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1.
Pluto's obliquity (the angle between its spin axis and orbit normal) varies between ～102 and ～126° over a period of about 3 million years. These oscillations are nearly sinusoidal and quite stable, leading to only modest changes in the insolation regime. Thus, Pluto's rotation has been slightly retrograde ever since its current orbit and rotation rate were established. 相似文献
2.
Cosmic abundance, vapor pressure, and molecular weight considerations restrict the likely gas candidates for Pluto's atmosphere to Ne, N2, CO, O2, and Ar, in addition to the already detected CH4. The vapor pressures and cosmic abundances of these gases indicate that all except Ne should be saturated in Pluto's atmosphere. The vapor pressure of Ne is so high that the existence of solid or liquid Ne on Pluto's surface is very unlikely; cosmic abundance arguments imply that Ne cannot attain saturation in Pluto's atmosphere. At both perihelion, N2 should dominate the saturated gases. CO2 should have the next highest mixing ratio, followed by O2 and Ar. CH4 should have the smallest mixing ratio. Because vapor pressures of these gases vary with temperature at diverse rates, the bulk and constituent mixing ratios of Pluto's atmosphere should vary with season. Between perihelion and aphelion, the column abundance of CH4 may change by a factor of 260 while that of N2 changes by only a factor of 52. The potential seasonal variation of Pluto's atmosphere was investigated by considering the behavior of these gases when individually mixed with CH4. The effects of diurnal and latitudinal variation of insolation and eclipses on the atmosphere also were investigated. Seasonal effects are shown to dominate. It was shown that the atmospheric bulk may not be a minimum near aphelion but rather at intermediate distances from the Sun during summer/winter inadequate ice deposits may allow the atmosphere to collapse by freezing out over winter latitudes. If the atmosphere does not collapse, its weight is sufficient to keep it distributed uniformly around Pluto's surface. In this case, the atmosphere tends to regulate the surface temperature to a seasonally dependent value which is uniform over the globe.Finally, the likely global circulation regimes for each model atmosphere as a function of temperature were investigated and it was concluded that if CH4, O2, or CO dominates the atmosphere, Pluto will exhibit cyclic variations between an axially symmetric circulation system at perihelion and a baroclinic wave regime at aphelion. However, if N2 dominates, as is likely, the wave regime should hold continuously. If the atmosphere collapses to a thin halo during summer/winter seasons, only a weak, symmetric circulation should occur. 相似文献
3.
L. Trafton 《Icarus》1984,58(2):312-324
Triton's seasons differ materially from those of Pluto owing to four important differences in the governing physics: First, the obliquity of Triton is significantly less than Pluto's obliquity. Second, Triton's inclined orbit precesses rapidly about Neptune so that a complicated seasonal variation in the latitude of the Sun occurs for Triton. Third, Neptune's orbit is much more circular than Pluto's orbit so that the sunlight intercepted by Triton's disk does not vary seasonally. Finally, Triton's atmosphere cannot be saturated at the lower latitudes so that the mass of the atmosphere is controlled by the temperature of the high-latitude ices or liquids (polar caps), as for CO2 on Mars. The consequences of Triton's entire surface being covered with volatile substances have been examined. It is found that the circularity of Neptune's orbit then implies that Triton would have hardly any seasonal variation at all in surface temperature or atmospheric bulk, in spite of the complicated precessional effects of Triton's orbit. The only seasonal effect would be the migration of surface ices and liquids. This scenario is ruled out because it implies a column CH4 abundance much higher than that observed and because it quickly depletes the lower latitudes of volatiles. It is concluded that Triton's most volatile surface substances are probably relegated to latitudes higher than 35° and probably form polar caps. The temperature of the polar caps should be nearly equal, even during midwinter/midsummer when the insolation of the summer pole is greatest. If the summer pole completely sublimates during one of the “major” summers, Triton's atmosphere may begin to freeze out over the winter caps. It is therefore expected that Triton's atmosphere undergoes large and complex seasonal variations. Triton is currently approaching a “maximum southern summer”, and over the remainder of this century, a dramatic increase in CH4 abundance above the current upper limit of 1 m-Am may be witnessed. 相似文献
4.
E. Van Hemelrijck 《Icarus》1982,52(3):560-564
Calculations of the daily solar radiation incident at the top of Pluto's atmosphere and its variability with latitude and season and of the latitudinal variation of the mean annual daily insolation are presented. The large eccentricity of Pluto produces significant north-south seasonal asymmetries in the daily insolation. As for Uranus, having a similarly large obliquity, the equator receives less annual average energy than the poles. 相似文献
5.
Harrington and Van Flandern (1979, Icarus39, 131–136) suggests that the irregular features of the Neptunian satellite system and Pluto's escape were caused by an encounter with a massive external body. They rule out the alternative mechanism based on the capture of Triton (which seems more plausible because it does not appeal to any unobserved object) on the basis of an incorrect deduction from McCord's (1966, Astron. J.71, 585–590) analysis on the tidal decay of Triton's orbit. As a matter of fact, many recent results show that satellite captures are possible, and in the case of Triton several arguments support this interpretation. 相似文献
6.
Michael H. Hart 《Icarus》1974,21(3):242-247
At the temperature of Pluto (～43°K) the only gas which would neither condense nor escape is neon. Since neon is cosmically abundant it is suggested that Pluto may have a fairly extensive atmosphere consisting of almost pure neon. The possibility that such an atmosphere exists is analyzed, along with the possibility that oceans of liquid neon may exist at the surface.A neon atmosphere would not produce any observable absorption lines. However, if it were very thick, then Rayleigh scattering would result in Pluto having a much higher albedo in the ultraviolet than in the visual, which is not observed to be the case. This enables us to set an upper limit on the mass of Pluto's atmosphere. 相似文献
7.
F. Merlin M.A. Barucci C. de Bergh F.E. DeMeo A. Alvarez-Candal C. Dumas D.P. Cruikshank 《Icarus》2010,210(2):930-943
We present new photometric and spectroscopic observations of the Pluto–Charon system carried out at the VLT-ESO (Chile) with two 8-m telescopes equipped with the FORS2, ISAAC and SINFONI instruments. The spectra were obtained in the 0.6–2.45 μm range with a spectral resolution from 300 to 1500. The SINFONI data were obtained using adaptive optics, allowing a complete separation of the two bodies. We derive both objects’ magnitudes in the near infrared and convert them into albedo values. These first near infrared photometric data allow to adjust the different parts of Pluto’s spectrum, provided by the three instruments. We run spectral models in order to give chemical and physical constraints on the surface of Pluto and Charon. We discuss the dilution properties of the methane ice and its implications on Pluto’s surface. The heterogeneities of the pure and diluted methane ice on Pluto’s surface is also investigated. The high signal-to-noise level of the data and our analyses may support the presence of ethane ice on the surface of Pluto, which is one of the main products of the methane irradiation and photolysis. The analyses of the spectra of Charon suggest that the water ice is almost completely in its crystalline form and that the ammonia compound is hydrated on the surface of this satellite. 相似文献
8.
L. Trafton 《Icarus》1980,44(1):53-61
The presence of CH4 ice on Pluto implies that Pluto may have a substantial atmosphere consisting of heavy gases. Without such an atmosphere, sublimation of the CH4 ice would be so rapid on a cosmogonic time scale that either such an atmosphere would soon develop through the exposure of gases trapped in the CH4 ice or else the surface CH4 ice would soon be all sublimated away as other, more stable, ices became exposed. If such stable ices were present from the beginning, the existence of CH4 frosts would also imply that Pluto's present atmosphere contains a remnant of its primordial atmosphere. 相似文献
9.
Photometric observations of Pluto in the BVR filter system were obtained in 1999 and in 1990-1993, and observations in the 0.89-μm methane absorption band were obtained in 2000. Our 1999 observations yield lightcurve amplitudes of 0.30 ± 0.01, 0.26 ± 0.01, and 0.21 ± 0.02 and geometric albedos of 0.44 ± 0.04, 0.52 ± 0.03, and 0.58 ± 0.02 in the B, V, and R filters, respectively. The low-albedo hemisphere of Pluto is slightly redder than the higher albedo hemisphere. A comparison of our results and those from previous epochs shows that the lightcurve of Pluto changes substantially through time. We developed a model that fully accounts for changes in the lightcurve caused by changes in the viewing geometry between the Earth, Pluto, and the Sun. We find that the observed changes in the amplitude of Pluto’s lightcurve can be explained by viewing geometry rather than by volatile transport. We also discovered a measurable decrease since 1992 of ∼0.03 magnitudes in the amplitude of Pluto’s lightcurve, as the model predicts. Pluto’s geometric albedo does not appear to be currently increasing, as our model predicts, although given the uncertainties in both the model and the measurements of geometric albedo, this result is not firm evidence for volatile transport. The maximum of methane-absorption lightcurve occurs near the minimum of the BVR lightcurves. This result suggests that methane is more abundant in the brightest regions of Pluto. Pluto’s phase coefficient exhibits a color dependence, ranging from 0.037 ± 0.01 in the B filter to 0.032 ± 0.01 in the R filter. Pluto’s phase curve is most like those of the bright, recently resurfaced satellites Triton and Europa. Although Pluto shows no strong evidence for volatile transport now (unlike Triton), it is important to continue to observe Pluto as it moves away from perihelion. 相似文献
10.
We use a radiative-conductive-convective model to assess the height of Pluto’s troposphere, as well as surface pressure and surface radius, from stellar occultation data from the years 1988, 2002, and 2006. The height of the troposphere, if it exists, is less than 1 km for all years analyzed. Pluto has at most a planetary boundary layer and not a troposphere. As in previous analyses of Pluto occultation light curves, we find that the surface pressure is increasing with time, assuming that latitude and longitude variations in Pluto’s atmosphere are negligible. The surface pressure is found to be slightly higher ( μbar in 1988, μbar in 2002, and 18.5 ± 4.7 μbar in 2006) than in our previous analyses with the troposphere excluded. The surface radius is determined to be . Comparison of the minimum reduced chi-squared values between the best-fit radiative-conductive-convective (i.e., troposphere-included) model and best-fit radiative-conductive (i.e., troposphere-excluded) shows that the troposphere-included model is only a slightly better fit to the data for all 3 years. Uncertainties in the small-scale physical processes of Pluto’s lower atmosphere and consequently the functional form of the model troposphere lend more confidence to the troposphere-excluded results. 相似文献
11.
A hypothesis on the origin of comets in the system of Pluto has been considered. It has been shown that none of the 59 near-parabolic
comets—candidates for Pluto’s family—passed through the sphere of its influence in the time interval from 2000 to −3000. 相似文献
12.
The hypothesis suggested by Guliev on transneptunian objects as sources of comets is considered. The motion equations for
137 near-parabolic comets over a time interval of 5000 years were numerically integrated. No interaction between 78 comets
and the transneptunian object 2003 UB 313 has been revealed: the comets were farther than 3 AU from it. It has been shown
that 59 comets—candidates to Pluto’s family-approached Pluto at a distance larger than 0.7 AU. The fulfilled analysis allows
us to conclude that Guliev’s hypothesis on transneptunian objects as sources of comets is groundless. 相似文献
13.
Based on the vapor pressure behavior of Pluto’s surface ices, Pluto’s atmosphere is expected to be predominantly composed of N2 gas. Measurement of the N2 isotopologue 15N/14N ratio within Pluto’s atmosphere would provide important clues to the evolution of Pluto’s atmosphere from the time of formation to its present state. The most straightforward way of determining the N2 isotopologue 15N/14N ratio in Pluto’s atmosphere is via spectroscopic observation of the 14N15N gas species. Recent calculations of the 80–100 nm absorption behavior of the 14N2 and 14N15N isotopologues by Heays et al. (Heays, A.N. et al. [2011]. J. Chem. Phys. 135, 244301), Lewis et al. (Lewis, B.R., Heays, A.N., Gibson, S.T., Lefebvre-Brion, H., Lefebvre, R. [2008]. J. Chem. Phys. 129, 164306); Lewis et al. (Lewis, B.R., Gibson, S.T., Zhang, W., Lefebvre-Brion, H., Robbe, J.-M. [2005]. J. Chem. Phys. 122, 144302), and Haverd et al. (Haverd, V.E., Lewis, B.R., Gibson, S.T., Stark, G. [2005]. J. Chem. Phys. 123, 214304) show that the peak magnitudes of the 14N2 and 14N15N absorption bandhead cross-sections are similar, but the locations of the bandhead peaks are offset in wavelength by ∼0.05–0.1 nm. These offsets make the segregation of the 14N2 and 14N15N absorption signatures possible. We use the most recent N2 isotopologue absorption cross-section calculations and the atmospheric density profiles resulting from photochemical models developed by Krasnopolsky and Cruickshank (Krasnopolsky, V.A., Cruickshank, D.P. [1999]. J. Geophys. Res. 104, 21979–21996) to predict the level of solar light that will be transmitted through Pluto’s atmosphere as a function of altitude during a Pluto solar occultation. We characterize the detectability of the isotopic absorption signature per altitude assuming 14N15N concentrations ranging from 0.1% to 2% of the 14N2 density and instrumental spectral resolutions ranging from 0.01 to 0.3 nm. Our simulations indicate that optical depth of unity is attained in the key 14N15N absorption bands located between 85 and 90 nm at altitudes ∼1100–1600 km above Pluto’s surface. Additionally, an 14N15N isotope absorption depth ∼4–15% is predicted for observations obtained at these altitudes at a spectral resolution of ∼0.2–0.3 nm, if the N2 isotopologue 15N/14N percent ratio is comparable to the 0.37–0.6% ratio observed at Earth, Titan and Mars. If we presume that the predicted absorption depth must be at least 25% greater than the expected observational uncertainty, then it follows that a statistically significant detection of these signatures and constraint of the N2 isotopologue 14N/15N ratio within Pluto’s atmosphere will be possible if the attainable observational signal-to noise (S/N) ratio is ?9. The New Horizons (NH) Mission will be able to obtain high S/N, 0.27–0.35 nm full-width half-max 80–100 nm spectral observations of Pluto using the Alice spectrograph. Based on the NH/Alice specifications we have simulated 0.3 nm spectral resolution solar occultation spectra for the 1100–1600 km altitude range, assuming 30 s integration times. These simulations indicate that NH/Alice will obtain spectral observations within this altitude range with a S/N ratio ∼25–50, and should be able to reliably detect the 14N15N gas absorption signature between 85 and 90 nm if the 14N15N concentration is ∼0.3% or greater. This, additionally, implies that the non-detection of the 14N15N species in the 1100–1600 km range by NH/Alice may be used to reliably establish an upper limit to the N2 isotopologue 15N/14N ratio within Pluto’s atmosphere. Similar results may be derived from 0.2 to 0.3 nm spectral resolution observations of any other N2-rich Solar System or exoplanet atmosphere, provided the observations are attained with similar S/N levels. 相似文献
14.
We apply scintillation theory to stellar signal fluctuations in the high-resolution, high signal/noise, dual-wavelength data from the MMT observation of the 2007 March 18 occultation of P445.3 by Pluto. A well-defined high wavenumber cutoff in the fluctuations is consistent with viscous-thermal dissipation of buoyancy waves (internal gravity waves) in Pluto’s high atmosphere, and provides strong evidence that the underlying density fluctuations are governed by the gravity-wave dispersion relation. 相似文献
15.
The dynamo explanation of Mercury's magnetic field leads to constraints on the thermal evolution of the planet. A heat-source density at least comparable to the Earth's mantle-wide average must have been retained throughout Mercury's mantle, if the core is still molten, and if Mercury's mantle possesses rheological properties similar to those of the Earth's upper mantle. 相似文献
16.
Stellar occultations have shown that vertical profiles of density fluctuations in the atmosphere of Pluto typically show wave-like structure with an amplitude of a few percent and vertical wavelengths of a few kilometers. Here we calculate the tidal response of Pluto’s atmosphere to solar-induced sublimation “breathing” from N2 frost patches. Solutions show global-scale wave-like density structure capable of explaining the observations. The atmospheric response is a combination of eastward and westward migrating tides, together with a zonally symmetric mode. Calculated vertical wavelengths and amplitudes are similar to observations. 相似文献
17.
Richard Greenberg 《Icarus》1976,29(3):427-433
The theory of the effect of Ariel and Umbriel on Miranda's orbit is completed with a generalization of Souillart's theory of the Laplace relation. Comparison of observations of Miranda's motion with the theory yields an upper limit for the product of Ariel and Umbriel's masses of about 10?9, where Uranus' mass is unity. Therefore the albedos of Ariel and Umbriel cannot both be as low as the albedos of the darkest asteroids. 相似文献
18.
We have used Pollack et al.'s 1976 calculations of the quasi-equilibrium contraction of Saturn to study the influence of the planet's early high luminosity on the formation of its satellites and rings. Assuming that the condensation of ices ceased at the same time within Jupiter's and Saturn's primordial nebulae, and using limits for the time of cessation derived for Jupiter's system by Pollack and Reynolds (1974) and Cameron and Pollack (1975), we arrive at the following tentative conclusions. Titan is the innermost satellite at whose position a methane-containing ice could condense, a result consistent with the presence of methane in this satellite's atmosphere. Water ice may have been able to condense at the position of all the satellites, a result consistent with the occurrence of low-density satellites close to Saturn. The systematic decrease in the mass of Saturn's regular satellites with decreasing distance from Saturn may have been caused partially by the larger time intervals for the closer satellites between the start of contraction and the first condensation of ices at their positions and between the start of contraction and the time at which Saturn's radius became less than a satellite's orbital radius. Ammonia ices, principally NH4SH, were able to condense at the positions of all but the innermost satellites.Water ice may bave been able to condense in the region of the rings close to the end of the condensation period. We speculate that the rings are unique to Saturn because on the one hand, temperatures within Jupiter's Roche limit never became cool enough for ice particles to form before the end of the condensation period and on the other hand, ice particles formed only very early within Uranus' and Neptune's Roche limits, and were eliminated by gas drag effects that caused them to spiral into the planet before the gas of these planets' nebula was eliminated. Gas drag would also have eliminated any rocky particles initially present inside the Roche limit.We also derive an independent estimate of several million years for the time between the start of the quasi-equilibrium contraction of Saturn and the cessation of condensation. This estimate is based on the density and mass characteristics of Saturn's satellites. Using this value rather than the one found for Jupiter's satellites, we find that the above conclusions about the rings and the condensation of methane-and ammonia-containing ices remain valid. 相似文献
19.
Intermediate resolution (6Å) photoelectric spectral scans of Titan, Saturn, Saturn's Rings and the Moon appear in two forms: ratio spectra of Titan vs the Rings and of Saturn vs the Rings, and relative reflectivities, which are compared to previously published results. Titan's geometrical albedo of 0.094 ± 0.012 was measured at 4255Å with a 50Å bandpass. From this and the spectral measurements, we derived the geometrical albedo as a function of wavelength. We find that the wavelength dependences of Titan's uv spectrum and the spectrum of Saturn's Rings are remarkably similar. No trace of any absorption bands is apparent. These results imply that uv gaseous absorption and Rayleigh scattering play a strongly subdued role in Titan's atmosphere. Any homogeneous atmospheric model implies that the absorber responsible for Titan's uv spectral albedo varies strongly with wavelength. On the other hand, we find that the uv observations can be satisfied by an absorber having a relatively weak dependence upon wavelength if an inhomogeneous atmospheric model is employed. In particular, a fine dust, which absorbs as 1/λ, can explain the uv observations provided that it is preferentially distributed high up in Titan's atmosphere where the optical depth from Rayleigh scattering is low. The likely presence of such a dust in Jupiter's atmosphere and the difficulty in explaining the nature of a continuous uv absorber which varies rapidly with wavelength suggest that the gas and aerosol in Titan's atmosphere are inhomogeneously distributed. 相似文献
20.
《Chinese Astronomy and Astrophysics》1982,6(2):144-147
We have re-calculated the first-order theory of Mars using Hansen's method and compared the results with Clemence's Theory of Mars (1949). An extensive list of descrepancies is given. In addition, comparison is made between our results and Kinoshita's (1979) results 相似文献