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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

SOFIA FORCAST Far-IR Photometry of Comet ISON and Constraints on the Coma Grain Size Distribution

Comet C/2012 S1 (ISON) was unique in that it was a dynamically new comet derived from the nearly isotropic Oort cloud reservoir of comets with a sun-grazing orbit. Infrared (IR) observations were executed on NASA's Stratospheric Observatory For Infrared Astronomy (SOFIA) by the FORCAST instrument on 2013 October 25 UT (r(sub h)=1.18 AU, Delta=1.5AU). Photometry was obtained in FORCAST filters centered at 11.1, 19.7, and 31.5 micron. The observations compliment a large world-wide effort to observe and characterize comet ISON.

Comet dust properties↗
NASA NTRS1986

The hydrogen coma of Comet Halley before perihelion: Preliminary observations with dynamics Explorer 1

The hydrogen coma of Comet Halley has been observed in resonantly scattered solar Lyman-alpha radiation during the period 1-29 January 1986 as the comet approached perihelion. These observations were obtained with the imaging photometer for vacuum-ultraviolet wavelengths on the spacecraft Dynamics Explorer 1. For the initial analysis of observations available in 17 orbits distributed throughout the period, least-squares fits are computed for the observed exponential decrease in brightness with radial distance from the nucleus. Brightness at the nucleus increased from approx. 3 to 17 kR during the observing period. Preliminary analysis yields water production rates of approx. 3.6 x 10 to the 29th power and 1.9 x 10 to the 30th power molecules/sec on 1 and 29 January, respectively.

Craven, J. D.↗
NASA NTRS1986

The hydrogen coma of Comet Halley before perihelion Preliminary observations with Dynamics Explorer 1

The hydrogen coma of Comet Halley has been observed in resonantly scattered solar Lyman-alpha radiation during the period 4-29 January 1986 as the comet approached perihelion. These observations were obtained with the imaging photometer for vacuum-ultraviolet wavelengths on the spacecraft Dynamics Explorer 4. For the initial analysis of observations available in 17 orbits distributed throughout the period, least-squares fits are computed for the observed exponential decrease in brightness with radial distance from the nucleus. Brightness at the nucleus increased from approx. 3 to 17 kR during the observing period. Preliminary analysis yields water production rates of approx. 3.6 x 10 to the 29th power and 1.9 x 10 to the 30th power molecules/sec on 1 and 29 January, respectively.

Craven, J. D.↗
NASA NTRS1978

Comet Tempel 2: Orbit, ephemerides and error analysis

The dynamical behavior of comet Tempel 2 is investigated and the comet is found to be very well behaved and easily predictable. The nongravitational forces affecting the motion of this comet are the smallest of any comet that is affected by nongravitational forces. The sign and time history of these nongravitational forces imply (1) a direct rotation of the comet's nucleus and (2) the comet's ability to outgas has not changed substantially over its entire observational history. The well behaved dynamical motion of the comet, the well observed past apparitions, the small nongravitational forces and the excellent 1988 ground based observing conditions all contribute to relatively small position and velocity errors in 1988 -- the year of a proposed rendezvous space mission to this comet. To assist in planned ground based and earth orbital observations of this comet, ephemerides are given for the 1978-79, 1983-84 and 1988 apparitions.

Yeomans, D. K.↗
DOE OSTI2021

A metabolic modeling platform for the computation of microbial ecosystems in time and space (COMETS)

Genome-scale stoichiometric modeling of metabolism has become a standard systems biology tool for modeling cellular physiology and growth. Extensions of this approach are emerging as a valuable avenue for predicting, understanding and designing microbial communities. Computation of microbial ecosystems in time and space (COMETS) extends dynamic flux balance analysis to generate simulations of multiple microbial species in molecularly complex and spatially structured environments. Here we describe how to best use and apply the most recent version of COMETS, which incorporates a more accurate biophysical model of microbial biomass expansion upon growth, evolutionary dynamics and extracellular enzyme activity modules. In addition to a command-line option, COMETS includes user-friendly Python and MATLAB interfaces compatible with the well-established COBRA models and methods, as well as comprehensive documentation and tutorials. Overall, this protocol provides a detailed guideline for installing, testing and applying COMETS to different scenarios, generating simulations that take from a few minutes to several days to run, with broad applicability to microbial communities across biomes and scales.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1987

Atomic hydrogen production rates for comet P/Halley from observations with Dynamics Explorer I

Newly analyzed observations of the Dynamics Explorer I (DE1), launched on August 3, 1981, were used to determine the hydrogen production rate for Comet Halley at heliocentric distances, r, less than about 1.5 AU from measurements of the total Lyman-alpha flux at earth due to the cometary neutral hydrogen distribution. The production rates, determined as a function of r, were found to be consistent with in situ measurements from the Giotto and Vega spacecraft. The calculated rates are also consistent with remote observations using two sounding rockets and with the Pioneer-Venus and IUE spacecraft.

Craven, J. D.↗
NASA NTRS1993

CCD imaging of Comet Wilson (1987VII) - A quantitative coma analysis

Distinctive cometary components (dust, ions, and radicals) are studied on the basis of 2D, narrow-band CCD images of Comet Wilson (1987VII). The fact that Comet Wilson showed no significant structures in the neutral coma during its first perihelion passage is additional evidence for the hypothesis that dynamically new comets do not show a heterogeneous nucleus, but still have a relatively uniform surface. The deviations from the 1/rho law for the decrease of surface brightness as a function of nuclear distance are explained by a combination of short-term variations in the dust production and the effects of solar radiation pressure. The C2 production rate remains basically constant during the whole observational period, while the CN production rate decreases with increasing heliocentric distance. It is inferred that the formation of C2 might be due both to photolytic destruction of some parent molecules as well as to chemical reactions between other species.

Schulz, Rita↗
NASA NTRS1991

Comets in the post-Halley era. Vols. 1 & 2

The present volume on comets in the post-Halley era discusses observing techniques and intepretation, laboratory studies and simulations, the origin and evolution of comets, the cometary nucleus and coma, cometary dust, and plasmas and fields. Attention is given to IR techniques for comet observations, UV spectroscopy of cometary comae, radio interferometric imaging of comets, and irradiation effects on comets and cometary debris. Topics addressed include laboratory simulation of cometary structures, chemical theories on the origin of comets, biological implications of organic compounds in comets, the dynamic history of the Oort cloud, and physical aspects of the evolution of cometary debris. Also discussed are possible mechanisms of cometary outbursts, isotopic ratios in comets, the hydrogen clouds of comets, and physical and optical properties of cometary dust.

Newburn, R. L., Jr.↗
NASA NTRS2024

The dynamical origins of the dark comets and a proposed evolutionary track

So-called ‘dark comets’ are small, morphologically inactive near-Earth objects (NEOs) that exhibit nongravitational accelerations inconsistent with radiative effects. These objects exhibit short rotational periods (minutes to hours), where measured. We find that the strengths required to prevent catastrophic disintegration are consistent with those measured in cometary nuclei and expected in rubble pile objects. We hypothesize that these dark comets are the end result of a rotational fragmentation cascade, which is consistent with their measured physical properties. We calculate the predicted size-frequency distribution for objects evolving under this model. Using dynamical simulations, we further demonstrate that the majority of these bodies originated from the 𝜈6 resonance, implying the existence of volatiles in the current inner main belt. Moreover, one of the dark comets, (523599) 2003 RM, likely originated from the outer main belt, although a JFC origin is also plausible. These results provide strong evidence that volatiles from a reservoir in the inner main belt are present in the near-Earth environment.

Aster G Taylor↗
NASA NTRS1984

Asteroid/comet mission possibilities using a Galileo spacecraft

Opportunities for rendezvous missions to three comets and two asteroids using a Galileo spacecraft have been identified. These missions are launched in the 1988 to 1990 time frame. Mission performance as measured by propellant margin after rendezvous is assessed for a ten-day launch period. Optimal trajectories are determined in each case subject to the maximum launch energy capability of the Shuttle/Centaur. These trajectories include third-body dynamics. The comet Tempel 2 mission uses a distant powered flyby of Jupiter, while each asteroid mission uses two flybys of Mars to accomplish rendezvous. Comparison of the results of the analysis using third-body dynamics with point-to-point conic results is made. The more accurate dynamic model is seen to be particularly important for the Tempel 2 mission. The results of this preliminary analysis indicate that a Galileo spacecraft launched with the Shuttle/Centaur system could be used for rendezvous with any of several comets or asteroids in the near future.

Byrnes, D. V.↗
NASA NTRS1993

The long-term dynamical behavior of short-period comets

The orbits of the known short-period comets under the influence of the Sun and all the planets except Mercury and Pluto are numerically integrated. The calculation was undertaken in order to determine the dynamical lifetimes for these objects as well as explaining the current orbital element distribution. It is found that a comet can move between Jupiter-family and Halley-family comets several times in its dynamical lifetime. The median lifetime of the known short-period comets from the time they are first injected into a short-period comet orbit to ultimate ejection is approximately 50,000 years. The very flat inclination distribution of Jupiter-family comets is observed to become more distended as it ages. The only possible explanation for the observed flat distribution is that the comets become extinct before their inclination distribution can change significantly. It is shown that the anomalous concentration of the argument of perihelion of Jupiter-family comets near 0 and 180 deg is a direct result of their aphelion distance being close to 5.2AU and the comet being recently perturbed onto a Jupiter-family orbit. Also the concentration of their aphelion near Jupiter's orbit is a result of the conservation of the Tisserand invariant during the capture process.

Levison, Harold F.↗
NASA NTRS1965

Precession model for the nucleus of periodic comet Giacobini-Zinner

The comet Giacobini-Zinner, which was discovered in 1900, is a short-period comet of the Jupiter family. It will become the first comet ever to be investigated by a spacecraft in situ, because the International Comet Explorer (ICE) is scheduled to fly through the plasma tail of this comet on September 11, 1985. For this project, it is useful to have as complete a model of the comet as can be deduced from available ground-based observations. The present paper represents, in this connection, an attempt to fill some of the many gaps with respect to an understanding of this particular comet. One of the major results of Yeomans' studies (1971, 1983, 1984) was the detection of a 'discontinuity' in the orbital motion, which qualifies P/Giacobini-Zinner as an 'erratic' comet. One objective of the paper is the formulation of a self-consistent working model of the cometary nucleus, taking into account questions regarding the applicability of the nucleus-precession model of Sekanina (1984) to the dynamically 'erratic' comets.

Sekanina, Z.↗
NASA NTRS1980

Physical loss of long-period comets

Loss of long-period comets from the solar system through a variety of physical processes is investigated. It is shown that planetary collision, defined as a comet passing within the Roche radius of any planet, has a probability of 1.35 x 10 to the -7th per perihelion passage for a long-period comet on a randomly oriented orbit. Sublimation of all volatiles for a one-kilometer radius hydrate ice nucleus would require on the order of 600 to 27,600 perihelion passages, depending on the surface albedo and assuming a perihelion distance of one astronomical unit. Analysis of observational records indicates that for dynamically 'new' comets in the Oort-Schmidt sense there is about a 10% probability of the comet randomly disrupting on its first perihelion passage. This probability drops to 4% per perihelion passage for older long-period comets, and less than 1% for short-period comets. The consequences of these loss mechanisms when incorporated into Monte-Carlo studies of long-period comet evolution are also discussed.

Weissman, P. R.↗
NASA NTRS1979

Physical and dynamical evolution of long-period comets

The source of long-period comets was investigated using a Monte Carlo simulation of comet evolution under the influence of a combination of physical and dynamical processes. The perturbation of cometary orbits by major planets and by non-gravitational forces was modeled, as was physical loss of comets due to random disruption (splitting) and planetary collision; a model was also derived for loss of all volatiles. The importance of each of these processes was examined. The primary end states found for long-period comets were: ejection on hyperbolic orbit, 65.2%; random disruption, 27.6%; and formation of silicate crusts, 7.1%. The basic correctness of the Ort hypothesis was confirmed.

Weissman, P. R.↗
NASA NTRS1989

Airborne infrared spectroscopy of Comet Wilson (1986l) and comparisons with Comet Halley

H2O and possibly CH4 have been detected in near-infrared spectra of Comet Wilson (1986l). The observed number and relative intensities of cometary H2O lines in the nu3 band at 2.65 microns were consistent with fluorescent excitation pumped by solar infrared photons. The H2O production rate in Comet Wilson was approximately 3 x 10 to the 29th/s at R = 1.2 AU; no pronounced temporal variability was observed. Lines in the nu3 band of CH4 at 3.3 microns were possibly detected at the 3 sigma confidence level. The CH4 abundance is in the range CH4/H2O = 0.014-0.045; the uncertainty is due primarily to the assumed effective excitation temperature of CH4. The CH4 abundance in this dynamically 'new' comet is similar to that observed in P/Halley. These values are low for equilibrium compositional models and very high for disequilibrium condensation in the solar nebula.

Larson, Harold P.↗
NASA NTRS2015

The Compositional Evolution of C/2012 S1 (ISON) from Ground-Based High-Resolution Infrared Spectroscopy as Part of a Worldwide Observing Campaign

Volatile production rates, relative abundances, rotational temperatures, and spatial distributions in the coma were measured in C/2012 S1 (ISON) using long-slit high-dispersion (lambda/delta lambda approximately 2.5 times 10 (sup 4)) infrared spectroscopy as part of a worldwide observing campaign. Spectra were obtained on Universal Time 2013 October 26 and 28 with NIRSPEC (Near Infrared Spectrometer) at the W.M. Keck Observatory, and Universal Time 2013 November 19 and 20 with CSHELL (Cryogenic Echelle Spectrograph) at the NASA IRTF (Infrared Telescope Facility). H2O was detected on all dates, with production rates increasing markedly from (8.7 plus or minus 1.5) times 10 (sup 27) molecules per second on October 26 (Heliocentric Distance = 1.12 Astronomical Units) to (3.7 plus or minus 0.4) times 10 (sup 29) molecules per second on November 20 (Heliocentric Distance = 0.43 Astronomical Units). Short-term variability of H2O production is also seen as observations on November 19 show an increase in H2O production rate of nearly a factor of two over a period of about 6 hours. C2H6, CH3OH and CH4 abundances in ISON (International Scientific Optical Network) are slightly depleted relative to H2O when compared to mean values for comets measured at infrared wavelengths. On the November dates, C2H2, HCN and OCS abundances relative to H2O appear to be within the range of mean values, whereas H2CO and NH3 were significantly enhanced. There is evidence that the abundances with respect to H2O increased for some species but not others between October 28 (Heliocentric Distance = 1.07 Astronomical Units) and November 19 (Heliocentric Distance = 0.46 Astronomical Units). The high mixing ratios of H2CO to CH3OH and C2H2 to C2H6 on November 19, and changes in the mixing ratios of some species with respect to H2O between October 28 to November 19, indicates compositional changes that may be the result of a transition from sampling radiation-processed outer layers in this dynamically new comet to sampling more pristine natal material as the outer processed layer was increasingly eroded and the thermal wave propagated into the nucleus as the comet approached perihelion for the first time. On November 19 and 20, the spatial distribution for dust appears asymmetric and enhanced in the antisolar direction, whereas spatial distributions for volatiles (excepting CN) appear symmetric with their peaks slightly offset in the sunward direction compared to the dust. Spatial distributions for H2O, HCN, C2H6, C2H2, and H2CO on November 19 show no definitive evidence for significant contributions from extended sources; however, broader spatial distributions for NH3 and OCS may be consistent with extended sources for these species. Abundances of HCN and C2H2 on November 19 and 20 are insufficient to account for reported abundances of CN and C2 in ISON near this time. Differences in HCN and CN spatial distributions are also consistent with HCN as only a minor source of CN in ISON on November 19 as the spatial distribution of CN in the coma suggests a dominant distributed source that is correlated with dust and not volatile release. The spatial distributions for NH3 and NH2 are similar, suggesting that NH3 is the primary source of NH2 with no evidence of a significant dust source of NH2; however, the higher production rates derived for NH3 compared to NH2 on November 19 and 20 remain unexplained. This suggests a more complete analysis that treats NH2 as a distributed source and accounts for its emission mechanism is needed for future work.

Russo, N. Dello↗
NASA NTRS2016

Isotopic Ratios of H, C, N, O, and S in Comets C2012 F6 (lemmon) and C2014 Q2 (lovejoy) * ** ***

The apparition of bright comets C/2012 F6 (Lemmon) and C/2014 Q2 (Lovejoy) in March-April 2013 and January 2015, combined with the improved observational capabilities of submillimeter facilities, offered an opportunity to carry out sensitive compositional and isotopic studies of the volatiles in their coma. We observed comet Lovejoy with the IRAM 30 meter telescope between 13 and 26 January 2015, and with the Odin submillimeter space observatory on 29 January - 3 February 2015. We detected 22 molecules and several isotopologues. The H2 O-16 and H2 O-18 production rates measured with Odin follow a periodic pattern with a period of 0.94 days and an amplitude of approximately 25 percent. The inferred isotope ratios in comet Lovejoy are O-16/O-18 = 499 +/- 24 and D/H equals 1.4 +/- 0.4 x 10(exp -4) in water, S-32/S-34 = equals 24.7 +/- 3.5 in CS, all compatible with terrestrial values. The ratio C-12/C-13 equals 109 +/- 14 in HCN is marginally higher than terrestrial and 14 N/ 15/N equals 145 +/- 12 in HCN is half the Earth ratio. Several upper limits for D/H or C-12/ C-13 in other molecules are reported. From our observation of HDO in comet C/2014 Q2 (Lovejoy), we report the first D/H ratio in an Oort Cloud comet that is not larger than the terrestrial value. On the other hand, the observation of the same HDO line in the other Oort-cloud comet, C/2012 F6 (Lemmon), suggests a D/H value four times higher. Given the previous measurements of D/H in cometary water, this illustrates that a diversity in the D/H ratio and in the chemical composition, is present even within the same dynamical group of comets, suggesting that current dynamical groups contain comets formed at very different places or times in the early solar system.

Biver, N.↗