Atmosphere Of Mercury Research Articles

Impact-driven supply of sodium and potassium to the atmosphere of Mercury

Vaporization due to meteoritic impact on Mercury supplies sodium atoms to the atmosphere from both the impacting meteoroids and the regolith. The supply rate of sodium depends on the spatial mass density, velocity distribution, and sodium abundance for the meteoritic material, as well as the elemental abundance of sodium in the regolith. In the most extreme case (which includes no sodium in the regolith), the average supply rate of sodium must be at least 0.15 × 10 23 atoms sec −1, and the supply rate could easily approach 1.4 × 10 24 atoms sec −1 (moderate amounts of sodium in the regolith). The production of vaporized sodium due to meteoritic impact varies with the instantaneous distance of Mercury from the Sun, and the form of this dependence differs from that characteristic of source and sink processes, which are driven by solar radiation. The spatial distribution of sodium production across the planet due to impact-driven vaporization should also be different from the spatial distribution of sodium production due to solar radiation-driven processes, and these differences may provide an observational test of the relative importance of the meteoritic impact-driven processes to the supply of sodium to the atmosphere of Mercury. Impact-driven vaporization will produce the Na/K ratio observed in the atmosphere only if both the meteoroids and the regolith of the planet are deficient in potassium relative to other sampled objects in the Solar System, with the exception of comets.

Correction to “Resonance scattering by sodium in Mercury's atmosphere I. The effect of phase and atmospheric smearing”

Geophysical Research LettersVolume 15, Issue 3 p. 283-283 Free Access Correction to “Resonance scattering by sodium in Mercury's atmosphere I. The effect of phase and atmospheric smearing” This article corrects the following: Resonance scattering by sodium in mercury's atmosphere I. The effect of phase and atmospheric smearing R. M. Killen, Volume 15Issue 1Geophysical Research Letters pages: 80-83 First Published online: December 7, 2012 R. M. Killen, R. M. KillenSearch for more papers by this author R. M. Killen, R. M. KillenSearch for more papers by this author First published: March 1988 https://doi.org/10.1029/GL015i003p00283Citations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume15, Issue3March 1988Pages 283-283 RelatedInformation

Resonance scattering by sodium in mercury's atmosphere I. The effect of phase and atmospheric smearing

We present the dependence of the intensity in the sodium D1 and D2 lines on the planetary phase and position on the disk. Theoretical intensities are convolved with an atmospheric point spread function with FWHM of 0″.5 and 2″.0 for planetary phases 60° and 90°. We show that although the absolute intensities are extremely dependent on seeing, the I(D2)/I(D1) ratio remains a reliable indicator of column abundance regardless of the seeing function. For a uniform distribution of sodium, limb brightening will be apparent for a seeing disk with FWHM of 0″.5 but will not be apparent for a FWHM of 2″.0.

Rapid annealing of Hg1−xCdxTe by immersion in a hot mercury bath

A simple technique for annealing ion implanted Hg1−xCdxTe in a mercury atmosphere has been developed. In this technique, Hg1−xCdxTe is sandwiched between two silicon wafers and immersed in a hot mercury bath. This permits rapid annealing at well defined temperatures and times. Indium-implanted Hg1−xCdxTe (x=0.23 and x=0.7) samples have been annealed using this method at temperatures ranging from 260 to 350 °C and for times ranging from 3 s to 1 h. The near surface crystalline quality, as measured by ion channeling, improved after annealing and was comparable to that obtained by other annealing techniques. No change in surface stoichiometry, as measured by particle-induced x-ray emission, was detected in the Hg0.77Cd0.23Te samples.

Variation of sodium on mercury with solar radiation pressure

Sodium atoms in the atmosphere of Mercury can be accelarated by solar radiation pressure, and several authors have suggested that radiation pressure could sweep sodium off the planet, provided that the sodium is nonthermal, with velocities in excess of 2.1 km/sec. As a consequence, the sodium abundance might be expected to decrease as the radiation pressure increases. We have measured the average sodium abundance over a range of solar radiation pressures and found that the sodium abundance does decrease with increasing radiation pressure. However, high-resolution line profile measurements of the sodium emission show that little, if any of the sodium is nonthermal, with the bulk at a temperature approximating that of the surface. Models which assume that the bulk of the sodium is nonthermal are ruled out. Possible explanations for the observed variation are (1) that radiation pressure sweeps away transient high-velocity sodium atoms generated upon meteoric material impacts, thus reducing the supply rate of sodium, or (2) that the accommodation coefficient of sodium for surface interactions is less than unity, so that radiation pressure can effectively push sodium to the dark side of the planet, where it cannot be detected by scattered sunlight.

Nature and variability of Mercury's sodium atmosphere

Our knowledge of Mercury has been derived almost exclusively from the analysis of a limited amount of data acquired by the Mariner 10 spacecraft during its three flybys of the planet (29 March 1974, 21 September 1974 and 16 March 1975). The surprising discovery of a sodium atmosphere on Mercury from ground-based observations1 has not only re-kindled interest in the planet but has also opened, through continuing ground-based observations2,3, a new and promising way to explore the planet, its atmosphere and its interactions with the solar wind. Here I examine the peculiar behaviour and likely spatial character of the sodium atmosphere. Because of the large and extremely variable solar radiation pressure experienced by sodium atoms and the suggested presence3 of a non-thermal surface source, the size and shape of the sodium atmosphere can vary tremendously with Mercury's orbital location about the Sun, thus providing valuable signatures for remote study.

Potassium in the atmosphere of Mercury

The discovery of potassium in the atmosphere of Mercury is reported. The average column density is approximately 10 9 atoms cm −2 column, which is about one percent of the average sodium column density.

Discovery of Sodium in the Atmosphere of Mercury

The spectrum of Mercury at the Fraunhofer sodium D lines shows strong emission features that are attributed to resonant scattering of sunlight from sodium vapor in the atmosphere of the planet. The total column abundance of sodium was estimated to be 8.1 x 10(11) atoms per square centimeter, which corresponds to a surface density at the subsolar point of about 1.5 x 10(5) atoms per cubic centimeter. The most abundant atmospheric species found by the Mariner 10 mission to Mercury was helium, with a surface density of 4.5 x 10(3) atoms per cubic centimeter. It now appears that sodium vapor is a major constituent of Mercury's atmosphere.

Some aspects of the solar radiation incident at the top of the atmospheres of Mercury and Venus

A formalism has been developed for the calculation of the insolation on the planets Mercury and Venus neglecting any atmospheric absorption. For Mercury, the instantaneous insolation curves are repeated in a 2-tropical year cycle, the distribution of the solar radiation being perfectly symmetric between both hemispheres. In addition to latitudinal variations, one observes a longitudinal effect expressed by different instantaneous insolation distributions during the course of the time; on the equator, the relative diurnal insolation variability may attain a factor of 3. The small obliquity of Venus results in a nearly symmetric solar radiation distributions with respect to the equator except at the poles, where an important seasonal effect has been found. It has to be noted that no longitudinal dependence exists. Finally, the insolation curves are repeated in a nearly half-year cycle.

The occultation of Mariner 10 by Mercury

An analysis of the Mariner 10 dual frequency radio occultation recordings has yielded new information on the radius and atmosphere of Mercury. The ingress measurements which were conducted near 1.1° North latitude and 67.4° East longitude on the night side of the planet, gave a value for the radius of 2439.5 ± 1 km. Egress near 67.6° North latitide and 258.4° East longitude in the sunlit side yielded a radius of 2439.0 ± 1 km. The atmospheric measurements showed the electron density to be less than 10 3 cm −3 on both sides of the planet. From the latter result one may infer an upper limit to the dayside surface gas density of 10 6 molecules per cm 3.

Mercury's atmosphere: A perspective after Mariner 10

Measurements made during the Mariner 10 flybys of Mercury have shown that this planet has a tenuous atmosphere, somewhat similar to that of the Moon, which consists of at least helium and can be classified as an exosphere. The amount of helium observed can be supplied by either the accretion of only a fraction of the solar wind He 2+ diffusing across the magnetopause, or from outgassing of radiogenic helium from the planetary crust. The role of solar wind in the maintenance and depletion of Mercury's atmosphere is discussed in view of the density upper limits established from Mariner 10. The argon supply rate on Mercury is probably not more than that on the Earth, but it is difficult to say whether Mercury is deficient in potassium or not on the basis of the present data. The global outgassing of CO 2 and H 2O from the planet interior is estimated to be at least four orders of magnitude smaller than for Earth which indicates that either Mercury is deficient in volatiles or that this planet is very inactive.

Some properties of photovoltaic Cd xHg 1− xTe detectors for infrared radiation

Photovoltaic p-n junction detectors made of Cd x Hg 1− x Te crystals and operating within the range of temperatures 77–300°K have been constructed. The junction were produced by heating the p-samples in vacuum and/or under mercury atmosphere. This procedure yielded an n-type surface layer some dozens of μm thick on the p-type material. Current-voltage characteristics and capacitancies of the junctions were measured over the temperature range 77–350°K and the photovoltage was determined at 77 and 300°K for the wavelength 1–15 μm. From the measurements performed it was found that for the detectors studied the maximum photosensitivities and detectivities were of the order of 1000 V/W and 10 9–10 10 cmHz 1 2 W −1, respectively and occurred at the temperature of 77°K. It appeared that the photosensitivity maxima could be shifted within the wavelength range 1–9 μm, by changing the stoichiometry in the junction region.

Optical polarimetry of planet mercury

Polarimetric measurements were collected at different areas of the surface of Mercury, and for the whole disk in six wavelengths. The curves of polarization are compared with telescopic observations of the Moon and laboratory studies of minerals and returned lunar samples. The negative branch of polarization proves that Mercury's surface is almost everywhere covered by a regolith layer of fines of the lunar type, also made of dark and adsorbing material, and most probably of the same impact generated origin. The polarization maximum of Mercury is reproduced by lunar samples of fines of intermediate albedo corresponding to the lightest regolith found in the Apollo explored maria. The albedo of Mercury at phase angle 5° deduced from telescopic photometry is to be corrected by a factor of 1.20 and the best “polarimetric” values of albedos are 0.130 at λ = 0.585 μm, 0.119 at λ = 0.520 μm, 0.093 at λ = 0.379 μm and 0.087 at λ = 0.354 μm. The contrast between light and dark-lined regions at the surface of Mercury is most probably much fainter than between the maria and continents on the Moon. The molecular atmosphere of Mercury, if any, has a surface pressure probably smaller than 2 × 10 −4 bars.

Mercury's Atmosphere from Mariner 10: Preliminary Results

Analysis of data obtained by the ultraviolet experiment on Mariner 10 indicates that Mercury is surrounded by a thin atmosphere consisting in part of helium. The partial pressure of helium at the terminator is about 5 x 10(-12) millibar. The total surface pressure of the atmosphere is less than about 2 x 10(-9) millibar. Upper limits are set for the abundance of various gases, including hydrogen, oxygen, carbon, argon, neon, and xenon. The wavelength dependence of Mercury's surface albedo is similar to that of the moon over a broad range of wavelengths from 500 to 1600 angstroms. Strong signals were recorded by the airglow instrument as Mariner 10 passed through the cavity behind Mercury. They are as yet unexplained but may provide information on the properties of the local plasma.

Model atmospheres for Mercury based on a lunar analogy

Similarities in daytime spectral reflectivities and nighttime infrared emission from Mercury and the moon are shown to imply that the atmosphere of Mercury must be tenuous, like that of the moon. The theory of formation, transport, and loss in the lunar atmosphere is applied to Mercury. Models of the Hermian atmosphere at perihelion and aphelion are presented, based on the solar wind as the dominant source of gases. Only the noncondensable species - hydrogen, helium and neon - are considered. Of these, helium is the most abundant atmospheric gas, with maximum concentration of about 40,000,000 per cu cm at the nighttime surface. The maximum concentration of H2 is 6,000,000 per cu cm, and that of neon is 700,000 per cu cm.

Atmosphere of Mercury

THE recently released news concerning the possible atmosphere surrounding Mercury seems to have taken the astronomical community by surprise. It had generally been expected that because of the high temperatures (of the order of 450 K) existing there and also because of the low surface gravity, any atmosphere originally present, or any released from subsequent events on the surface would quickly evaporate since the random thermal speed of the atoms would be greater than the escape velocity. If VE is the escape velocity from Mercury, ρA the density of its atmosphere and A the surface area, then a simple computation indicates1,2 that the rate of mass loss from this atmosphere is where β = m/2 kT, k being Boltzmann's constant and m the atomic mass. All this ignores the solar wind which carries mass into the atmosphere. In reality the problem becomes a boundary layer problem in which the magnetic field of Mercury plays a part, but we can see simply that the main effect is to generate an atmosphere. If the wind has a density ρw and a velocity Vw, then it adds matter to Mercury at the rate and the stead state situation is given when Inserting the appropriate numerical values, β≈10−11, VE2≈ 2 × 1010, and Vw≈ 108 (all in c.g.s. units gives) There should therefore be a very tenuous atmosphere, basically composed of hydrogen being maintained in this way. Any helium and argon released by radioactivity would become trapped in this atmosphere and should be detected.

Mercury: Does Its Atmosphere Contain Water?

The atmosphere of Mercury, like that of the moon, is maintained in an extremely tenuous minimum state by weak solar wind accretion and radioactive decay processes, and depleted by strong removal mechanisms. Unlike the moon, it has a high daytime surface temperature that promotes the production of water vapor, which may be the dominant atmospheric constituent derived from solar wind protons.

Neutral and ion-exospheres in the solar wind with applications to mercury

A model of planetary neutral and ion-exospheres in the solar wind is formulated for weak or lunar like solar-wind interaction with a planet. The neutral exosphere model allows for density and temperature variations and for rotation at the exobase. The ion-exosphere is produced by ionization of the neutral exosphere in the solar wind and its density distribution is obtained by solving the continuity equation in the drift approximation. Applying to Mercury a surface temperature distribution inferred from infra-red data and a vanishing bound neutral flux at the base, He and He + density distributions are found. When the He atmosphere of Mercury is due entirely to the surface bombardment by solar wind He ++, the resulting He + density is found to vary from 1.5 × 10 −1 to 10 −3 cm −3 over the range 1.5–5 planetocentric radii on the dayside. These densities are found to be detectable by typical solar-wind plasma instruments. The possible effects of cyclotron-resonant scattering by interplanetary magnetic field fluctuations are examined and shown to be negligible. An electromagnetic plasma instability, triggered by the birth of ions in the exosphere, is shown to be important for the thermalization of the energy mode transverse to the interplanetary magnetic field, allowing more ions to be detected by solar-wind ion probes.

Solar wind-Mercury atmosphere interaction: Determination of the planet's atmospheric density

It is shown that the atmosphere of Mercury can be detected and possibly its density determined from solar wind data such as those that will be obtained with the Mariner-Venus-Mercury spacecraft during the flyby mission of 1974.

Ultra-violet argon dayglow lines in the atmosphere of mercury

We investigate the response of an atmosphere of argon to solar ultra-violet radiation. With the assumption that Mercury has an argon atmosphere that is optically thick to ionizing radiation the intensities of the ultra-violet dayglow lines resulting from photoelectron impact are calculated. For most of the model atmospheres, the predicted intensities are above the detection threshold of the 1973 Venus-Mercury ultra-violet spectrometer of Broadfoot, McElroy and Belton.