ALBERT

Description: Asymptotic relations between Thomas-Fermi-Dirac and Thomas-Fermi atom models

Description: Temperature perturbation in Thomas-Fermi functions for atom radius as related by Gilvarry to simpler Feynman-Metropolis-Teller case

Description: Asymptotic relation between Thomas-Fermi-Dirac and Thomas-Fermi atom models for pressure with and without exchange, considering Coulomb contribution to energy

Description: Knowledge gained from measurements and models is used to study the high-speed plasmas interacting with the atmospheres and ionospheres of Titan and Venus. Considering the similarities of the interactions, comparative analysis is used to support the interpretations of observations made at each body. Ionospheric flow inferred to exist by analysis of measurements made from the Pioneer Venus Orbiter supports the interpretation of similar flow in the ionosphere of Titan. The concept that cold ions escape from the ionosphere of Venus is supported by the Voyager I observation that cold ions escape down the magnetic tail of Titan. Pickup O+ ion energy distributions observed at their source in the ionosheath of Venus are shown to be influenced by finite gyroradius effects. The signatures of such effects are expected to be retained as the ions move into the wakes of Titan and Venus.

Description: Many of the small to medium sized objects in the solar system can be characterized as having surface bounded exospheres, or atmospheres so tenuous that scale lengths for inter-particle collisions are much larger than the dimensions of the objects. The atmospheres of these objects are the product of their surfaces, both the surface composition and the interactions that occur on them and also their interiors when gases escape from there. Thus by studying surface bounded exospheres it is possible to develop insight into the composition and processes that are taking place on the surface and interiors of these objects. The Moon and Mercury are two examples of planetary bodies with surface bounded exospheres that have been studied through spectroscopic observations of sodium, potassium, and, on the moon, mass spectrometric measurements of lunar gases such as argon and helium.

Description: Titan and Venus are unmagnetized bodies that interact directly with the high speed plasmas flowing around them. The similarities of these interactions are used to reinforce the interpretations of measurements made at each body from different measurement sites. In particular, observations of plasma properties at Titan and Venus from Voyager I and Pioneer Venus, respectively, when considered together, tend to reinforce the concept that ions of ionospheric origin escape down the ionotails of each body. The plasma measurements at Titan were made in its ionotail, well above its ionosphere. They revealed plasma flowing from Titan and escaping down its ionotail. On the other hand, the measurements at Venus were made in its ionosphere, where ionospheric ions were inferred to be flowing upward toward Venus' ionotail. When these processes are applied to Titan's ionosphere, upward flow toward the ionotail is found to be possible, consistent with the plasma observed escaping further down the ionotail. Applying similar reasoning to Venus, the upward ionospheric flow is expected to accelerate and escape down its ionotail. The latter result is reinforced by the recent detection, from SOHO, of cold ions in the distant wake (at 1 AU), which were interpreted to originate in the ionosphere of Venus.

Description: The similarities and differences of the escape mechanisms for H+ and D+ from Venus, H+ and D+ from Mars, and heavier ions (approximately 17 and approximately 28 amu) from Titan are described. The dominant escape process for hydrogen and deuterium on Venus is thought to originate in the night side ionosphere, located in the night side H and D bulge region, where the polarization electric field is the dominant force accelerating ionospheric H+ and D+ upward into the induced magnetic tail of Titan. The resulting loss rates approximately 8.6 x 10(exp26)/s and approximately 3.2 x 10(exp 23)/s for H+ and D+, respectively, are consistent with the large observed D/H ratio - 160 times that of terrestrial water and an ancient ocean more than 10 m of liquid uniformly distributed on the surface. In contrast, Jeans escape is the dominant loss mechanism for H and D on Mars, which has a D/H ratio approximately 5.3 times that of terrestrial water. The resulting loss rates for H and D of approximately 3.7 x 10(exp 26/s and approximately 10(exp 22)/s, respectively, can be related to possible ancient water reservoirs below the surface. When horizontal atmospheric winds are taken into account, the Jeans escape rates for H and D are enhanced considerably, as are the corresponding water reservoirs. On Titan, 28 amu ions were observed to escape along its induced magnetic tail by the Voyager 1 Plasma Science Instrument (PLS). In analogy with Venus, the escaping ions were thought to originate in the ionosphere. The Cassini mission permits a test of this principle due to the numerous flybys of Titan through both the ionosphere and the tail. A polarization electric field is obtained in the ionosphere of the TA flyby, yielding an upward acceleration of 17 and 28 amu ionospheric ions that is consistent with the flux of heavy ionospheric ions observed escaping along the magnetic tail by the Cassini Ion Mass Spectrometer (CAPS) during the T9 flyby.

Description: The Cassini Plasma Spectrometer (CAPS) instrument is scheduled to observe the plasma environment at Titan October 26,2004 from the Cassini Orbiter. Preliminary CAPS ion measurements from this encounter will be compared with measurements made by the Voyager I Plasma Science Instrument (PSI). The comparison will be used to evaluate previous interpretations and predictions of the Titan plasma environment that have been made using PSI measurements. The comparisons will focus on the composition and nature of the ambient plasma and pickup ions. Using the CAPS ion measurements, some of the questions to be addressed, as stimulated by the previous interpretations and predictions made evaluating PSI data, are the following: A) Are H+ and N+ the major ion components of Saturn's rotating magnetosphere in the vicinity of Titan? B) Are other ambient ions present? C) Are finite gyroradius effects apparent in ambient N+ as the result of its interaction with Titans atmosphere? D) Are the principal pickup ions composed of H+, H2+, N+, N2+ and CH4+? E) Is the dominant pickup ion closest to Titan's ionopause N2+? F) Is there evidence of slowing down of the ambient plasma due to pickup ion mass loading? F) If so, does the ambient plasma slow down rapidly, as the ionopause is approached and heavier pickup ions like N2+ are added? During the Voyager I flyby, Titan was in Saturn's magnetosphere. If Titan is in Saturn's magnetosheath or the solar wind at the encounter, questions similar to the above will be addressed as appropriate.

Description: The principle source of pickup ions at Titan is its neutral exosphere, extending well above the ionopause into the magnetosphere of Saturn or the solar wind, depending on the moon's orbital position. Thermal and nonthermal processes in the thermosphere generate the distribution of neutral atoms and molecules in the exosphere. The combination of these processes and the range of mass numbers, 1 to over 28, contribute to an exospheric source structure that produces pickup ions with gyroradii that are much larger or smaller than the corresponding scale heights of their neutral sources. The resulting phase space distributions are dependent on the spatial structure of the exosphere as well as that of the magnetic field and background plasma. When the pickup ion gyroradius is less than the source gas scale height, the pickup ion velocity distribution is characterized by a sharp cutoff near the maximum speed, which is twice that of the ambient plasma times the sine of the angle between the magnetic field and the flow velocity. This was the case for pickup H(sup +) ions identified during the Voyager 1 flyby. In contrast, as the gyroradius becomes much larger than the scale height, the peak of the velocity distribution in the source region recedes from the maximum speed. Iri addition, the amplitude of the distribution near the maximum speed decreases. These more beam like distributions of heavy ions were not observed from Voyager 1 , but should be observable by more sensitive instruments on future spacecraft, including Cassini. The finite gyroradius effects in the pickup ion velocity distributions are studied by including in the analysis the possible range of spatial structures in the neutral exosphere and background plasma.

Description: We propose a combined Titan orbiter and Titan Aerorover mission with an emphasis on both in situ and remote sensing measurements of Titan's surface, atmosphere, ionosphere, and magnetospheric interaction. The biological aspect of the Titan environment will be emphasized by the mission (i.e., search for organic materials which may include simple organics to 'amono' analogues of amino acids and possibly more complex, lightening detection and infrared, ultraviolet, and charged particle interactions with Titan's surface and atmosphere). An international mission is assumed to control costs. NASA will provide the orbiter, launch vehicle, DSN coverage and operations, while international partners will provide the Aerorover and up to 30% of the cost for the scientific instruments through collaborative efforts. To further reduce costs we propose a single PI for orbiter science instruments and a single PI for Aerorover science instruments. This approach will provide single command/data and power interface between spacecraft and orbiter instruments that will have redundant central DPU and power converter for their instruments. A similar approach could be used for the Aerorover. The mission profile will be constructed to minimize conflicts between Aerorover science, orbiter radar science, orbiter radio science, orbiter imaging science, and orbiter fields and particles (FP) science. Additional information is contained in the original extended abstract.