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Mercury surface erosion and sun-induced exospheric escape

Mercury surface erosion and sun-induced exospheric escape Stefano Orsini, Anna Milillo, Alessandro Mura @INAF-IFSI, Roma, Italy. Mercury has an extremely thin mantle/crust, so that it is the densest terrestrial planet in the solar system.

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Mercury surface erosion and sun-induced exospheric escape

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  1. Mercury surface erosion and sun-induced exospheric escape Stefano Orsini, Anna Milillo, Alessandro Mura @INAF-IFSI, Roma, Italy 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

  2. OUTLINE 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.

  3. [Newkirk, Jr.: Geochi. Cosmochi. Acta Suppl., 13, 293301; Kulikov et al.: PSS, 54, 1325, 2006] Evolution of the Solar Radiation and of the Solar Wind [Guinan and Ribas: ASP, 269, 85 – 107, 2002] [Ribas et al.: ApJ, 622, 680 – 694, 2005] Total Luminosity Energetic Radiation Solar Wind Velocity

  4. 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 EST application: escape rate estimate Only 3 processes considered: PSD, IS, TD

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

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

  7. 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

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

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

  10. 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

  11. 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

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

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