Hermean sputtering:

SERENA/ELENA

Simulated

observation

Conf. Planetologia, S.Felice irco06/09/2006

Solar wind

ionsions

SurfaceSurfaceIon SputteringIon Sputtering

eV ENA

KeV ENA

ENA features in the solar system

Exospheric gasExospheric gasCharge-ExchangeCharge-Exchange

AtomosphericAtomosphericSputteringSputtering

eV ENA

Neutral Solar wind

Magnetized bodies (Earth, Mercury, Jupiter, Saturn…)Magnetospheric Plasma Circulation

Charge exchange! Non-magnetized bodies with atmosphere (Mars, Venus…)

Solar wind-induced neutral gas escapeCharge exchange & sputtering!

Bodies without atmosphere (Mercury, Moon, Asteroids…)Solar wind-induced surface erosion

Sputtering! Solar wind acceleration region & heliospheric border

Neutral SW, SW - interstellar gas interaction Charge exchange!

PROCESSES INVESTIGATED VIA ENARemote sensing of:

Astrid (SAC-B)

Cassini IMAGE Doble StarMars ExpressVenus ExpressTWINSChandrayaan !IBEX !BepiColombo !Solar Orbiter !?Kua-Fu ?Laplace (Europa Orbiter) ?MarcoPolo ?Tandem ?

ENVIRONMENTS I

NVESTIGATED V

IA H

IGH ENERGY ENA

SOLAR ORBITER

Sun and corona traced by NSWD

coronal hole

Solar Orbiter / SCENARIO

Neutral Solar Wind

Detector (NSWD)(S. Orsini, M. Hilchenbach, J.K. Hsieh, A.M. Di Lellis, M. Collier, A. Czechovski, I. Dandouras, R. D’Amicis, M. Gruntmann, G. Ho, S. Habal, E. Kallio, S. Livi, A. Mura, P. Wurz, et al.) Beyond 3 solar radii, the neutral atoms become more and more decoupled from the plasma of the solar corona. The neutral solar wind constitues an in-situ trace particle population of the solar wind plasma.

The expected neutral atom flux

is about 103 atoms cm-2 s-1, at 0.21

AU, but it could increase up to 104-

105 atoms cm-2 s-1 during Coronal

Mass Ejections (CME).

Angular resolution ~ 1°Field-of-view = 7°Aberration = 9.2°(Vsw = 400 km/s, Vorbiter = 65 km/s)Aberration = 4.6°(Vsw = 800 km/s and Vorbiter = 65 km/s)

FUTURE APPLICATIONSImaging of the SW Expansion

Pseudo-color map of ENA differential flux as a function of angle from Sun’s direction (in degrees) for different models. The azimuth angle is along the ecliptic plane and the elevation angle is across the ecliptic plane. Flux is integrated over all energies (upper panel). Bottom panels are for the Solar Orbiter reference frame during the corotation phase (i.e. with the aberration effect included).

FAST WIND SLOW WIND

Fast, reference Fast, Allen Slow, reference Slow, Lie-Svendsen Our approach Allen et al (2000) Our approach Lie-Svendsen et al (2003)

… IMAGING THE NEUTRAL SOLAR WINDSignal simulation vs 2 different sw models

Ion Sputtering

2

1

3 1)(i

be

be

ee E

EE

EE

EEF

0

1ee dEEF

Ei incident particle energy 800 - 1600 eVEb binding energy 1 eVEe Energy of the released particleTe Exospheric temperature T

1E-001 1E+000 1E+001 1E+002 1E+003Energy, eV

1E-006

1E-005

1E-004

1E-003

1E-002

1E-001

1E+000Energy distribution

Lammer and Bauer (1997), Planet. Space Sci., 45, 73-79

Na – 1600

Na -800

Ion sputtering products depend on:• the composition and the chemical structure of the surface; • the impinging plasma flux.The basic quantities of interest are: • the composition of the ejected particles • the space flux distribution and the space density distribution of the sputtered particles

Production of ENA from bombardment of a surface by energetic ions

: asteroid or comet nucleus in an evolving population with a lifetime limited to a few million years and an

orbit with perihelion distance <1.3 AU

Near Earth Object (NEO)

NEOs appear heterogeneous in shapes, sizes, spin rates and compositions.they offer clues to the chemical mixture from which the planets were formed carry records in the interplanetary space from - the Solar System’s birth and early phases - the geological evolution of small bodies

Current knowledge

NEO (433) Eros (John Hopkins

University)

CI chondrite - type NEO surface

Sputtering is considered as the only source for neutral particle production

Results of the MC simulations

Results – Discussion

• Particles fluxes (up to 1011 particles m-2 s-1) appear in a region up to 1 km above the NEO surface (in the solar wind direction).

• Maximum density (~ 106.5 particles m-3) appears in a region extending from the NEO surface up to an altitude of about 0.7 km above (in the solar wind direction).

x particles m-2 s-1

x particles m-3

I-S Directional NA from Europa C-E ENA from plasma – tori

interaction

C-E ENA from auroral regions

The Natural Satellites Emissivity in the Jovian System

EUROPA

Disrupted ice crust in the Conamara region of Jupiter's moon Europa (NASA courtesy)

Surface composed mainly by water ice and other components as Na, K, etc... Na and K atmosphere has been observed (Brown and Hill, Nature, 1996; Brown, Icarus, 2001)

Ion flux @ Europa

Energetic ion fluxes observed by Galileo spacecraft impacting on the surface of Europa.(Paranicas et al., GRL, 2002)

H+ O+ S+

Ion-sputtering .The emitted flux is

proportional to the yield, much higher for higher energies and for heavier

ions. (Baragiola et al., NIM B, 2003)

The Natural Satellites Emissivity in the Saturnian Sysytem

Exobase ~ 1500 km altitude

Atmosphere ~ mainly N2

Two different incident particles:

• protons H+ deriving from the solar wind and from Saturn’s magnetosphere

• nitrogen ions N+ of the Saturn’s magnetosphere.

(Garnier et al., 2007)

Titan

Atmospheric SputteringSame process as surface

sputtering, but acting on atmospheric particles. Particles may escape directly or after a series of bouncing.

At Titan, the atmospheric sputtering is the most efficient escape mechanism (Lammer and Bauer, 1993)

(Shematovich et al. JGR, 2003)

H+ N+

ANGLE

ION ENERGYANGLE

ION ENERGY

Our analysis of atmospheric sputtering on Titan, using previous theory and newly data, allow us to be confident in a very high efficiency of the process

Y ~ 1÷10 for H+

Y >10 for N+

Our simulation

Energy and pitch angle spectra

Yields

PROCESSES IN THE HERMEAN ENVIRONMENT

GOING TO MERCURY WITH BEPICOLOMBOGOING TO MERCURY WITH BEPICOLOMBO

…ARE ION SPUTTERING AND PSD RELATED TO EACH OTHER?

See presentation from a. mura during this conference

New prospect: ENA direct detectionBepiColombo / SERENA - ELENA is a Time-of-

Flight Detector, based on the state-of-the art of ultra-sonic oscillating micro-shutters (>100 kHz) and mechanical gratings.

Energy range: <20eV-5keV.

STOP detector

Shuttering membrane

Position encoder

START section

ToF chamber

ENA flux

Fixed membrane

Sputtered O imagesimulation, polar

viewSputtered signal detection by the

SERENA/ELENA unit(simulation)

Nowadays, more and more interest is growing about the capabilities of investigating crucial aspects of the particle regimes present in the solar system by means of ENA detection.

These studies range form the properties of the

expanding corona, to the escape of matter from the planetary surfaces; from the plasma distributions in the magnetospheres to the interaction between solar and interstellar matter; from the characteristics of escaping fractions of the planetary atmospheres, to the transfer of energy to the internal atmospheric regions.

Such an increase of interest in ENA signal detection is pushing the technological community to produce more and more sophisticated devices, able to accomplish the scientific goals over a wide spectrum of energies and mass species.

S U M M A R Y

MANY THANKSFOR YOUR ATTENTION!