Facilitating Mercury surface process
and exosphere generation research
H. Todd Smith & Strofio
Team
JHU APL (Strofio)
Mercury Exosphere - Magnetosphere Coupling
Workshop : 3 November 2010
Introduction

Mercury exospheric generation is dependant on
many surface processes (sputtering, TD, MIV,
PSD, ESD…)

Our understanding of these processes is rapidly
evolving

Accurate understanding of surface source
processes are essential for interpreting
exospheric and surface observations

Exospheric models are very sensitive to
representations of these processes

Therefore, we are preparing surface and
exospheric models to enhance utilization of
Strofio (neutral particle time-of-flight mass
spectrometer) on Bepi-Columbo
H. Todd Smith
Accurate understanding of surface
processes is essential:
Current data is limited

Theoretical formulas often used for sputtering with
assumed binding energy
• f(E) ~ Ey /(E + U)x ; often x ~ 2- 3 and y ~0-1
• U is related to the surface binding but often just a fit parameter

Lab results are more accurate but most deal with ices
(when we do have experimental results they often differ
noticeably from theoretical results; for metals the
situation is better)

Little current experimental results dealing with regolith
• surface chemical properties and porosity can affect yields and
energy spectra of ejecta significantly
H. Todd Smith
Accuracy of surface processes is
essential: Sputtering example

Small changes in U, the binding energy,
can have large impact on spatial distribution of the ejecta
Frame 001  28 Oct 2010  Converted Excel Data
Frame 001  28 Oct 2010  Converted Excel Data
Na/cc
3
1.0E+01
1.5E+01
2.3E+01
3.5E+01
5.3E+01
8.0E+01
1.2E+02
1.8E+02
U=2.0 eV
Na/cc
2.8E+02
3
1
1
Y (Rm)
2
0
-1
-2
-2
Sun
-2
2.3E+01
3.5E+01
5.3E+01
8.0E+01
1.2E+02
1.8E+02
U=1.6 eV
2.8E+02
0
-1
-3
-3
1.5E+01
Co-rotation
2
Sun
-1
0
1
-3
-3
Na observations over 1 orbit
2
3
X (Rm)
-2
-1
0
1
2
3
X (Rm)
350
300
250
Na/cc
Y (Rm)
Co-rotation
1.0E+01
200
150
U=2.0 eV
100
U=1.6 eV
50
0
0
10
20
30
40
50
60
Time step
H. Todd Smith
Temporal/spatial variations complicate
things even more
Co-rotation
Sun

Nominal Na distribution for a 2500 m/s source
over one mercury orbit
H. Todd Smith
Establishing a website

The most accurate and up to date understanding of
current state of knowledge is essential for Mercury
data interpretation & research

With these issues in mind, we intend to set up a
website for Strofio but want to open up it to
community

Central database for easy determination of what we
currently know and still require (assist laboratories)

Include data and models for different surface
compositions

Possibly allow individuals to place their models on
site with other users comments and critiques
H. Todd Smith
What we want to store

Sputtering/desorption (ions, electrons, photons)
• Vs. energy, temperature, mineral type
• Ejecta: yields, composition, charge (energy
spectra)

Adsorption: chemical & physical
• Roles of defects & porous regolith

Radiation enhanced diffusion & effects of charging

Connect to reflectance spectra

Effect of surface charging
H. Todd Smith
Summary

The proposed website is being constructed for
Strofio but we hope it may be of use to the
community

Feel free to contact us for more information or
with any questions (h.todd.smith@jhuapl.edu)

Stay tuned…
H. Todd Smith