Engineering topics

Mcdonough, T. R.

Publications and source records attributed to Mcdonough, T. R..

11 records

NASA NTRS1980

Structure of the ionosphere and atmosphere of Saturn from Pioneer 11 Saturn radio occultation

The paper deals with radio occultation measurements of Saturn's ionosphere and upper neutral atmosphere, made by Pioneer 11 near the terminator at latitudes of 9.7 deg south and 11.6 deg south. The principal electron density peak (of about 11,400 cu cm), in the ionosphere occurred at an altitude of about 1800 km, with a sharp lower peak of about 9000 cu cm at 1200 km. The scale height above the main peak corresponds to an exosphere temperature of about 1150 K for an H(+) ionosphere. Ionization appears to extend to 30,000 km. The low density of the lower portion of the ionosphere may be explained by ring shadowing and equatorial anomaly. In the neutral atmosphere, measurements were made to a pressure level of about 180 mbar, showing a temperature inversion region with a triple minimum.

Kliore, A. J.↗

NASA NTRS1980

Vertical structure of the ionosphere and upper neutral atmosphere of Saturn from the Pioneer radio occultation

Radio occultation measurements at S band (2.293 GHz) of the ionosphere and upper neutral atmosphere of Saturn were obtained during the flyby of the Pioneer 11 Saturn spacecraft in September 1979. Preliminary analysis of the occultation exit data taken at a latitude of 9.5 deg S and a solar zenith angle of 90.6 deg, revealed the presence of a rather thin ionosphere. It contained a main peak electron density of about 9.4 times 10 to the third/ccm at an altitude of about 2800 above the level of a neutral number density of 10 to the 19th/ccm and a lower peak of about 7000/ccm at 2200 km. Data in the neutral atmosphere were obtained to a pressure level of 120 millibars.

Kliore, A. J.↗

NASA NTRS1979

The role of energetic particle precipitation in Jovian magnetospherics. I - Secondary electrons from the ionosphere of Jupiter

Escape of photoelectrons from the Jovian ionosphere produces only a meager source of thermal plasma for the inflated centrifugally unstable magnetosphere and is unable to account for the 100 eV thermal plasma temperatures of the magnetosphere. Since the Jovian magnetosphere is well populated with highly energetic electrons, the creation of secondaries and the energy degradation of the primaries precipitating into the lower ionosphere provide additional sources of magnetospheric thermal plasma as well as of the energy for further elevating the plasma temperatures in the top side ionosphere. The efficiencies with which escaping electrons are created by precipitating electrons with energies up to several MeV are computed using energetic electron transport and thermalization codes. The more energetic incident fluxes are far less efficient in creating escaping electrons than the lower energy fluxes with only 0.001% of the secondaries escaping for a 1 MeV source versus 3% for a 1 keV source. Incident fluxes of the order of 10 to 100 per sq cm per sec per eV between 100 eV and 100 keV are required to produce 50 eV escape fluxes comparable to those generated by solar EUV.

Swartz, W. E.↗

NASA NTRS1975

A theory of the Jovian hydrogen torus

The Jovian hydrogen torus associated with Io, that was observed by Judge and Carlson, has been found by them to be a third of a torus rather than a complete torus. It is shown that the energetic particles observed by Pioneer 10 do not ionize atomic hydrogen sufficiently fast to erode the torus as observed. It is proposed that the reason an incomplete torus exists is the presence of a corotating cold magnetospheric plasma. If this explanation is correct, the angular extent of the fractional torus is a measure of the density of the magnetospheric plasma near Io's orbit, which is found to be about 100 per cu cm. It is shown that such a plasma may provide an adequate input to Io, where it can recombine and escape, to form enough hydrogen atoms to explain the number of observed torus atoms. Thus the magnetospheric plasma may serve as both the source and the sink of the torus.

Mcdonough, T. R.↗

NASA NTRS1975

Photoelectron escape from the ionosphere of Jupiter

Photoelectron escape fluxes and ambient electron heating from the Jovian ionosphere are computed as a function of local time and latitude. Several differences for the fluxes expected from a hydrogen atmosphere, rather than a terrestrial type of atmosphere, are described, including an increase in structure in the energy spectra due to the paucity of ionic states entering the photo-ionization processes and lower escape fluxes above 10 eV than were expected from a simple scaling of earth fluxes.

Swartz, W. E.↗

NASA NTRS1974

Jupiter after Pioneer - A progress report

In December 1973, Pioneer 10 became the first spacecraft to reach the vicinity of Jupiter. The spacecraft passed through the Jovian magnetosphere in two weeks and sent back more than 300 pictures of the big planet. Measurements were conducted of EM fields, energetic particles, and micrometeoroids. Radio occultations observed are discussed along with observations in the infrared and ultraviolet range, magnetic measurements, questions of trajectory analysis, and data obtained with the aid of a plasma analyzer. Pioneer 10 has confirmed as inescapable the fact that Jupiter radiates more energy than it receives from the sun.

Mcdonough, T. R.↗

NASA NTRS1974

Gaseous toroid around Saturn

The trapping of Titan's escaping atmosphere in the Saturnian system by a toroidal ring is discussed. The radius of the toroid is comparable to Titan's orbit, or about ten times larger than the visible rings. Theoretical atmospheric models are formulated that consider Saturn's gravitational attraction and magnetospheric properties in forming this toroid and in protecting toroid particles from direct ionization by solar wind particles.

Mcdonough, T. R.↗

NASA NTRS1974

The Saturnian 'gas-doughnut' hypothesis

It is hypothesized that constituents escaping the atmosphere of Titan are unlikely to have sufficient velocity to escape from Saturn. Thus most of the material will enter into elliptical orbits which, at some point, cross Titan's orbit at a small angle. In total, this matter will form a 'doughnut' shaped feature, roughly centered on Titan's orbit and having dimensions of about 20 Saturn radii in the Saturnian-equatorial plane and 10 Saturn radii normal to this plane. It is assumed that the material is lost from the doughnut when it is ionized or is recaptured by Titan's atmosphere. The upper limit on the density of hydrogen in the ring is estimated to be about 1,000 particles per cu cm, with up to 99% of the particles in the doughnut being recaptured by Titan.

Mcdonough, T. R.↗

NASA NTRS1973

A Saturnian gas ring and the recycling of Titan's atmosphere

Atoms which escape Titan's atmosphere are unlikely to possess escape velocity from Saturn and can orbit the planet until lost by ionization or collision with Titan. It is predicted that a toroidal ring of between 1 and 1,000 atoms or molecules per cubic centimeter exists around Saturn at a distance of about 10 times the radius of the visible rings. This torus may be detectable from earth orbit and detection or nondetection of it may provide some information about the presence or absence of a Saturnian magnetic field, and the exospheric temperature and atmospheric escape rate of Titan. It is estimated that, if Titan has a large exosphere, 97% or more of the escaping atoms can be recaptured by Titan, thereby decreasing the effective net atmospheric loss rate by up to two orders of magnitude. It is shown that, if Saturn has a magnetic field comparable to Jupiter's the magnetospheric plasma can supply Titan with hydrogen at a rate comparable to the loss rates in some of the models of Trafton (1972) and Sagan (1973).

Mcdonough, T. R.↗

NASA NTRS1973

New kind of ring around Saturn.

It is believed that barring extraordinary circumstances the Saturn satellite Titan must lose its atmosphere at a prodigious rate. The velocity of the atmospheric particles, however, although sufficient to escape from the satellite, does not quite reach Saturnian escape velocity. Consequently, atoms and molecules lost by Titan are forced by the planet's gravitational field to orbit Saturn until ionized or until they are recaptured by Titan, forming a gaseous torus encompassing Titan's orbit.

Mcdonough, T. R.↗

NASA NTRS1973

Jupiter's radiation belts.

A model for the production and loss of energetic electrons in Jupiter's radiation belt is presented. It is postulated that the electrons originate in the solar wind and are diffused in toward the planet by perturbations which violate the particles' third adiabatic invariant. At large distances, magnetic perturbations, electric fields associated with magnetospheric convection, or interchange instabilities driven by thermal plasma gradients may drive the diffusion. Inside about 10 Jupiter radii, the diffusion is probably driven by electric fields associated with the upper atmosphere dynamo which is driven by neutral winds in the ionosphere. The diurnal component of the dynamo wind fields produces a dawn-dusk asymmetry in the decimetric radiation from the electrons in the belts, and the lack of obvious measured asymmetries in the decimetric radiation measurements provides estimates of upper limits for these Jovian ionospheric neutral winds.

Brice, N.↗