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All sourcesNASA NTRSDOE OSTI
NASA NTRS2021

Testing Short-term Variability and Sampling of Primary Volatiles in Comet 46P/Wirtanen

The exceptionally favorable close approach of Jupiter-family comet 46P/Wirtanen in 2018 December enabled characterization of its primary volatile composition with exceptionally high spatial resolution and sensitivities using the iSHELL spectrograph at the NASA Infrared Telescope Facility on Maunakea, HI. We sampled emissions from H2O, HCN, C2H2, NH3,C2H6, and CH3OH on UT 2018 December 21 using two instrumental settings that spanned the 2.9–3.6μm spectral region. We also obtained a sensitive 3σupper limit for H2CO and for the rarely studied molecule HC3N. We report rotational temperatures, production rates, and mixing ratios(relative to H2O as well as to C2H6). We place our results in context by comparing them with other comets observed at near-IR wavelengths. We also compare our results with those obtained using the NIRSPEC-2 spectrograph on Keck II on UT December 17 and 18 and with results obtained from iSHELL on other dates during the same apparition. Within1–2σ uncertainty, production rates obtained for all molecules in this work were consistent with those obtained using NIRSPEC-2 except H2O, indicating low-level variability on a timescale of days. Mixing ratios with respect to H2O in 46P/Wirtanen were consistent with corresponding values from NIRSPEC-2 within the uncertainty with the exception of CH3OH, which yielded a higher ratio on December 21. Our measurements afforded a high temporal resolution that spanned∼2/3 of the rotational period of 46P/Wirtanen, enabling us to test short-term variability in the production rates of H2O and HCN due to rotational effects. Both H2O and HCN production rates showed similar temporal variability, resulting in nearly constant HCN/H2O

Younas Khan↗
NASA NTRS2021

The Volatile Composition of the Inner Coma of Comet 46P/Wirtanen: Coordinated Observations Using iSHELL at the NASA-IRTF and Keck/NIRSPEC-2

The 2018 perihelion passage of comet 46P/Wirtanen afforded an opportunity to measure the abundances andspatial distributions of coma volatiles in a Jupiter-family comet with exceptional spatial resolution for severalweeks surrounding its closest approach to Earth(Δmin∼0.078 au on UT December 16). We conducted near-infrared spectroscopic observations of 46P/Wirtanen using iSHELL at the NASA Infrared Telescope Facility onUT 2018 December 18 in direct coordination with observations using the newly upgraded NIRSPEC-2 instrumentat the W. M. Keck Observatory, and securely detectedfluorescent emission from CH3OH, C2H6, and H2O. Thiscoordinated campaign utilizing the two premier near-infrared facilities in the northern hemisphere enabled us tosample distinct projections of the coma into the plane of the sky simultaneously, and provided an unprecedentedview into the inner coma of 46P/Wirtanen near closest approach. We report rotational temperatures, productionrates, and abundance ratios(i.e., mixing ratios)for all sampled species and compare our iSHELL results tosimultaneous(or near-simultaneous)measurements taken with NIRSPEC-2. We demonstrate the extraordinarysynergy of coordinated measurements using iSHELL and NIRSPEC-2, and advocate for future cometary studiesthat jointly leverage the capabilities of these two facilities.

Nathaniel X Roth↗
NASA NTRS2021

The Volatile Composition of the Inner Coma of Comet 46P/Wirtanen: Coordinated Observations Using iSHELL at the NASA-IRTF and Keck/NIRSPEC-2

The 2018 perihelion passage of comet 46P/Wirtanen afforded an opportunity to measure the abundances and spatial distributions of coma volatiles in a Jupiter-family comet with exceptional spatial resolution for several weeks surrounding its closest approach to Earth (Δ(min) ~0.078 au on UT December 16). We conducted near-infrared spectroscopic observations of 46P/Wirtanen using iSHELL at the NASA Infrared Telescope Facility on UT 2018 December 18 in direct coordination with observations using the newly upgraded NIRSPEC-2 instrument at the W. M. Keck Observatory, and securely detected fluorescent emission from CH3OH, C2H6, and H2O. This coordinated campaign utilizing the two premier near-infrared facilities in the northern hemisphere enabled us to sample distinct projections of the coma into the plane of the sky simultaneously, and provided an unprecedented view into the inner coma of 46P/Wirtanen near closest approach. We report rotational temperatures, production rates, and abundance ratios (i.e., mixing ratios) for all sampled species and compare our iSHELL results to simultaneous (or near-simultaneous) measurements taken with NIRSPEC-2. We demonstrate the extraordinary synergy of coordinated measurements using iSHELL and NIRSPEC-2, and advocate for future cometary studies that jointly leverage the capabilities of these two facilities.

Nathaniel X. Roth↗
NASA NTRS2022

Oxygen Isotopes of Anhydrous Primary Minerals Show Kinship Between Asteroid Ryugu and Comet 81P/Wild2

The extraterrestrial materials returned from asteroid (162173) Ryugu consist predominantly of low-temperature aqueously formed secondary minerals and are chemically and mineralogically similar to CI (Ivuna-type) carbonaceous chondrites. Here we show that high-temperature anhydrous primary minerals in Ryugu and CI chondrites exhibit a bimodal distribution of oxygen isotopic compositions: 16 O-rich (associated with refractory inclusions) and 16 O-poor (associated with chondrules). Both the 16 O-rich and 16 O-poor minerals probably formed in the inner solar protoplanetary disk and were subsequently transported outwards. The abundance ratios of the 16 O-rich to 16 O-poor minerals in Ryugu and CI chondrites are higher than in other carbonaceous chondrite groups, but are similar to that of comet 81P/Wild2, suggesting that Ryugu and CI chondrites accreted in the outer Solar System closer to the accretion region of comets.

Noriyuki Kawasaki↗
NASA NTRS2014

Badger COMET Compartmentalized Onboard Material Extrusion Technology

In response to the 2014 NASA Academic Innovation Challenge, the University of Wisconsin – Madison team presents the design of a collapsible Fused Deposition Modeling (FDM) system for in situ manufacturing in a space habitat environment, the Badger Compartmentalized Onboard Material Extrusion Technology (COMET). The proposed mechanism incorporates one year of design and testing on an array of current additive manufacturing techniques, with the goal of providing a reliable and maintainable manufacturing solution. Seven Level 1 requirements were employed to guide the design process, based on information in the challenge, communications with NASA, and the evolving systems feedback of project work groups. These requirements provided a baseline for the development of the System Requirements Document (SRD, Appendix I), which framed the design of the system. The design requirements deemed critical to the success of the systems are as follows: - The system shall compose an FDM workstation capable of producing parts within industry standard tolerances. - The system shall reduce to a minimum of 50 percent or less of its deployed volume when not in use, and must collapse without the need for disassembly. - The system shall meet all relevant NASA safety and functional standards. The final design for the Badger COMET was selected from multiple design iterations, which balanced the critical design requirements listed above with system reliability, with the final goal of providing a minimal system weight. The system collapses in the vertical direction, allowing for a maximum reduction in volume. Guide rods and precision, anti-backlash lead screws provide all linear movement in the device. Stepper motors were chosen to actuate each system axis, due to their high precision and repeatable accuracy. The system is controlled through an on-board computer system and embedded electronics package.

Frederick T. Elder↗
NASA NTRS2026

The Evolution in Coma Molecular Composition of Comet C/2017 K2 (PanSTARRS) Across the H 2 O Sublimation Zone: ALMA Imaging of an H 2 O-Dominated Coma

We report a survey of molecular emission from cometary volatiles using the Atacama Large Millimeter/Submillimeter Array (ALMA) toward comet C/2017 K2 (PanSTARRS) carried out on UT 2022 September 21, 22, and 23 at a heliocentric distance r H 3 OH, and H 2 CO (along with continuum emission from dust) sampled molecular chemistry in C/2017 K2 at the inner edge of the H 2 O sublimation zone, the region from r H 2 O begins vigorously subliming and increasingly dominating comet activity, discerning parent from daughter or extended source species. This work presents spectrally integrated flux maps, production rates, and parent scale lengths for each molecule. CH 3 OH, CO, and HCN were produced within ~250 km of the nucleus, potentially including contributions from sublimation of icy grains. CS was consistent with production from CS 2 photolysis, and H 2 CO required production from extended sources in the coma. An ortho-to-para ratio of 2.9 ± 0.4 for H 2 CO was derived from simultaneously measured transitions of each spin species. The continuum was extended and spatially resolved, consistent with thermal emission from dust in the coma. Analysis of the continuum visibilities provided an upper limit on the nucleus diameter d <6.6 km and coma dust masses of (1.2-2.4) times10 11 kg.

Nathan X Roth↗
DOE OSTI2018

Experiment Design with Confidence: CoMET

The Nuclear Science User Facilities (NSUF) has been facilitating nuclear materials research since 2007 by providing access to national laboratory and other partner capabilities at no cost to the researchers. With funding from the Department of Energy – Office of Nuclear Energy, approximately 400 projects have been awarded to support research into radiation effects on fuels and materials. During these ten years, the NSUF has created tools to help researchers write better proposals and perform better research projects. In 2018, several of those tools have been combined to create a single point of access to NSUF information management resources. The Combined Materials Experiment Toolkit or CoMET, combines the Nuclear Energy Infrastructure Database (NEID), the Nuclear Fuels and Materials Library (NFML), and the NSUF proposal system, with a new subject matter expert database and an experiment design tool. The NEID contains information on 500 nuclear R&D facilities around the world, including 85 NSUF partner facilities. The NFML has information on nearly 10,000 material specimens, mostly irradiated materials, which can be used for research in NSUF projects. The new SME database includes contact information for NSUF researchers and scientists. The experiment design tool is an expert system that can guide a researcher through the process of designing an NSUF project by interacting with the other resources. Once a researcher has worked through this process, they will be able to save their experiment plan and input it into the NSUF proposal system. These tools are intended to aid both new and veteran researchers build solid research projects and take full advantage of NSUF resources. They also help the NSUF administer the hundreds of proposals that it receives each year. In the future, NSUF plans to add integrated data storage and retrieval to CoMET.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

The COMET method in 3-D hexagonal geometry

The hybrid stochastic-deterministic coarse mesh radiation transport (COMET) method developed at Georgia Tech now solves reactor core problems in 3-D hexagonal geometry. In this paper, the method is used to solve three preliminary test problems designed to challenge the method with steep flux gradients, high leakage, and strong asymmetry and heterogeneity in the core. The test problems are composed of blocks taken from a high temperature test reactor benchmark problem. As the method is still in development, these problems and their results are strictly preliminary. Results are compared to whole core Monte Carlo reference solutions in order to verify the method. Relative errors are on the order of 50 pcm in core eigenvalue, and mean relative error in pin fission density calculations is less than 1% in these difficult test cores. The method requires the one-time pre-computation of a response expansion coefficient library, which may be compiled in a comparable amount of time to a single whole core Monte Carlo calculation. After the library has been computed, COMET may solve any number of core configurations on the order of an hour, representing a significant gain in efficiency over other methods for whole core transport calculations. (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS1998

A Double Nucleus of Comet Evans-Drinkwater (C/1996 J1)

The nucleus of comet C/1996 J1, whose duplicity was first detected in early May 1997, ~4 months after perihelion, is found to have split nontidally ~70 days before perihelion at 1.65 AU from the Sun.

comet Evans-Drinkwater double nucleus nontidal spl↗
NASA NTRS1994

The Light Curve of Periodic Comet Wirtanen

Teh light curve of Periodic Comet Wirtanen has been analyzed for the 1986 and 1991 apparitions, the only two monitored by visual observers.

Wirtanen comet light curve periodic comets apparit↗
DOE OSTI2022

Mascon distribution techniques for asteroids and comets

The mass-concentration model is an approach that has been used to model the gravitational fields of irregularly shaped bodies such as asteroids and comets. By this approach, the body is treated as a collection of point masses. The method is conceptually simple, easy to program, valid down to the surface, and capable of modeling arbitrary density heterogeneities. How the mass concentrations are distributed as well as how mass is assigned to these concentrations is, however, nontrivial. These aspects significantly affect the accuracy and efficiency of the gravitational model. In this paper, we frame the distribution process in terms of numerical integration applied to finite volume meshes. We describe a new method using unstructured, curvilinear, finite volume meshes to significantly improve the accuracy of the mass-concentration model. We then compare the accuracy and efficiency of several variations of our distribution technique to those from literature using Asteroid Eros and Bennu as example bodies. Our results show that the mascon model can be as accurate as the analytic polyhedral model at the surface using an equivalent number of computational elements—i.e., mascon to surface facets. We report the improvement in the model’s performance can be mainly attributed to the volume mesh topology while mesh curving can provide modest case-dependent improvements.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Comets and carbonaceous chondrites delivered noble gases to the Moon

Trapped xenon isotopes in two Apollo 17 mare basalt fragments are similar to those in primitive meteorites. Xenon would have been effectively excluded from the Moon in the aftermath of its formation in a giant impact. As such, lunar mantle xenon trapped in the mare basalts is best explained as being derived from late accretion occurring before or concurrent with the formation of the lunar crust. Here, the isotopic composition indicates that a combination of comets and carbonaceous chondrites delivered this xenon to the lunar mantle. The inferred mass of accreted cometary ice would have delivered significantly less than a part per million of water to the lunar mantle. The inferred mass of accreted carbonaceous chondrites would have supplied at least a half of a part per million of water. The data further indicate that enstatite chondrites are unlikely to have supplied the majority of late accreted mass.

Chemistry↗
DOE OSTI2010

THE FLUORESCENCE EFFICIENCIES OF THE CN VIOLET BANDS IN COMETS

We have carried out calculations of the fluorescent equilibrium of the CN molecule in the solar radiation field as a function of heliocentric radial velocity and distance. The detailed rotational line intensities of the CN violet 0-0 band have been recalculated for radial velocities between -60 and +60 km s{sup -1} and at 10 distances in steps of {radical}2 from 0.25 to 5.7 AU. Comparisons with observed CN violet 0-0 band profiles yield reasonable agreement and remaining discrepancies are well understood. Based on the derived equilibrium rotational level populations of the ground state, 1-1 band rotational line intensities were also calculated. Total band fluorescence efficiencies for the violet {Delta}{nu} = 0 sequence are tabulated for the above range of distances and velocities, permitting the interpolation to any given comet's observational circumstances. These fluorescence efficiencies, L/N, or 'g-factors', needed to reduce CN emission band fluxes to CN abundances, are also accessible via a Web-based service. The values at any heliocentric distance vary by about a factor of two with varying velocities, but the specific structure of this variation with velocity changes dramatically with distance.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

THE INCREASING ROTATION PERIOD OF COMET 10P/TEMPEL 2

We imaged comet 10P/Tempel 2 on 32 nights from 1999 April through 2000 March. R-band light curves were obtained on 11 of these nights from 1999 April through 1999 June, prior to both the onset of significant coma activity and perihelion. Phasing of the data yields a double-peaked light curve and indicates a nucleus rotational period of 8.941 {+-} 0.002 hr with a peak-to-peak amplitude of {approx}0.75 mag. Our data are sufficient to rule out all other possible double-peaked solutions as well as the single- and triple-peaked solutions. This rotation period agrees with one of five possible solutions found in post-perihelion data from 1994 by Mueller and Ferrin (Icarus, 123, 463-477) and unambiguously eliminates their remaining four solutions. We applied our same techniques to published light curves from 1988 which were obtained at an equivalent orbital position and viewing geometry as in 1999. We found a rotation period of 8.932 {+-} 0.001 hr in 1988, consistent with the findings of previous authors and incompatible with our 1999 solution. This reveals that Tempel 2 spun-down by {approx}32 s between 1988 and 1999 (two intervening perihelion passages). If the spin-down is due to a systematic torque, then the rotation period prior to perihelion during the 2010 apparition is expected to be an additional 32 s longer than in 1999.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

FROZEN HYDROCARBONS IN COMETS

Recent investigations of the luminescence of frozen hydrocarbon particles of icy cometary halos have been carried out. The process of luminescence of organic icy particles in a short-wavelength solar radiation field is considered. A comparative analysis of observed and laboratory data leads to 72 luminescent emission lines in the spectrum of the comet 153P/Ikeya-Zhang. The concept of cometary relict matter is presented, and the creation of a database of unidentified cometary emission lines is proposed.

79 ASTRONOMY AND ASTROPHYSICS↗