Investigation of the atmospheres of
Europa, Ganymede, and Callisto with
PEP/JUICE
Peter Wurz, Marek Tulej, Audrey Vorburger, and
Nicolas Thomas
Universität Bern, Physikalisches Institut, 3012 Bern, Switzerland
(peter.wurz@space.unibe.ch, 41 31 631 44 05)
Stas Barabash, Martin Wieser,
Swedish Institute of Space Physics, S-981 28 Kiruna, Sweden
Helmut Lammer
Austrian Academy of Sciences, A-8042 Graz, Austria
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Moscow 4–8 Mar 2013
Jupiter Icy Moons Explorer (JUICE)
The JUpiter ICy moons Explorer (JUICE) will perform detailed investigations
of Jupiter and its system in all their inter-relations and complexity with
particular emphasis on Ganymede as a planetary body and potential habitat.
Investigations of Europa and Callisto would complete a comparative picture
of the Galilean moons.
In early May 2012 ESA announced the selection of JUICE as L-Class
mission, with launch in June 2022, and 7.6 years cruise to Jupiter. In
February 2013 the scientific instruments for JUICE have been selected.
Most important, new light will be shed on the potential for the emergence of
life in the galactic neighbourhood and beyond. The overarching theme for
EJSM has been formulated as:
What are the conditions for planet formation and emergence of life?
How does the Solar System work?
To understand the Galilean satellites as a system, Europa and Ganymede
are singled out for detailed investigation.
Moscow 4–8 Mar 2013
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Particle Environment Package (PEP)
PEP consists of three units with elegant, modular
design hosting sensors and electronics, and welldefined, minimal interfaces to the spacecraft
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—
—
Zenith Unit (IRF, Sweden)
Nadir Unit (UBe, Switzerland)
JENI (APL / USA)
PEP combines remote global imaging with insitu measurements, obtaining 3D plasma flows in
less than 10s, and first-ever gas mass
spectroscopy at the icy moons;
> PEP uses mutual shielding, single to triple
coincidence detection schemes in all
sensors for operation in the harsh Jovian
environment;
> TRL≥6 building on direct flight & team heritage
JoEE
JDC
JEI
>
>
—
Galileo, Cassini, Juno, Mars Express (ASPERA3), Venus Express (ASPERA-4), Rosetta, SOHO,
New Horizons, Chandrayaan-1, IMAGE, & RBSP.
Zenith Unit
Nadir Unit
JoEE
JDC
NIM
JEI
JENI
JNA
PEP team includes world leaders on the outer
planets and recognised providers of space
hardware.
Moscow 4–8 Mar 2013
Scientific Objectives of NIM
The science goal of the Neutral gas and Ion Mass (NIM)
spectrometer is the determination of the extended atmospheres
of Europa, Ganymede and Callisto, in particular the neutral
and the ionised component. The main scientific goals are:
> The chemical composition of regular atmosphere produced
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>
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by energetic particle and photon interaction with the surface
The ion composition of the ionosphere
Chemical analysis of geysers (if encountered) and their
temporal evolution
Isotopic analysis when signal levels are sufficiently high.
Assist in the identification of the chemical nature various
surface elements
Moscow 4–8 Mar 2013
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NIM/PEP: A TOF-MS Instrument
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>
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Time-of-flight technique
All masses are measured simultaneously
High dynamic range
Mass spectra easy to interpret
Robust, simple system
Moderate need for resources
D.
Abplanalp,
P. Wurz, et al., Adv. Space Res. 44 (2009) 870–878.
8. April
2015
5
Moscow 4–8 Mar 2013
Residual gas recorded at a total
pressure of 5.0·10–10 mbar
Detection level
≈10–16 mbar
Moscow 4–8 Mar 2013
Prototype Results: Mass Resolution
PEP / NIM
Krypton at 2·10–9 mbar
P. Wurz, D. Abplanalp, M. Tulej, and H. Lammer, Planet. Planet. Sp. Science 74 (2012) 264–269.
Moscow 4–8 Mar 2013
Europa
T.A. Cassidy, et al., Icarus 2009
Shematovich et al.,2004, Surface-bounded atmosphere of Europa
Pressure (mbar)
10
10
-12
10
-11
10-10
10-9
10-8
10-7
100
Height (km)
This image shows the approximate natural colour appearance of Europa,
predominantly ice-rich regions of the crust. Europa is about 3160 km in
diameter, or about the size of Earth's moon. This image was taken on 7
September 1996, at a range of 677’000 km by the solid state imaging
television camera onboard the Galileo spacecraft during its second orbit
around Jupiter. Long, dark lines are fractures in the crust, some of which are
more than 3’000 km long. The bright feature containing a central dark spot
in the lower third of the image is a young impact crater 'Pwyll' some 50 km in
diameter.
-13
10
O
O2
H2O
Dark brown areas (ice-poor) represent rocky material derived from the
interior, implanted by impact, or from a combination of interior and exterior
sources.
1
103
104
105
106
107
108
109
1010
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-3
Number density (cm )
Europa
Atmosphere composition
Surface composition
•Bright Areas (ice-rich regions)
–H20, CO2,
–SO2, Sx,
–H2O2, ...
•Dark Areas (ice-poor regions)
–MgSO4 • xH20
–Na2SO4 • xH20
–Na2CO3 • xH20
–H2SO4 • xH20
•Possible extremophile bacteria
–Cyanidium
–Deinococcus radiodurans
–Sulfolobus shibatae
–Escherichia coli
The surface composition of the dark areas is not
well constrained by infra-red (IR) spectroscopy,
even with high spectral resolution. Moscow 4–8 Mar 2013
Europa Atmosphere Model
> NIM flyby operations
— Full mass spectra at 5-sec cadence
— Detection threshold 30 cm–3, in
Europa’s radiation environment
— dynamic range of > 105
> All species known in Europa‘s
exosphere can be detected by
NIM/PEP during the JUICE flybys
— O, O2, H2, H2O, Na, SO2, SO, CO2,
CO
> Expected exospheric species from
non-ice surface
— Detection if surface concentration is
>= 10–3
— Mg, MgO, NaO, Ca, CaO, Al, AlO,
...
> Isotopes:
— With a threshold of 30 cm–3 and a
dynamic range of > 105 the D/H
ratios can be resolved in the
thermal component of H2
— 18O/16O from the O2 and H2O in the
sputtered signal
Moscow 4–8 Mar 2013
Ganymede
This Voyager 2 colour photo of Ganymede, the largest Galilean satellite,
was taken on 7 July 1979, from a range of 1.2·106 km. The photo shows
a large dark circular feature about 3200 km in diameter with narrow
closely-spaced light bands traversing its surface. The bright spots dotting
the surface are relatively recent impact craters, while lighter circular
areas may be older impact areas. The light branching bands are ridged
and grooved terrain first seen on Voyager 1 and are younger than the
more heavily cratered dark regions. The nature of the bright region
covering the northern part of the dark circular feature is uncertain, but it
may be some type of condensate. Most of the features seen on the
surface of Ganymede are probably both internal and external responses
of the very thick icy layer which comprises the crust of this satellite.
Moscow
4–8 Mar
2013
M.L. Marconi,
Icarus,
2007
Ganymede Exosphere
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Molecular oxygen (O2): Spencer et al. JGR 1996
— Leading / trailing side differences
— Oxygen trapped in surface
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Ozone detection: Noll et al. Science 1996
— Ozone gas trapped in ice
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Oxygen atoms: Hall et al. ApJ, 1998
— Inferred vertical O2 column densities are in the range (1–10)·1014 cm2
— Localised emission regions near north and south pole
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Oxygen atoms: Feldman et al. ApJ, 2000
— Correlation of oxygen emissions with magnetic field topology
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Ionosphere: Eviatar et al. PSS, 2001
— Bound ionosphere, mostly molecular oxygen
— Corona of hot oxygen atoms
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Exosphere modelling: M.L. Marconi, Icarus, 2007
— H2O, O2, H2
— Surface densities up to 109 cm–2 (~ 10–7 mbar)
Moscow 4–8 Mar 2013
Callisto
Liang, M.-C., B. F. Lane, R. T. Pappalardo, M. Allen, and Y. L. Yung (2005),
Atmosphere of Callisto, J. Geophys. Res., 110, E02003, doi:10.1029/2004JE002322.
Moscow 4–8 Mar 2013
Radiation Environment
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Coaxial closed cylinder shells
Three variable shielding layers
One fixed inner layer to represent the
detector housing (1.5 mm of Titanium)
MCP as disc target
Moscow 4–8 Mar 2013
Radiation optimisation of NIM
detector shield
Moscow 4–8 Mar 2013
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NIM S/N Estimate at
Europa
Assuming maximum high-energy
flux of penetrating particles
(electrons) of 3·10+8 e– / (cm2 s1).
No shielding of detector:
— 500 background counts in each
0.5-ns bin of the TOF spectrum
accumulated for 5 seconds.
— This limits the dynamic range to
about 3 decades
— Reduces the life-time of the
MCPs
Graded-Z shielding (Al/Ta)
— Reduces the penetrating electron
flux to 4·104 e–/(cm2 s)
— In addition, secondary -radiation
of 5·105 /(cm2 s).
— Shielding improves the dynamic
range to >5 decades
Moscow 4–8 Mar 2013
Summary
>
The atmospheres of Europa,
Ganymede and Callisto are largely
unknown
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— Result of evaporation / sublimation
and exogenic processes
(sputtering)
— Atmospheric species are directly
related to the surface
>
With NIM / PEP we will characterise
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these atmospheres
Dekompressor „“
— Chemical composition
benötigt.
— Contribution from non-ice material
on the surface
— Isotopic composition of major
species
Moscow 4–8 Mar 2013
Moscow 4–8 Mar 2013