Astronomy 101 The Solar System Tuesday, Thursday Tom Burbine tomburbine@astro.umass

1. Astronomy 101The Solar SystemTuesday, ThursdayTom Burbinetomburbine@astro.umass.edu

2. Course • Course Website: • http://blogs.umass.edu/astron101-tburbine/ • Textbook: • Pathways to Astronomy (2nd Edition) by Stephen Schneider and Thomas Arny. • You also will need a calculator.

3. There is an Astronomy Help Desk that is open Monday-Thursday evenings from 7-9 pm in Hasbrouck 205. • There is an open house at the Observatory every Thursday when it’s clear. Students should check the observatory website before going since the times may change as the semester progresses and the telescope may be down for repairs at times. The website is http://www.astro.umass.edu/~orchardhill/index.html.

4. Exam #3 • The average was 77.3 and the grades ranged from 97.5s to a 35.

5. HW #16 • Due by April 20th at 1 pm • I will take the top 20 HWs out of 24 • As of today, HW averages range from 99.3s to a 11.3 (without dropping any scores) • If you want to make up a missing HW, you can write a 10 page paper on a planetary science subject

6. Types of Planetary Missions • Fly By • Orbiter • Lander • Atmospheric Probe • Rover • Manned • Sample Return

7. Mercury/Venus • Mercury is the closest planet to the Sun • Venus is next closest

8. Both planets will be visible to the naked eye for the next two weeks as bright, starlike objects that will dominate the low western sky shortly after sunset. http://news.nationalgeographic.com/news/2010/04/100401-mercury-venus-planets-conjunction-april/

9. http://www.skyandtelescope.com/observing/home/89279827.html

10. Mercury • orbit: 0.38 AU from Sun • diameter: 4,880 km (38.3% of Earth) • mass: 3.30 x 1023 kg (5.5% of Earth) • temperature: 90 K (minimum) 440 K (average) 700 K (maximum) • Satellites: Zero

11. Difficult to study Mercury • Because of Mercury's proximity to the Sun • makes reaching it with spacecraft technically challenging • Earth-based observations difficult.

12. Mercury • Videos • http://www.gecdsb.on.ca/d&g/astro/html/Mercury.html

13. Mariner 10 • The first spacecraft to approach Mercury was NASA's Mariner 10 (1974-1975).

15. Caloris Basin

16. Caloris Basin(Some of the hill are 1,800 meters tall)

17. Messenger data Mariner 10 data

18. Caloris Basin • A basin was defined by Hartmann and Kuiper (1962) as a "large circular depression with distinctive concentric rings and radial lineaments." • Others consider any crater larger than 200 kilometers a basin. • The Caloris basin is 1,550 kilometers in diameter, and was probably caused by a projectile larger than 100 kilometers in size. • The impact produced concentric mountain rings three kilometers high and sent ejecta 600 to 800 kilometers across the planet.

21. Weird Terrain The weird terrain is almost opposite Caloris Basin. It consists of hills, ridges and grooves that cut across craters. The weird terrain my have been formed by shock waves that raced through the center of the planet and outward early in Mercury's history.

22. Mercury has high density • Its density is 5.44 g/cm3 which is comparable to Earth's 5.52g/cm3 density. • In an uncompressed state, Mercury's density is 5.5 g/cm3 where Earth's is only 4.0 g/cm3.

24. http://www.psrd.hawaii.edu/WebImg/MercuryCore.gif

25. Magnetic Field • Despite its small size and slow 59-day-long rotation, Mercury has a significant, and apparently global, magnetic field. • It is about 1.1% as strong as the Earth’s. • Particularly strong tidal effects caused by the planet's high orbital eccentricity would serve to keep the core in the liquid state so it could have a dynamo

26. Messenger • Mission to Mercury • Launched August 3, 2004 • Flew by Mercury in 2008 and 2009 • Will orbit Mercury in 2011

28. Messenger video • A set of five 11-band images was captured by MESSENGER just after the spacecraft crossed the night/day line (the “terminator”), which are the highest-resolution color images ever obtained of Mercury’s surface. • At the beginning of this movie, it is dawn in that region of Mercury, and the Sun is just off the horizon. The long shadows that are cast by crater walls exaggerate the ruggedness of the terrain and highlight variations in topography. • Though Mercury’s true colors are subtle, the 11 color bands of MDIS were combined in a statistical method used to highlight differences in color units. Older, low-reflectance, and relatively blue material is encroached by younger, relatively red smooth plains. Several lobate scarps or cliffs are observed, which are places where compressional stresses caused Mercury’s crust to fracture and shorten. http://messenger.jhuapl.edu/news_room/presscon5_images/Robinson%20Image%205.7.mov

29. Mercury Much of the image to the right of the Kuiper crater (in the centre here) had never been imaged by a spacecraft before. Researchers were surprised to see long crater rays that extend thousands of kilometers from a crater at the planet's north pole http://space.newscientist.com/data/images/ns/cms/dn14893/dn14893-1_450.jpg

30. Mercury Dark material, shown in deep blue in the enhanced colour image at right (a composite of visible and near-infrared images), was kicked up by impacts. The material seems to be widespread but patchy, suggesting the planet's interior is not homogenous. http://space.newscientist.com/data/images/ns/cms/dn15077/dn15077-1_600.jpg

31. Mercury • Double ringed basin • 290 km in diameter • Appears young (few craters on it) • ~ 1 billion years old • Lava may have covered up the central part of the basin http://messenger.jhuapl.edu/gallery/sciencePhotos/pics/presscon6_img4_5_lg.jpg

32. 160 km in diameter http://en.wikipedia.org/wiki/File:Mercury_Double-Ring_Impact_Basin.png

33. Spectra of Mercury Weak to absent absorption features – no iron in the silicates

34. Mercury’s Surface • Possibly made of Enstatite (MgSiO3) – Mg-rich pyroxene • Possibly made of material like the Lunar Highlands • Plagioclase feldspar - CaAl2Si2O8

37. Questions: • Why does Mercury have such a large iron core?

38. One possibility • Mercury may have been struck by a planetesimal of approximately 1/6 its mass and several hundred kilometers across. • The impact would have stripped away much of the original crust and mantle, leaving the core behind as a relatively major component.

39. Venus • orbit: 0.72 AU from Sun • diameter: 12,103.6 km (94.9% of Earth) (called Earth‘s twin) • mass: 4.869 x 1024 kg (81.5% of Earth) • Temperature on surface: 726 K(average) • Satellites: Zero

41. Venus’ atmosphere • Atmospheric pressure at surface is 92 times the pressure on the Earth’s surface • Atmospheric content: • Carbon dioxide 96.5 % • Nitrogen 3.5 % • Sulfur dioxide 150 ppm • Argon 70 ppm • Water vapor 20 ppm

42. Venus’ clouds • Venusian clouds are thick and are composed of sulfur dioxide and droplets of sulfuric acid. • These clouds reflect about 75%of the sunlight that falls on them,

43. Greenhouse Effect • The greenhouse effect is the rise in temperature that a planet experiences because certain gases in the atmosphere (H2O, CO2, CH4) trap energy emitted from the surface. • Visble light hits the surface • Surface warms and emits infrared radiation • Atmospheric gases absorb some of the infrared light • Surface and Atmosphere heat up

45. Stefan-Boltzman Law Emitted power (per square meter of surface) = σT4 λ·Tmax = 2,900,00 nm

48. Runaway Greenhouse Effect • Runaway greenhouse effect to describe the effect as it occurs on Venus • Venus is sufficiently strongly heated by the Sun that water is vaporized and so carbon dioxide is not reabsorbed by the planetary crust