Cometary Hydrogen Research Articles

Evidence for pyroxene dust grains in C/2001 C2 sungrazing comet

In this paper we analyze SOHO/UVCS data of the sungrazing comet C/2001 C2, a member of the Kreutz family, that was observed on February 7, 2001, at the heliocentric distances of 4.98 and 3.60 solar radii. This comet splits in a main nucleus and a fragment which have been identified in UV data. A study of the cometary Hydrogen Lyα emission from these two objects revealed that the Lyα signal from the fragment decays exponentially with time, while the signal from the main object consists of an exponentially decaying term superposed onto a constant background. The latter emission has been ascribed to the sublimation of pyroxene dust grains, whose end products neutralize coronal protons via charge exchange processes. This interpretation allowed us to estimate, for the first time, the number density of pyroxene dust grains in a sungrazing comet.

Temporal deconvolution of the hydrogen coma I. A hybrid model

This paper describes a semi-analytical model, tentatively called the time-resolved model (TRM), for calculating the proper temporally resolved column density and Lyman-alpha intensity profiles of the extended cometary hydrogen coma, with potentially arbitrary number of photodissociation sources with different initial velocity profiles. The non-analytical part consists of a true 3D particle simulator whose results are used to obtain the necessary corrective parameters for the analytical, spherically symmetric formulas for the column density and intensity profiles. The hybrid approach provides a physically accurate and computationally effective method to recreate the extended coma profiles and supports a new analysis method that can provide hydrogen lifetime estimates and a much enhanced temporal resolution for the water production curve, for which a method is described. The ability to recreate the water production profile by different analysis methods is studied with a combination of real and simulated data. This is the first part of a two part publication with the second part dedicated to real data analysis.

UVCS Observation of Sungrazer C/2001 C2: Possible Comet Fragmentation and Plasma‐Dust Interactions

In this paper we analyze SOHO Ultraviolet Coronagraph Spectrometer (UVCS) observations of the sungrazing cometC/2001C2,amemberoftheKreutzfamily,observedon2001February7atheliocentricdistancesof4.98and 3.60 R� . This comet apparently went through sequential fragmentation events along its path: further indication of fragmentation processes is provided by UVCS observations, which show the presence of two separate tails in the 4.98 Rdata set, which we interpret as two fragments unresolved by LASCO images, one of which sublimates before reaching 3.60 R� . The cometary hydrogen Lysignal, decaying exponentially with time, has been inter- preted in terms of the H2O outgassing rate and the interactions of coronal protons with atoms created by the photodissociation of water. However, one of the fragments shows an additional Lycontribution, constant with time, which adds to the temporally decaying signal. This contribution has been ascribed to the sublimation of pyroxene dust grains, whose end products neutralize coronal protons via charge exchange processes. Hence, the twofragmentshavedifferentcomposition;differencesthroughoutthecometbodymayhavebeentheprimarycause for the comet fragmentation. Subject headingg comets: general — comets: individual (C/2001 C2) — ultraviolet: general

Where do the oceans come from?

The chronology of the Earth's formation and the clues of origin given by stable isotopes for the Earth itself and the different water sources in the solar nebula and solar system, indicate that the present Earth's water budget comes from three main sources: hydrogen trapped in the Earth's mantle, with a very low D/H ratio, and water and hydrogen coming with a late veneer of water-rich bodies, mainly between 25 and 100 Myr after the birth of the solar system. These water-rich bodies are now represented by some carbonaceous meteorites (CI and CM) with a bulk D/H ratio roughly terrestrial (∼ 1.5 x 10 -4 ) and comets with a D/H ratio about double (∼ 3 x 10 -4 ) of the terrestrial ratio. The CI and CM D/H's result from a mixture of deuterium-poor, lower than terrestrial and deuterium-rich, roughly cometary hydrogen. Directly or indirectly, cometary water has participated (from 17 to ∼ 50%) to the Earth's water budget. The data presently available, in particular those concerning the labelling of the late veneer by osmium isotopes, and the atmospheric distribution of rare gases favour the idea of a direct participation of comets (50%) mixed with mantle-outgassed water (50%), very poor in deuterium. This model can also be applied successfully to Venus, but with a much lower cometary contribution. The strong initial isotope heterogeneity of terrestrial water calls for a very thorough initial mixing by outgassing and mantle recycling, made possible by the very high initial convection rates of the hot primary mantle, which can isotopically homogenize the two sources in the first 100 Myr of the Earth's history.

Multiple Scattering of Hydrogen Lyα Radiation in the Coma of Comet Hyakutake (C/1996 B2)

The Goddard High Resolution Spectrograph on board the Hubble Space Telescope measured hydrogen Lyα (H Lyα) line profiles at different locations around the coma of comet Hyakutake (C/1996 B2) in 1996 April. The spectral resolution of about 4 km s-1 (Doppler velocity, FWHM) was significantly better (by a factor of 2-3) than any previous measurement and is sufficient to constrain models of atomic hydrogen production processes and inner coma thermodynamics. In a recent paper, we reported the line profile measurements and the results of an explicit model of the optically thin region of the coma. The spectrally integrated emission rates in all but the nucleus-centered spectrum were computed, but the inner coma line profiles were only discussed qualitatively. In the present paper, we investigate the details of the line profiles using a first-principles numerical model of the H coma and a new radiative transfer model based on the Monte Carlo method to account for the line radiation transport throughout the coma. This multiple scattering model uses number densities and velocity distributions of H atoms produced by the water dissociation processes, along with angle-dependent frequency redistribution to describe each scattering process. The computed spectra, when convolved with the instrument function, are in excellent agreement with the measured spectra. The model is able to reproduce features, such as the saturation of the line profiles in the optically deep regions, and the strong asymmetry of the isophotes due to shadowing of the nightside by H atoms of the inner coma. For the first time, a consistent and detailed radiative transfer treatment of a physically realistic cometary hydrogen density and velocity distribution confirms our overall understanding of water dissociation processes and partial thermalization in the coma.

The Hydrogen Clouds of Comets

Abstract.In a cometary coma, various hydrogen compounds, especially water, that are photodissociated by solar ultraviolet radiation form a gigantic hydrogen cloud with a radius of several million kilometers around the cometary nucleus. These cometary hydrogen clouds have been observed by a number of spacecraft outside the terrestrial atmosphere and in interplanetary space. For instance, the hydrogen cloud of Comet Halley was a good target for the ultraviolet photometers and spectrometers on board the International Ultraviolet Explorer (IUE), Suisei, Pioneer Venus, DE-1, and sounding rockets. Hydrogen cloud activity could be used as a good measure of cometary activity, but some problems remain to be explored in the future.

Influence of multiple ion species on low‐frequency electromagnetic wave instabilities

Analysis of the stability of low‐frequency electromagnetic modes excited by coexisting newborn ion species shows that the effect of multiple (singly ionized) ions on wave growth, for given background magnetoplasma conditions and relative densities, depends not only on their mass but also on the physical nature of the wave modes. Whereas each one of the coexisting ion beams tends to stimulate instabilities without undue influence from the other species, if the ion masses are disparate, newborn ions of similar masses can strongly catalyze wave growth of fluidlike, nonresonant modes, but only bring about weak growth enhancements in cyclotron resonant instabilities. We contrast wave characteristics due to the coexistence of hydronium, water vapor, and oxygen newborn ions with previous results involving cometary hydrogen and oxygen ions and provide a physical interpretation of the results.

Monte Carlo particle-trajectory models for neutral cometary gases. I - Models and equations. II - The spatial morphology of the Lyman-alpha coma

The mathematical derivations of various methods employed in the Monte Carlo particle-trajectory model (MCPTM) are presented, and the application of the MCPTM to the calculation of the photochemical heating of the inner coma through the partial thermalization of cometary hydrogen atoms produced by the photodissociation of water is discussed. This model is then used to explain the observed morphology of the spatially extended Ly-alpha comas of comets. The rocket and Skylab images of the Ly-alpha coma of Comet Kohoutek are examined.

Pioneer Venus lyman‐α observations of comet P/Giacobini‐Zinner and the life expectancy of cometary hydrogen

Pioneer Venus observed the hydrogen coma of Comet P/Giacobini‐Zinner on 11 September 1985 during the ICE fly‐by. Analysis of these data with a time‐dependent 3‐D particle‐trajectory model implies a water production rate of 2.2 × 1028 s−1 on that day. The model includes the irregular variations in the H lifetime and the H Lyman‐α fluorescence rate determined from simultaneous measurements of the solar wind by ICE and of the solar UV by SME, respectively. The H lifetime varied from 2 × 105 to 3 × 106 s during the 42 days preceding the observation.

Hydrogen production rate from comet Austin 1982g

Meaningful measurements with respect to the cometary Balmer-alpha (H-alpha) emission are difficult and require the use of special equipment. The first ground-based observations of H-alpha emission from a cometary hydrogen corona were conducted on comet Kohoutek 1973 XII with a large-aperture Fabry-Perot spectrometer installed at the McMath solar telescope at Kitt Peak National Observatory. The present investigation is concerned with the second ground-based observations of cometary H-alpha emission carried out during the apparition of comet Austin 1982g. A 150 mm dual-etalon Fabry-Perot spectrometer was employed in the experiment. Use was made of an observatory which is designed for the high spectral resolution study of faint extended sources such as interstellar and geocoronal emission lines. The investigation demonstrates that hydrogen production rates from comets as faint as about 7th magnitude can be routinely measured from the ground at minimal cost.

Planet-A mission to Halley

Looking at the chance of the next apparition of the Halley comet in 1986, ISAS decided to send a first Japasanese interplanetary spacecraft for the study of cometary hydrogen coma and solar wind. The Planet-A spacecraft which carries VUV imaging camera and solar wind plasma analyser will be launched in August 1985 and flyby the Halley comet in early March 1986 with the distance of several million kilometers from the comet nucleus. This mission is not only self-consistent but collaborative with other space mission as well as earth-bound observations. In the present paper, the Planet-A mission to Halley is described with brief explanation of the spacecraft.

Hydrogen production rates from ground-based Fabry-Perot observations of comet Kohoutek

The only ground-based observations of a cometary hydrogen corona that have been obtained up to the present were carried out during the appearance of comet Kohoutek (1973 XII). Hydrogen Balmer alpha (H-alpha) emission from the gas cloud surrounding the comet was detected using a Fabry-Perot spectrometer at Kitt Peak National Observatory. These observations have been reexamined using (1) recently obtained solar full-disk Lyman beta emission line profiles, (2) a new calibration of the absolute sensitivity of the Fabry-Perot spectrometer based on comparison of NGC 7000 with standard stars and the planetary nebula NGC 7662, and (3) corrections for atmospheric extinction instead of the geocoronal H-alpha comparison method used previously to obtain comet H-alpha intensities. The new values for hydrogen production rates are in good agreement with results obtained from Lyman alpha observations of comet Kohoutek.

On the Cometary Hydrogen Coma and Far UV Emission

Comet Tago-Sato-Kosaka (1969 IX, hereafter TSK) was the first medium bright comet passing by in the era of ultraviolet satellites. The Orbiting Astronomical Observatory (OAO-2), observed in January 1970 the strong Lyman alpha signal at 1216 A which led to the first detection of cometary hydrogen. The peak signal in the photometer field-of-view (FOV) of 10′ diameter was about 70 kR (Code et. al , 1970) The resonance scattering emission of hydrogen was optically thick in the central part of the coma. A rocket experiment of Jenkins and Wingert (1972) using an objective grating spectrograph confirmed the OAO-2 observations Later in Spring 1970 comet Bennett (1970 II) was observed in Lα by OAO-2 and by two photometers onboard the Orbiting Heophysical Observatory (0G0-5) (Bertaux and Blamont, 1970; Keller and Thomas, 1973).

A High-Velocity Component of Atomic Hydrogen in Comet Bennett (1970 II)

The Lyman alpha emission from Comet Bennett (1970II) was measured near perihelion (March 1970) by the University of Colorado ultraviolet photometer experiment on OGO-5 The spectrometer field of view of about 3° crossed the cometary hydrogen coma four times. The hydrogen coma was observed to extend more than 30 x 106 km in the antisolar direction.A model for the hydrogen density was developed which took the actual cometary motion and the gradients of the forces of gravitation and radiation pressure into account Exact trajectories of atoms in the orbital plane representing the column densities perpendicular to the plane were calculated. The variation of the hydrogen lifetime along the trajectory as well as the solar Lα profile were considered.

Lyman-α imagery of Comet Kohoutek

Electrographic imagery of Comet Kohoutek in the 1100–1500 Å wavelength range was obtained from a sounding rocket on January 8, 1974, and from the Skylab space station on 13 occasions between November 26, 1973 and February 2, 1974. These images are predominantly due to Lyman-α (1216 Å) emission from the hydrogen coma of the comet. The rocket pictures have been calibrated for absolute sensitivity and a hydrogen production rate has been determined. However, the Skylab camera suffered degradation of its sensitivity during the mission, and its absolute sensiti vity fbservation ofn only be estimated by comparison of the comet images with those taken by the rocket camera, with imagery of the geocoronal Lyman-α glow, of the moon in reflected Lyman-α, and of ultraviolet-bright stars. The rocket and geocoronal comparisons are used to derive a preliminary, qualitative history of the development of the cometary hydrogen coma and the associated hydrogen production rate.

Cometary Hydrogen and Hydroxyl Comas

Cometary Hydrogen and Hydroxyl Comas

Response :Cometary Hydrogen and Hydroxyl Comas

<i>Response</i> :Cometary Hydrogen and Hydroxyl Comas

Cometary Hydrogen and Hydroxyl Comas

Cometary Hydrogen and Hydroxyl Comas