The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

OUTLINEOUTLINE

•General scientific aspects: Mercury’s General scientific aspects: Mercury’s Exosphere.Exosphere.

•Surface emission: Ion Sputtering and Surface emission: Ion Sputtering and BackscatteringBackscattering

•ELENA Instrument description (part of ELENA Instrument description (part of the BepiColombo/SERENA suite)the BepiColombo/SERENA suite)

Plasma

ionsions

keV ENA

Plasma-airless bodies interaction

Charge-ExchangeCharge-Exchange

SurfaceSurfaceIon-SputteringIon-Sputtering

10s eV ENA

ionsions

SurfaceSurfaceIon-BackscatteringIon-Backscattering

100s eV ENA

The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

SW precipitation

(Massetti et al, 2003)

BIMF =(0,0,-10) nT

BIMF =(0,5,-10) nTPdyn=16 nPa

BIMF =(0,5,-10) nTPdyn=60 nPa

Flux(cm

-2 s sr keV)

-1

The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

Solar wind impact on a surface

An ion impacting (1) on the surface produces different effects:(2) back scattering, (3) neutralization and back scattering, (4) surface ion sputtering(5) electron emission (6) photon emission (7) adsorption (8) chemical sputtering: displacement and change of the surface mineralogy

The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

•Reflection•Backscattering

•Ion sputtering•Chemical sputtering.

Solar wind impact on a surface

The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

Surface Ion Sputtering process

Ion sputtering products depend on:• the composition and the chemical structure of the surface; • the impinging plasma flux.

Surface release of neutrals due to energetic ion impacts

The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

Back-scattering from the Moon

•The BS energy spectrum goes up to almost 1 keV (Wieser et al., 2009)•The backscattering reflection yield is between 10-20% (Mc Comas et al., 2009)

The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

Energy distribution of sputtered particles

H escape O escape

Ca escape

Fe escape

Ca O HFe

The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

Surface release processesDifferent release processes can have different efficiencies as a function of latitude and longitude/LT at Mercury due to surface compositions and mineralogy together with external conditions, as solar irradiance or plasma precipitation. (from Killen and Ip, 1999)

The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

Generally, the upper part of the atmosphere where the column density is so low (less than 1014 cm-2) that the collision frequency between particles becomes negligible. Exobase is the boundary between collisional and not collisional regimes (Earth case: about 500 km altitude).

In the case of absence of an atmosphere (Mercury case), we refer to surface-bounded exospheres. It is the result of a complex dynamic equilibrium with the surrounding systems, mainly: surface, magnetosphere and outer space. In this case the exobase is considered the surface itself.

Exosphere

The exosphere is the boundary between the planet and the open space. So its investigation is a way to know the mechanisms and interactions acting today as a proxy of what happened in the ancient times.

The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

Sputtered High Energy AtomsWhy do we wish to detect SHEA (neutrals at energies >10 eV) to investigate the ion sputtering process?Because below 10 eV the ion-sputtering

products mix to other release process, and the particles do not maintain the initial direction (due to gravitational effects) so that the emission location on the surfaces cannot be easily recognized (Milillo et al., 2011).

The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

(Environment Simulation Tool@IFSI)The Goldel Age of Solar System

Exploration

Particles released at different energy rangesEnergy range: <0.06 eVEnergy range: 0.06-0.3 eVEnergy range: 0.3-1.5 eVEnergy range: 1.5-10 eVEnergy range: 10-40 eVEnergy range: 40-200 eVSHEA detection provides a map of

plasma precipitation regions and an imaging of particle emission from surface.

Stefano Orsini

Settembre 2012

Instrument package on board BepiColombo/MPO

SERENASearch for Exospheric

Refilling and Emitted Natural

Abundances

Units:ELENA: Emitted Low-Energy

Neutral Atoms

STROFIO: Start from a ROtating FIeld spectrOmeter

MIPA: Miniature Ion Precipitation Analyser

PICAM: Planetary Ion CAMera

The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

ELENA is a Time-of-Flight (TOF) system, based on oscillating shutter (operated at frequencies up to a 100 kHz) and mechanical gratings: the incoming neutral particles directly impinge upon the entrance with a definite timing (START) and arrive to a STOP detector after a flight path. In this way the low-energy neutral particles are directly detected, without using elements of interaction.

STOP detector

Shuttering membrane

Position encoder

START section

ToF chamber

ENA flux

Fixed membrane

Parameter ActualEnergy range <0.02- 5 keV (mass dependent)Velocity resolution v/v Down to 10% Viewing angle 4.5ox76o

Angular resolution 4.5ox4.5o (actual)4.5°x2.4° (nominal pixel)

Mass resolution M/M H and heavy speciesOptimal temporal resolution 40 sGeometric factor G 2. 10–5 cm2 sr Integral Geometric factor 6 10–4 cm2 sr

The ELENA Instrument

The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

ELENA START Section: shutter system

The shuttering element of the ELENA detector consists in a couple of nano-patterned self standing silicon nitride membranes, one facing the other and separated by a distance between 1 and 5 μm, in order to have the correct number of time of flight channels. One membrane is fixed while the second one is moved respect to the other by means of a piezoelectric actuator, at a frequency up to 50 kHz.

ELENA membranes are of 10x10 mm2 area, 1µm thick Si3N4 with slits of

the order of 200nm and 1,4 mm pitch.

SERENA PM#19, Milan, 22-23 May, 2012

ELENA shutter Static and dynamic High-frequency test

with ion beam

Dynamic case: V=23V: freq=42kHz

Static case: 0-100V (0-6m) piezo elongation : 3 apertures at step 1,4m.

Static test: verifies the 1.4mm pitch of the membranes; it confirms the open/closed condition inside the 24 Volt elongation available.

Dynamic test: up to 52kHz (without damage) in the requested voltage range (DV≤24V). The offset has to be optimized to see the double aperture in the oscillation.

0 20 40 60 80 100

0

500

1000

1500

2000

2500

3000V=24V

Data: Data1_BModel: Gauss Chi^2 = 13517.88693R^2 = 0.98728 y0 123.79287 ±46.18093xc 48.99452 ±0.09244w 7.04025 ±0.25959A 22993.10289 ±1019.78183

C/1

0s

Piezo Voltage (V)

Ion beam He+, 1keV15-02-2012

SERENA PM#19, Milan, 22-23 May, 2012

0 20 40 60 80 100

0

500

1000

1500

2000

2500

3000V=24V

Data: Data1_BModel: Gauss Chi^2 = 13517.88693R^2 = 0.98728 y0 123.79287 ±46.18093xc 48.99452 ±0.09244w 7.04025 ±0.25959A 22993.10289 ±1019.78183

C/10

s

Piezo Voltage (V)

Ion beam He+, 1keV15-02-2012

Static test1keV He+ beam

Dynamic test (10kHz)1keV H beam

Dynamic test (52 kHz)2keV He+ beam

The Goldel Age of Solar System Exploration Stefano OrsiniSettembre 2012

MCP EfficiencyMCP EfficiencyEfficiency measurement for the standard MCP with Hydrogen, Helium and Oxygen at energies from 10 to 1000 eV.

We can observe a good agreement with the only existing data on this argument in the range of 30-1000 eV (Stephen et al, 2000; Peko et al., 2000)

The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

Time-of-flight resolution for a membrane hole of 200 nm, 0.7 um of amplitude, and 1.5 um of membrane separation (those parameters are

best expectations from technological development) Expected ToF resolution is 1/8.

The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

Left panel: analytical prediction of countrates for Ion Sputtering signal.

Right panel: Montecarlo simulation of countrates.

The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

Left panel: analytical prediction of countrates for Ion Back-scattering signal.

Right panel: Montecarlo simulation of countrates.

The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

Noise – Background due to the neutral generation of ion-sputtering and back-scattering inside the instrument.

Simulation of SHEA detection at Mercury by

BepiColombo/MPO/SERENA-ELENA

(Orsini et al, 2008)

Thanks to the BepiColombo/SERENA package we will have simultaneous measurements of precipitating plasma (MIPA), circulating plasma (PICAM), and neutral gas composition (STROFIO) and SHEA observation (ELENA), for a complete investigation of the IS process.

The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

The Goldel Age of Solar System Exploration

Stefano Orsini

Settembre 2012

IN SUMMARY…..IN SUMMARY…..

•The exosphere of Mercury is the region where the interaction between planet and Solar System environment occurs.

•The SERENA particle suite is designed for observing this region along the BepiColombo MPO Orbit. In particular, ELENA will be able to measure the planet’s surface emission via Ion Sputtering and Backscattering, thus providing an image of the ion precipitation areas, together with an estimate of the soil emitted elements.