Engineering topics

Mall, U.

Publications and source records attributed to Mall, U..

4 records

NASA NTRS1994

Origin of the O(+) pick-up ions in the hehiosphere

The main sources for the ions in the interplanetary medium are the solar wind and the interstellar gas intruding into the heliosphere. Other sources, i.e. comets and planets can, however, contribute significantly locally. We present approximate expressions for deriving fluxes of pick-up ions originating from local neutral gas sources. Since the Io-torus is thought to be a relatively strong emitter of fast atoms, particular O and S, we used the O(+) data obtained by SWICS-Ulysses as a function of distance from Jupiter, both in and out-off the ecliptic plane in order to recognize a possible contribution of the Ionian source to the measured O(+). We find that - except for a very limited zone near the Jovian magnetosphere - the contribution of the Io-torus to the O(+) fluxes is minor, thus confirming our previous results on the pick-up H(+), He(+), N(+), O(+), and Ne(+) fluxes of interstellar origin.

Geiss, J.↗

NASA NTRS1994

Interstellar oxygen, nitrogen and neon in the heliosphere

Oxygen, nitrogen and neon pick-up ions of interstellar origin were detected for the first time with the Solar Wind Ion Spectrometer (SWICS) on board Ulysses. The interstellar origin of these ions is established by the following criteria: (a) they are singly charged, (b) they have the broad velocity distributions characteristic of pick-up ions, with an upper limit of twice the solar wind speed, (c) their relative abundance as a function of distance from the sun corresponds to the theoretical expectation, and (d) there is no relation to a planetary or cometary source. The interstellar abundance ratios He(+)/O(+), N(+)/O(+), Ne(+)/O(+) were investigated. At approximately 5.25 AU in the outermost part of Ulysses' trajectory He(+)/O(+) = 175(sup +70 sub -50) N(+)/O(+) = 0.13(sup +0.05 sub -0.05) and Ne(+)/O(+) = 0.18(sup +0.10 sub -0.07) were determined. For the interstellar gas passing through the termination region and entering the heliosphere (He/O)(sub 0) = 290(sup +190 sub -100), (N/O)(sub 0) = 0.13(sup +0.06 sub -0.06) and (Ne/O)(sub 0) = 0.20(sup +0.12 sub -0.09) were obtained from the pick-up ion measurements. Upper limits for the relative abundances of C(+) and C were also determined.

Geiss, J.↗

NASA NTRS1992

Plasma composition in Jupiter's magnetosphere - Initial results from the Solar Wind Ion Composition Spectrometer

The ion composition in the Jovian environment was investigated with the Solar Wind Ion Composition Spectrometer on board Ulysses. A hot tenuous plasma was observed throughout the outer and middle magnetosphere. In some regions two thermally different components were identified. Oxygen and sulfur ions with several different charge states, from the volcanic satellite Io, make the largest contribution to the mass density of the hot plasma, even at high latitude. Solar wind particles were observed in all regions investigated. Ions from Jupiter's ionosphere were abundant in the middle magnetosphere, particularly in the high-latitude region on the dusk side, which was traversed for the first time.

Geiss, J.↗

NASA NTRS1992

Ions with low charges in the solar wind as measured by SWICS on board Ulysses

We present new data on rare ions in the solar wind. Using the Ulysses-SWICS instrument with its very low background we have searched for low-charge ions during a 6-d period of low-speed solar wind and established sensitive upper limits for many species. In the solar wind, we found He(1+)/He(2+) of less than 5 x 10 exp -4. This result and the charge state distributions of heavier elements indicate that all components of the investigated ion population went through a regular coronal expansion and experienced the typical electron temperatures of 1 to 2 million Kelvin. We argue that the virtual absence of low-charge ions demonstrates a very low level of nonsolar contamination in the source region of the solar wind sample we studied. Since this sample showed the FlP effect typical for low-speed solar wind, i.e., an enhancement in the abundances of elements with low first ionization potential, we conclude that this enhancement was caused by an ion-atom separation mechanism operating near the solar surface and not by foreign material in the corona.

Geiss, J.↗