Saturday, May 19, 2007

Simultaneous Ionization response to high energy radiation

Ionospheric physics deals with the basic structure and variability of plasma within the upper atmospheres of the Earth and planets. Comparative studies foster both exploration and synthesis within diverse settings.

Using photochemical-equilibrium arguments applicable to the peak electron density layer on Mars and the E-layer on Earth, we can see basic agreement in scaling laws between the planets, and response to high energy variability.

The ionized component of a planet’s upper atmosphere depends on a blend of in situ production and loss processes, plus effects of transport of ionization into or out of the local region of interest. As described in basic texts on ionospheric physics.

The truly common input for all solar system ionospheres on a given day is the Sun’s photon flux, a simple function of heliospheric distance. All other effects are planet specific:
(1) rotation rate and solar obliquity conditions,
(2) the thermal structure, constituent reactions, and dynamics
of its neutral atmosphere,
(3) the degree to which energetic particles (of solar wind and/or magnetospheric origin) impinge upon its atmosphere,
(4) diffusion and electrodynamics associated with coupling from above, and
(5) tides, waves, and electrodynamics arising from coupling to regions below.

Simplifying assumptions employed in such a formulation affect scaling laws for
ionospheric behavior among the planets. If all planetary atmospheres had
(1) a single molecular gas that is photoionized to form a molecular ion,
(2) for which dissociative recombination is the dominant loss process,
(3) located in a dense atmosphere, making transport negligible, and
(4) with no magnetospheric or solar wind interaction (or considering latitudes and altitudes where they are small), then simple photochemical equilibrium would govern each planet’s peak electron density. Under such conditions, the daytime electron (and ion) density N is never far from the steady state value derived from ‘‘Chapman theory’’ [Chapman, 1931;

In 1997, the group, (International School for Advanced Studies, Trieste), tried to predict the behaviour of methane (CH4) in the interior of the giant planet Neptune.About 15 years earlier, scientists at Lawrence Livermore National Laboratory in the United States had concluded that extreme pressure inside Neptune, the solar system’s fourth largest planet (Jupiter, Saturn and Uranus are larger) causes methane molecules to completely dissociate, enabling carbon atoms to reassemble into carbon-only diamond clusters. Their analysis created this tantalising hypothesis:
Could a giant diamond mine be hiding in the core of Neptune? Simulations carried out at ICTP over the past seven years confirm that Neptune’s central core could indeed be loaded with diamonds. But the vast majority of the planet’s mass likely consists of hydrocarbon chains since less intense pressures found throughout most of the region would mean that the methane molecules only partially dissociate to create an endless series of carbon atom chains surrounded by hydrogen atoms list of chemical constituents despite the fact that it had once been counted—along with water (H2O) and ammonia (NH3)—as one of the planet’s three most abundant constituents. Similarly, the wafting of hydrocarbons from the interior into the atmosphere may also help explain why Neptune’s life-denying atmosphere is laden with hydrocarbons.
Jupiter and Saturn are believed to be compositionally much simpler than Neptune.

A single atomic species, hydrogen, makes up most of their mass, with traces of helium and other light elements. No experimental apparatus is presently able to recreate in the laboratory the extreme conditions found in the interiors of these two planets. Simulations are the only method available. And the picture that has emerged from simulations, which began in spring 2002, have proven quite interesting.

Extreme pressures and temperatures cause hydrogen to dissociate inside Jupiter and Saturn, much like methane in Neptune. But even more surprising is the observation that the pressure-induced transition from a molecular fluid to a dissociated fluid has been accompanied by a large and sudden increase in the density of hydrogen.In light of this finding, the current picture of Jupiter and Saturn as homogeneous fluid spheres will need to be dramatically modified to account for the sharp transition between a molecular fluid envelope and a dissociated fluid core. Is there any chance we will ever be able to verify this hypothesis? And, more generally speaking, how much trust should we place in the outcomes of numerical simulations?For those who are impatient, the answer may be soon forthcoming.

The spacecraft Cassini, launched by NASA in October 1997, will enter Saturn’s orbit during the first week in July to begin a four-year tour of the ‘ringed’ planet. By monitoring Saturn’s magnetic field and gravitational impulses, Cassini will provide a more detailed density profile of the planet that should help determine whether the atom clusters that my colleagues and I have ‘virtually’ squeezed in our computers are conveying the truth.

Enter Cassini

Titan is the only satellite in our Solar System with a dense atmosphere. The surface pressure is 1.5 bar and, similar to the Earth, N2 is the main component of the atmosphere. Methane is the second most important component, but it is photodissociated on a timescale of 107 years. This short timescale has led to the suggestion that Titan may possess a surface or subsurface reservoir of hydrocarbons to replenish the atmosphere. Here we report near-infrared images of Titan obtained on 26 October 2004 by the Cassini spacecraft. The images show that a widespread methane ocean does not exist; subtle albedo variations instead suggest topographical variations, as would be expected for a more solid (perhaps icy) surface. We also find a circular structure, 30 km in diameter that does not resemble any features seen on other icy satellites.We propose that the structure is a dome formed by upwelling icy plumes that release methane into Titan's atmosphere.

The very low abundances of Ar, Kr and Xe in Titan's atmosphere can be easily explained by our experimental findings. These gases are trapped in the aerosols, which are formed by UV photolysis of acetylene in their presence. When the aerosols fall down to the surface, they clean the atmosphere of these gases. A continuous supply of the radiogenic produced 40Ar from the interior can explain its small abundance in the atmosphere. 2. The originally soft and sticky photochemical aerosols, as found by us experimentally, were calculated to harden by spontaneous and radiation induces chemical cross-linking. Indeed the camera and other detectors were not covered by sticky aerosols and the intake ports were not clogged. 3. As we predicted, no lightning discharges were detected in the quiescent Titan atmosphere. Therefore, Titan's atmospheric chemistry is driven mainly by solar UV irradiation and not by electrical discharges. 4. The mixing ratios of the major gas phase species produced by UV photolysis of acetylene, as found experimentally: methylacetylene ; diacetylene ; divinyl ; and benzene were observed by the Cassini spacecraft in Titan's upper atmosphere, with an agreement within better than an order of magnitude. 5. The N:C ratio in Titan's aerosols was measured by the Huygens probe, but no results were published yet. UV photolysis of gas mixtures containing C2H2:HCN=10 yield aerosols with a ratio N:C=0.007 up to 0.01. Electrical discharges through a N2:CH4~10 gas mixtures yield a much higher N:C ratio. 6. We anticipate mountains not higher than 1900 m on Titan's surface.

What are of interest is the effects of photolysis from UV which retains its energetic values at distance from the sun.and or

The increasing effects of galactic CR intensity from lessening solar wind modulation, and Increased CR acceleration (Fermi Mechanism) from the inter stellar space due to proximity to the interstellar boundary.

NASA Hubble Space Telescope observations in August 2002 show that Neptune's brightness has increased significantly since 1996. The rise is due to an increase in the amount of clouds observed in the planet's southern hemisphere. These increases may be due to seasonal changes caused by a variation in solar heating. Because Neptune's rotation axis is inclined 29 degrees to its orbital plane, it is subject to seasonal solar heating during its 164.8-year orbit of the Sun. This seasonal variation is 900 times smaller than experienced by Earth because Neptune is much farther from the Sun. The rate of seasonal change also is much slower because Neptune takes 165 years to orbit the Sun. So, springtime in the southern hemisphere will last for several decades! Remarkably, this is evidence that Neptune is responding to the weak radiation from the Sun. These images were taken in visible and near-infrared light by Hubble's Wide Field and Planetary Camera 2.

Observations obtained by the NASA/ESA Hubble Space Telescope and ground-based instruments reveal that Neptune's largest moon, Triton, seems to have heated up significantly since the Voyager spacecraft visited it in 1989.

"Since 1989, at least, Triton has been undergoing a period of global warming percentage-wise, it’s a very large increase," said James L. Elliot, an astronomer at the Massachusetts Institute of Technology (MIT), Cambridge, MA. The warming trend is causing part of Triton’s frozen nitrogen surface to turn into gas, thus making its thin atmosphere denser. Dr. Elliot and his colleagues from MIT, Lowell Observatory, and Williams College published their findings in the June 25 issue of the journal Nature.

Since 1989 Triton's temperature has risen from about 37 on the absolute (Kelvin) temperature scale (-392 degrees Fahrenheit) to about 39 Kelvin (-389 degrees Fahrenheit)

Therefore as we can see from the observations the increased solar system planetary response (warming) in the outer planets is caused by the solar mechanisms


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