arXiv subjects

Theodore Kareta

Publications and source records attributed to Theodore Kareta.

34 records · Page 2Linked to original sources

arXiv2023

Nuclear and Orbital Characterization of the Transition Object (4015) 107P/Wilson-Harrington

Comet 107P/Wilson-Harrington, cross-listed as asteroid 4015, is one of the original transition objects whose properties do not neatly fit into a cometary or asteroidal origin. Discovered in a period of apparently gas-dominated activity in 1949, it was subsequently lost and recovered as the inactive asteroid 1979 VA. We obtained new and re-analyzed archival observations of the object, compared to meteorites, and conducted new orbital integrations in order to understand the nature of this object and to understand where it falls on the asteroid-comet continuum. Wilson-Harrington's reflectance spectrum is approximately neutral from visible to near-infrared wavelengths, but has a reflectance maximum near 0.8-0.9 microns. The object's spectrum is well matched by laboratory spectra of carbonaceous chondrite meteorites like the CM Murchison or the CI Ivuna. The object's phase curve is compatible with either an asteroidal or cometary origin, and its recent orbital history has no periods with high enough temperatures to have altered its surface. While it is possible that some unknown process has acted to change the surface from an originally cometary one, we instead prefer a fundamentally asteroidal origin for Wilson-Harrington which can explain its surface and orbital properties. However, this would require a way to maintain significant (hyper-)volatile supplies on the near-Earth objects beyond what is currently expected. Wilson-Harrington's similar meteorite affinity and possible orbital link to sample return targets (162173) Ryugu and (101955) Bennu suggest that the returned samples from the Hayabusa-2 and OSIRIS-REx missions might hold the key to understanding this object.

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arXiv2023

Ice, Ice, Maybe? Investigating 46P/Wirtanen's Inner Coma For Icy Grains

The release of volatiles from comets is usually from direct sublimation of ices on the nucleus, but for very or hyper-active comets other sources have to be considered to account for the total production rates. In this work, we present new near-infrared imaging and spectroscopic observations of 46P/Wirtanen taken during its close approach to the Earth on 2018 December 19 with the MMIRS instrument at the MMT Observatory to search for signatures of icy or ice-rich grains in its inner coma that might explain its previously reported excess water production. The morphology of the images does not suggest any change in grain properties within the field of view, and the NIR spectra do not show the characteristic absorption features of water ice. Using a new MCMC-based implementation of the spectral modeling approach of Protopapa et al. (2018), we estimate the areal water ice fraction of the coma to be less than 0.6%. When combined with slit-corrected Afrho values for the J, H, and K bands and previously measured dust velocities for this comet, we estimate an icy grain production rate of less than 4.6 kg/s. This places a strict constraint on the water production rate from pure icy grains in the coma, and in turn we find that for the 2018-2019 apparition approximately 64% of 46P's surface was sublimating water near perihelion. WE then discuss 46P's modern properties within the context of other (formerly) hyper-active comets to understand how these complex objects evolve.

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arXiv2023

Implications for the Formation of 2005 UD from a New Convex Shape Model

(155140) 2005 UD has a similar orbit to (3200) Phaethon, an active asteroid in a highly eccentric orbit thought to be the source of the Geminid meteor shower. Evidence points to a genetic relationship between these two objects, but we have yet to fully understand how 2005 UD and Phaethon could have separated into this associated pair. Presented herein are new observations of 2005 UD from five observatories that were carried out during the 2018, 2019, and 2021 apparitions. We implemented light curve inversion using our new data, as well as dense and sparse archival data from epochs in 2005--2021 to better constrain the rotational period and derive a convex shape model of 2005 UD. We discuss two equally well-fitting pole solutions ($λ= 116.6^{\circ}$, $β= -53.6^{\circ}$) and ($λ= 300.3^{\circ}$, $β= -55.4^{\circ}$), the former largely in agreement with previous thermophysical analyses and the latter interesting due to its proximity to Phaethon's pole orientation. We also present a refined sidereal period of $P_{\text{sid}} = 5.234246 \pm 0.000097$ hr. A search for surface color heterogeneity showed no significant rotational variation. An activity search using the deepest stacked image available of 2005 UD near aphelion did not reveal a coma or tail but allowed modeling of an upper limit of 0.04 to 0.37~kg s$^{-1}$ for dust production. We then leveraged our spin solutions to help limit the range of formation scenarios and the link to Phaethon in the context of nongravitational forces and timescales associated with the physical evolution of the system.

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arXiv2022

The Volatile Carbon to Oxygen Ratio as a Tracer for the Formation Locations of Interstellar Comets

Based on the occurrence rates implied by the discoveries of 1I/`Oumuamua and 2I/Borisov, the forthcoming Rubin Observatory Legacy Survey of Space and Time (LSST) should detect $\ge1$ interstellar objects every year (Hoover et al. 2021). We advocate for future measurements of the production rates of H$_2$O, CO$_2$ and CO in these objects to estimate their carbon to oxygen ratios, which traces formation locations within their original protoplanetary disks. We review similar measurements for Solar System comets, which indicate formation interior to the CO snowline. By quantifying the relative processing in the interstellar medium and Solar System, we estimate that production rates will not be representative of primordial compositions for the majority of interstellar comets. Preferential desorption of CO and CO$_2$ relative to H$_2$O in the interstellar medium implies that measured C/O ratios represent lower limits on the primordial ratios. Specifically, production rate ratios of ${\rm Q}({\rm CO})/{\rm Q}({\rm H_2O})<.2$ and ${\rm Q}({\rm CO})/{\rm Q}({\rm H_2O})>1$ likely indicate formation interior and exterior to the CO snowline, respectively. The high C/O ratio of 2I/Borisov implies that it formed exterior to the CO snowline. We provide an overview of the currently operational facilities capable of obtaining these measurements that will constrain the fraction of ejected comets that formed exterior to the CO snowline. This fraction will provide key insights into the efficiency of and mechanisms for cometary ejection in exoplanetary systems.

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arXiv2022

The Nature of Low-Albedo Small Bodies from 3-$μ$m Spectroscopy: One Group that Formed Within the Ammonia Snow Line and One that Formed Beyond It

We present evidence, via a large survey of 191 new spectra along with previously-published spectra, of a divide in the 3-$μ$m spectral properties of the low-albedo asteroid population. One group ("Sharp-types" or ST, with band centers $<$ 3 $μ$m) has a spectral shape consistent with carbonaceous chondrite meteorites, while the other group ("not-Sharp-types" or NST, with bands centered $>$ 3 $μ$m) is not represented in the meteorite literature but is as abundant as the STs among large objects. Both groups are present in most low-albedo asteroid taxonomic classes, and except in limited cases taxonomic classifications based on 0.5-2.5-$μ$m data alone cannot predict whether an asteroid is ST or NST. Statistical tests show the STs and NSTs differ in average band depth, semi-major axis, and perihelion at confidence levels $\ge$98\%, while not showing significant differences in albedo. We also show that many NSTs have a 3-$μ$m absorption band shape like Comet 67P, and likely represent an important small-body composition throughout the solar system. A simple explanation for the origin of these groups is formation on opposite sides of the ammonia snow line, with the NST group accreting H2O and NH3 and the ST group only accreting H2O, with subsequent thermal and chemical evolution resulting in the minerals seen today. Such an explanation is consistent with recent dynamical modeling of planetesimal formation and delivery, and suggests that much more outer solar system material was delivered to the main asteroid belt than would be thought based on the number of D-class asteroids found today.

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arXiv2022

Near-Infrared Spectroscopy Of The Nucleus Of Low-Activity Comet P/2016 BA$_{14}$ During Its 2016 Close Approach

The Near-Earth Comet P/2016 BA$_{14}$ (PanSTARRS) is a slow-rotatating nearly-dormant object, a likely dynamical twin of 252P/LINEAR, and was recently shown to have a mid-infrared spectrum very dissimilar to other comets. BA$_{14}$ also recently selected one of the back-up targets for the ESA's \textit{Comet Interceptor}, so a clearer understanding of BA$_{14}$'s modern properties would not just improve our understanding of how comets go dormant, but could also aid planning for a potential spacecraft visit. We present observations of BA$_{14}$ taken on two dates during its 2016 Earth close approach with the NASA Infrared Telescope Facility, both of which are consistent with direct observations of its nucleus. The reflectance spectrum of BA$_{14}$ is similar to 67P/Churyumov-Gerasimenko, albeit highly phase-reddened. Thermal emission contaminates the reflectance spectrum at longer wavelengths, which we correct with a new Markov Chain Monte Carlo thermal modeling code. The models suggest $BA_{14}$'s visible geometric albedo is $p_V=0.01-0.03$, consistent with radar observations, its beaming parameter is typical for NEOs observed in its geometry, and its reflectrance spectrum is red and linear throughout H and K band. It appears very much like a "normal" comet nucleus, despite its mid-infrared oddities. A slow loss of fine grains as the object's activity diminished might help to reconcile some of the lines of evidence, and we discuss other possibilities. A spacecraft flyby past BA$_{14}$ could get closer to the nucleus than with a more active target, and we highlight some science questions that could be addressed with a visit to a (nearly-)dormant comet.

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arXiv2021

Physical Characterization of Metal-rich Near-Earth Asteroids 6178 (1986 DA) and 2016 ED85

Metal-rich near-Earth asteroids (NEAs) represent a small fraction of the NEA population that is mostly dominated by S- and C-type asteroids. Because of this, their identification and study provide us with a unique opportunity to learn more about the formation and evolution of this particular type of bodies, as well as their relationship with meteorites found on Earth. We present near-infrared (NIR) spectroscopic data of NEAs 6178 (1986 DA) and 2016 ED85. We found that the spectral characteristics of these objects are consistent with those of metal-rich asteroids, showing red slopes, convex shapes, and a weak pyroxene absorption band at $\sim$0.93 $μ$m. The compositional analysis showed that they have a pyroxene chemistry of Fs$_{40.6\pm3.3}$Wo$_{8.9\pm1.1}$ and a mineral abundance of $\sim$15% pyroxene and 85% metal. We determined that these objects were likely transported to the near-Earth space via the 5:2 mean motion resonance with Jupiter. Asteroid spectra were compared with the spectra of mesosiderites and bencubbinites. Differences in the NIR spectra and pyroxene chemistry suggest that bencubbinites are not good meteorite analogs. Mesosiderites were found to have a similar pyroxene chemistry and produced a good spectral match when metal was added to the silicate component. We estimated that the amounts of Fe, Ni, Co, and the platinum group metals present in 1986 DA could exceed the reserves worldwide.

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arXiv2021

Investigating the Relationship between (3200) Phaethon and (155140) 2005 UD through Telescopic and Laboratory Studies

The relationship between the Near-Earth Objects (3200) Phaethon and (155140) 2005 UD is unclear. While both are parents to Meteor Showers, (the Geminids and Daytime Sextantids, respectively), have similar visible-wavelength reflectance spectra and orbits, dynamical investigations have failed to find any likely method to link the two objects in the recent past. Here we present the first near-infrared reflectance spectrum of 2005 UD, which shows it to be consistently linear and red-sloped unlike Phaethon's very blue and concave spectrum. Searching for a process that could alter some common starting material to both of these end states, we hypothesized that the two objects had been heated to different extents, motivated by their near-Sun orbits, the composition of Geminid meteoroids, and previous models of Phaethon's surface. We thus set about building a new laboratory apparatus to acquire reflectance spectra of meteoritic samples after heating to higher temperatures than available in the literature to test this hypothesis and were loaned a sample of the CI Chondrite Orgueil from the Vatican Meteorite Collection for testing. We find that while Phaethon's spectrum shares many similarities with different CI Chondrites, 2005 UD's does not. We thus conclude that the most likely relationship between the two objects is that their similar properties are only by coincidence as opposed to a parent-fragment scenario, though the ultimate test will be when JAXA's DESTINY+ mission visits one or both objects later this decade. We also discuss possible paths forward to understanding Phaethon's properties from dynamical and compositional grounds.

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arXiv2021

Constraining the Regolith Composition of Asteroid (16) Psyche via Laboratory Near-infrared Spectroscopy

(16) Psyche is the largest M-type asteroid in the main belt and the target of the NASA Discovery-class Psyche mission. Despite gaining considerable interest in the scientific community, Psyche's composition and formation remain unconstrained. Originally, Psyche was considered to be almost entirely composed of metal due to its high radar albedo and spectral similarities to iron meteorites. More recent telescopic observations suggest the additional presence of low-Fe pyroxene and exogenic carbonaceous chondrites on the asteroid's surface. To better understand the abundances of these additional materials, we investigated visible near-infrared (0.35 - 2.5 micron) spectral properties of three-component laboratory mixtures of metal, low-Fe pyroxene, and carbonaceous chondrite. We compared the band depths and spectral slopes of these mixtures to the telescopic spectrum of (16) Psyche to constrain material abundances. We find that the best matching mixture to Psyche consists of 82.5% metal, 7% low-Fe pyroxene, and 10.5% carbonaceous by weight, suggesting that the asteroid is less metallic than originally estimated (~94%). The relatively high abundance of carbonaceous chondrite material estimated from our laboratory experiments implies the delivery of this exogenic material through low velocity collisions to Psyche's surface. Assuming that Psyche's surface is representative of its bulk material content, our results suggest a porosity of 35% to match recent density estimates.

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arXiv2021

Contemporaneous Multi-Wavelength and Precovery Observations of Active Centaur P/2019 LD2 (ATLAS

Gateway Centaur and Jupiter co-orbital P/2019 LD2 (ATLAS) (Sarid et al. 2019) provides the first opportunity to observe the migration of a Solar System small body from a Centaur orbit to a Jupiter Family Comet (JFC) four decades from now (Kareta et al., 2020; Hsieh et al. 2020). The Gateway transition region is beyond where water ice can power cometary activity, and coma production there is as poorly understood as in all Centaurs. We present contemporaneous multi-wavelength observations of LD2 from 2020 July 2-4: Gemini-North visible imaging, NASA IRTF near-infrared spectroscopy, and ARO SMT millimeter-wavelength spectroscopy. Precovery DECam images limit the nucleu's effective radius to <=1.2 km and no large outbursts were seen in archival Catalina Sky Survey observations. LD2's coma has g'-r'=0.70+/-0.07, r'-i'=0.26+/-0.07, a dust production rate of ~10-20 kg/s, and an outflow velocity between v~0.6-3.3 m/s. We did not detect CO towards LD2 on 2020 July 2-3, with a 3-sigma upper limit of Q(CO) < 4.4 * 10^27 mol/s (<200 kg/s). Near-infrared spectra show evidence for water ice at the 1-10% level depending on grain size. Spatial profiles and archival data are consistent with sustained activity. The evidence supports the hypothesis that LD2 is a typical small Centaur that will become a typical JFC, and thus it is critical to understanding the transition between these two populations. Finally, we discuss potential strategies for a community-wide, long baseline monitoring effort.

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arXiv2020

P/2019 LD2 (ATLAS): An Active Centaur in Imminent Transition to the Jupiter Family

The recently discovered object P/2019 LD2 (ATLAS) was initially thought to be a Jupiter Trojan asteroid, until dynamical studies and the appearance of persistent cometary activity revealed that this object is actually an active Centaur. However, the dynamical history, thermal environment, and impact of such environments on the activity of 2019 LD2 are poorly understood. Here we conduct dynamical simulations to constrain its orbital history and resulting thermal environment over the past 3000 years. We find that 2019 LD2 is currently in the vicinity of a dynamical "Gateway" that facilitates the majority of transitions from the Centaur population into the Jupiter Family of Comets (JFC population; Sarid et al. 2019). Our calculations show that it is unlikely to have spent significant amounts of time in the inner solar system, suggesting that its nucleus is relatively pristine in terms of physical, chemical, and thermal processing through its history. This could explain its relatively high level of distant activity as a recently activated primordial body. Finally, we find that the median frequency of transition from the Gateway population into the JFC population varies from once every ~3 years to less than once every 70 years, if 2019 LD2's nucleus is ~1 km in radius or greater than 3 km in radius. Forward modeling of 2019 LD2 shows that it will transition into the JFC population in 2063, representing the first known opportunity to observe the evolution of an active Centaur nucleus as it experiences this population-defining transition.

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arXiv2020

Near-infrared observations of active asteroid (3200) Phaethon reveal no evidence for hydration

Asteroid (3200) Phaethon is an active near-Earth asteroid and the parent body of the Geminid Meteor Shower. Because of its small perihelion distance, Phaethon's surface reaches temperatures sufficient to destabilize hydrated materials. We conducted rotationally resolved spectroscopic observations of this asteroid, mostly covering the northern hemisphere and the equatorial region, beyond 2.5-micron to search for evidence of hydration on its surface. Here we show that the observed part of Phaethon does not exhibit the 3-micron hydrated mineral absorption (within 2-sigma). These observations suggest that Phaethon's modern activity is not due to volatile sublimation or devolatilization of phyllosilicates on its surface. It is possible that the observed part of Phaethon was originally hydrated and has since lost volatiles from its surface via dehydration, supporting its connection to the Pallas family, or it was formed from anhydrous material.

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arXiv2019

Carbon Chain Depletion of 2I/Borisov

The composition of comets in the Solar System come in multiple groups thought to encode information about their formation in different regions of the outer protosolar disk. The recent discovery of the second interstellar object, 2I/Borisov, allows for spectroscopic investigations into its gas content and a preliminary classification of it within the Solar System comet taxonomies to test the applicability of planetesimal formation models to other stellar systems. We present spectroscopic and imaging observations from 2019 September 20th to October 26th at the Bok, MMT, and LBT telescopes. We identify CN in the comet's spectrum and set precise upper limits on the abundance of C2 on all dates. We use a Haser model to convert our integrated fluxes to production rates and find Q(CN) = 5.0 +/- 2.0 * 10^24 mol/s on September 20th and Q(CN) = 1.1 - 1.9 * 10^24 mol/s on later dates, both consistent with contemporaneous observations. We set our lowest upper limit on a C2 production rate, Q(C2) < 1.6 * 10^23 mol/s, on October 10th. The measured ratio upper limit for that date, Q(C2)/Q(CN) < 0.095 indicates that 2I/Borisov is strongly in the (carbon chain) 'depleted' taxonomic group. The only comparable Solar System comets have detected ratios near this limit, making 2I/Borisov statistically likely to be more depleted than any known comet. Most 'depleted' comets are Jupiter Family Comets, perhaps indicating a similiarity in formation conditions between the most depleted of the JFCs and 2I/Borisov. More work is needed to understand the applicability of our knowledge of Solar System comet taxonomies onto interstellar objects, and we discuss future work that could help clarify the usefulness of the approach.

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arXiv2019

Physical Characterization of the December 2017 Outburst of the Centaur 174P/Echeclus

The Centaurs are the small solar system bodies intermediate between the active inner solar system Jupiter Family Comets and their inactive progenitors in the trans-Neptunian region. Among the fraction of Centaurs which show comet-like activity, 174P/Echeclus is best known for its massive 2005 outburst in which a large apparently active fragment was ejected above the escape velocity from the primary nucleus. We present visible imaging and near-infrared spectroscopy of Echeclus during the first week after its December 2017 outburst taken at the Faulkes North & South Telescopes and the NASA IRTF, the largest outburst since 2005. The coma was seen to be highly asymmetric. A secondary peak was seen in the near-infrared 2D spectra, which is strongly hinted at in the visible images, moving hyperbolically with respect to the nucleus. The retrieved reflectance spectrum of Echelcus is consistent with the unobscured nucleus but becomes bluer when a wider extraction aperture is used. We find that Echeclus's coma is best explained as dominated by large blue dust grains, which agrees with previous work. We also conducted a high-resolution orbital integration of Echeclus's recent evolution and found no large orbital changes that could drive its modern evolution. We interpret the second peak in the visible and near-infrared datasets as a large cloud of larger-than-dust debris ejected at the time of outburst. If Echeclus is typical of the Centaurs, there may be several debris ejection or fragmentation events per year on other Centaurs that are going unnoticed.

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arXiv2019

Physical Characterization of Active Asteroid (6478) Gault

Main belt asteroid (6478) Gault has been dynamically linked with two overlapping asteroid families: Phocaea, dominated by S-type asteroids, and Tamara, dominated by low-albedo C-types. This object has recently become an interesting case for study, after images obtained in late 2018 revealed that it was active and displaying a comet-like tail. Previous authors have proposed that the most likely scenarios to explain the observed activity on Gault were rotational excitation or merger of near-contact binaries. Here we use new photometric and spectroscopic data of Gault to determine its physical and compositional properties. Lightcurves derived from the photometric data showed little variation over three nights of observations, which prevented us from determining the rotation period of the asteroid. Using WISE observations of Gault and the near-Earth Asteroid Thermal Model (NEATM) we determined that this asteroid has a diameter $<$6 km. NIR spectroscopic data obtained with the Infrared Telescope Facility (IRTF) showed a spectrum similar to that of S-complex asteroids, and a surface composition consistent with H chondrite meteorites. These results favor a compositional affinity between Gault and asteroid (25) Phocaea, and rules out a compositional link with the Tamara family. From the spectroscopic data we found no evidence of fresh material that could have been exposed during the outburst episodes.

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arXiv2018

Rotationally-Resolved Spectroscopic Characterization of near-Earth object (3200) Phaethon

(3200) Phaethon is a compelling object as it has an asteroidal appearance and spectrum, produces a weak dust tail during perihelion at just 0.14 AU, and is the parent body of the Geminid Meteor Shower. A better understanding of the physical properties of Phaethon is needed to understand the nature of its current and previous activity, relationship to potential source populations, and to plan for the upcoming flyby of the DESTINY+ spacecraft of Phaethon in the 2020s. We performed rotationally-resolved spectroscopy of Phaethon at visible and near-infrared wavelengths (0.4-2.5 microns) in 2007 and 2017, respectively, to better understand its surface properties. The visible and near-infrared observations both spanned nearly a full rotation or more and were under similar observing geometries, covering the whole surface with the exception of the north pole. The visible wavelengths show blue slopes with only minor slope variations and no absorption features. The NIR data is minimally varying and concave upwards, from very blue to blue-neutral with increasing wavelength. We fit the short-wavelength tail of Phaethon's thermal emission and retrieve an average visible albedo of pv = 0.08 +/- 0.01, which is lower than previous measurements but plausible in light of the recent larger radar-measured diameter of Phaethon. We retrieve an average infrared beaming parameter of Phaethon of eta = 1.70 +/- 0.05, which is similar to previous results. We discuss the implications of Phaethon's visible and near-infrared spectrum as well as the lower albedo on its origin, source population, and evolutionary history.

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