014
Speaker:   Christine Hartzell (UMD)
Title:  Dust Dynamics on Small Bodies

Small regolith grains have been observed on asteroids, specifically in the smooth neck region of Itokawa and the Eros dust ponds. Since the gravity of these bodies is very small, cohesion and electrostatic forces, which are usually negligible on Earth, become important forces. In fact, it has been hypothesized that electrostatic charging of dust grains could cause them to be lofted off the surface of asteroids and that the resulting redistribution of regolith could have created the Eros dust ponds. However, others have argued that the Eros dust ponds are due to mass wasting. In this talk, we will present analytical and experimental results showing the importance of cohesion in evaluating the feasibility of electrostatic dust lofting and the new computational granular mechanics model that we are creating to simulate granular flows in the small body surface environment. Our goal is to model the behavior of regolith on small bodies taking into account non-gravitational forces for the purpose of understanding the evolution of these bodies as well as improving the design of spacecraft to visit them.

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

Date:   Tuesday 04-Mar-2014
Speaker:   Carolyn Ernst (JHU/APL)
Title:  Riddles in the Dark: Water Ice at the Poles of Mercury

Numerous lines of evidence independently point to the presence of water ice in Mercury's polar regions: Earth-based radar shows radar-bright regions; Mariner 10 and MESSENGER Mercury Dual Imaging System images reveal that these regions are permanently (south polar region) or persistently (north polar region) shadowed; neutron spectrometry indicates hydrogen-rich material; thermal models support the presence of water ice; and Mercury Laser Altimeter reflectance measurements at 1064 nm show high and low reflectance deposits consistent in location to where models predict surface and buried water ice, respectively. Throughout 2013, MESSENGER executed a campaign dedicated to imaging the permanently shadowed crater floors of Mercury's north polar region using sunlight scattered from nearby terrain. I will discuss these observations, efforts to characterize the morphology of small craters that host radar-bright deposits, and what the findings may mean for the source, nature, emplacement timeframe, and migration of water ice on the planet closest to the Sun.

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

Date:   Tuesday 11-Mar-2014
Speaker:   Your Colleagues
Title:  LPSC Preview

Join your pals for a preview of the 45th Lunar and Planetary Science Conference:

L. C. Cheek - Spectral Mixture Analysis as a Tool for Characterizing the Distribution of Vesta's Olivine-Rich Material

J. M. Sunshine - Widespread Exposures of Small Scale Spinel-Rich Pyroclastic Deposits in Sinus Aestuum

M. M. McAdam - Seeing Past Alteration: Revealing the Spectral Signature of the Primary Mineralogy of GRA 06128/9

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

Date:   Tuesday 25-Mar-2014
Speaker:   Silvia Protopapa (UMD)
Title:  Optical Constants of the Methane-Nitrogen Binary Ice System: Implications for Methane-Dominated Transneptunian Objects

Pluto, Eris, and Makemake, unlike most Transneptunian objects (TNOs) with water ice-rich or featureless surfaces (Barucci et al., 2008), display infrared spectra dominated by methane ice (Brown, 2008). These three TNOs are often compared with Neptune's large satellite Triton, since its spectrum is similarly dominated by methane ice and it is thought to have formed similarly to Pluto, Eris, and Makemake, prior to its capture into a retrograde orbit around Neptune. In addition to methane ice, nitrogen ice has been directly detected on Pluto and Triton via the 2.148 micron absorption band (Cruikshank et al., 1984; Owen et al., 1993). Thermodynamic equilibrium dictates that if methane and nitrogen ices are both present, for most of the range of possible nitrogen/methane relative abundances, two distinct phases must coexist at temperatures relevant to the surfaces of these icy dwarf planets (Prokhvatilov and Yantsevich, 1983; Lunine and Stevenson, 1985): methane ice saturated with nitrogen, and nitrogen ice saturated with methane. We present infrared absorption coefficient spectra in the wavelength range 0.8-2.5 micron of methane diluted in nitrogen, and nitrogen diluted in methane at temperatures between 40 and 90 K and at different mixing ratios, allowing a proper model to be constructed for any TNO where the methane/nitrogen ratio falls between the two solubility limits such that both phases are present.

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

Date:   Tuesday 08-Apr-2014
Speaker:   Leah Cheek (UMD)
Title:  Lunar Highland Crustal Mineralogy from Reflectance Spectroscopy of Plagioclase-Dominated Materials

The anorthositic crust of the Earth's moon is one of the best laboratories to study the end products of magma ocean crystallization processes. Not only have samples of the primitive, plagioclase-dominated component of the lunar crust been analyzed in terrestrial facilities, but this lithology is readily exposed across the Moon's surface for global analysis by remote sensors. However, only in the past five years have remote sensing data become available of sufficient quality to reveal the mineralogic character of these most plagioclase-rich exposures. As we are poised to conduct outcrop-scale mineralogic analyses of the anorthositic crust across the globe, I am interested in building up ground-truth data with which to interpret the new types of spectral characteristics coming into view from orbital near-infrared spectrometers. I will present a combination of laboratory reflectance analyses and lunar remote sensing observations aimed at deciphering small variations in mineral abundances in plagioclase-dominated materials. The results emphasize that minor variations in the relative proportions of plagioclase and other more absorbing minerals produce substantial and easily observable changes in bulk spectral properties. I will show examples of select locations on the Moon where spectral properties resemble the unique composite absorption features characterized in the laboratory data, and discuss the implications for the crystallization processes that constructed the Moon's anorthositic crust early in its evolution.

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

Date:   Tuesday 15-Apr-2014
Speaker:   Fiorangela La Forgia (Univ. Padova)
Title:  Modeling the Surface Properties of Asteroid 21 Lutetia and Detection of OH Prompt Emission in the Innermost Coma of 103P/Hartley 2 using Spacecraft Imaging

The European space mission Rosetta and the NASA EPOXI mission share the common goal to investigate the many unanswered questions that still concern asteroids and comets. Space missions have the unique capability of allowing observations of small bodies at very short distances and, at the same time, from a very quickly changing geometry. Investigations of a secondary target of Rosetta, asteroid Lutetia, allowed us to model its surface reflectance and its dependence on the observation geometry. Lutetia displays a bright surface, made of very small and opaque particles with an overall smooth outer layer, presenting a very strong phase reddening effect and a slight color variegation. Observations of comet Hartley 2, target of EPOXI, allowed on the other hand to investigate the very innermost coma regions, usually inaccessible from Earth, revealing a strong OH feature coming directly from the nucleus of the comet which we possibly attribute to UV prompt emission of OH in the very vicinity of the nucleus.

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

Date:   Tuesday 22-Apr-2014
Speaker:   Daniel Jontof-Hutter (NASA Ames)
Title:  Measuring the masses and radii of sub-Neptunes with transit timing variations

The bounty of sub-Neptunes discovered by Kepler enables us to study a regime in planetary size and mass that is absent from the Solar System. This regime includes a transition from rocky planets, to those with substantial envelopes of volatiles-- either ices or gases. Characterizing these worlds by their bulk densities can probe this transition, but this requires mass and radius determinations.

Outside our solar system, there is a small sample of planets with known masses and radii, mostly hot jupiters whose radii are known from transit depths, and whose masses are determined from radial velocity spectroscopy (RV). In the absence of mass determinations via RV observations, transit timing variations (TTVs) offer a chance to probe perturbations between planets that pass close to one another or are near resonance, and hence dynamical fits to observed transit times can measure planetary masses and orbital parameters. Such modeling can probe planetary masses at longer orbital periods than RV targets, although not without some challenges. For example, in modeling pairwise planetary perturbations, a degeneracy between eccentricity and mass exists that limits the accuracy of mass determinations. Nevertheless, in several compact multiplanet systems, fitting complex TTV signals can break the degeneracy, permitting useful mass determinations.

The precision in measuring the radius of a transiting planet rests on the uncertainty in the stellar radius, which is typically ~10% for targets with spectral follow-up. With dynamical fits, however, solutions for the orbital parameters including the eccentricity vectors can, alongside the transit lightcurves, tightly constrain the stellar density and radius. Our dynamical fits to TTVs, alongside spectroscopic data on the host star, permit stellar and hence planetary radius uncertainties of just 2% at Kepler-11 and Kepler-79 (KOI-152), permitting useful planetary density determinations. Both of these systems harbor low mass planets of remarkably low density. These results reveal fascinating systems that challenge formation scenarios, but also reveal and contrast the detection biases of RV and TTV.

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

Date:   Tuesday 29-Apr-2014
Speaker:   **CANCELLED**
Title:  **CANCELLED**

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

Date:   Thursday 26-Jun-2014
Speaker:   Your Colleagues
Title:  Asteroids, Comets, Meteors

A special edition of PALS: practice talks for the upcoming Asteroids, Comets, Meteors conference. Potential speakers are listed below. The format will be the same as the meeting: 8 min for the talk, 2 min for speaker change.

Leah Cheek - Evidence of differentiated near-surface plutons on Vesta in integrated Dawn color images and spectral datasets.

Tony Farnham - Comet Siding Spring (C/2013 A1) and its close approach to Mars.

Lori Feaga - Comet 103P/Hartley's volatiles within 100 kilometers:

Matthew Knight - Sungrazing comets: Probing the inner extremes of the Solar System.

Ludmilla Kolokolova - Modeling of light scattering by icy bodies. Sources of water and volatile dependence on illumination.

Jian-Yang Li - Imaging C/2013 A1 (Siding Spring) with the Hubble Space Telescope

Lev Nagdimunov - Modeling the ejecta cloud in the first seconds after Deep Impact

Maggie McAdam - Alteration on asteroids: Insights from CM/CI meteorite mineralogy and midwave-infrared spectroscopy.

Silvia Protopapa - Further characterization of the physical makeup and dynamical behavior of water ice and dust in comet 103P/Hartley 2

Derek Richardson - Applications of granular-dynamics numerical simulations to asteroid surfaces.

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

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