Energetic Neutral Atoms around Mars Latest results from

Energetic Neutral Atoms around Mars Latest results from NPD onboard Mars Express Futaana Yoshifumi Stas Barabash, Alexander Grigoriev Mars Express ASPERA-3 team

INTRODUCTION

ASPERA-3/NPD 2004. 12. 09 Futaana et al. , Energetic Neutral Atoms around Mars

Specification NPD = Neutral Particle Detector 2 Sensors x 3 FOVs. 30 x 5 [deg] FOV for each channel ~180 x 5 [deg] by all 6 channels Time of flight (TOF) + Pulse height(PH) 100 e. V - 10 ke. V 2004. 12. 09 Futaana et al. , Energetic Neutral Atoms around Mars

ENAs around the Mars Backscattered ENAs Related to the gyromotion of the shocked solar wind. Subsolar ENAs Related to the deflection of the shocked solar wind at around the subsolar point 2004. 12. 09 Futaana et al. , Energetic Neutral Atoms around Mars

BACKSCATTERED ENA

Backscattered ENAs Generated by collisions between the gyrating solar wind protons and the exospheric neutral particles. Global generation Solar zenith angle dependence of the ENA generation 2004. 12. 09 Futaana et al. , Energetic Neutral Atoms around Mars

TOF spectrogram 2004. 12. 09 Futaana et al. , Energetic Neutral Atoms around Mars

18: 40 19: 00 2004. 12. 09 Futaana et al. , Energetic Neutral Atoms around Mars

Precipitation Map ENA scattering location mapped on the MSE coordinate system Bad resolution of for the longitudinal direction due to the finite FOV of NPD. We can make the map using all observations so far. 2004. 12. 09 Futaana et al. , Energetic Neutral Atoms around Mars

Backscattered ENAs come from every SZA. Solar wind protons penetrate into the exosphere globally. Count rate of ENAs depends on averaged SZA. There is a correlation between SZA and count rates, but it’s not a simple relation (e. g. cos SZA) 2004. 12. 09 Futaana et al. , Energetic Neutral Atoms around Mars

Flux of backscattered ENAs G-factor = 1 -2 x 10^-4 [cm^2 str/str] Calibration by 0. 7 -1. 3 ke. V H+ 600 -1000 counts/sec (Integration by energy) Differencial flux J~3 -10 x 10^6[/cm^2 str sec] Flux Fbs~2 pi J~ 2 -6 x 10^7 [/cm^2 sec] 2004. 12. 09 Futaana et al. , Energetic Neutral Atoms around Mars

Summary ASPERA-3/NPD instrument detected ENAs coming from the direction of Martian body in all solar zenith angle. The flux of these ENAs depends on the solar zenith angle. These ENAs are possibly the backscattered ENAs that are generated by collisions between solar wind protons and exospheric particles. 2004. 12. 09 Futaana et al. , Energetic Neutral Atoms around Mars

Further studies Precipitation map covering all observation Comparison with model calculations Solar zenith angle dependence Consideration of angular response of NPD Comparison with solar wind proton flux 2004. 12. 09 Futaana et al. , Energetic Neutral Atoms around Mars

SUBSOLAR ENA

Subsolar ENAs are expected to have characteristics such as Generated at limited area around subsolar region Beam-like emission Strong directivity 2004. 12. 09 Futaana et al. , Energetic Neutral Atoms around Mars

TOF spectrogram 5/30 NPD-1 CH-2 10: 50 11: 15 NPD-1 CH-1 2004. 12. 09 Futaana et al. , Energetic Neutral Atoms around Mars

TOF spectrogram 5/30 NPD-1 CH-2 NPD-1 CH-1 11: 03 2004. 12. 09 Futaana et al. , Energetic Neutral Atoms around Mars

11: 00 11: 05 2004. 12. 09 Futaana et al. , Energetic Neutral Atoms around Mars

Subsolar ENAs TOF spectrum is very sharp, that means the ENAs are mono -energetic Sudden decrease can be interpreted by directional beam of subsolar ENAs 2004. 12. 09 Futaana et al. , Energetic Neutral Atoms around Mars

Solar wind driven event 04/06/07 2004. 12. 09 Futaana et al. , Energetic Neutral Atoms around Mars

Futaana et al. Backscattered ENAs from Martian Upper Atmosphere

Flux of subsolar ENAs G-factor = 1 -2 x 10^-4 [cm^2 str/str] 1000 -2000 counts/sec (Integration by energy) Differencial flux J~5 -20 x 10^6[/cm^2 str sec] 2004. 12. 09 Futaana et al. , Energetic Neutral Atoms around Mars

Summary & Problems Subsolar ENAs exist and identified Monoenergetic and directional flux from subsolar region Quick response to the upstream parameters What is the size of generation region? 2004. 12. 09 Futaana et al. , Energetic Neutral Atoms around Mars