Mercury has an extremely thin mantle/crust, so that it is the densest terrestrial planet in the solar system.

May sun-induced loss processes be considered as responsible for Mercury surface erosion?

Not proved, but… this is a fascinating hypothesis, which needs observations

OUTLINE• In this presentation, we approach the Hermean surface

evolution task by applying the Environment SimulationTool (EST) developed by Mura et al (2007), able to derive the exospheric profiles (both gravitationally bound and escaping), depending on external input parameters (surface composition, solar and space conditions, etc.).

• In view of a more refined calculation, we now simply apply EST to the O component by using two different solar conditions: the present one, and the one expected at the solar system formation, about 4.5 Gy ago.

• No other assumptions, (e.g.: related to the possible different evolving planet characteristics) have been presently considered, but they will be added in the future.

OUTLINE

Evolution of the Solar Radiation and of the Solar Wind

[Newkirk, Jr.: Geochi. Cosmochi. Acta Suppl., 13, 293301; Kulikov et al.: PSS, 54, 1325, 2006]

Total Luminosity Energetic Radiation

Solar Wind Velocity

[Guinan and Ribas: ASP, 269, 85 – 107, 2002]

[Ribas et al.: ApJ, 622, 680 – 694, 2005]

EST application: escape rate estimateINPUT DATAASSUMPTIONS

• (Young Sun) UV Radiation: Actual * 100 Luminosity Actual – 30% SW vel Actual * 4 SW dens Actual * 100• (Exosphere) Ionisation lifetime Actual / 100• (Soil) Soil density 2 g/cm^3 Oxygen abundance 50% Binding Energy 3 eV Only 3 processes considered: PSD, IS, TD

EST: PSD and IS exospheric refilling. Profiles vs, some external solar

parameters

Mercury exospheric profiles: solar conditions: today

Ion SputteringPhoton-stimulated Desorption

Thermal Desorption,

Mercury O Exospheric Loss rates: Solar Conditions: today

RM= 2440 km = 2440000 m SM= 4*pi* RM2 = 7.481E13 m2

ds= 2 g/cm3 = 2000 kg/m3 Gy=3.157E+16 s

Erosion = Er (m/Gy)= rate/(SM* ds)*1Gy = rate * 0.211

IS + PSD + TD Rate (part/s) Rate (Kg/s)Jeans Escape 0.45165E+27 0.11996E+02

Photoionisation 0.78408E+26 0.20825E+01Total 5.3E+26 14(Er=3m/Gy)

Mercury O Exospheric Profiles: Solar Conditions: 4,5 Gy ago

Thermal Desorption

Photon-stimulated DesorptionIon Sputtering

Mercury Surface O Particle EscapeSolar Conditions:

TODAY

Mercury Surface O Particle EscapeSolar Conditions:

4,5 Gy Ago

IS Rate (part/s) Rate (Kg/s)Jeans Escape 0.34292E+30 0.12606E+04

Photoionisation 0.26528E+29 0.94205E+03total 3.7E+29 2200PSD

Jeans Escape 0.45979E+28 0.12212E+03Photoionisation 0.16460E+31 0.43717E+05

total 1.6E+30 43840TD

Jeans Escape 0.58323E+13 0.15491E-12Photoionisation 0.76708E+23 0.20374E-02

total 7°.7+23 0.0002

Total 2.0E+30 46040(Er=10km/Gy)

Mercury Exospheric O Loss rates: Solar Conditions: 4,5 Gy ago

RM= 2440 km = 2440000 m SM= 4*pi* RM2 = 7.481E13 m2

ds= 2 g/cm3 = 2000 kg/m3 Gy=3.157E+16 s

Erosion = Er (m/Gy)= rate/(SM* ds)*1Gy = rate * 0.211

CONCLUSIONS

• We have applied the EST code developed by Mura et al (2007), to derive the escaping O intensity using two different solar conditions: the present one, and the one expected at the solar system formation, about 4.5 Gy ago.

• Significant differences have been noticed, so that the mass amount eroded by the young sun is quite significant (about 10 km/Gy); whereas at present the erosion rate is of the order of a few meters/Gy

• These calculations encourage to further refine our approach, in order to get a more reliable result

MANY THANKSFOR YOUR ATTENTION!

SPECULATIONS?SO MANY.....