Neutral hydrogen in interplanetary space

129

124

Abstract. Energetic neutral atom (ENA) imaging is a powerful technique, which can remotely probe the properties of distant hot plasmas. Hot plasmas are abundant at the heliospheric boundary, the region where the expanding solar wind meets the surrounding local interstellar cloud. Here we present a new concept for imaging this boundary in ENA fluxes. Heliospheric ENAs are born from charge exchange between energetic protons and the background interstellar atomic hydrogen gas. The technique is ideal for studying the asymmetric threedimensional heliospheric interface region remotely, from 1 AU. We show that ENA imaging in the 0.2-6 keV energy range will establish the nature of the telTnination shock and properties of hot proton populations in the heliosheath. We also examine how the evolution of pickup proton populations at and beyond the shock can be explored. Global heliosphere ENA images will distinguish among the competing models of the interaction between the Sun and the local interstellar medium, and they will reveal the physics of important processes in the interface region. Heliospheric ENA fluxes are exceptionally weak, which makes imaging implementation difficult. Nonetheless, we show how single-pixel ENA sensors can image the heliosphere from a spicming spacecraft on a typical mission near 1 AU. The required instrumentation is briefly discussed. HeliosphereThe interaction of the expanding solar wind plasma and local interstellar medium (

Section: Heliospheric Energetic Neutral Atomsmentioning

confidence: 99%

Energetic neutral atom imaging of the heliospheric boundary region

Gruntman¹,

Roelof²,

Mitchell³

et al. 2001

129

124

“…The conditions of pickup protons and their influence on the solar wind have been considered by several authors [Axford, 1972;Burlaga et al, , 1996Gloeckler, 1996;Gloeckler et al, 1993;Holzer, 1972Holzer, , 1977Holzer, , 1989Isenberg, 1986Isenberg, , 1987 [Gloeckler, 1996]. These input data give the production rate of pickup protons by charge exchange-7 times of the production rate of pickup protons by photoionization.…”

Section: Pickup Proton Solar Windmentioning

confidence: 99%

Interaction of a strong interplanetary shock with the termination shock

Lu¹,

Whang²,

Burlaga³

1999

Abstract. The 1991 global merged interaction region (GMIR) shock is a strong forward shock observed from Voyager 2 on day 146 of 1991 at 34.6 AU. As the GMIR shock propagated outward in the distant heliosphere, it eventually encounters the termination shock. We study the interaction of the GMIR shock with the termination shock taking into account the influence of interstellar pickup protons on the solar wind and the shocks. Because the location of the termination shock is an unknown parameter, it remains uncertain about when and where the GMIR shock penetrates through the termination shock. This paper carries out calculations for the interaction to take place over a wide range of possible locations between 70 and 110 AU. The interaction can significantly modify the conditions of both shocks. For the GMIR shock, the interaction can cause a decrease of the shock speed by -120 km/s, a decrease of the shock Mach number from -1.9 to -1.4, and a decrease of the shock strength from -2.2 to -1.6. For the termination shock, the interaction can cause an increase of the shock speed by -95 km/s, a decrease of the shock Mach number from-3.6 to -2.6, and a decrease of the shock strength from -•3.2 to -2.8.

“…[42] Along similar lines, the ratio of the neutral solar wind to ionized solar wind due to charge transfer in the interplanetary medium (i.e., without an exosphere) is expected to be 10 À5 -10 À4 [e.g., Holzer, 1977;Gruntman, 1994], so that the lunar dust-generated neutral solar wind signal is comparable to this population at slow solar wind speeds but dominates it at higher solar wind speeds. Furthermore, Figure 5.…”

Section: Discussionmentioning

confidence: 99%

“…[3] Despite neutral solar wind having been discussed for many years [Fahr, 1968;Holzer, 1977] it has only recently been observed by the Low Energy Neutral Atom (LENA) imager at Earth [Collier et al, 2001] and by the Analyzer of Space Plasma and Energetic Atoms (ASPERA-3) at Mars [Brinkfeldt et al, 2006]. At Earth, neutral solar wind generated by the charge exchange interaction of solar wind protons with the exosphere has provided remote observations of changes in the location of the magnetosphere and high-latitude reconnection points [e.g., Taguchi et al, 2005Taguchi et al, , 2006Collier et al, 2005].…”

Section: Introductionmentioning

confidence: 99%

Neutral solar wind generated by lunar exospheric dust at the terminator

Collier

Stubbs

2009

[1] We calculate the flux of neutral solar wind observed on the lunar surface at the terminator due to solar wind protons penetrating exospheric dust grains with (1) radii greater than 0.1 mm and (2) radii greater than 0.01 mm. For grains with radii larger than 0.1 mm, the ratio of the neutral solar wind flux produced by exospheric dust to the incident ionized solar wind flux is estimated to be $10 À4 -10 À3 for solar wind speeds in excess of 800 km s À1 but much lower (<10 À5 ) at average to slow solar wind speeds. However, when the smaller grain sizes are considered, this ratio is estimated to be !10 À5 at all speeds and at speeds in excess of 700 km s À1 reaches $10 À3 . These neutral solar wind fluxes are easily measurable with current low-energy neutral atom instrumentation. Observations of neutral solar wind from the surface of the Moon would provide independent information on the distribution of very small dust grains in the lunar exosphere that would complement and constrain optical measurements at ultraviolet and visible wavelengths.Citation: Collier, M. R., and T. J. Stubbs (2009), Neutral solar wind generated by lunar exospheric dust at the terminator, J. Geophys.