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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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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS2026

CH3OH and HCN in Interstellar Comet 3I/ATLAS Mapped with the ALMA Atacama Compact Array: Distinct Outgassing Behaviors and a Remarkably High CH3OH/HCN Production Rate Ratio

We report the detection of methanol (CH3OH) toward interstellar comet 3I/ATLAS using the At-acama Compact Array of the Atacama Large Millimeter/Submillimeter Array (ALMA) on UT 2025 August 28, September 18 and 22, and October 1, and of hydrogen cyanide (HCN) on September 12 and 15. These observations spanned pre-perihelion heliocentric distances (r H ) of 2.6 – 1.7 au. The molecules showed outgassing patterns distinct from one another, with HCN production being depleted in the sunward hemisphere of the coma, whereas CH3OH was enhanced in that direction. Statistical analysis of molecular scale lengths in 3I/ATLAS indicated that CH3OH included production from coma sources at Lp > 258 km at 99% confidence. However low signal-to-noise on long baselines, which sample emission on small spatial scales closest to the nucleus, prevented definitively ruling out CH3OH as purely a parent species. In contrast, HCN production was indistinguishable from direct nucleus sublimation. The CH3OH production rate increased sharply from August through October, including an uptick near the inner edge of the H2O sublimation zone at rH = 2 au. Compared to comets measured to date at radio wavelengths, the derived CH3OH/HCN ratios in 3I/ATLAS of 124+30−34 and 79+11−14on September 12 and 15, respectively, are among the most enriched values measured in any comet, surpassed only by anomalous solar system comet C/2016 R2 (PanSTARRS)

Comae↗
NASA NTRS1995

Long-Period Comets and the Oort Cloud

The long-period comets pose a unique problem for the impact hazard problem. Because of their very long orbital period and generally large distances form the Sun, they cannot be surveyed and catalogued in the same manner as the near-Earth asteroids and short-period comets..Improved technologies are needed to detect approaching long-period comets at large heliocentric distances so as to increase the warning time for potential impactors.

long-period comets comets comet impact↗
NASA NTRS1995

The Splitting of the Nucleus of Comet Shoemaker-Levy 9

The breakup of comet Shoemaker-Levy 9 is discussed both in the context of splitting as a cometary phenomenon, comparing this object with other split comets, and as an event with its own idiosyncrasies. The physical appearance of the comet is described, features diagnostic of the nature of the tidal disruption are identified, and the implications for modelling the event are spelled out.

comet Shoemaker-Levy 9 comet nucleus comet splitti↗
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 NTRS1972

Study of a comet rendezvous mission. Volume 2: Appendices

Appendices to the comet Encke rendezvous mission consider relative positions of comet, earth and sun; viewing condition for Encke; detection of Taurid meteor streams; ephemeris of comet Encke; microwave and optical techniques in rendezvous mission; approach instruments; electrostatic equilibrium of ion engine spacecraft; comet flyby data for rendezvous spacecraft assembly; observations of P/Encke extracted from a compilation; and summary of technical innovations.

Source record↗
NASA NTRS1972

The Lyman-alpha image of comet Tago-Sato-Kosaka /1969g/.

An f/2 objective-grating spectrograph aboard an Aerobee rocket recorded a faint image of Comet Tago-Sato-Kosaka (1969g) in L-alpha emission. Some sharpening of the image and reduction of film grain noise was accomplished by multiplying the picture's Fourier transform by an optimum filter function. After this processing, which was carried out digitally, the L-alpha comet image appeared as a nearly circularly symmetric diffuse glow approximately 800,000 km in diameter. There was also the suggestion of a faintly visible core of emission whose dimensions are less than 100,000 km. The sublimation of ice in the nucleus of the comet and the subsequent dissociation of the free water molecules by sunlight could produce a large cloud of hydrogen atoms around the comet. Resonant reradiation of solar L-alpha emission by this cloud is probably responsible for the most of the observed emission.

Jenkins, E. B.↗
NASA NTRS1972

Comet Tails of Type 2

A summary is presented of a theory for the head and tail regions of Type 2 (dust) comets, wherein dust particles having a wide distribution of sizes are assumed to be released from the comet nucleus in an essentially continuous manner in time during the period of distinctive cometary phenomena. The dust particles are assumed to be accelerated radially outward from the nucleus as a result of a drag interaction with the expanding gas in the comet head. In the tail region the only significant forces assumed to act on the dust particles are solar gravity and the force of solar radiation pressure. It is shown how results describing the surface density in the tail are obtained and how by matching calculated distributions with measured ones it is possible to determine the dust and head-gas emission rates as a function of time, the distribution of dust particle sizes, and the emission velocity from the inner head region as a function of particle size and time. The results of matching calculated density distributions with light intensity measurements from Comet Arend-Roland 1956h are summarized.

Probstein, R. F.↗
NASA NTRS1971

Comet rendezvous mission study

Four periodic comets with perihelia between 1980 and 1986 (Encke, d'Arrest, Kipff, and Halley) are used as candidates for the comet rendezvous mission study. All these comet apparitions are especially favorable for rendezvous missions, because of early earth-based comet recovery, good opportunities to view their activity from earth, and reasonable launch vehicle and trajectory requirements for nominal payloads.

Friedlander, A. L.↗
NASA NTRS1972

Does a continuous solid nucleus exist in comets.

The implication of actual cometary observations for the physical nature of comets is briefly reviewed, bringing out the complete conflict with observation of the ice-dust solid nucleus model put forward in recent years as representing the fundamental structure of comets. That under increasing solar heat the nucleus develops an expanding atmosphere is inconsistent with the well-established phenomenon that the coma contracts with decreasing distance from the sun. Several comets remaining always beyond Mars have nevertheless been strongly active and produced fine tails. That some comets show at times a star-like point of light is readily explicable on the dust-cloud structure and by no means establishes that a solid nucleus exists. With the nucleus-area corresponding not to a small solid mass but to an optical phenomenon, there would be no reason to expect that it would describe a precise dynamical orbit. On the hypothesis of a nucleus, it is necessary to postulate further some internal jet-propulsion mechanism to account for the orbital deviations.

Lyttleton, R. A.↗
NASA NTRS1973

Comet Bennett 1970 II.

The model for dust comets, formulated by Finson and Probstein, which had previously been tested only on Comet Arend-Roland 1957 III, has been successfully applied to three calibrated photographic plates of Comet Bennett. The size distribution, emission rate, and initial velocities of dust particles emitted from the comet's nucleus are given.

Sekanina, Z.↗
NASA NTRS1973

Kohoutek - A great comet coming.

Passing inside the earth's orbit in late November, the comet Kohoutek will travel through the inner solar system during a unique period in the history of the space program, when Skylab and Mariner Venus-Mercury are in operation and the new C-141 Airborne Infrared Observatory is ready for flight. It is planned to investigate comprehensively the nature and evolution of the coma and tails of the comet. The detailed goals of the investigation include the identification of the parent molecules of the gases observed in comets, the determination of the processes that break down the parent molecules, the study of the physical nature of transient events in the comet, and the measurement of the solar-wind velocity in the inner solar system.

Maran, S. P.↗
NASA NTRS1974

Magnetisation of comets

Construction of a model explaining the means by which the interplanetary magnetic field could mix with the plasma of a comet tail. It is suggested that the magnetic fields in comet tails derive from the hydromagnetic conversion of kinetic energy into magnetic energy in the nuclear region of the comet. In particular, it is shown that, if the nuclear region consists of a supplementary distributed source for the coma gases, a turbulent flow with maximum velocities of the order of thermal velocity may be expected in this region, with the necessary ordering in the turbulent velocity field provided by the rotation of the nuclear region. It is concluded that a comet, when sufficiently close to the sun, may be able to generate an appreciable magnetic field and that the magnetic fields observed in the tail may then result from processes analogous to those producing the earth's magnetotail.

Mendis, A.↗
NASA NTRS1974

On the nature of the anti-tail of Comet Kohoutek /1973f/. I - A working model

The model derived for the anti-tail of Comet Kohoutek describes it as a flat formation, confined essentially to the comet's orbit plane and composed of relatively heavy particles (mostly in the size range 0.1-1 mm) whose motions are controlled by solar gravity and solar radiation pressure. Almost all the material was produced by the comet before perihelion at a rate about an order of magnitude higher than for Comets Arend-Roland and Bennett. The latent heat of vaporization of the particle material is estimated at 40-45 kcal/mole or higher.

Sekanina, Z.↗
NASA NTRS1975

Observing prospects for Halley's comet

The expected path and brightness development of Halley's comet soon before and after its perihelion on February 9, 1986 are described. It is concluded that the comet will prove disappointing to most U.S. observers, since it is not expected to equal Kohoutek in peak magnitude (and since this latter comet was disappointing to the general public). Moreover, Halley's comet will be brightest (3rd magnitude) in the southern hemisphere, and increased outdoor lighting by the year 1986 will probably obscure its tail near cities.

Roosen, R. G.↗
NASA NTRS1976

Spectroscopic observations of comet Kohoutek (1973f), 2

Spectroscopic observations of comet Kohoutek at the Asiago Astrophysical Observatory are described. Spectra cover six nights before perihelion and five nights after perihelion. The spectra of the coma and tail of comet Kohoutek are characterized by fairly strong, asymmetric H2O(+) emissions in the red and the near infrared spectral regions and by the appearance of the 01 forbidden lines at 6300-6364 A, already at heliocentric distance r=1.55 A.U. These peculiarities suggest that some differences in chemical abundances or in physical conditions exist between comet Kohoutek and other comets.

Benvenuti, P.↗
NASA NTRS1976

The neutral coma of comets: A review

The hypothesis that water snow controls the vaporization of the nucleus of some comets seems verified from the general order of magnitude of the size of their nucleus and of their nuclear albedo; the largest observed production rates are H and OH which both seem to originate from the photodissociation of H2O, as also confirmed by the scale length of the invisible parent molecule producing OH. However, comet Encke is not uniformly covered by water snow, as it produces only one tenth of the expected vaporization. Early results on comet Kohoutek suggest that the conclusions could be slightly different for some of the new comets in Oort's sense. If the far ultraviolet observations confirm the early assessments of the production rates of C, O and H, then at least another major constituent competing with water has not yet been detected. Such a major constituent is suggested by the ratios C/O = 0.24 and H/O = 2.5.

Delsemme, A. H.↗
NASA NTRS1975

Shuttle-launched multi-comet mission 1985

A low-cost multi-comet intercept mission with a launch in March 1985 is proposed. Two cometary spacecraft of identical design will be placed into a low earth parking orbit using a single Shuttle launch vehicle. Solid kick stages will then be used to boost each spacecraft into its required interplanetary trajectory. It is planned to have one spacecraft intercept comet Giacobini-Zinner in September 1985 and then go on to comet Borrelly with an encounter in December 1987. Earth swingby maneuvers will be used to achieve the double cometary intercept. The other spacecraft will be targeted for a pre-perihelion encounter with Halley's comet in December 1985.

Farquhar, R. W.↗
NASA NTRS1976

The neutral atmospheres of comets

A comprehensive review of current knowledge about the neutral gas atmospheres of comets is given, with emphasis on the task of deriving the chemical composition of the cometary nucleus. The discussion centers on the following major topics: photometric and spectrophotometric observations of the neutral atmosphere and its constituent neutral radicals, molecules, and atoms; excitation processes responsible for the observed emissions from the neutral coma; the parent molecules of the neutral radicals; the gas-phase chemistry likely to take place in the dense inner coma; dynamic models (both exospheric and hydrodynamic) of the neutral atmosphere; and the chemical compositions of comets. The primary conclusions reached on the basis of all the data considered are that: (1) the chemical composition of the dust component is most likely to be the same as that of the stream meteoroids which burn up on hitting the earth's upper atmosphere; (2) the dominant icy component in most comets is probably H2O; and (3) anomalous abundances of other volatile species are present in some comets.

Mendis, D. A.↗