The ionosphere of Saturn as observed by the Cassini Radio Science System

Fifty‐nine ionsopheric radio occultation observations of the vertical electron density profile in the Saturn ionosphere have been made since the Cassini spacecraft was inserted in orbit around Saturn in 2004. Significant orbit to orbit variations were observed, but the general trend noted in earlier orbits, namely, increasing electron densities with increasing latitude was reconfirmed and bolstered with this extended data base. This trend is likely to be due to some combination of increasing ionization rates and decreasing water influx with latitude. Key Points Density properties of the ionosphere diminish with decreasing latitude This diminution starts over the main rings and is maximum inside the D ring This confirms transport of water from the tingsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108640/1/grl52007.pd

Hot oxygen corona at Europa

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95283/1/grl11783.pd

First results from the ionospheric radio occultations of Saturn by the Cassini spacecraft

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94835/1/jgra18257.pd

The Structure of Titan's Atmosphere from Cassini Radio Occultations

We present results from the two radio occultations of the Cassini spacecraft by Titan in 2006, which probed mid-southern latitudes. Three of the ingress and egress soundings occurred within a narrow latitude range, 31.34 deg S near the surface, and the fourth at 52.8 deg S. Temperature - altitude profiles for all four occultation soundings are presented, and compared with the results of the Voyager 1 radio occultation (Lindal et al., 1983), the HASI instrument on the Huygens descent probe (Fulchignoni et al., 2005), and Cassini CIRS results (Flasar et al., 2005; Achterberg et al., 2008b). Sources of error in the retrieved temperature - altitude profiles are also discussed, and a major contribution is from spacecraft velocity errors in the reconstructed ephemeris. These can be reduced by using CIRS data at 300 km to make along-track adjustments of the spacecraft timing. The occultation soundings indicate that the temperatures just above the surface at 31-34 deg S are about 93 K, while that at 53 deg S is about 1 K colder. At the tropopause, the temperatures at the lower latitudes are all about 70 K, while the 53 deg S profile is again 1 K colder. The temperature lapse rate in the lowest 2 km for the two ingress (dawn) profiles at 31 and 33 deg S lie along a dry adiabat except within approximately 200m of the surface, where a small stable inversion occurs. This could be explained by turbulent mixing with low viscosity near the surface. The egress profile near 34 deg S shows a more complex structure in the lowest 2 km, while the egress profile at 53 deg S is more stable

Mars Aeronomy Observer: Report of the Science Working Team

The Mars Aeronomy Observer (MAO) is a candidate follow-on mission to Mars Observer (MO) in the Planetary Observer Program. The four Mariner and two Viking spacecraft sent to Mars between 1965 and 1976 have provided a wealth of information concerning Martian planetology. The Mars Observer, to be launched in 1990, will build on their results by further examining the elemental and mineralogical composition of the surface, the strength and multipolar composition of the planetary magnetic field, the gravitational field and topography, and the circulation of the lower atmosphere. The Mars Aeronomy Observer is intended to address the last major aspects of Martian environment which have yet to be investigated: the upper atmosphere, the ionsphere, and the solar wind interaction region

Cassini radio occultations of Saturn's ionosphere: Model comparisons using a constant water flux

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94688/1/grl22099.pd

Ionosphere: Solar Cycle Variations

We summarize here the current state of knowledge of solar cycle variations in the morphology of the Venus dayside and nightside ionospheres, and in the mechanisms for maintaining the nightside ionosphere. The solar cycle variability of the dayside ionosphere is well understood. The dayside peak ion or electron density varies approximately as F10.70.35 for short-term or long-term solar variations. The non-Chapman behavior is mostly due to concomitant changes in the neutral atmosphere, and such changes also produce a large amplitude response to solar flux variations well above the peak. Similar behavior is observed on the night side, where the variation of the electron density is a factor of 2 near the peak, but is much larger at high altitudes. On the night side the ionotail extends thousands of kilometers behind the planet. The large response of the ionotail to solar flux variations and to solar wind dynamic pressure indicates that the ions found there originate on the day side. Pioneer Venus measurements have convincingly shown that the major source of nightside ionization at solar maximum is day-to-night plasma transport. Most estimates of the contribution of electron precipitation at high solar activity are in the range 20 to 30%, but the exact value is still not certain. Neither the solar cycle response of the nightside ionosphere, nor its behavior with solar zenith angle, nor its overall variability can be accounted for by electron precipitation as the major ion source

Ionosphere: Solar Cycle Variations

We summarize here the current state of knowledge of solar cycle variations in the morphology of the Venus dayside and nightside ionospheres, and in the mechanisms for maintaining the nightside ionosphere. The solar cycle variability of the dayside ionosphere is well understood. The dayside peak ion or electron density varies approximately as F10.70.35 for short-term or long-term solar variations. The non-Chapman behavior is mostly due to concomitant changes in the neutral atmosphere, and such changes also produce a large amplitude response to solar flux variations well above the peak. Similar behavior is observed on the night side, where the variation of the electron density is a factor of 2 near the peak, but is much larger at high altitudes. On the night side the ionotail extends thousands of kilometers behind the planet. The large response of the ionotail to solar flux variations and to solar wind dynamic pressure indicates that the ions found there originate on the day side. Pioneer Venus measurements have convincingly shown that the major source of nightside ionization at solar maximum is day-to-night plasma transport. Most estimates of the contribution of electron precipitation at high solar activity are in the range 20 to 30%, but the exact value is still not certain. Neither the solar cycle response of the nightside ionosphere, nor its behavior with solar zenith angle, nor its overall variability can be accounted for by electron precipitation as the major ion source