XXVIII Canary Islands Winter School of Astrophysics
La Laguna, Tenerife (Spain) - 7th to 16th November 2016

List of submitted abstracts ordered by presenting author:

1 - Long-Term Volatile Transport Modeling on Pluto 
Alissa M. Earle
The data returned from NASA’s New Horizons’ reconnaissance of the Pluto system shows striking albedo variations from polar to equitorial latitudes as well as sharp boundaries for longitudinal variations. Pluto has a high obliquity (currently around 119 degrees) which varies by about 23 degrees over a period of less than 3 million years. This, combined with its regressing longitude of perihelion (360 degrees over 3.7 million years), creates epochs of “Extreme Seasons” on Pluto where one pole experiences a short, relatively warm summer and long period of winter darkness while the other experiences a much longer, less intense summer and short winter season. We explore the relationship between albedo variations and volatile transport for the current epoch as well as historical epochs during which Pluto experienced these “Extreme Seasons”. Our investigation suggests Pluto’s orbit creates the potential for runaway albedo variations, particularly in the equitorial region, which would create and support stark longitudinal contrasts like the ones we see between the informally named Tombaugh and Cthulhu Regios. 

 

2 - A search for water and methanol ices in Trans Neptunian Objects 
Ana Carolina de Souza Feliciano
The region beyond Neptune (transneptunian region) has more than 1900 objects composed of ices, which are considered the most pristine objects in the solar system. To analyze these objects from the ground, some techniques are available, as photometry and spectroscopy. We utilize reflection spectroscopy in the near infrared region for to try understand better the surface composition of these bodies. In this poster we will show the analysis of the spectra of 6 trans-Neptunian objects (TNOs) obtained at VLT using the instrument SINFONI during 2007: 38628 Huya, 90482 Orcus, 120061 2003 CO1, 136108 Haumea, 145453 2005 RR43, and 307616 2003 QW90. Our goal is try to find absorption bands of water and methanol ices, because they were present at the time of formation of the solar system and could tell us the story of their evolution. However, the spectra of TNOs show a considerable amount of noise and to better analyze them, we need to use filtering techniques to reduce the noise and better recover the absorption bands of these spectra. The technique that meets these requirements is the one using Wavelets. After filtering the whole sample we compare the cleaned spectra with spectra obtained from optical constants obtained in laboratory for water and methanol ices. In this way we find evidence of superficial water ice on 38628 Huya and 120061 2003 CO1. Also, there is evidence of methanol ice on the surfaces of 38628 Huya, 90482 Orcus, 136108 Haumea, 145453 2005RR43, and 307616 2003 QW90. We tried to find a possible grouping of objects with those ices in the orbital elements space but did not identify any preferred location. 

 

3 - Properties of resonant trans-Neptunian objects based on Herschel Space Observatory data 
Anikó Farkas-Takács
The goal of our work is to characterise the physical characteristics of resonant, detached and scattered disk objects in the trans-Neptunian region, observed in the framework of the "TNOs are Cool!" Herschel Open Time Key Program. Based on thermal emission measurements with the Herschel/PACS and Spitzer/MIPS instruments we were able to determine size, albedo, and thermal properties for 23 objects using radiometric modelling techniques. This is the first analysis in which the physical properties of objects in the outer resonances are determined for a larger sample. In addition to the results for individual objects, we have compared these characteristic with the bulk properties of other populations of the trans-Neptunian region. The newly analysed objects show e.g. a large variety of beaming factors, indicating diverse surfaces, and in general they follow the albedo-colour clustering identified earlier for Kuiper belt objects and Centaurs, further strengthening the evidence for a compositional discontinuity in the young solar system.

 

4 - Evidence of a Dawn-Dusk Molecular Oxygen Asymmetry at Europa's Exosphere 
Apurva V. Oza
Europa's icy surface is constantly bombarded by ions trapped in the Jovian magnetosphere, which sputter the surface populating a water product exosphere. Here we simulate Europa's exosphere using a ballistic 3D Monte Carlo routine and find that the O2 component, while global, is not at all homogeneous in Europa local time. The O2 exosphere, formed and ejected primarily by Jovian magnetospheric ions at a rate of ~5 kg/s with an orbit-averaged column density of N_O2 ~ 10^14 O2/cm^2, preferentially accumulates towards Europa's dusk. The inhomogeneities persist and evolve throughout the satellite's orbit, implying a diurnal cycle of the exosphere, recently evidenced by a detailed HST oxygen aurorae campaign (Roth et al. 2016). We conclude that the consistently observed 50% increase in FUV auroral emission from dusk to dawn is principally driven by Europa's rotation. This results in an O2 atmospheric bulge, whose radial column density peaks near Europa's leading hemisphere. This exospheric oxygen cycle, is primarily due to the ram direction of the incident plasma changing with respect to the subsolar and subjovian points over an orbital period. Lastly, when comparing HST observations to simulations with minimal assumptions, we find the tightly coupled O2 exosphere may be strongly influenced by Europa's non-uniform surface. Remarkably, the behavior of the near-surface O2 exosphere when compared to the FUV oxygen aurorae, acts as a tracer for the physical processes occurring in Europa's icy regolith. A similar exospheric phenomenon, driven by rotation, has been observed (McGrath et al. 2013) and simulated at Ganymede (Leblanc et al. 2016).

 

5 - Identifying the source of colours in the Jovian atmosphere 
Ashwin Braude
We wish to identify the source of Jupiter's colours through spectral analysis of images of Jupiter in the visible-to-near-infrared in conjunction with observations made by Juno in the mid-infrared and at super-high frequency. Three sets of observations were made of Jupiter by the MUSE integral-field spectrograph between 2014-2016 in the spectral range 0.48-0.93um, and reduced using a standard pipeline. Some large high-altitude hazes were observed in 2014 in the North Tropical Zone and the North Temperate Belt which appeared to have vanished by 2016. A single spectral image cube from 2014 was selected for analysis, and attempts at retrieving vertical cloud profiles, imaginary refractive indices and single-scattering albedos using the Nemesis radiative transfer model were made in different locations on Jupiter corresponding to the most prominent features close to the Equatorial region. Differences in lower tropospheric cloud altitude and opacity were found between the zones and the belts, and the belt cloud particles were seen to be significantly more blue-absorbing than the zone particles. Attempts were made at retrieving the real refractive index of the cloud particles in the upper tropospheric haze, where the majority of the colour-producing particles, or 'chromophores', are thought to be located, and values of refractive index greater than that of ammonia ice were observed, indicating the presence of a foreign substance. Further ground-based observations from MUSE in the visible and from TEXES in the mid-Infrared combined with localised observations from Juno later this year should shed more light on the origin of the colour-producing substance in the Jovian clouds, as well as of any seasonal changes in colour. 

 

6 - Photometry and colors of NEAs at the origin of meteor showers 
Bogdan A. Dumitru
Near-Earth Asteroids and comets are the parent bodies of meteor showers. The association between meteor showers and their possible parent bodies are usually based on dynamical elements similarity. However, the parent body physical properties are essential in characterizing meteoroids production, size and mineralogical composition. These characteristics are very important mainly in the case of NEAs possible parent bodies. From our dynamical analysis, 41 of meteor showers have probabilities to be produced by asteroids. Our sample of asteroids contains more than 1,000 objects, all of them belonging to the Near-Earth Asteroid population. Into our sample, we reproduce the association of 3200 Phaeton to Geminid meteor shower, as well as the association of 1991 AQ to Northern delta Capricornids. Some of our associations are puzzling while the results seem to diverge from the one of the literature. A systematic approach concerning the physical properties of our sample was performed and reinforced the link between asteroids and the associated meteor shower. An observational campaign was started in 2014 at Pic du Midi 1 meter telescope for the characterization of NEAs potential parent bodies of meteors. Five objects were observed in April 2016 in order to obtain colors and lightcurves. The results of this campaign will be presented. 

 

7 - Decimetre-scaled spectrophotometric properties of the nucleus of comet 67P/C.-G. from the OSIRIS observations. 
Clement Feller
The ROSETTA mission is the cornerstone mission of the European Space Agency devoted to the study of the minor bodies of the Solar System. Its primary objective is to perform an extensive study of the comet 67P/Churyumov-Gerasimenko. Since its encounter with 67P/CG in July 2014, the spacecraft has been escorting the nucleus thus allowing us to study it with cameras, spectrometers, dust analysers and radio science experiments. The spacecraft will continue its escort until the end of September 2016. The OSIRIS instrument (Keller et al., 2007) is the scientific imaging system on-board the Rosetta spacecraft, composed of a Narrow-Angle Camera (optimized for the study of the nucleus mineralogy) and a Wide-Angle Camera (optimized for the study of gaseous species and dust in the coma). On the 14th of February 2015, the spacecraft performed a flyby manoeuvre 6km away from the surface near to the frontier between the Ash, Apis and Imhotep morphological regions (El-Maary et al. 2015). The OSIRIS instrument obtained close to a hundred filter images with a decimetre resolution and on which the phase angle ranges from 0 to  37 degrees. Those images were treated with the OSIRIS standard pipeline, coregistered and assembled into hyper-spectral cubes. A Digital Terrain Model of the region overflown was generated to retrieve the illuminations conditions at a high resolution scale. We applied the Lommel-Seeliger disk law to correct the dataset for the illuminations conditions in the spectrophotometric analysis. For the photometric analysis, we fitted the data set with the Hapke 2002 model with a porosity correction (Helfenstein et al. 2011). We present here the results of our analyses, and their comparison with laboratory samples studies.

 

8 - Sulamitis: A link Between Two Families? 
David Morate
Asteroid families are formed by the fragments produced by the disruption of a common parent body resulting from a collision event (Bendjoya et al. 2002, Asteroids III, University of Arizona Press, p 613). Primitive asteroids (C, B, and X classes, and their respective subclasses) in the solar system are believed to have undergone less thermal processing compared with the differentiated asteroids (S class and subclasses). The study of primitive asteroid families provides information about the solar system formation period. The Sulamitis collisional family is located in the inner part of the asteroid belt, and, together with other three families (Polana, Erigone, and Clarissa) and a population of background asteroids, it is believed to be the origin of the two primitive Near-Earth asteroids that are the main targets of the NASA’s OSIRIS-REx and JAXA’s Hayabusa 2 missions, Bennu and Ryugu, respectively. The two asteroids will be visited by these spacecrafts and a sample of their surface material will be returned to Earth. Therefore, understanding of the families that are considered potential sources will enhance the scientific return of the missions.
The main goal of the work presented here is to compositionally characterize the Sulamitis collisional family. Asteroid (752) Sulamitis is a primitive object, and we expect the members of this family to be compositionally consistent with the spectral type of the parent body. At the moment, we have obtained visible spectra (0.5-0.9 microns) of a total of 67 members of the Sulamitis family, using the OSIRIS instrument at the 10.4m Gran Telescopio Canarias. We performed a taxonomical classification of these asteroids, finding that the number of primitive asteroids in our sample is in agreement with the hypothesis of a common primitive parent body. In addition, we have found a significant fraction of asteroids in our sample that present evidence of aqueous alteration, in a proportion very similar to that shown in Morate et al. 2016 for the Erigone family, which might point to a special relationship between these two asteroid clusters.

 

9 - Boulders at the Surface?: Searching for the Brazil-Nut Effect on NEAs 
Eric M. MacLennan
It has been shown that "spectrally fresh" (Q- and Sq-type) asteroids are always found in orbits that can bring them in close proximity to at least one terrestrial planet. This observation is used to infer that these close planetary encounters (i.e. tidal interactions) are likely causing regolith mobilization on these bodies. This mechanism may lead to particle size segregation on the surface and interior of these bodies, particularly the sorting of large boulders to the surface. Since a large spatial fraction of boulders will raise the thermal inertia of a surface, we aim to constrain the thermal inertia of our targets using thermal emission observations with the Spitzer Space Telescope/IRAC. The thermal inertia of boulders is much larger than that of fine-grained regolith. Therefore, we hypothesize that the thermal inertia small spectrally fresh asteroids will be systematically larger compared to the whole near-Earth asteroid population. The thermal inertia constraints will be made by using measurements of the thermal emission of approximately one dozen Q- and Sq-type near-Earth asteroids combined with a thermophysical model. The observations are made such that we can detect the effect of different diurnal temperature variation brought on by different thermal inertia values. We will present our thermal inertia estimates and a preliminary analysis of the data as it relates to our hypothesis.

 

10 - Physical properties of Centaur (54598) Bienor from photometry. 
Estela Fernández-Valenzuela
Centaurs are objects with unstable orbits located between Jupiter and Neptune. They came from the Trans-Neptunian Belt and are thought to be the progenitors of short period comets. Due to their relatively large distant to the Sun, Centaurs are not heavily processed. Therefore, they yield important information about the formation of the Solar System specially for its outer part. For this reason, they are very interesting objects and only a hundred of them are known, fewer than Trans-Neptunian Objects. Bienor is one of the biggest centaurs so its study is even more interesting. In addition, ring material around two Centaurs of similar size was found, Chariklo and Chiron. In this work, we present time series photometry of Bienor in two observation runs in years 2014 and 2015 and compare them with previous observations in 2000. The results show a remarkable decrease in the amplitude of the rotational light curve. This suggests that the angle between the rotation axis and the line of sight direction has changed notably during the last 15 years due to the orbital movement around the Sun. From these data, from absolute photometry and from other data in the literature we are able to determine the orientation of the rotation axis of Bienor. In addition, we are also able to constrain the three axis dimensions of an ellipsoidal body (which is used as a starting shape) and we have determined a density based on the assumption of hydrostatic equilibrium. Bienor is the fourth Centaur for which these achievements have been made. 

 

11 - Spectral modeling for the Chelyabinsk meteorite at UV-VIS-NIR wavelengths 
Julia Martikainen
Asteroids provide us information on the evolution of the Solar System. Meteorites and asteroids can be linked by matching their respective reflectance spectra. However, this is difficult because the spectral features depend strongly on the surface properties. To better interpret the spectra, we need to gain more knowledge of the light-scattering physics involved. The University of Helsinki integrating-sphere spectrometer has been utilized to measure the reflectance spectra of two lithologies of the Chelyabinsk meteorite (light-colored and dark-colored) at UV-Vis-NIR wavelengths (0.25-3.2 microns). Microtomography images of the light-colored and the dark-colored lithologies have also been taken. The light-colored lithology has the highest reflectance and shows broad absorption bands of olivine and pyroxene near 1.0 and 2.0 microns. The dark-colored lithology has a flat spectrum with diminished intensity. The differences in the spectra are caused by different patterns of iron and iron sulfides in the samples that can be seen in the microtomography and scanning electron microscope images. We utilize the SIRIS-code (Muinonen et al.,JQSRT 110, 2009), which simulates light scattering by Gaussian-random-sphere particles that are large compared to the wavelength of the incident light, to model the effects of iron and iron sulfides in the spectra of the two lithologies of the Chelyabinsk meteorite by entering the physical properties, such as refractive indexes, of the two lithologies as input parameters for the simulations. Acknowledgments. The research is funded by the ERC Advanced Grant No. 320773 (SAEMPL) and Academy of Finland grant 1257966.

 

12 - Asteroid mass estimation using Markov-Chain Monte Carlo techniques 
Lauri Siltala
Estimates for asteroid masses are based on their gravitational perturbations on the orbits of other objects such as Mars, spacecraft, or other asteroids and/or their satellites. In the case of asteroid-asteroid perturbations, this leads to a 13-dimensional inverse problem where the aim is to derive the mass of the perturbing asteroid and six orbital elements for both the perturbing asteroid and the test asteroid using astrometric observations. We have developed and implemented three different mass estimation algorithms utilizing asteroid-asteroid perturbations into the OpenOrb asteroid-orbit-computation software: the very rough 'marching' approximation, in which the asteroid orbits are fixed at a given epoch, reducing the problem to a one-dimensional estimation of the mass, an implementation of the Nelder-Mead simplex method, and most significantly, a Markov-Chain Monte Carlo (MCMC) approach. We will introduce each of these algorithms with particular focus on the MCMC algorithm, and present example results for real data. Our results agree with the published mass estimates, but suggest that the published uncertainties may be misleading as a consequence of using linearized mass-estimation methods. Finally, we discuss remaining challenges with the algorithms as well as future plans, particularly in connection with ESA's Gaia mission.

 

13 - L type asteroids: a link to the primordial solar system ? 
Maxime Devogèle
A few years ago, asteroid polarimetry allowed to discover a class of asteroids exhibiting peculiar phase polarization curves, collectively called "Barbarians" from the prototype of this class, the asteroid (234) Barbara. All such objects belong to the L visible plus near infrared based taxonomic class. The anomalous polarization has been tentatively interpreted in terms of high-albedo, spinel-rich Calcium-Aluminum inclusions (CAI) which could be abundant on the surfaces of some of these asteroids, according to their spectral reflectance properties and to analogies with CO3/CV3 meteorites. Such CAIs are thought to be among the oldest mineral assemblages ever found in the Solar System. Barbarians' surfaces could therefore be rich in this very ancient material and bring information on the early phases of planetary formation. Based on such information, a systematic campaign for photometric, polarimetric and spectroscopic characterization has been conducted. These observation campaigns allowed to improve our general knowledge about these peculiar asteroids and highlight the link between polarization and polarimetric properties. As it was suggested, a link between the presence of CAI and the polarimetric response was found. Our observations show that the relative abundance of CAI is correlated with the polarimetric inversion angle. This is the first time that a direct link between polarimetric and spectroscopic properties is found. 

 

14 - The source of PacMan's Power: Radiation induced sintering of icy regoliths. 
Micah J. Schaible
A unique space weathering phenomenon has been identified on several icy Saturnian moons. Cassini revealed anomalous lens shaped regions in both optical and thermal wavelengths, colloquially known as the 'PacMan' feature, which are centered on the leading hemispheres and approximately symmetric about the equators. In particular, the Cassini InfraRed Spectrometer (CIRS) measurements of thermal emission in the mid-IR showed that surface temperature variations during a diurnal cycle were smaller inside the anomalous regions. The locations of the anomalies were shown to closely match the expected deposition profile of high energy (~ MeV) electrons moving counter rotational to the moons, suggesting an energetic source to drive their formation. However, the mechanisms by which thermal conductivity enhancement occur lack quantitative comparison with theoretical and experimental results. Electron interactions with the grains can excite molecules, which, if near enough to an intergrain contact, can cause atoms or molecules to migrate into the contact region, thus increasing the contact volume or 'sintering' the grains. Sintering improves the thermal contact between grains, leading to increased effective thermal conductivity of the regolith. The unique electron energy distribution measured in the vicinity of each of the moons was to determine the rate of electron excitation events. Molecular dynamics simulations of excited electrons in water ice were carried out to determine the number of mobilized molecules and their average diffusion length. These parameters are used to determine an effective radiation induced diffusion coefficient which was then used with standard sintering equations to estimate the timescale for the energetic electrons to increase the contact volume sufficiently to describe the enhanced thermal conductivity of the anomalous regions. The sintering timescales were compared to published values for micrometeorite resurfacing rates in order to determine if electron induced sintering can create a stable equilibrium on the surface of the moons.

 

15 - Absolute V-R colors of trans-Neptunian objetcs 
María del Carmen Ayala Loera
The Transneptunian objects, TNOs, are primitive bodies in the Solar System which are beyond Netune's orbit. Photometric observations of TNOs provide information about their physical and dynamical properties such as albedo and rotation. The reduced magnitude of a TNO is the calibrated magnitude to the standard system, M, normalized to r and Delta, which are the heliocentric and the geocentric distance respectively, V(1,1,alpha) = M – 5 log(r dDelta). The absolute magnitude, H, is defined as the reduced magnitude of the object at zero phase angle, alpha=0. The phase angle, alpha, is defined as the angle, measured at the location of the body, that the Earth and the Sun subtend. We estimate the absolute magnitude following the procedure used by Alvarez-Candal et al. 2016. V(1, 1, alpha) = H + alpha x beta, where alpha is the phase angle of the TNO, H is the absolute magnitude and beta is the change of magnitude per degree. What is done in practice is to create the phase curve using the reduce magnitude, to fit a first order equation obtaining H as the y-intercept and beta as slope of the latter equation. The estimation of absolute magnitudes is necessary to constrain diameters and geometric albedos of TNOs. The main scope of this work is to calculate the absolute magnitudes, H, and the phase coefficients of TNOs and obtaining their phase curves. We present results for XX objects in filters V and R. We show their distribution according to H and beta and compute the absolute colors (HV-HR) of YY objects.

 

16 - Lightcurves of main belt asteroids for shape reconstruction 
Róbert Szakáts
In the framework of the Small Bodies Near and Far Horizons 2020 project our team is characterising asteroids, from the near-Earth environment to the outskirts of the Solar system, using data from multiple sources: ground based and space-born observations obtained at radio, submm, infrared and visual wavelengths. As part of this programme we observe the light curves of main belt asteroids using the 1m RCC and 60/90 Schmidt telescopes of Konkoly Observatory which are then used in light curve inversion techniques to obtain shape solutions. In this poster I present the latest results for a sample of these targets including 1499 Pori and 727 Nipponia.

 

17 - Dynamics of the Oort Cloud in the Gaia Era I: Close Encounters 
Santiago Torres 
The comets in the Oort cloud evolve under the influence of internal (giant planets) and external (stellar passages, the galactic tide, and interstellar medium) perturbations. The external perturbations are difficult to describe, because the past (and future) orbit of the Sun in the Galaxy is not know. However, from the observed stars in the solar neighborhood, it is possible to identify some stellar encounters, the Sun had in the recent past or will have in near future. Using the positions, parallaxes and proper motions from TGAS in Gaia DR1 and combining with the radial velocities from RAVE DR5, we computed backward and forward in time (-/+10Myr) the 6D elements for the stars in the immediate solar neighborhood (<30pc) to identify past and future encounters with those, and to study the selection effects influencing the inferred encounter rates and ultimately to assess the impact of encounters on the dynamics of the Oort cloud. I will present the first results from the study to identify the past and future encounters.

 

18 - Towards a new kind of radiative transfer 
Timo Väisänen
Electromagnetic scattering problems can be solved using exact or approximate methods. Exact methods are closest to reality but these methods are too impractical for large objects like asteroid surfaces due to high demand of computing resources. The radiative transfer is a method which is based on heavily approximated Maxwell's equations. The radiative transfer is applicable to sparse media but we have developed a new kind of radiative transfer approach, which expands the applicability of the radiative transfer to dense media. This is achieved by representing the electric field with spherical harmonics, computing interactions between waves and scatterers exactly, and using incoherent field treatment. 

 

19 - Computational and Experimental Simulation of Exhaust-Regolith Interactions 
Wesley A. Chambers
Space missions operating near the surface of a small body must consider the potentially hazardous effects of thrusting. We present current progress in simulating the effects of rocket exhaust on asteroid regolith. This effort includes both computational and experimental components. The Python Regolith Interaction Calculator (PyRIC) simulates gas diffusion into regolith and quantifies regolith instability resulting from pressure gradients. Pressure at the regolith surface is calculated for exhaust gas produced from a small hydrazine engine. The resulting diffusion into regolith is computed according to Darcy’s Law, which approximates gas flow through a porous medium. Areas of potential instability due to this flow are then analyzed. Our parameter space is tailored to NASA’s Asteroid Redirect Mission (ARM); we determine soil ejection for nominal engine height to be unlikely. To improve our simulation, we are building an experiment to test gas impingement on regolith simulant in vacuum and microgravity conditions. A vacuum chamber will house the experiment, which will be undergo free-fall in a drop tower to generate microgravity conditions for a brief period. Preliminary ground-based tests direct compressed air through a rocket nozzle at regolith simulant, and we will discuss the resulting behavior around the instability threshold. These tests will inform our final experiment design, and aid in the characterization of actual regolith distributions. 

 

20 - Global Explorations of Inner Gas Coma of Comet 67P/ Churyumov-Gerasimenko with DSMC Approach 
Ying Liao
Direct Simulation Monte Carlo (DSMC) is a powerful numerical method to study rarefied gas flows such as cometary comae and has been used by several authors over the past decade to study cometary outflow. For the target of ESA’s Rosetta mission, comet 67P/Churyumov–Gerasimenko, we have identified to what extent modification of several parameters influence the 3D flow and gas temperature fields and have attempted to establish the reliability of inferences about the initial conditions from in situ and remote sensing measurements. A large number of DSMC runs have been completed with varying input parameters. In this work, we present the simulation results and conclude on the sensitivity of solutions to certain inputs. It is found that among cases of water outgassing, the surface production rate distribution is the most influential variable to the flow field.