Date: Tuesday 24-Feb-2015
Speaker: Jordan Steckloff (Purdue)
Title: Gas Leaks Are Dangerous!!! How Sublimating Volatiles Break Up, Push Around, and Striate Comets
Comets are composed of an intimate mixture of refractory materials and volatile ices, the sublimation of which drives cometary activity. Volatile sublimation occurs predominantly on the sunward side of the nucleus, which produces an anti-sunward pressure that pushes on its illuminated surfaces. The resulting unbalanced force produces differential stresses within the nucleus that can exceed material strength and beak it into fragments. The anti-sunward nature of this sublimation pressure leads to observable, non-gravitational perturbations in the orbital motion of the comet. We use the non-gravitational motion of Comet ISON (C/2012 S1) to estimate the size of the nucleus, the change of which over time clearly reveals that the nucleus fragmented three times, which is consistent with light curve data. We then propose that sublimation pressure caused these disruption events, and use this mechanism to estimate the strength of its nucleus and fragments.
The isotropic sublimation of volatiles also produces a sublimation-driven analogue to the YORP effect (a mechanism that changes the rotation rate of bodies). This Sublimation-YORP (SYORP) effect is 10^4-10^5 times stronger than the YORP effect, and can quickly spin up small icy bodies to the point where they fission into fragments. We apply this SYORP mechanism to hypothetical, H2O-rich parent grains (~10m in radius) ejected from the nucleus of Comet West (C/1975 V1), and show that SYORP would lead to the formation of striae (rare, linear dust features that align with the Sun, which are found within the tail of some comets) near perihelion. Unlike existing radiation pressure-driven models of stria formation, the strength of sublimation pressure readily explains how the mass of a stria (~10^6 kg) can be moved into the tail of a comet to the location of stria formation. Additionally, our SYORP mechanism naturally explains why comets with perihelia <0.6 AU only produce striae within 1 AU and only after perihelion.
For further information contact PALS coordinator Dr. Michael Kelley at msk@astro.umd.edu or 301-405-3796.
Date: Tuesday 03-Mar-2015
Speaker: ** No Speaker ** CANCELLED **
Title: ** CANCELLED **
This week's talk has been cancelled. See you next week.
For further information contact PALS coordinator Dr. Michael Kelley at msk@astro.umd.edu or 301-405-3796.
Date: Tuesday 10-Mar-2015
Speaker: Your colleages
Title: LPSC Preview
Join your pals for a preview of the 46th Lunar and Planetary Science Conference.
For further information contact PALS coordinator Dr. Michael Kelley at msk@astro.umd.edu or 301-405-3796.
Date: Tuesday 24-Mar-2015
Speaker: Carl Schmidt (UVA)
Title: Modern Planetary Applications for Small Telescopes
For bright planetary objects, telescopes <1 m can generally offer two simple advantages: time is allocated freely and operational expenses are modest. This talk will give an overview of current studies of the atmospheres of Mercury, the Moon, Io and comets using small aperture telescopes. Particular attention is given to the bright sodium component of these atmospheres due to the unique resonant scattering property. Source mechanisms of the surface-bound exospheres of Mercury and the Moon include micro-meteorite vaporization, photon-stimulated desorption, sputtering, and thermal evaporation. Na observations have proved effective in characterizing and disentangling the relative importance of each process. Small near-IR telescopes are an ideal tool to monitor volcanism on Io, and sodium observations provide a valuable proxy for it's atmospheric loss processes and interaction with the plasma torus. The relative sodium abundance in cometary comae varies by nearly two orders of magnitude, and is released through a combination of nuclear and dusty grain sources. While the Io observations evidence sodium-bearing molecular ions as a parent species (most likely NaCl+), cometary comae show marked differences between the ion and Na spatial distributions that cannot be attributed to solar radiation pressure or ion pick up.
For further information contact PALS coordinator Dr. Michael Kelley at msk@astro.umd.edu or 301-405-3796.
Date: Tuesday 31-Mar-2015
Speaker: Cancelled
Title: Cancelled
Due to a suprise emergency with our speaker, today's PALS has been cancelled and the speaker will be rescheduled for a future date.
For further information contact PALS coordinator Dr. Michael Kelley at msk@astro.umd.edu or 301-405-3796.
Date: Tuesday 07-Apr-2015
Speaker: Cancelled
Title: Cancelled
Due to a personal issue, todays's PALS has been cancelled and the speaker will be rescheduled for a future date.
For further information contact PALS coordinator Dr. Michael Kelley at msk@astro.umd.edu or 301-405-3796.
Date: Tuesday 14-Apr-2015
Speaker: Lillian Ostrach (GSFC)
Title: Revelations from MESSENGER: The Northern Smooth Plains on Mercury
MESSENGER orbital images show that the north polar region of Mercury contains smooth plains that occupy ~7% of the planetary surface area. Within the northern smooth plains (NSP) we identify two crater populations, those superposed on the NSP (“post-plains”) and those partially or entirely embayed (“buried”). The existence of the second of these populations is clear evidence for volcanic resurfacing. The post-plains crater population reveals that the NSP do not exhibit statistically distinguishable subunits on the basis of crater size–frequency distributions, nor do measures of the areal density of impact craters reveal volcanically resurfaced regions within the NSP. These results suggest that the most recent outpouring of volcanic material resurfaced the majority of the region, and that this volcanic flooding emplaced the NSP over a relatively short interval of geologic time, perhaps 100 My or less. Stratigraphic embayment relationships within the buried crater population, including partial crater flooding and the presence of smaller embayed craters within the filled interiors of larger craters and basins, indicate that a minimum of two episodes of volcanic resurfacing occurred. From the inferred rim heights of embayed craters, we estimate the NSP to be regionally 0.7–1.8 km thick, with a minimum volume of volcanic material of 4 × 106 to 107 km3. Because of the uncertainty in the impact flux at Mercury, the absolute model age of the post-plains volcanism could be either ∼3.7 or ∼2.5 Ga, depending on the chronology applied.
For further information contact PALS coordinator Dr. Michael Kelley at msk@astro.umd.edu or 301-405-3796.
Date: Tuesday 21-Apr-2015
Speaker: Matthew Knight (Lowell Obs.)
Title: Continued investigation of 103P/Hartley 2's rotational state from combined KPNO and Lowell Observatory data
Comet 103P/Hartley 2 was extensively studied during the second half of 2010 due to it being the target of the EPOXI flyby on 2010 November 4 as well as having a close approach to Earth with favorable viewing geometry. Numerous results from EPOXI and Earth-based observatories have already been published, revealing among other things, that Hartley 2 was in non-principal axis rotation and that its apparent period increased rapidly during the apparition. I will present an analysis of Kitt Peak National Observatory and Lowell Observatory observations of Hartley 2 obtained from August through December 2010. Each dataset has previously been investigated individually; the combined dataset has complementary coverage that reduces the time between observing runs and allows us to determine additional apparent periods at intermediate times. These allow us to place new constraints on the apparent period before and after intensive EPOXI observations. I will also show that our ground-based lightcurve aligns with the published EPOXI lightcurve, indicating that the lightcurve represents changing activity rather than viewing geometry of structures in the coma. Finally, I will discuss how phasing of the published EPOXI inner coma lightcurve can explain scatter in measured apparent periods.
For further information contact PALS coordinator Dr. Michael Kelley at msk@astro.umd.edu or 301-405-3796.
Date: Tuesday 28-Apr-2015
Speaker: Clara Maurel (ISAE, Toulouse, Fr)
Title: Dynamical Characterization of the Hoffmeister Asteroid Family
The (1726) Hoffmeister asteroid family is located in the middle of the Main Belt, between 2.75 and 2.82 AU. This family is close to the fourth order secular resonance z1 = s − s6 + g − g6, and in the neighborhood of the most massive asteroid of the Asteroid Belt, namely (1) Ceres. Those two features could be responsible for the strange distribution of the Hoffmeister family population in the proper semi-major axis versus inclination plane. In this paper, we investigate the dynamical behavior of the family members. From this will stem the characterization of the evolution of the Hoffmeister family in time, the estimation of its age, and an explanation of its shape in the proper elements space. To do so, we proceed to numerical integrations of orbital elements of test particles, starting from an estimated initial distribution resulting from an isotropic ejection after the catastrophic event.
For further information contact PALS coordinator Dr. Michael Kelley at msk@astro.umd.edu or 301-405-3796.
Date: Tuesday 05-May-2015
Speaker: Martin Cordiner (GSFC/Catholic Univ.)
Title: Zooming in on cometary comae: Measuring the distribution and excitation of cometary volatiles with ALMA
Comets are believed to have accreted at around the time the planets formed (c. 4.5 Gyr ago), and many have remained in a frozen, quiescent state since then. Studies of the compositions of cometary nuclei thus provide unique information regarding the physical and chemical conditions of the early Solar System. Use of gas-phase coma observations as a probe of cometary ice requires a complete understanding of the gas-release mechanisms. However, previous observations have been unable to ascertain the precise origins of fundamental coma species such as H2CO, HCN and HNC, and details regarding the possible formation of these species in the coma are not well understood. In this work, we report results from the first cometary observations using the Atacama Large Millimeter/submillimeter Array (ALMA), and present measurements of spectrally, spatially and temporally-resolved distributions of HCN, HNC, H2CO, CH3OH and dust within the comae of comets C/2012 F6 (Lemmon), C/2012 S1 (ISON) and C/2012 K1 (PanSTARRS). Highlights include the identification of time-variable, clumpy HNC structures and a calculation of the first ever 2D rotational temperature map for methanol.
For further information contact PALS coordinator Dr. Michael Kelley at msk@astro.umd.edu or 301-405-3796.
Date: Tuesday 19-May-2015
Speaker: Patrick Michel (Obs. Cote d'Azure)
Title: Asteroid Impact and Deflection Assessment (AIDA) mission: science return and technology demonstration
AIDA is a joint ESA-NASA cooperative project, which includes the ESA Asteroid Impact Mission (AIM) rendezvous spacecraft and the NASA Double Asteroid Redirection Test (DART) mission. The AIM study entered Phase A/B1 at ESA (in the technology department) in early 2015 and will proceed through summer 2016. The DART study should enter NASA Phase A in late spring 2015 and will also proceed through summer 2016. The primary goals of AIDA are (i) to investigate the binary near-Earth asteroid (65803) Didymos, including its subsurface and internal properties, (ii) to test our ability to impact its moon by an hypervelocity projectile in 2022 and (iii) to measure and characterize the deflection caused by the impact both from space with AIM and from ground based observatories. AIDA will thus be the first well documented impact experiment on a small (170 m) asteroid, including both the detailed characterization of the target, as well as the impact conditions and outcome. I will present the current status of the mission study, as well as its science and technological objectives.
For further information contact PALS coordinator Dr. Michael Kelley at msk@astro.umd.edu or 301-405-3796.
Date: Wednesday 27-May-2015
Speaker: Maggie McAdam (UMD)
Title: Aqueous Alteration on Asteroids: Linking the mineralogy and spectroscopy of primitive carbonaceous meteorites
Some primitive carbonaceous meteorites have undergone interactions (sometimes extensive interactions) with liquid water on their parent bodies soon after their formation. These interactions resulted in the production of amorphous material and phyllosilicates. The variability observed is likely caused by the distribution of water in the early Solar System. We present a coordinated spectral-mineralogical study of a large suite of carbonaceous meteorites including samples from CM, CI, CR, CO and CV groups. Meteorites from these groups represent the a wide range of initially accreted water ice as well as other initial materials. Correlations are found between degree of alteration (amount of phyllosilicates and/or amorphous material) and mid-infrared (MIR) vibrational features but few correlations are found with the visible/near-infrared overtone features. These results have been applied to the spectra of asteroids in an effort to quantify and map the amount of water in small bodies in the asteroid belt.
For further information contact PALS coordinator Dr. Michael Kelley at msk@astro.umd.edu or 301-405-3796.
Date: Friday 26-June-2015
Speaker: Brian Jackson (Boise State)
Title: Summoning Devils in the Desert
Dust devils are small-scale (few to many tens of meters) low-pressure vortices rendered visible by dust lofted in moderate to high (> 10 m/s) winds. They persist for minutes to hours and can travel kilometers, usually carried by the ambient wind. On Earth, they occur primarily in arid locations and can reduce air quality and endanger small aircraft. On Mars, they occur ubiquitously and likely dominate the supply of atmospheric dust, influence climate, and even lengthen the operating lifetimes of solar-powered landers. Studied for decades, the underlying formation, dynamics, and statistics of dust devils remain poorly understood, but the same technology revolution that brought us stealth drones and iPhones is helping to change that. In this presentation, I’ll discuss on-going field surveys involving miniature, autonomous instrumentation deployed at sites known for dust devil activity. Using a combination of pressure loggers and photovoltaic cells, these surveys are helping to reveal the underlying natures and structure of dust devils in a totally novel way. We’ve found, for example, that not all devils are dusty, but the dustiest devils are also probably the biggest. The most vigorous dust devils occur most frequently during the middle of the day in the summer, when convection driven by insolation is the most active, but low-pressure vortices apparently occur year-round, throughout the day and night. As in astronomical surveys, statistical inference using these results requires assessing important biases, including selection and detection biases, largely unconsidered in previous surveys. Accurately assessing the role of dust devils requires a complete knowledge of their population statistics since the influence of the largest and most rare devils may drastically outweigh that of smaller, more common devils.
For further information contact PALS coordinator Dr. Michael Kelley at msk@astro.umd.edu or 301-405-3796.
