Modeling Ganymede’s environment
Credit : CNES / CDPP / GFI / LATMOS
R. Modolo, G. Carnielli, D. Borius, M. Galand and the
RPWI team
WG3 – JUICE – Ganymede Phase Observations
Outline
• JUICE trajectory information of Ganymede Phase
• Tail current sheet crossing
• Open-Closed Field line Boundary (OCFB) crossings
• Identification of Polar cap
• Variability of boundary crossings to external driver
• Update on Ionospheric modeling by G. Carnielli and
M. Galand
WG3 – JUICE – Ganymede Phase Observations
JUICE trajectory during Ganymede Phase
• JUICE trajectory : SPICE kernel Crema 3.0
• Period of interest : 24/08/2032 – 04/06/2033
• Reference frame : GPHIO – Center : Ganymede
• Temporal resolution : 60 s
JUICE trajectory in Ganymede’s environment
WG3 – JUICE – Ganymede Phase Observations
Identification of tail current sheet crossing
26/10/2032
tail
J map in XZ plane, projection of tail CS
crossing (magenta points)
CS
Criteria :
 X>0 (JUICE in the tail)
Generation of a Time Table (Catalogue) of CS
 Bx(t)×Bx(t+1min) <0 (change of polarity) crossing
 |Jy(t-5min)-Jy(t+5min)|> 5nA/m² (Current
density jump within 10 min window)
WG3 – JUICE – Ganymede Phase Observations
Magnetic field lines connected to
JUICE S/C
Methodology : for each trajectory point, we compute the magnetic field lines and
follow them until either the obstacle or the edge of the simulation box
 Identification of 3
types of field lines :
- Open-Open
- Open-Closed
- Closed-Closed
 Catalogue (Time Table)
of field line
classification along
JUICE trajectory
 Ex : JUICE in ClosedClosed field line region
(pink dots)
WG3 – JUICE – Ganymede Phase Observations
OCFB crossing
 Identification of OCFB
crossings : when the
S/C moves from an
Open-Closed to a
Closed-Closed field
line (and reciprocally)
 Green dots indicate
the position of the S/C
when crossing OCFB
 Generation of a time
table with JUICE at
OCFB
WG3 – JUICE – Ganymede Phase Observations
Polar cap crossing
 Identification of time
intervals when the S/C
fly over the Polar cap –
these times
correspond to the
intersection between
the external envelop
of the Open-Closed
field lines the S/C
trajectory
 Generation of a time
table with inbound
and outbound polar
cap crossing
WG3 – JUICE – Ganymede Phase Observations
Variability to external field driver
 Simulation performed with different 𝐵𝐵𝑗𝑗𝑗𝑗𝑗𝑗 direction gives different
boundary crossing times  needs to determine a buffer time
window to capture the boundary
 Simu 1 : 𝐵𝐵𝑗𝑗𝑗𝑗𝑗𝑗 = [0, -79,-79]nT
 Within a 5 min window about
70% of boundary crossings
overlapped between the two
catalogues (simu 1 vs simu 2)
 OCFB and Current Sheet
crossing are less sensitive to
the 𝐵𝐵𝑗𝑗𝑗𝑗𝑗𝑗 orientation (>80% of
crossing are identified within
3 min window)
Simu2 : 𝐵𝐵𝑗𝑗𝑗𝑗𝑗𝑗 = [0, -6.7, -77]nT
WG3 – JUICE – Ganymede Phase Observations
Catalogues
• For CS and OCFB catalogues, Simu 1 & 2 catalogues
have been merged. Two consecutive times shorter
than 10 min have been replaced by the average
time
• For the polar cap catalogue, Simu 1 & 2 catalogues
have been merged. Two consecutive inbound and
outbound times shorter than 10 min have been
replaced by the average inbound and outbound
time.
WG3 – JUICE – Ganymede Phase Observations
Update on the ionospheric
model developped by
Carnielli, Galand et al
3D ionospheric model
 3D test-particle ionospheric model
developed by Carnielli et al, 2019
 MHD (Jia et al, 2009) or Hybrid
(Leclercq et al, 2016) EB field
 3D exosphere (O2,H2,H2O), Leblanc et
al, 2017
 Ionization source : photoionization and
e- impact
 O2+ is the most abundant species
 Ion outflow velocity measured by PLS
is more consistent with O2+ escaping
ions
 Lower density than PWS can be
explained by an underestimation of
exospheric densities (and e- impact
ionisation frequency)
WG3 – JUICE – Ganymede Phase Observations
Constraining Ganymede's neutral and plasma environments
through simulations of its ionosphere and Galileo observations
Understanding the factors contributing
to observation-simulation differences :
 Collisions - Charge exchange reactions
between ionospheric ions (O2+) and
neutrals negligible
 Boosted exosphere – different models
differ by 1 order of magnitude in ejection
rates (uncertainty on the sputtering yield)
 inbound/outbound asymmetry cannot
be explained  it does contribute but it is
not the only factor
 Electron impact ionization frequency –
energetic e- count rates differences
observed between inbound and outbound
(no phase-space distribution observed
inside the magnetosphere)  a factor 4
tested on e- impact frequency in the antijovian hemisphere
 Boosted exosphere + asymmetric e- impact
frequency relatively good agreement on
ne profile and energy spectra
Carnielli et al,
2019b, submitted
to Icarus
WG3 – JUICE – Ganymede Phase Observations
Simulations of ion sputtering at
Ganymede
Estimate the contribution of ionospheric ion to the surface sputtering
 Evaluation of the contribution of (injection in a test-particle model) :
 Thermal jovian plasma – O+ (n=1.75 cm-3 and V=140 km/s)
 Energetic jovian ions – O2+ and S3+ 20keV-3MeV
 Ionospheric ions – O2+, O+, H2O+, H2+, H+ and OH+
Carnielli et al,
2019c, submitted
to Icarus
WG3 – JUICE – Ganymede Phase Observations