Pickup protons and pressure-balanced structures from 39 to 43 AU: Voyager 2 observations during 1993 and 1994

Details Pickup protons and pressure-balanced structures from 39 to 43 AU: Voyager 2 observations during 1993 and 1994 Pickup protons and pressure-balanced structures from 39 to 43 AU: Voyager 2 observations during 1993 and 1994

Jul 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996jgr...10115523b&link_type=abstract

Journal of Geophysical Research, Volume 101, Issue A7, p. 15523-15254

Physics

22

Interplanetary Physics: Pickup Ions, Interplanetary Physics: Interplanetary Magnetic Fields, Interplanetary Physics: Solar Wind Plasma, Interplanetary Physics: Interstellar Gas

Scientific paper

The pressure of interstellar pickup protons in the distant heliosphere can be determined by analyzing pressure-balanced structures, observed on a scale of a few hundredths of an AU. This paper extends the earlier work of L. F. Burlaga et al. (Journal of Geophysical Research, 99, 21, 511, 1994) by analyzing pressure-balanced structures observed by Voyager 2 from 39.3 to 40.6 AU in 1993 and from 42.6 to 43.2 AU during 1994. The pickup proton temperature is high in the region of the distant heliosphere that we considered: (5.4+/-0.1)×106 K at 39-41 AU and (6.0+/-0.4)×106 K at ~43 AU. The density of the pickup protons is (1.6+/-0.3)×10-4 cm-3 at 39-41 AU and (1.2+/-0.2)×10-4 cm-3 at ~43 AU. The ratio of the pickup proton density to the solar wind proton density (Ni/N) is small, only 0.03+/-0.01 during both 1993 and 1994. Nevertheless, the pickup proton pressures are relatively high because of their high temperatures. The pickup proton pressure was (11+/-2)×10-14 ergcm-3 at 39-41 AU and (9+/-1)×10-14 ergcm-3 at 43 AU. There is a possible decrease in Pi with increasing distance from the Sun. The pickup proton pressure is an order of magnitude greater than the solar wind proton pressure: Pi/Pswp=10+/-2 at 39-41 AU and 8+/-2 at 43 AU. Our results support the hypothesis of Burlaga et al. that the pickup proton pressure is more important than the solar wind thermal pressure in the dynamics of the distant heliosphere. The ratio of the pickup ion pressure to the magnetic pressure is Pi/(B2/8π)=1.7+/-0.3 at 39-41 AU and 1.7+/-0.72 at ~43 AU. These results are compared with a model.

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