Mission completed. Review of ASPERA-4 results on Venus solar wind interaction: After 8 years operation at Venus

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1 Mission completed Review of ASPERA-4 results on Venus solar wind interaction: After 8 years operation at Venus Yoshifumi Futaana Stas Barabash Swedish Institute of Space Physics, Kiruna and Venus Express/ASPERA-4 team

2 International Venus Conference 2016, , Oxford, UK 2/15 ASPERA-4 instrument ASPERA-4 = IMA + ELS + NPI + NPD 2 Scanner ELS NPI NPD1 NPD2 IMA Scanner

3 International Venus Conference 2016, , Oxford, UK 3/15 History of Venus Exploration Hot plasma measurement Sun spot number Energy [ev] Energy [ev] M2 M5 V4 V5 V6 V9 V10 V9 V10 PVO/OPA PVO/OIMS PVO/RPA PVO/OPA PVO/RPA Vega 1-2 Vega 1-2 Galileo Galileo VEX/ASPERA-4 Messenger VEX/ASPERA-4 ION Electron BepiColombo JUICE Produced by Persson M.

4 International Venus Conference 2016, , Oxford, UK 4/15 First data near Venus ( ) First & last data IMA Energy ELS Energy Last data near Venus ( ) IMA Energy ELS Energy Almost no degradation over 8.5 years, or 2000 pericenter pass, operations in space

5 International Venus Conference 2016, , Oxford, UK 5/15 Data coverage IMA ELS NPI NPD scan Observation time Notes Pericenter 1) 2),3) Fix 3 6 hr near pericenter Venus environment Fix or Eclipse Scan In shadow Limited scanner operation Apocenter 1) 2) Fix 1 2 hr near apocenter Avoid WOL IMA

6 International Venus Conference 2016, , Oxford, UK 6/15 Scientific objectives Venus: No intrinsic magnetic field. Atmosphere interacts with solar wind directly. Different from Earth. Rather similar to Mars. Original scientific goals Atmosphere coupling with the solar wind Mass addition/removal from the atmosphere Structure of the induced magnetosphere Mass composition of the escaping plasma Loss of water Neutral plasma interaction Comparative planetology (Earth, Mars) Extended phases Long-term variabilities (solar-cycle) Lower ionosphere (aerobraking)

7 International Venus Conference 2016, , Oxford, UK 7/15 Science 1: Stoichiometric escape Venus loses water! H+ / O+ = 1.9 O+ O H+ H H ++ Venus loses water! Ongoing work: Dependence on Solar activity Barabash et al. 2007

8 Science 1: Outflow flux Outflow flux at solar maximum: Masunaga et al., 2011 Nordström et al., 2012 } 3-6 x /s at solar minimum Adopted from Dubinin et al Ongoing work: Comparative aspect International Venus Conference 2016, , Oxford, UK 8/15

9 International Venus Conference 2016, , Oxford, UK 9/15 Science 2: Space weather impact SEP arrival Venus Energy 10 kev 1 kev 100 ev Flare Mars December 2006 Energy 10 kev 1 kev 100 ev December 2006 Solar flare onset Futaana et al. 2008

10 International Venus Conference 2016, , Oxford, UK 10/15 Science 2: Space Weather impact (Mars) "Storm" enhanced escaping flux by >10x (clearly seen at Mars) Further investigations Mars comparison (MEX, MAVEN). Aurora. Nightglow...

11 Science 3: lium balance Pre-ASPERA-4 knowledge: product < escape Pre-ASPERA-4 Hypothesis: product + input ~ escape U-238 U Th-232 Krasnopolsky and Gladstone, 2005 Gombosi et al., 1980 (based on PVO) Zhang et al., 2007 (VEX) Figure courtesy from G. S. Wieser 1 International Venus Conference 2016, , Oxford, UK 11/15 + +

12 International Venus Conference 2016, , Oxford, UK 12/15 Science 3: ++ observations Pre-ASPERA-4 knowledge: product < escape Post-ASPERA-4 knowledge: product + input < escape O2 + O+ ++ H + Yet unaccountable balance by SW precipitation (solar min) The average net inflow: ~10 21 s -1 (Stenberg et al., 2015) The escape of +: 8x10 22 s -1 (Fedorov et al., 2011) Stenberg et al., 2015

13 International Venus Conference 2016, , Oxford, UK 13/15 Science 4: Photoelectrons Differential energy flux [m -2 sr -1 s -1 ] Coates et al., 2015 Energy [ev] Time Photoelectrons present in the shadow Estimated loss of atmosphere ~2.2x10 23 [/s]

14 Science 5: Energetic Neutral Atoms First ENA images of Venus ever. The observed tailward flow of hydrogen ENA is magnetosheath plasma neutralized by exosphere (but assuming less dense than expected) ENA for diagnosing exosphere sounding No Oxygen ENA found ASPERA-4/NPD observation (2006) Model (VIRA + MHD) Galli et al., 2008 International Venus Conference 2016, , Oxford, UK 14/15

15 International Venus Conference 2016, , Oxford, UK 15/15 Summary Mission completed Science forever ASPERA-4, the IRF (Kiruna) led instrument has achieved many high-impact scientific results to the field of Venus plasma environment. The efforts of producing scientific results are continuing. We would like to appreciate all the community who has supported the mission and the instrument; all the scientists and engineers, Swedish National Space Board, ESA, and industry!