Date: Tuesday 12-Feb-2019
Speaker: Amaya Moro-Martin (STScI)
Title: 1I/'Oumuamua
1I/'Oumuamua is the first interstellar interloper that has been detected (Williams et al. 2017) and, even though it was the subject of an intense observational campaign, its brief visit left several key questions unanswered. One of them is the number density of free-floating 1I/'Oumuamua-like objects inferred from its detection frequency, an aspect that relates to 1I/'Oumuamua's origin. I will describe how this estimate is orders of magnitude larger than what would be expected from the ejection of planetesimals from circumstellar and circumbinary disks (Moro-Martín 2018), and also from the ejection of exo-Oort cloud objects under the effect of post-main sequence mass loss, stellar encounters, and the galactic tide, even when considering the large uncertainties involved in these calculations, like the size distribution of ejected bodies (Moro-Martín 2019a). Another open question is 1I/'Oumuamua's physical properties: observations with Spitzer could not detect its thermal emission, with the 3-sigma upper limit at 4.5 mm leading to an effective spherical radius of less than [49, 70, 220] m, for an albedo greater than [0.2, 0.1, 0.01] (Trilling et al. 2018), with an axis ratio of 6±1:1, making it unusually elongated (McNeill et al. 2018). And the other puzzle regarding 1I/'Oumuamua is its non-gravitational acceleration, a 30-sigma detection that has been interpreted as evidence of outgassing (Micheli et al. 2018). The newly released Spitzer results, however, imply a 3-sigma upper limit to the CO outgassing level that is four orders of magnitude lower than what would be required to support this outgassing scenario, unless one assumes relative volatile abundances that are very different from those found in comets. Bialy & Loeb (2018) have suggested that, rather than outgassing, the non-gravitational acceleration could be due to radiation pressure. According to these authors, this would require an area-to-mass ratio corresponding to the physical properties of a thin sheet 0.3--0.9 mm in width, suggesting that 1I/'Oumuamua represents a new class of thin interstellar material that is either produced naturally by an unknown process or artificially, like a lightsail. As an alternative to this scenario, I discuss whether a naturally-produced, mass fractal structure with a high area-to-mass ratio could contribute to a radiation-pressure-driven 1I/'Oumuamua (Moro-Martín 2019b).
For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.
Date: Thursday 28-Feb-2019
Speaker: Jasmeet Dhaliwal (Penn State)
Title: Linking magmatic outgassing and atmospheric chemistry--Implications for Earth & Beyond!
The volcanic and atmospheric conditions on the early Earth are less well understood than the present, but do provide important clues to changes in magmatic and atmospheric regimes over its evolution. In particular, the Earth's mantle is an important reservoir of C-O-H-S compounds, and when these volatiles are released during magmatic and volcanic outgassing, they can become important constituents of the terrestrial atmosphere. The oxidation state of a planet, including the effects of core formation, and its volatile inventory (both intrinsic, and those acquired through bombardment processes) can also influence volatile concentrations in magmatic melts, and their subsequent outgassing. Herein, I will discuss ongoing work to develop a magmatic outgassing model with the goal of better understanding and constraining the effects of magmatic outgassing on planetary atmospheric evolution. This model requires careful parametrizations of C-O-H-S solubility in melts, conservation of mass balance and redox balance, and calculations of melt-gas equilibria. The goal is to develop an open-source model that can be used both to explore the past and present inputs of volcanic outgassing to the Earth's atmosphere, and to model the possible magmatic regimes and their volatile contributions to the atmospheres of distant exoplanets. This work is relevant to terrestrial planets within our Solar System, including Earth, and is further applicable to evaluating atmospheric compositions of exoplanets, particularly with the high-resolution data expected from next generation telescopes.
For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.
Date: Monday 4-Mar-2019
Speaker: CANCELLED: Kirby Runyon (JHU-APL)
Title: CANCELLED
CANCELLED
For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.
Date: Monday 11-Mar-2019
Speaker: Jessica Sunshine (UMD)
Title: How do Asteroids and Comets Differ: Potatoes vs. Peanuts and Other Considerations
The simple distinction between asteroids and comets, rocky vs. icy, no longer apply. Current data from many sources suggest there is both a continuum between the two groups, yet there are also real and significant difference in composition, structure, evolution, and origin.
For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.
Date: Monday 25-Mar-2019
Speaker: Maria Camarca (GSFC)
Title: A Postcard from the Young Solar System: Infrared Signatures of Comet 252P/LINEAR
Comets are remnants of our early solar system, and the ice and dust in their nuclei might help us reveal the primordial conditions of the natal environment where planets, moons, and other minor bodies eventually formed the planetary system we know today. In early 2016, comet 252P/LINEAR presented ground-based telescopes with a prime opportunity to survey a comet at close-range. In fact, on 2016 March 21, 252P made the fifth closest cometary approach to Earth on record, reaching a minimum geocentric distance of ~0.036 au (about 14 lunar distances). Just weeks after 252P made its near-Earth passage, we surveyed the molecular profile of the comet using NIRSPEC, a high-resolution infrared spectrograph at the Keck Observatory in Hawaii. In this talk, I will share the organic composition we obtained for 252P during April 2016 and discuss possible interpretations of the retrieved abundances. Furthermore, I will show the spatial profiles we derived for high signal-to-noise species and draw comparisons to other observations of 252P, including some made using the Discovery Channel Telescope.
For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.
Date: Tuesday 9-Apr-2019
Speaker: Kirby Runyon (JHU-APL)
Title: Ultima Thule: The (Continuing) Initial Results
The earliest hours of New Year’s Day, 2019, featured the most-distant robotic planetary reconnaissance ever. The varied terrain and composition on Kuiper Belt Object 2014 MU69 “Ultima Thule”) points to a formation scenario consistent with gravitational collapse of a pebble cloud and the slow merger of two bodies.
For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.
Date: Tuesday 16-Apr-2019
Speaker: Scott Sheppard (DTM)
Title: The Solar System Beyond Pluto
The Kuiper Belt, which has Pluto as the largest member, is a region of comet-like objects just beyond Neptune. This belt of objects has an outer edge, which we are only now able to explore in detail with new wide-field imagers on the worlds largest telescopes. For the past few years, our team has been performing the largest and deepest survey ever attempted to search for distant solar system objects. The ongoing search has discovered the object with the most distant orbit known in our solar system and some of the largest known trans-Neptunian objects. The uniform survey has shown that the most extremely distant objects are strangely grouped closely together in orbital space, which suggests a yet unobserved Super-Earth or larger planet is shepherding them into similar orbits that some have called Planet X or Planet Nine. I will discuss the most recent discoveries at the fringe of our solar system.
For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.
Date: Monday 22-Apr-2019
Speaker: Derek Richardson, Harrison Agrusa, Matthew Knight
Title: UMD DART Collaboration Update
NASA's Double Asteroid Redirection Test (DART) will impact binary asteroid (65803) Didymos in September 2022 in order to demonstrate asteroid deflection. This will be the first kinetic impact test at a realistic scale for planetary defense, and the resulting change in orbital period of the moon will be observable with Earth-based telescopes. Researchers from UMD are involved in many aspects of the DART mission. Derek Richardson will give an introduction and overview of the mission, Harrison Agrusa will discuss his work modeling the orbital dynamics of the Didymos system, and Matthew Knight will discuss the state of ground-based observations to characterize the system prior to the impact.
For further information contact PALS coordinator Dr. Matthew Knight at knight@astro.umd.edu or (301)-405-2629.
