The Planets. The Terrestrial Planets. Admin. 9/19/17. Key Concepts: Lecture 13. Formulae (will be displayed for you in Midterm 1):

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1 Admin. 9/19/17 1. Class website 2. Optional Discussion sections: Tue. ~11.30am (period 5), Bryant 3; Thur. ~12.35pm (end of period 5 and period 6), start in Pugh 170, then Bryant 3 [only Tue. discussion this week] 3. Office hr: Tuesday pm; Wed pm, Bryant 302 (but me if coming on Wed.). [only Tue. office hr. this week] 4. Reading this week: Chapters 0, 1, , 4.1, 5, 6 5. Midterm 1: Thur. Sept. 21st, in class BRING YOUR UF ID TO THE EXAM. For review go to Discussion Sections or Office Hrs. Best preparation is to review class notes (up to & including Lecture 12) and homework & quizzes, then also the textbook. You will not be able to use a calculator or refer to your class notes in the exam. You will receive a list of formulae (see next slide). Exam is multiple choice, similar to HWs. Bring a pencil. 6. Observing project deadline: Thursday Oct. 26th 2017, however, you are strongly advised to complete observing by Fri. Oct. 6th. 7. me Astro-news, jokes, tunes, images: ast1002_tan-l@lists.ufl.edu 8. Printed class notes? Name tags? Key Concepts: Lecture 13 Terrestrial Planets: Overview - How do the properties of planets depend on their mass? Mercury Formulae (will be displayed for you in Midterm 1): Speed = distance / time Angular size: θ = size / distance Kepler s 3rd Law: P 2 = a 3 [ Newton s version of Kepler s 3rd: P 2 a 3 /(m 1 +m 2 ) ] Newton s 2nd Law: F = m a Newton s Law of Gravity: F m 1 m 2 / r 2 The Planets The Terrestrial Planets Density = mass / volume Volume of a sphere = (4/3)πr 3 Surface area of sphere = 4πr 2 Frequency: f = 1/Period Speed of wave (light) = frequency x wavelength: c = f λ

2 Mercury - Overview Closest planet to the Sun: a=0.4au Only a little bigger than the Moon Property Mercury Earth Radius 2430 km 6378 km Mass 3.3 x Kg 6.0 x kg Density 5430 kg/m kg/m 3 Escape Speed 4.3 km/sec 11.2 km/sec Atmosphere (Very thin!!) Sodium, Potassium Nitrogen, Oxygen Magnetic Field 3.0 x 10-7 T 4.0 x 10-5 T Basically no atmosphere Orbit and Rotation Orbital Period = 88 days Most eccentric orbit of any planet 46 million km to 70 million km Sunlight varies by factor of 2.3 [INVERSE SQUARE LAW FOR FLUX Flux from Sun = Luminosity/(4πr 2 ), where r is distance from Sun; we will discuss later in class] Was found to precess more than Newton s Laws would predict Planet Vulcan? Never found Einstein's Theory of Relativity is the explanation (more later in the class) Rotation = 59 days Rotates 3 times in 2 orbits This synchronization is due to tidal effects from Sun Exploration of Mercury Telescopic Observations Very difficult to observe since it is always near the Sun Giocanni Schiaparelli made a map of subtle dark and bright areas (1877) Space craft exploration Mariner 10 ( ) Messenger (2008+) Structure of Mercury No seismic data Small planet - interior will be relatively cool and solid Large metal core Density roughly equal to Earth Mercury has less gravity so material will be compressed less Thus metallic core should be relatively larger than Earth s Thin solid mantle

3 Surface of Mercury Similar to Moon Lots of impact craters Surface is very old No plate tectonics Craters flatter & have thinner ejecta rims than lunar craters - due to higher gravity on Mercury than on the Moon Some large filled basins similar to lunar Maria (but not as extensive) Less cratered and younger Probably filled with lava from mantle - after large impact Scarps - Cracks and cliffs in the crust; Young - few craters cut them; Probably due to Mercury shrinking as its core cooled not due to plate tectonics Scarp Water on Mercury? Polar craters never have sunlight in them Radar maps from the Earth see: Pole is a bright region of planet Could be frozen water Mercury s Atmosphere North Pole Very, Very thin!!! Basically no atmosphere, because very hot surface with low escape velocity. Large temperature changes: Day = 700K; Night = 90K Small amounts of some elements are trapped from solar wind Sodium and Potassium (gas phase metals) most abundant in the atmosphere From surface impacts or solar wind - Overview Smaller than Earth Two very small moons Property Earth Radius 3397 km 6378 km Mass 6.4 x kg 6.0 x kg Density 3040 kg/m kg/m 3 Escape Speed 5.0km/sec 11.2 km/sec Atmosphere Carbon dioxide, Nitrogen Nitrogen, Oxygen

4 Early Earth-Based Telescopic Exploration of Giovanni Schiaparelli mapped bright and dark regions saw polar caps which changed with seasons Surface colors appeared to change Plant life? identified long narrow features (channels - canale) Percival Lowell ( ) Built observatory in Flagstaff to study Thought the canals were used by a civilization to bring water to a desert planet Spirit & Opportunity Spirit travelled ~5 miles; Opportunity ~15miles Evidence liquid water was once on Space Craft Exploration of [You do not need to remember all the details of these missions] 1965 Mariner 4, 6 & 7 flew by Craters 1971 Mariner 9 orbited and mapped in detail Valleys and volcanoes July 20, 1976 Viking 1 landed on Searched for life Pathfinder (1997) placed a small rover on to study the chemistry of its rocks Rovers, Spirit and Opportunity (2004) Phoenix lander (2008) Curiosity (2012) Astro News

5 Curiosity Structure of Relatively low density compared to earth Small dense core Thick mantle global surveyor found a very weak magnetic field (1997) Liquid/rotating core

6 The Surface of It really is red Due to iron oxide (Rust!) Lots of loose rocks and sand Loose sand from wind erosion blows and drifts around rocks Loose rocks from impacts flooding etc. The Surface of No evidence of plate tectonics (e.g., no horizontal motion of the crust) Impact craters Surface is old and heavily cratered Some are eroded Volcanoes on Volcanism is not as wide spread on as on Earth A few large Volcanoes Olympus Mons 24 km high (78000ft) 500 km in diameter All located on Tharsis bulge Why so big? lower gravity hot spot stayed in one place - no continental drift thicker mantle to hold it up The Surface of - Valleys Valles Marineris 4000 km long 2-7 km deep Large crack Due to stretching and cracking when Tharsis bulge formed Not due to water flow

7 Surface of Flood Plains and River Systems Many flood plains and river systems Liquid water certainly flowed over much of Many are old (~4 billion years) i.e. cratered. Liquid water on today? Possible recent flows of water Wind Features Sand dunes and erosion features Wind erosion features are due to loose dust blowing around objects These are very wide spread Seasonal dust storms occur with very high winds when is warmest The Face on One Viking orbiter image revealed a mountain that looked somewhat like a monkey face Commented on in a NASA press release Immediately seized by tabloids Taken by some as proof that an advanced civilization existed on Example of how our minds find familiar patterns Resolution: each pixel = 43m

8 The Face with Global Surveyor Resolution: each pixel = 1.5m The Atmosphere of Low density: only 1% of Earth s atmosphere CO 2 (95%), Nitrogen(3%), O 2 (.15%) Due to lack of large scale volcanism to return CO 2 to atmosphere Weak greenhouse effect Temperature range: 150K to 295 K Only about +5C warmer than without Large dust storms When Mariner 9 arrived surface completely covered by dust Explanation of color changes rather than plants Seasonal: occur when is heated most by the Sun Ice Caps on The Moons of Northern ice cap is much larger than southern ice cap We re not sure why. Composed of C0 2 ice & some water ice Size varies with season Seasons on are due to its axial tilt and somewhat elliptical orbit tilt of orbital axis is primary cause CO 2 in northern hemisphere completely sublimes in summer leaving mostly water has two very small moons Phobos and Deimos 27 and 15 km across Do not look like our Moon Too small for their gravity to make them round Cratered and very irregular Origin May be fragments from a moon-asteroid collision Phobos Deimos

9 Open Questions About Are there still active volcanoes? Where has the water gone? How much sub-martian water is there? Could there be life hiding some place on? Humans to? Discussed in class Life on? Viking landers performed experiments to test for presence of microbial life - inconclusive. Claims of microbial structures in a Martian meteorite: inconclusive.