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NEAR-INFRARED OBSERVATIONS OF COMET-ASTEROID TRANSITION OBJECTS
Title
NEAR-INFRARED OBSERVATIONS OF COMET-ASTEROID TRANSITION OBJECTS.
Creator
Ziffer, Julie, Campins, Humberto, University of Central Florida
Abstract / Description
The primary objective of this research is to characterize the surface composition of five comet-asteroid transition objects via near-infrared spectroscopy. The five targets include two asteroids with Tisserand invariants lower than 3.0 (1373 Cincinnati and 2906 Caltech), one asteroid that is likely an extinct comet (944 Hidalgo), one intermittent activity comet (162P/Siding Spring), and one nearly dormant comet (28P/Neujmin1). Previous research regarding cometary end states and dynamical and...
Show moreThe primary objective of this research is to characterize the surface composition of five comet-asteroid transition objects via near-infrared spectroscopy. The five targets include two asteroids with Tisserand invariants lower than 3.0 (1373 Cincinnati and 2906 Caltech), one asteroid that is likely an extinct comet (944 Hidalgo), one intermittent activity comet (162P/Siding Spring), and one nearly dormant comet (28P/Neujmin1). Previous research regarding cometary end states and dynamical and physical properties of comets and asteroids provides the foundation for this work. Focusing primarily on the 1-2.5 ?m spectral region of the five target objects, this project specifically searches for mineral species such as olivine, pyroxene, hydrated silicates, and organics. Comparisons are made with comets, main belt asteroids, and Trojan asteroids. All our targets have near-infrared spectra with varying "red" slopes from S'=1.7 to 5.3. Slopes in this range are characteristic of both primitive asteroids and comets. Three of our objects, 944 Hidalgo, 162P/Siding Spring, 28P/Neujmin 1, showed relatively featureless near-infrared spectra. The two objects dynamically most likely to be of asteroidal origin, 1373 Cincinnati and 2906 Caltech, both displayed features in the 0.8 to 2.5 micron range, not present in any of our other targets or the comparison cometary nuclei. Spectra of 944 Hidalgo were acquired at several rotational phases and clear rotational variations were found. Hints of spectral variability were also observed in 28P/Neujmin 1 and 162P/Siding Spring. Neither 1373 nor 2906 were examined for rotational variability. Based on our results, we believe that 1373 Cincinnatti and 2906 Caltech are not cometary. The spectral range of our targets and cometary spectra in the near-infrared is the same as that of Trojan asteroids. Recommendations for future investigation are suggested.
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Date Issued
2006
Identifier
CFE0001152, ucf:46855
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001152
Investigating compositional variations of S-complex near-Earth asteroids: (1627) Ivar
Title
Investigating compositional variations of S-complex near-Earth asteroids: (1627) Ivar.
Creator
Jones, Jenna, Fernandez, Yan, Britt, Daniel, Campins, Humberto, Howell, Ellen, University of Central Florida
Abstract / Description
We seek to investigate the complexity and heterogeneity of the surfaces of near-Earth asteroids (NEAs). In particular, we are studying the S-complex NEAs, which account for a large portion of the observed near-Earth objects. Here we present our results for (1627) Ivar, an Amor class NEA with taxonomic type Sqw. In 2013, Ivar's large size and close approach to Earth (minimum distance 0.32 AU) provided an opportunity to observe the asteroid over many different viewing angles for an extended...
Show moreWe seek to investigate the complexity and heterogeneity of the surfaces of near-Earth asteroids (NEAs). In particular, we are studying the S-complex NEAs, which account for a large portion of the observed near-Earth objects. Here we present our results for (1627) Ivar, an Amor class NEA with taxonomic type Sqw. In 2013, Ivar's large size and close approach to Earth (minimum distance 0.32 AU) provided an opportunity to observe the asteroid over many different viewing angles for an extended period of time. We collected delay-Doppler radar images and Doppler spectra using the Arecibo Observatory's 2380 MHz radar, and, by incorporating an extensive lightcurve collection, we have constrained the shape and spin state. In addition, we observed Ivar using NASA's IRTF's SpeX mode to gather rotationally resolved reflected and thermal spectra in the near-IR regime. We have created a high-resolution shape model, and we have found Ivar to have a sidereal period of 4.7951689 (&)#177; 0.0000026 hours with a pole at ecliptic longitude and latitude 336(&)deg;, +37(&)deg; ((&)#177; 6(&)deg;) respectively. We also show that Ivar is more elongated than previous studies suggests, with dimensions along the principal axis 15.15 x 6.25 x 5.66 (&)#177; 10%. This model has been incorporated into our thermal modeling code, SHERMAN, in order to determine which reflective, thermal, and surface properties best reproduce our numerous and rotationally resolved spectra. Primarily, we vary thermal inertia, geometric albedo, and crater fraction (surface roughness) although SHERMAN has many parameters that are allowed to vary. Our findings show that Ivar's thermal observations cannot be reproduced with a homogeneous model, but rather a heterogeneous model with a thermal inertia spot, and possibly different crater fraction values, needs to be applied in order to reproduce all of the spectra. Due to the variations in observing geometry for our thermal spectra, the properties of this spot are well constrained. We find that, with this spot, that the values of thermal inertia, geometric albedo, and crater fraction are 80 (&)#177; 20 J m-2 s-1/2 K-1, 0 (-) 0.3, and 0.27 (&)#177; 0.02, respectively. This work shows the advantage of having many datasets for deep study of an individual NEA, and with these results, we will learn more about the detailed regolith and surface properties of Ivar and how those properties compare to those of other NEAs.
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Date Issued
2018
Identifier
CFE0007022, ucf:52044
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007022
Characterizing Exoplanet Atmospheres: From Light-curve Observations to Radiative-Transfer Modeling
Title
Characterizing Exoplanet Atmospheres: From Light-curve Observations to Radiative-Transfer Modeling.
Creator
Cubillos Vallejos, Patricio, Harrington, Joseph, Mucciolo, Eduardo, Campins, Humberto, Fortney, Jonathan, University of Central Florida
Abstract / Description
Multi-wavelength transit and secondary-eclipse light-curve observations are some of the most powerful techniques to probe the thermo-chemical properties of exoplanets. Although the large planet-to-star brightness contrast and few available spectral bands produce data with low signal-to-noise ratios, a Bayesian approach can robustly reveal what constraints we can set, without over-interpreting the data. Here I performed an end-to-end analysis of transiting exoplanet data. I analyzed space...
Show moreMulti-wavelength transit and secondary-eclipse light-curve observations are some of the most powerful techniques to probe the thermo-chemical properties of exoplanets. Although the large planet-to-star brightness contrast and few available spectral bands produce data with low signal-to-noise ratios, a Bayesian approach can robustly reveal what constraints we can set, without over-interpreting the data. Here I performed an end-to-end analysis of transiting exoplanet data. I analyzed space-telescope data for three planets to characterize their atmospheres and refine their orbits, investigated correlated noise estimators, and contributed to the development of the respective data-analysis pipelines. Chapters 2 and 3 describe the Photometry for Orbits, Eclipses and Transits (POET) pipeline to model Spitzer Space Telescope light curves. I analyzed secondary-eclipse observations of the Jupiter-sized planets WASP-8b and TrES-1, determining their day-side thermal emission in the infrared spectrum. The emission data of WASP-8b indicated no thermal inversion, and an anomalously high 3.6 micron brightness. Standard solar-abundance models, with or without a thermal inversion, can fit the thermal emission from TrES-1 well. Chapter 4 describes the most commonly used correlated-noise estimators for exoplanet light-curve modeling, and assesses their applicability and limitations to estimate parameters uncertainties. I show that the residual-permutation method is unsound for estimating parameter uncertainties. The time-averaging and the wavelet-based likelihood methods improve the uncertainty estimations, being within 20 - 50% of the expected value. Chapter 5 describes the open-source Bayesian Atmospheric Radiative Transfer (BART) code to characterize exoplanet atmospheres. BART combines a thermochemical-equilibrium code, a one-dimensional line-by-line radiative-transfer code, and the Multi-core Markov-chain Monte Carlo statistical module to constrains the atmospheric temperature and chemical-abundance profiles of exoplanets. I applied the BART code to the Hubble and Spitzer Space Telescope transit observations of the Neptune-sized planet HAT-P-11b. BART finds an atmosphere enhanced in heavy elements, constraining the water abundance to ~100 times that of the solar abundance.
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Date Issued
2015
Identifier
CFE0005935, ucf:50838
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005935
The physical properties and composition of main-belt asteroids from infrared spectroscopy
Title
The physical properties and composition of main-belt asteroids from infrared spectroscopy.
Creator
Landsman, Zoe, Campins, Humberto, Britt, Daniel, Fernandez, Yan, Emery, Joshua, Hernandez, Florencio, University of Central Florida
Abstract / Description
Asteroids are the remnants of planet formation, and as such, they represent a record of the physical and chemical conditions in the early solar system and its evolution over the past 4.6 billion years. Asteroids are relatively accessible by spacecraft, and thus may be a source of the raw materials necessary for future human exploration and settlement of space. Those on Earth-crossing orbits pose impact hazards for which mitigation strategies must be developed. For these reasons, several...
Show moreAsteroids are the remnants of planet formation, and as such, they represent a record of the physical and chemical conditions in the early solar system and its evolution over the past 4.6 billion years. Asteroids are relatively accessible by spacecraft, and thus may be a source of the raw materials necessary for future human exploration and settlement of space. Those on Earth-crossing orbits pose impact hazards for which mitigation strategies must be developed. For these reasons, several missions to asteroids are in progress or planned with the support of the National Aeronautics and Space Administration (NASA) and other national space agencies. The study of asteroid composition and physical surface properties is vital to both our scientific understanding of the solar system's formation and evolution and to the development of asteroid missions and resource utilization schemes. This dissertation uses infrared spectroscopy to investigate the composition and physical properties of main-belt asteroid surfaces. Our efforts are focused on two populations that are especially relevant to constraining thermal and collisional processes in the asteroid belt: the "M-type" asteroids and primitive asteroid families.To investigate volatiles in the M-type asteroids, we obtained 2-4 micron spectra of six M-type asteroids using NASA's Infrared Telescope Facility. We find spectral signatures of hydrated minerals on all six asteroids, with evidence for rotational variability of hydration in one target. Diversity in the shape of the 3-micron feature in our sampled asteroids suggests there are different modes of hydration in the M-type population. Next, we carried out a thermal and compositional study of M-type asteroid (16) Psyche using 5-14 micron spectra from the Spitzer Space Telescope. Psyche is suspected to be a remnant iron core, and it is the target of an upcoming NASA mission. Using thermophysical modeling, we find that Psyche's surface is smooth and most likely has a thermal inertia of 5-25 J/m^2/K/s^(1/2), and a bolometric emissivity of 0.9, although a scenario with an emissivity of 0.7 and thermal inertia up to 95 J/m^2/K/s^(1/2) is possible if Psyche is somewhat larger than previously determined. From comparisons with laboratory spectra of silicate and meteorite powders, Psyche's emissivity spectrum is consistent with the presence of fine-grained ((<)75 micron) silicates. These silicates may include a magnesian pyroxene component. We conclude that Psyche is likely covered in a fine silicate regolith, which may also contain iron grains, overlying an iron-rich bedrock.Finally, we compared the mid-infrared properties of two primitive asteroids families, ancient Themis (~2.5 Gyr) and young Veritas (~8 Myr). Visible and near-infrared studies show spectral differences between the two families attributed to different degrees of space weathering. To test whether these differences are apparent in the mid-infrared, we analyzed the 5-14 micron Spitzer Space Telescope spectra of 11 Themis-family asteroids and 9 Veritas-family asteroids. We detect a broad 10-micron emission feature, attributed to fine-grained and/or porous silicate regolith, in all 11 Themis-family spectra and six of nine Veritas-family asteroids, with 10-micron spectral contrast ranging from 1% +/- 0.1% to 8.5% +/- 0.9%. Comparison with laboratory spectra of primitive meteorites suggests these asteroids are similar to meteorites with relatively low abundances of phyllosilicates. We used thermal modeling to derive diameters, beaming parameters and albedos for our sample. Asteroids in both families have beaming parameters near unity and geometric albedos in the range 0.031-0.14. Spectral contrast of the 10-micron silicate emission feature is not correlated with asteroid diameter; however, higher 10-micron contrast may be associated with flatter spectral slopes in the near-infrared. There is a slight trend of increasing 10-micron contrast with decreasing albedo in the Veritas asteroids, but not the Themis asteroids. Overall, our results indicate the Themis and Veritas family members show variation in regolith texture and/or structure within both families that is not directly related to family age.
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Date Issued
2017
Identifier
CFE0007124, ucf:51966
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007124
Saturn's Rings: Measuring Particle Size Distributions Using Cassini UVIS Occultation Data
Title
Saturn's Rings: Measuring Particle Size Distributions Using Cassini UVIS Occultation Data.
Creator
Becker, Tracy, Colwell, Joshua, Fernandez, Yan, Campins, Humberto, Showalter, Mark, Klemm, Richard, University of Central Florida
Abstract / Description
Since its arrival to Saturn in 2004, the Cassini spacecraft has utilized its suite of sophisticated instruments to further our understanding of the Saturnian ring system. We analyze occultation data from Cassini's Ultraviolet Imaging Spectrograph (UVIS) in order to measure the particle size distribution and place limits on the minimum particle sizes in Saturn's rings.Throughout the ring system, particle accretion is countered by collisional and tidal disruption and Keplerian shear. Therefore,...
Show moreSince its arrival to Saturn in 2004, the Cassini spacecraft has utilized its suite of sophisticated instruments to further our understanding of the Saturnian ring system. We analyze occultation data from Cassini's Ultraviolet Imaging Spectrograph (UVIS) in order to measure the particle size distribution and place limits on the minimum particle sizes in Saturn's rings.Throughout the ring system, particle accretion is countered by collisional and tidal disruption and Keplerian shear. Therefore, the particle size distribution of the rings is continually evolving. The presence of sub-centimeter particles, which have short lifetimes due to these processes, is indicative of ongoing dynamics in the rings. Sub-centimeter-sized particles efficiently diffract light at ultraviolet wavelengths, and thus produce signatures of diffraction in the occultation data. The shape and intensity of the diffraction signatures are indicative of the sizes of the particles that produce them. The UVIS wavelength bandpass, 51.2 - 180 nm, contains the shortest wavelengths of the Cassini instruments, making it most sensitive to the smallest particles in the rings. We have developed a computational model that reconstructs the geometry of a UVIS observation and produces a synthetic diffraction signal for a given truncated power-law particle size distribution, which we compare with the observed signal. We implement this model for two sets of observations: (1) diffraction spikes at sharp ring edges during stellar occultations and (2) the light curve due to attenuated and diffracted sunlight by particles in Saturn's F ring during solar occultations. Near sharp ring edges, ring particles can diffract light such that there is a measurable increase in the signal of an unocculted star exterior to the ring. In Saturn's A ring, diffracted light can augment the stellar signal by up to 6% and can be detected tens of kilometers radially beyond the edge. The radial profile of the diffraction signal is dependent on the size distribution of the particle population near the ring edge. These diffraction signals are observed at sharp edges throughout Saturn's rings, although in this work we focus on diffraction at the outer edge of Saturn's A ring and at the edges of the Encke Gap. We find an overall steepening of the power-law size distribution and a decrease in the minimum particle size at the outer edge of the A ring when compared with the Encke Gap edges. This suggests that interparticle collisions caused by satellite perturbations in the region result in more shedding of regolith or fragmentation of particles in the outermost parts of the A ring. We rule out any significant population of sub-millimeter-sized particles in Saturn's A ring, placing a lower limitation of 1-mm on the minimum particle size in the ring.We also model the light curves produced as Saturn's F ring occults the Sun. We consider both the attenuated signal and the light diffracted by the particles in the ring during the occultation. Five of the eleven solar occultations analyzed show a clear signature of diffracted light that surpasses the unocculted solar signal. This includes a misaligned solar occultation that placed most of the solar disk outside of the instrument's field of view, reducing the solar signal by 97.5% and resulting in the serendipitous detection of diffracted light. We measure a large variation in the the size distribution of the particles that fill the broad, ~500 km region surrounding the F ring core. We find that smaller particles ((<) 50 micrometers) are present during solar occultations for which diffraction was detected, and place a lower limit on the minimum particle size of 100 micrometers for occultations during which diffraction was not detected. A comparison with images of the F ring observed by the Cassini Imaging Science Subsystem near the times of the occultations reveals that the detections of small particles in the UVIS data correspond with locations of collisional events in the F ring. This implies that collisions within the F ring core replenish the sub-millimeter-sized dust in the 500-km region that encompasses the F ring core.
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Date Issued
2016
Identifier
CFE0006073, ucf:50940
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006073