Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Titan”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

C4H2, HC3N and C2N2 in Titan's atmosphere

Voyager 1 took IR measurements of the atmosphere of Titan, and obtained an average of 346 spectra, mostly from the center of the disk. The compounds C4H2, HC3N, and C2N2 were detected in the atmosphere of Titan. The identification of two compounds containing nitrogen, in addition to HCN, provides further evidence for the abundance of free N2 on Titan. The organic compounds observed in the atmosphere of Titan are summarized in a table, which also indicates the approximate mole fraction for each compound identified previously. The observed compounds originate by reactions of methane and nitrogen radicals in a predominantly nitrogen atmosphere.

Kunde, V. G.↗
NASA NTRS1982

EUV emission from Titan's upper atmosphere - Voyager 1 encounter

Most of the observed emission short of Lyman-alpha is shown to be accounted for by electron impact on N2 above 3600 km, in an analysis of Titan's EUV emission spectra obtained at the Voyager 1 encounter. It is determined that N2 is the major component of Titan's upper atmosphere, with 3900-km upper limit mixing ratios of NeI, ArI, CO, H2, and HI of 0.01, 0.06, 0.05, 0.06 and 0.1, respectively. Magnetospheric electron precipitation produces an average dayside electron density of about 3000/cu cm between 3600 and 4000 km, which is the region of bright limb emission, and magnetospheric electron impact dissociation of N2 generates an N atom escape rate of 3 x 10 to the 26th/sec from Titan's exosphere when Titan is within Saturn's magnetosphere.

Strobel, D. F.↗
NASA NTRS1982

Titan's ion exosphere observed from Voyager 1

The plasma wake surrounding Titan in Saturn's rotating magnetosphere is characterized by a plasma which is denser and cooler than the surrounding subsonic magnetospheric plasma, and which is produced by the deflection of magnetospheric plasma around Titan and the addition of exospheric ions picked up by the rotating magnetosphere. A resemblance to the interaction between the solar wind and Venus is shown for the case of ion pickup in the ion exosphere outside Titan's magnetic tail and ion flow within the boundaries of the tail as Saturn's rotating magnetosphere interacts with Titan. The boundary of the tail is indicated by a sharp reduction in the flux of high-energy electrons, which are removed by inelastic scattering with the atmosphere and centrifugal drift produced when the electrons traverse the magnetic field draped around Saturn.

Hartle, R. E.↗
NASA NTRS1982

The structure of Titan's wake from plasma wave observations

The electron density profile inferred from plasma wave emissions detected during the Voyager 1 flyby of Titan exhibits three distinct peaks with densities of about 40/cu cm, the first peak corresponding to the entry into the magnetic tail, the second corresponding to the neutral sheet crossing from the northern to the southern tail lobe, and the third corresponding to the outbound exit from the tail. Large depressions in the magnetic field strength are observed coincident with each of the density peaks, indicating that a dense plume of plasma is being carried downstream of Titan by the interaction with the rapidly rotating magnetosphere of Saturn. The 8600 K plasma temperature estimated suggests that the plasma originates from the ionosphere of Titan, probably forming a plasma plume with a theta or H cross section extending downstream from Titan.

Gurnett, D. A.↗
NASA NTRS1982

Planetary radio astronomy observations during the Voyager 1 Titan flyby

During the Voyager 1 Titan flyby, unusual radio emissions were observed by the planetary radio astronomy experiment in the 20- to 97-kHz frequency range. It is shown that Titan itself is not the source of the observed radio emission. The emission features are attributed to modification of the normal Saturn kilometric radiation by propagation effects in enhanced density structures within the Titan wake. Furthermore, spiky emissions observed in the magnetic wake of Titan are interpreted in terms of local electrostatic instabilities at the electron plasma frequency. From these measurements a range of electron densities in the wake region is derived, and the consistency of the results is discussed.

Daigne, G.↗
NASA NTRS1982

Effects of Titan on trapped particles in Saturn's magnetosphere

Magnetic field data from Voyager 1 magnetometer experiment are used with angular distribution data from the same spacecraft's low energy charged particle experiment to investigate the influences of Titan on the magnetosphere energetic particle distributions, with attention to the pitch angle distributions of ions and electrons. Titan appears to disrupt the corotation motion of the ions, since, while the fluxes of the ions in the corotation direction are of diminished intensity, those observed in the equatorial plane perpendicular to this direction are almost unaffected. The resulting distribution and trajectory modeling conclusions suggest that the convection electric field is absent in the wake of Titan, and that the presence of Titan produces a reduction in the fluxes of the electrons and flatter distributions with pitch angle.

Maclennan, C. G.↗
NASA NTRS1982

The tide in the seas of Titan

The parameters of the tides in the near-global ocean that may exist on Titan are assessed. A formula for the difference between the maximum heights of the oceanic and body tides is used to determine that the amplitude of the apparent, near-stationary, oceanic tide on Titan is greater than about 100 m. The effects of tidal dissipation are evaluated, showing that the amplitude of the tide will vary by nine percent over its 15.95-day period. The observed eccentricity of Titan's orbit is used to establish limits on the satellite's surface topography and oceanic depths. It is concluded that either Titan is covered by a near-global methane ocean over 400 m deep, or that there is no methane ocean at all. Reflectivity measurements can decide between these alternatives.

Sagan, C.↗
NASA NTRS1984

Comparison of induced magnetospheres at Venus and Titan

Analyses of the similarities and differences of the magnetic tails of Venus and Titan are presented. Voyager 1 data showed that the Titan bipolar tail is produced by passage through the subsonic plasma flow of Saturn's magnetosphere. Venera 9 and 10 gathered data on the Venus tail, which is produced by the interaction of the Venus atmosphere and ionosphere with the solar wind. Both nonmagnetic bodies have induced two-lobe magnetic tails, field reversal in the tail and display characteristics of decreased energetic electron densities. The plasma flow is supersonic near the Venus tail boundary but not near Titan. Magnetic merging of the tail lobes is continuous behind Titan and irregular in the Venus tail.

Verigin, M. I.↗
NASA NTRS1984

Titan

It is pointed out that Titan, which is the second largest satellite in the solar system, is considerably larger than Mercury. It is made unique by its dense atmosphere, which consists mainly of nitrogen, although a substantial component of methane is present. The basic properties of Titan are summarized in a table. Many of the data were obtained during the close pass of Voyager 1 in November 1980. The atmospheric temperature decreases from its surface value of 94 K at a pressure of 1500 mbar to a minimum of 71 K at a height of 42 km and a pressure of 128 mbar. Details of atmospheric composition and thermal structure are discussed, taking into account chemical identifications and abundances, the vertical temperature structure, the horizontal temperature and opacity structure, and the radiative equilibrium. The upper atmosphere composition and temperature is considered along with the properties of aerosols, and meteorology and atmospheric dynamics. Titan's interior has an average density of 1.88 g per cu cm. Attention is given to Titan's surface and interior, and its formation.

Hunten, D. M.↗
NASA NTRS1984

Titan's magnetospheric interaction

Voyager 1 encounter data are used to theoretically examine the interaction of Titan with the solar wind, the Saturn magnetosheath and the Saturn magnetosphere. The spacecraft data comprised magnetometer, plasma wave, radio signal and charged particle measurements. Attention is given to the Alfven (1.9) and Mach (0.57) numbers detected in the Saturn magnetosheath, along with a fast hydrodynamic Mach number of 0.55. Incident plasma interacted with the Titan atmosphere and produced a magnetosphere through mass capture and field-line draping. The tail region was loaded with N(+) and N2(+)/H2CN(+) ions instead of the strong H(+) signals typical of other regions. The magnetotail featured four lobes, and the Titan atmosphere was calculated to lose 10 to the 24th ions/sec. Finally, the Titan internal rotationally aligned magnetic field has an estimated strength of 7 x 10 to the 20th gauss/cu cm.

Neubauer, F. M.↗
NASA NTRS1985

Aerothermodynamic environment for a Titan probe with deployable decelerator

It is pointed out that further exploration of Titan, Saturn's largest moon, is of current interest to the scientific community, particularly from the standpoint of the organic chemical evolution of its atmosphere. For a suitable study of this Saturnian satellite, a mission involving a Titan atmospheric entry probe is to be conducted. The probe is to employ a deployable decelerator with the aim to allow scientific measurements in the haze layer. The present investigation is concerned with an assessment of the aerothermodynamic environment for the considered probe during its hypervelocity, low-Reynolds-number entry. Attention is given to the employed computational method, the Titan probe configuration, the Titan probe trajectory, the viscous-layer regime of the aerothermodynamic environment, and the incipient merged-layer regime.

Green, M. J.↗
NASA NTRS1986

The organic aerosols of Titan

A dark reddish organic solid, called tholin, is synthesized from simulated Titanian atmospheres by irradiation with high energy electrons in a plasma discharge. The visible reflection spectrum of this tholin is found to be similar to that of high altitude aerosols responsible for the albedo and reddish color of Titan. The real (n) and imaginary (k) parts of the complex refractive index of thin films of Titan prepared by continuous dc discharge through a 0.9 N2/0.1 CH4 gas mixture at 0.2 mb is determined from X-ray to microwave frequencies. Values of n (approx. 1.65) and k (approx. 0.004 to 0.08) in the visible are consistent with deductions made by groundbased and spaceborne observations of Titan. Many infrared absorption features are present in k(lambda), including the 4.6 micrometer nitrile band. Molecular analysis of the volatile components of this tholin was performed by sequential and nonsequential pyrolytic gas chromatography/mass spectrometry. More than one hundred organic compounds are released; tentative identifications include saturated and unsaturated aliphatic hydrocarbons, substituted polycylic aromatics, nitriles, amines, pyrroles, pyrazines, pyridines, pyrimidines, and the purine, adenine. In addition,acid hydrolysis produces a racemic mixture of biological and nonbiological amino acids. Many of these molecules are implicated in the origin of life on Earth, suggesting Titan as a contemporary laboratory environment for prebiological organic chemistry on a planetary scale.

Khare, B. N.↗
NASA NTRS1986

Measurements of physical properties of model Titan atmospheres

One aspect of the study of Titan's atmosphere is the elucidation of the chemical and physical nature of the aerosols. In order to facilitate this, a program to produce laboratory synthesized model materials for Titan's aerosol and to study their chemical and physical properties is now in progress. Various processes, including electric discharge, photolysis by ultraviolet light, and irradiation by energetic particles, will be used to produce the materials. A first set of experiments where a nominal Titan mixture (97%N2, 3% CH4, 0.2% H2) was subjected to pulsed high temperature shocks yielded a reddish brown waxy solid. This material was subjected to pyrolysis/gas chromatography, a technique that has been proposed as a method for analysis of the Titan aerosols. Preliminary results show the material to consist of simple hydrocarbons but little else, at least up to temperatures of 600 C. Since the material was colored, compounds other than those mentioned above must be present.

Scattergood, T. W.↗
NASA NTRS1986

A gas chromatograph experiment for a Titan entry probe

Development of a gas chromatographic technique for analysis of aerosols and volatile organics from a Titan probe is now in progress. Preliminary investigations of aerosol collectors have shown that an electrostatic device should be the most efficient for the particle sizes expected in Titan's atmosphere. Such a device particularly lends itself to development of a simple pyrolyzer which can be used to break down any collected organic conglomerate structures into volatile fragments. Those fragments can subsequently be analyzed by GC providing information about the original chemical structure of the aerosols. Studies show that as little as 1 to 5 micrograms of model aerosol can be successfully analyzed. High altitude atmospheric gas sampling will also be important on Titan due to the great depth of the atmosphere. Studies show that a GC analysis of model Titan atmospheres at pressures approximating this altitude can be made with a sensitivity of a few ten's of parts-per-billion for the trace gases of interest.

Carle, G. C.↗
NASA NTRS1985

Evolution of Titan's coupled ocean-atmosphere system and interaction of ocean with bedrock

A recent model for the surface state of Titan proposes a liquid ethane-methane-molecular nitrogen layer of order one kilometer thick which because of stratospheric methane photolysis has become increasingly ethane-rich with time. The interaction of such an ocean with the underlying 'bedrock' of Titan (assumed to be water-ice or ammonia hydrate) and with the primarily nitrogen atmosphere is explored. It is concluded that although modest exchange of oceanic hydrocarbons with enclathrated methane in the bedrock can in principle occur, it is unlikely for reasonable regolith depths. The surprisingly high solubility of water-ice in liquid methane implies that topographic features on Titan of order 100 meters in height can be eroded away on a time scale of one-billion years. The large solubility difference of N2 in methane versus ethane implies that the ocean composition is a strong determinant of atmospheric pressure; a simple radiative model of the Titan atmosphere is employed to demonstrate that significant surface pressure and temperature changes can occur as the oceanic composition evolves with time.

Lunine, J. I.↗
NASA NTRS1986

D to H ratio and the origin and evolution of Titan's atmosphere

Potential causative factors for the unusually large ratio of CH3D to CH4 reported in the stratosphere of Titan (6 x 10 to the -4th) compared to that of Saturn (8.7 x 10 to the -5th) or Jupiter (6.7 x 10 to the -5th) are examined. With uncertainty in the observations and data reduction taken into account, an atmospheric enrichment factor of three or more is calculated for Titan relative to the planets. This enrichment factor is seen to be accounted for by condensation to form tropospheric methane clouds, fractionation occurring over a hypothetical CH4-C2H6 ocean and between the ocean and the clathrate crust beneath, fractionation which occurred during the formation of Titan, and fractionation as a result of the evolution of Titan's atmosphere. It is concluded that the greater part of the observed fractionation is probably derived from the last two of these mechanisms. The mechanisms studied do not account for the observed CH3D/CH4 value of 1.7 x 10 to the -3rd obtained by Kim and Caldwell (1982).

Pinto, J. P.↗
NASA NTRS1988

High-temperature shock formation of N2 and organics on primordial Titan

Theoretical models suggest that the initial form of nitrogen in Titan's atmosphere may have been NH3. The possible importance of strong shocks produced during high-velocity impacts accompanying the late stages of accretion are investigated as a method for converting NH3 to N2, of which Titan's atmosphere is now primarily composed. The focused beam of a high-power laser is used to simulate the effects of an impact in Titan's atmosphere. For mixtures of 10, 50, and 90 percent NH3, yields of 0.25, 1, and 6 x 20 to the 17th molecules of N2 per joule, respectively, were obtained. It is also found that the yield of HCN is comparable to that for N2. Several other hydrocarbons are produced, many with yields in excess of theoretical high-temperature-equilibrium models. The above yields, when combined with models of the satellite's accretion, result in a total N2 production comparable to that present in TItan's atmosphere and putative ocean.

Mckay, Christopher P.↗
NASA NTRS1989

Present state and chemical evolution of the atmospheres of Titan, Triton, and Pluto

An evaluation is made of the current understanding of the atmospheres of Titan, Triton, and Pluto, as well as of theoretical models for their origin and evolution. All three atmospheres contain methane, while Titan, and probably Triton, have nitrogen. The primary driver in the evolution of the Titan atmosphere has been the irreversible photolysis of methane. If a surface reservoir of liquid methane exists to resupply the atmosphere, it is subject to enrichment in ethane due to the long-term photolysis of methane. The key issue in the origin and early evolution of Titan's atmosphere is the source of molecular nitrogen; two schemes for the conversion of ammonia to nitrogen have been considered.

Lunine, J. I.↗