Figure 6.1B

1. Figure 6.1B

2. Mercury – ORBIT news.discovery.com • Lies close to the horizon and is visible for no more than 2 hours before the Sun rises or after it sets…only visible to naked eye when Sun’s light is mostly gone. • Always near the Sun’s location in the sky • Large average density tells us it must have a large iron core (why does this make sense from what we learned from the condensation theory?)

3. Mercury - Atmosphere • Temps range: 700K (800 ° F) at noon to 100K (-280 °F) at night • Largest range of any planet in the system • At poles, temps remain low all the time • No seasonal weather changes • You would either burst into flames or freeze, depending on where you landed.  • Size is about 1.5x that of our Moon • Mass is approx 4.5 x that of our Moon • Why so much more mass than size???

4. Mercury - Atmosphere • Mercury has no atmosphere to speak of thanks to the high temps and low mass – H and He from the solar winds as well as other trace elements from the surface are briefly trapped but leak away within a few weeks. 60 Seconds –Mercury: http://youtu.be/OJrl733eyfY

5. Mercury - Surface • The surface of Mercury resembles the cratered surface of Moon’s highlands…. • More mass (and therefore gravity, 2+x Moon’s) so craters are not as deep, sides not as high and ejected material landed closer to impact site • No extensive lava flow regions • Extensive intercrater plains • Believed to be because lave flows had covered the craters • Mercury also has scarps that cut across the craters, indicating the occurred after much of the bombardment ended • No evidence of tectonic motion • Believed to be formed as the planet cooled, shrank and split

6. Mercury-Scarps • www.messenger-education.org cde.nwc.edu

7. Mercury – the Lennon Crater • Named for John Lennon • Image credit nasa/john Hopkins applied physics lab/Carnegie institution

8. Mercury - Missions • Mariner 10 made three fly-bys during 1974 &1975 • Took many pictures and was the source of almost all that we knew until 2008 • Messenger flew by three times in 2008 and entered orbit in 2011

9. Mercury – Internal Structure • Mariner 10 discovered that Mercury has a magnetic field – weak, but there. Shocked scientists who assumed it didn’t have one since our Moon doesn’t. • Two things are necessary for a magnetic field (as we currently understand things) – a liquid metal core and rapid rotation • Mercury does not rotate very rapidly and may lack the liquid core, but there is definitely dynamic action going on in the core as on Earth, so how the slowly rotating planet produces the magnetic field is a mystery. • Mercury is dominated by a large, iron-rich core that accounts for about 60% of its mass. • Appears to be geologically dead for around 4 billion yrs due to a solid mantle (no volcanic or tectonic activity)

10. Mercury Missions • Messenger spent a year mapping the surface and topography of Mercury. • How does a spacecraft spend that much time near the Sun? • Equipped with a heat-resistant and highly reflective heat shield backed up with layers of Nextel ceramic cloth (used to protect some sections of the Space Shuttle), surrounding several layers of Kapton plastic insulation. • Temps in front of the shield may reach as high as 698F when closest to the Sun, but behind the shield, the temps are a comfy 68F. • The rest of the spacecraft is covered in layers of insulation.

11. Venus - Orbit Venus:Death of a Planet: http://youtu.be/uPpP4gcPFGE • Visible for up to 3 hours depending on time of year • Always near the Sun’s location in the sky • Extremely bright due to the heavy cloud cover – reflects almost all of the sunlight • No direct seismic data of this planet, but based on what we know of the other interior planets, we assume it is similar in internal composition, i.e,. Iron core, density www.trinity.edu

12. Venus - Atmosphere • Thanks to the thick cloud cover, it traps the Sun’s radiation = atmosphere and the hottest temperatures in the system. • Upper atmosphere is not much different from Earth’s, so we erroneously assumed that the heavy cloud cover would just result in a very tropical planet much like ours. NOPE! • Atmosphere more massive and extends much higher resulting in a surface pressure of about 90x that of Earth’s = diving depth of about 1km (unprotected, humans can only dive to around 100m) • The atmosphere is mostly comprised of carbon dioxide with about 3.5% N, and temperatures reach around 860K

13. Venus - Atmosphere • The incredibly high temperatures on Venus are a result of the greenhouse effect. • Greenhouse gases in the atmosphere (on Earth, water vapor and CO2) stop the escape of much of the infrared radiation emitted by the Earth’s surface, which increases the planet’s equilibrium temperature (like a blanket keeps you warm) • Venus’ atmosphere is predominately CO2, which absorbed about 99% of the infrared radiation and is the main cause of the temps • Our oceans act as CO2 sinks, keeping it out of our atmosphere. Put Earth where Venus is, and oceans evap putting all of that water vapor and CO2 into the air and you have runaway greenhouse effect – hotter = more evap = hotter. • Global warming probably won’t get us there, but it shows how fragile the system can be.

14. Venus • NASA photo taken by the Magellan spacecraft is able to penetrate the cloudcover and shows a planet that looks like Earth. • Magellan completed a full map of the surface in 1993.

15. Venus – Surface • The images we have of the surface of Venus are radar images. • Blue indicates low elevations; white indicates the highest • Venus has two continent-sized features – Ishtar Terra and Aphrodite Terra (the larger), each with mountains comparable to those on Earth in height, with the highest about 14km above the deepest surface depressions. (Mt. Everest is about 20k above the deepest point in the ocean floor) www.fas.org

16. Venus - Surface • Aphrodite Terra is located on Venus’ equator and is about the size of Africa. • Shows extensive buckling and fracturing, suggesting large compressive forces, as well as evidence of extensive lava flows en.wikipedia.org Lava Domes www.fvalk.com

17. Venus - Surface • There is indirect evidence to indicate that volcanic activity on Venus continues today… • Levels of sulfur dioxide in the atmosphere fluctuates frequently and largely, possibly due to eruptions on the surface. • Orbiting spacecraft have observed bursts of radio energy from Venus’ surface similar to those often produced by lightning discharges that occur in the plumes of erupting volcanoes on Earth. ONLY circumstantial though

18. Venus - Surface • UPDATE!!! • Europe’s Venus Express orbiter, in March 2014, snapped images that showed 4 transient bright spots in a relatively young rift zone known as GankikiChasma, near Maat Mons, a huge shield volcano that has been dormant for 10-20 million years. • The flashes showed temperatures of 980-1520F, well over the average surface temps of 800 F. • Analysis suggests the flashes may be lava flows, stretching 16 miles, a chain of cinder cones, or a volcanic hot spot. • Further study is obviously planned.  • http://m.space.com/25106-venus-volcanoes-active.html?utm_content=buffer32bda&utm_medium=social&utm_source=facebook.com&utm_campaign=buffer

19. Venus - Surface • In 1975 USSR sent two spacecraft to Venus, Venera 9 and Venera 10. These landers were the very first to reach the planet’s surface. Each survived about an hour and they sent back images to the Earth. • Later Soviet landers would perform basic chemical analysis of the surface and some of the samples were found to be predominately basaltic, again implying a volcanic past. www.planetsforkids.org

20. Venus - Surface • The mountains and craters on Venus have all been given female names such as the crater called Billie Holiday after a female American jazz singer. • There is only one male name -  the Maxwell Mountains which are called after the Scottish scientist James Clerk Maxwell.

21. Venus – Internal Structure • No magnetosphere has been detected around Venus • As similar to Earth as Venus seems, it is assumed that it does have a partially molten iron-rich core, and that the lack of magnetosphere is due to its slow rotation. • No seismic equipment was on the Veneralanders so no measurements of the interior have been made. • Venus appears to be a stunted Earth – one that did not develop plate tectonics as Earth did, possibly due to the high surface temps that kept the crust too soft….or maybe the soft crust led to more volcanic activity which kept the large amounts of energy from building up that would be needed for tectonic motion.

22. Venus • Oh yeah – Venus’ rotation is retrograde!

23. Mars - Orbit • Travels the entire sky, always near the ecliptic (remember, it’s retrograde loops!) • Orange-red, visible to naked eye at it’s brightest. www.thetimes.co.uk 60 Seconds-Mars: http://youtu.be/SIkvVQrOpMM

24. Mars - Atmosphere • Very little atmosphere, but evidence of flowing water at one time, so there must have been an atmosphere at one time to hold it there. …. MAVEN’s mission is to find out what happened to that atmosphere. Basic idea behind is on next slide….. • Atmosphere is 95.3% Cos, 2.7% N, 1.6& Ar and small amounts of CO, O and water vapor. • Average surface temps are about 70K cooler than on Earth.

25. Mars - MAVEN • Planets were all hot inside when they were young. Interior heat can help a planet sustain a global magnetic field, and the magnetic field can protect a planet’s atmosphere from the effects of the solar wind. Indeed, this protective effect is very important to life on Earth, and we suspect that Mars once had a similarly protective magnetic field. So you can now see the outline of what we think happened to Mars: • When Mars was young, it had an atmosphere that was thick enough to allow liquid water to be stable on the surface. Mars apparently had lakes, rivers, and possibly even oceans at that time, although there’s some debate about whether the water was constant or intermittent. • For its first 1 to 2 billion years, Mars had a hot interior that helped generate a global magnetic field that protected its atmosphere from the solar wind. • After that, however, the interior of Mars cooled to the point that its magnetic field turned off. The reason this happened to Mars but not Earth is because Mars is smaller, and smaller objects cool faster than larger ones. • Once the magnetic field turned off, the solar wind gradually began to strip gas away, ultimately leaving Mars with the very thin atmosphere that it has today.

26. Mars - Atmosphere • A reverse runaway greenhouse effect idea goes into the loss of Mars’ atmosphere. • On Earth, volcanic activity returns CO2 to the atmosphere, while the oceans pull it out (CO2 dissolves in water, i.e. rain, etc) and it is absorbed in rocks. A balance is usually reached and all is well. • On Venus, the balanced went to one extreme – on Mars, the lack of gravity and the demise or lack of a magnetic field meant that the CO2 that was in the atmosphere was slowly leaking away. • The CO2 that was absorbed in rocks and water on the planet had no mechanism to be returned to the atmosphere, so the planet cooled as its greenhouse effect diminished, causing further cooling, and so on and so on….

27. Mars - Surface • At it’s closest approach to Earth, we would be able to distinguish objects as small as 100km across unaided – unfortunately, at this point, it is also full so the angle of the Sun does not allow us to see detail like craters and mountains (no shadows) • Mars does have seasonal changes (thanks to the tilt and slightly eccentric orbit) • Polar ice caps of mostly carbon dioxide (dry ice) grow and shrink, almost disappearing during the summer, and there are intense snowstorms during the winters • Dust storms can envelop the entire planet in the summer, making it appear that the surface topography is changing

28. Mars - Surface planetologia.elte.hu

29. Mars - Surface • The northern and southern hemispheres are very different on Mars: • The northern hemisphere is mostly characterized by rolling volcanic plains, seemingly formed by eruptions of enormous amounts of lava. • There are large blocks of volcanic rock and boulders blasted out of impact areas by infallingmeteroids. • The southern hemisphere is made up of heavily cratered highlands lying several kilometers above the level of the lowland north.

30. Mars - Surface • The Tharsis bulge is about the size of N.America and is the closest thing Mars has to a continent. • No plate tectonics so it is not drifting but stays put. • Even less cratered than the northern hemisphere so appears to be the youngest region on the planet at about 2-3 billion years old.

31. Mars - Surface • The VallesMarineris is a huge crack in the surface - not really a canyon, no running water formed it. • Believed to have been formed by the same crustal forces that pushed the Tharsis region upward, causing the surface to split and crack. • Runs for almost 4000 km along the equator and about 1/5 of the way around the planet. • 120km wide at its widest, 7km deep in places. • The Grand Canyon would easily fit into one of it’s ‘tributary’ cracks. • The Hellas Basin is an impact feature based on its shape and structure. • Contains the lowest point on Mars

32. Mars Surface • The largest known volcanoes in the solar system are on Mars, we do not know if any are still active, though all appear to be extinct, the last erupting as recently as 100million years ago. • They do not appear to be associated with any plate tectonics, but instead, like Venus, sit atop hot spots….unlike on Earth, the hot spots don’t move!!!!! • Most of the largest are associated with the Tharsis bulge, but many smaller ones are found on the northern plains. • The great heights is a direct result of the low surface gravity on Mars…. • When a shield volcano forms and lava spreads, the height depends on its ability to hold its own weight. • Mars’ gravity is 40% of Earth’s & its volcanoes rise about 2.5X higher.

33. Mars - Surface • Evidence for past water….. • Viking orbiters saw runoff channels in the southern highlands • Extensive systems resembling river systems on Earth • Outflow channels are most Likely relics of tremendous Floods BUT – if there had been lots of water, we should have found carbonate rock layers, and we have found few. The debate rages on….. www.astro.virginia.edu

34. Outflow channel from some catastrophic flood Figure 6.24

35. Looks like a river delta, however not all scientists agree….. Figure 6.25

36. Mars - Surface • Where is the water today? • No direct evidence for liquid water anywhere • Tiny amounts of water vapor in the atmosphere • Most believed to be locked in a layer of permafrost just below the surface • The permanently frozen residual polar caps are now known to be composed of water ice (as opposed to the seasonal caps that grow and shrink and are made up of CO2) • Observations of water vapor in the air above the northern cap in summers • The southern cap was imaged by ESA’s Mars Express in 2004 • In 2002, the Mars Odyssey orbiter detected extensive deposits of water ice crystals (actually the hydrogen they contain) mixed with the Martian surface layers – up to 50% by volume of the planet’s soil in some locations

37. Mars - Surface • Indirect evidence for a permafrost layer – Yuty, a ‘splosh’ crater formed by an impact. • The impact would have heated & liquefied the permafrost, resulting in the fluid appearance of the ejecta

38. Mars - Surface • In 2000 the Mars Global Surveyor sent back photos of “gullies” in the cliffs and crater walls that appeared to be carved by running water in the relatively recent past. • There are indications that these gullies are still active

39. Mars - Surface • Current Thought…. • 4 billion years ago, Martian climate changed and the running water that formed the runoff channels began to freeze, forming the permafrost and drying out the river beds. • A billion years or so later, volcanic activity (or something) heated large regions, melting the permafrost, causing flash floods and causing the outflow channels. • Volcanic activity ended, water refroze and Mars is again a dry world • The current amount of water vapor in the atmosphere is the maximum possible with the present density and temperature. • Estimates are that the total amount of water on Mars, if made liquid, would cover the surface to a depth of 10 meters

40. Mars – Internal Structure • Mars has no magnetic field. **In 1997, Mars Global Surveyor detected a weak Martian field, 1/800 of Earth’s, but it is believed this was a localized anomaly, not a global field. • As Mars does rotate rapidly, this is taken to mean there is no liquid core or it is nonmetallic, or both. • Mars is small, so any internal heat would have escaped much more quickly than from a larger planet. • There is evidence of volcanic activity suggesting parts of the interior must have been molten in the past, but it cannot have been as extensive as on Earth. • Latest data indicates that Mars’ core is composed of iron sulfide (about 2x the density of surface rock) and is at least partially molten. • Appears that large-scale tectonic activity began, but was stifled by the planet’s rapidly cooling outer layers & much of the planet geologically died about 2 billion years ago.

41. Mars Missions • Mars Global Surveyor - Orbited for just over a decade and allowed us to get repeated pictures of the same area – stopped working in 2006. • First gave us the evidence that the northern hemisphere is very different from the southern hemisphere. • SIDE NOTE – new thinking among scientists is that the northern hemisphere is one giant impact crater; would explain how the ground there appears to be smoother and without the volanoes and cratering that mark the southern and the dimple feature at the northern pole. NOT without controversy!

42. Curiosity Selfie

43. Mars Landers • The US has landed 7 spacecraft on Mars for the purposes of • Conducting detailed geological and chemical analyses of Martian surface rocks • Searching for life • Searching for water (essential for life as we know it) • Conducting human habitability studies

44. Mars Landers - Viking • Both Viking missions sent landers to the surface • Chemical analyses of rocks and several experiments specifically designed to test for life • Found a high iron content in the planets crust, the interaction of it and the oxygen in the air give the planet its red color • Turned off while still functional because the scientific return no longer warranted the cost.

45. Mars Landers – Pathfinder & Sojourner • Mars Pathfinder in 1997 • First lander to be dropped from a parachute, wrapped in balloons. • Lasted 3 months (expected to last only 1) and took measurements of the atmosphere while its rover, Sojourner, ran around within about 50 meters of its parent craft testing soil and rock samples. • Soil chemistry was similar to that sampled by the Vikinglanders • Rock analyses showed different chemical makeups from the Martian meteorites found on Earth

46. Mars Landers • The Mars Exploration Rover (MER) mission launched in summer 2003 - twins. • Spirit and Opportunity landed on opposite sides of the planet for a planned 3 month mission. • Primary goal was a search for evidence of liquid water at any time in the past, and they succeeded, changing the minds of many skeptics • Mission Success depended on each rover: surviving 90 days; traveling at least 600 meters, imaging and describing the geological environments they found • This was the first time in history that anyone with a web browser could tap into the data flow from Mars and watch from Earth (there was a 14 minute transmission delay, but still!)

47. Mars Landers - MER • Spirit launched on June 10, 2003 & landed right on time on January 3, 2004. It bounced around for more than 16 minutesbefore stopping and phoning home to report its safe arrival. • First pictures were sent back 3 hours later and within 72 hours, the websites of JPL, NASA and other organizations affiliated with the program had 1.2 billion hits, setting the Internet record at that time for a single event, and this was before social media. landed in a rocky area and would travel 4.8 miles from its landing point. http://www.nasa.gov/multimedia/imagegallery/image_feature_107.html

48. Mars Landers - MER • Spirit Highlights: • Made history as the first robot to summit a mountain and take pictures of the planet’s dust devils. • http://photojournal.jpl.nasa.gov/catalog/PIA07139 • Returned the first evidence for carbonates on Mars, a sure sign of near-neutral water, like water on Earth http://www.google.com/imgres?q=martian+dust+devil&safe=strict&client=firefox-a&hs=LLL&sa=X&rls=org.mozilla:en-US:official&channel=sb&tbm=isch&tbnid=Vpx9heW57BQjtM:&imgrefurl=http://mars.nasa.gov/multimedia/marsasart/&docid=pc0miEE4RouF9M&imgurl=http://mars.nasa.gov/images/21_The_Serpent_Dust_Devil_on_Mars_PIA15116-full.jpg&w=2093&h=1389&ei=IIT6UuyrCYSdyQG5yoHAAQ&zoom=1

49. Mars Landers - MER • Spirit last communicated with NASA in March of 2010 and it’s mission officially ended in May 2011. • The original mission was planned for 3 months and lasted 6 years. • Even after becoming stuck to where it could no longer move in 2006, the Rover’s mission was transitioned to a stationary platform, sending back well over 100,000 images. • Driving backward, dragging the inoperable front wheel in 2007, plowed up white soil, which would be analyzed by Spirit's Alpha Particle X-ray Spectrometer and Miniature Thermal Emission Spectrometer revealed that the bright material was nearly pure silica • Spirit returned 128,224 images and traveled 7.7 km (4.8 miles) during its 6 year mission.

50. Mars Landers - MER • Opportunity launched July 7, 2003 and landed January 24th 2004. • Opportunity was considered the luckier of the two landings, landing very near an exposure of layered rock that within weeks yielded compositional and textural evidence of a water-rich ancient environment. • It’s site showed signs of having been underwater and then dry numerous times, like a shallow lake would • Opportunity was not equipped to search for fossil records, though this would be a great place to search!