2. 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

3. 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

4. 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 LuminosityEnergetic Radiation Solar Wind Velocity [Guinan and Ribas: ASP, 269, 85 – 107, 2002] [Ribas et al.: ApJ, 622, 680 – 694, 2005]

5. EST application: escape rate estimate INPUT DATA ASSUMPTIONS (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

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

7. Mercury exospheric profiles: solar conditions: today Ion Sputtering Photon-stimulated Desorption Thermal Desorption,

8. Mercury O Exospheric Loss rates: Solar Conditions: today R M = 2440 km = 2440000 m S M = 4*pi* R M 2 = 7.481E13 m 2 d s = 2 g/cm 3 = 2000 kg/m 3 Gy=3.157E+16 s Erosion = Er (m/Gy)= rate/(S M * d s )*1Gy = rate * 0.211 IS + PSD + TD Rate (part/s)Rate (Kg/s) Jeans Escape0.45165E+270.11996E+02 Photoionisation0.78408E+260.20825E+01 Total5.3E+2614(Er=3m/Gy)

9. Mercury O Exospheric Profiles: Solar Conditions: 4,5 Gy ago Thermal Desorption Photon-stimulated Desorption Ion Sputtering

10. Mercury Surface O Particle Escape Solar Conditions: TODAY Mercury Surface O Particle Escape Solar Conditions: 4,5 Gy Ago

11. ISRate (part/s)Rate (Kg/s) Jeans Escape0.34292E+300.12606E+04 Photoionisation0.26528E+290.94205E+03 total3.7E+292200 PSD Jeans Escape0.45979E+280.12212E+03 Photoionisation0.16460E+310.43717E+05 total1.6E+3043840 TD Jeans Escape0.58323E+130.15491E-12 Photoionisation0.76708E+230.20374E-02 total7°.7+230.0002 Total2.0E+3046040(Er=10km/Gy) Mercury Exospheric O Loss rates: Solar Conditions: 4,5 Gy ago R M = 2440 km = 2440000 m S M = 4*pi* R M 2 = 7.481E13 m 2 d s = 2 g/cm 3 = 2000 kg/m 3 Gy=3.157E+16 s Erosion = Er (m/Gy)= rate/(S M * d s )*1Gy = rate * 0.211

12. 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

13. MANY THANKS FOR YOUR ATTENTION! SPECULATIONS? SO MANY.....