Topography of MercuryCourse AnnouncementsAssignmentsMercury’s Orbit and RotationMercury’s Orbit and RotationMercury’s Orbit and RotationSurface of MercurySurface of Mercury - ScarpsSurface of Mercury - HollowsCaloris Basin, MercuryCaloris Basin, MercuryMercury – Permanently-shadowed craters… water ice?Mercury AtmosphereMercury’s strange interiorEvolution of MercuryEvolution of MercuryEvolution of MercuryEvolution of MercuryEvolution of MercuryChapter 9Venus vs. EarthVenus Data Sheet IVenus Data Sheet IIVocabulary Aside: AlbedoOrbital Properties of VenusOrbital Properties of VenusRetrograde RotationSolar Day of VenusGlobal Views of Venus – Visible LightUV Global View of Venus - CloudsRadio Global View of Venus - SurfaceSurface of VenusSurface of VenusSlide 34Lakshmi PlanumOvda RegioLava FlowsTopography of MercuryCredit : NASA/MessengerCourse Announcements•Thanksgiving Week planningNo classes Wednesday, 23 Nov.•Exam 2 grading underway–Expect to hand them back on Friday•Extra Credit sessions still underway– 2 More this week (Night and Solar)–Only 2 more weeks of EC sessions (last day 18 Nov)•Quiz 5 next Wednesday, 9 Nov.–Hints on Friday and MondayAssignmentsReading Assignments•Chapter 9: Sections 9.1 – 9.4[Read by Friday, 4 Nov.]•Parallel LecturesCC Astronomy Episode 14: Venus[Watch before Friday, 4 Nov.]Mastering Astronomy•Chapter 8 Homework[Due Wed., 2 Nov. at 11:59 PM EDT]Mercury’s Orbit and Rotation•Mercury’s large eccentricity (e = 2.01) combined with the tidally-locking process to the Sun, give Mercury a 3:2 spin-orbit resonance.•The 3:2 spin-orbit resonance gives a Mercurian solar day (noon-to-noon) of two Mercury years, or 176 days.•It gets stranger…The 3:2 spin-orbit resonance gives Mercury the strangest day in the Solar SystemMercury’s Orbit and Rotation•The 3:2 spin-orbit resonance gives a Mercurian solar day (noon-to-noon) of two Mercury years, or 176 days.•It gets stranger…The 3:2 spin-orbit resonance gives Mercury the strangest day in the Solar SystemMercury’s Orbit and Rotation•Because of Mercury’s faster and slower orbital motion but constant rotation rate, during one of these extremely long days, there will be a brief period where the Sun appears to “move backwards” from its normal east-to-west motion.–If you positioned yourself at just the right spot on the surface, you could watch the Sun rise, immediately turn around and set, and then rise again!The 3:2 spin-orbit resonance gives Mercury the strangest day in the Solar SystemSurface of Mercury•Similar to the Moon’s cratered highlands, Mercury’s surface is dominated by impact craters (Named after artists, writers, musicians, etc.)–Mercury’s craters are less densely packed•Between craters there are gently rolling intercrater plains covering some 40% of the planet’s surface–Oldest visible part of the surface forming roughly 4 billion years agoSurface dominated by craters and intercrater plainsSurface of Mercury - ScarpsRight: Long (~ 200 km) scarp in the Rembrandt Impact Basin on Mercury•Scarps on Mercury can stretch hundreds of km and be as high as 3km–Called Rupes and named after ships•Cut across ancient craters indicating shrinkage occurred after Late Heavy Bombardment•That’s right, the scarps are caused by the Mercury shrinking (it still is!) as it cools and becomes more solid.Mercury also shrunk while cooling, but to a much greater extant than the Moon.ScarpSurface of Mercury - Hollows•Hollows are dark, steep-walled pits•Appear in or near crater rims and floors•Bright and fresh appearance suggesting current formation•Lack of superimposed craters suggesting current formation–Above two suggest they are very young in age.•May be exposed volatiles being eroded away by solar interactions–Details still not understoodUnique geologic feature to Mercury. Exact cause is under investigationCaloris Basin, Mercury•Caloris Basin (“Hot” basin) is the largest single surface feature, and it is an crater impact basin•Ringed by concentric mountains up to 3 km high•Directly opposite side of planet (i.e., antipodal) has an oddly rippled, wave, and jumbled terrain, called the weird terrain,–seismic waves ‘focusing’ on the directly opposite the impact site (on the other side of the planet!!!)Most prominent geologic feature. A 1400 km basin through to be caused by a giant impact. Falsely colored for emphasisCaloris Basin, MercuryNamed Caloris because Mercury gets so hot… and caloris means hot.The “Weird” TerrainThe focusing of seismic waves on opposite side jumbled the crust breaking it into a series of complex blocks seen as “hilly” terrain.800 kmMercury – Permanently-shadowed craters… water ice?A snowball’s chance in hell might actually be pretty good •Like, the Moon, Mercury has permanentely-shadowed craters at the poles•Red regions are areas entirely shadowed during Messenger Yellow regions are radar bright regions•Best explanation: Water-ice•Correlate to ‘slow’ neutrons released from surface (indicates hydrogen)–No smoking-gun definitive proof yetUpdated from Chabot et al. (2012). NASA/JHUAPLMercury AtmosphereIf you can call it that…•Non-permanent atmosphere generated by the Solar Wind, cosmic rays, and micrometeor impacts•Very trace amounts of Hydrogen, Helium, Oxygen, Sodium, Calcium, Potassium •10-14 atmospheres (100,000 billionths of Earth’s atmosphere)•Escapes to space on short timescales. NO PERMANENT ATMOSPHERECredit:NASA/ JHUAPLMercury’s strange interior•Huge iron core: ~ 2100 km–May be totally or partially molten–85% of the diameter of Mercury•Thin and iron-poor mantle and crust: approximately top 400 km•Weird rotational inertia indicate a very strange layer of iron-sulfide (FeS; troilite) between core and mantle•Most complicated terrestrial planet interiorExtraordinarily large iron core! Accounts for up to 85% of the diameter!Evolution of Mercury•After formation, Mercury melted and differentiated –internal heating from radioactivity and leftover heat from formationFormation of Intercrater Plains1. Being more massive than the Moon, it cooled slower and had a thinner crust when the Late Heavy Bombardment pummeled the surface with large impactors–Cracked the crust like formation of lunar maria, but the crust was thinner and higher percentage still molten led to filling and overflowing of crater basins resulting in “flood volcanic
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