1. Mercury, seen from Earth through a moderate telescope.

2. Venus

3. Mars

4. Ch. 5: part 1 - the Terrestrial Planets We survey the four terrestrials first, then look at details for Mercury, Venus, and Mars.

5. Planetary Radar allows us to determine the distance to Venus. Then we can determine all the other distances to planets.

6. Terrestrial Planets’ Spin Axis and Rotation Rate

7. Mercury’s Rotation is tidally locked to the Rotation period. The solar day on Mercury is 176 days long, which is two Mercury-years!

8. Terrestrial Planets’ Spin Mercury’s sidereal rotation is tidally locked to 2/3 of an orbit. Venus rotates very slowly backwards compared to the other Planets, so that it is rotating clockwise (others are CCW). Mercury and Venus both have almost no axial tilt, Earth and Mars both have similar axial tilts and rotation rates.

9. Atmospheres and Temperatures Mercury has no atmosphere just like our moon. Because there is no atmosphere to trap heat, the night side of Mercury gets very cold (100K or -173C). The day side of Mercury gets up to 700K. The atmosphere of Venus is made up of carbon dioxide, with clouds of sulfuric acid. The atmosphere is some 90 times denser than Earth’s. The Greenhouse effect causes the surface temperature of Venus to be close to 730K day or night. Mars has a very thin atmosphere (less than 1% of Earth’s) of mainly carbon dioxide. The surface temperature is around 50K lower than Earth’s.

10. Mercury, Up Close

11. Mercury, Very Close, from Mariner 10 photos

12. Mercury’s Surface Mercury’s surface has a large number of these scarps or cliffs like giant cracks in its surface. Mercury never had plate tectonics like the Earth. When the crust of Mercury cooled it shrank causing the crust to crack.

13. Mercury’s Caloris Basin, due to a very large impact

14. Mercury Maps and images USGS has a website with planet maps http://astrogeology.usgs.gov/Projects/Messenger/ Tennis ball projects for kids ! http://astrogeology.usgs.gov/Gallery/MapsAndGlobes/ New results are expected from the MESSENGER spacecraft. Launched in August 2004, the Mercury Surface, Space Environment, Geochemistry and Ranging spacecraft, known as MESSENGER, conducted a third and final flyby of Mercury in September 2009. The probe completed a critical maneuver using the planet's gravity to remain on course to enter into orbit around Mercury next year. These photos are from this craft:

21. MESSENGER insertion into Mercury orbit, March 2011 Launched Aug. 3, 2004 from Kennedy Space Center Earth flyby in August 2005 Venus flybys in October 2006 and June 2007 Mercury flybys in January 2008, October 2008 and September 2009

22. Venus, Up Close Because of Venus’s dense cloud cover most of what we know about Venus’s surface and rotation comes from using radar. There have been only a few spacecraft to land on Venus, but each survived for only a short time. (This is an ultraviolet photo.)

23. Venus Radar Map taken by the Pioneer Venus spacecraft

24. Earth Radar Map, shown with scale similar to the Venus map

25. Venus map made by the Magellan spacecraft In 1995 the Magellan spacecraft was able to make a much more detailed radar map of Venus. Possibly active shield volcanoes, craters, and volcanic structures called coronae were seen by Magellan.

26. Venus’s Surface Features

27. Venus Corona

28. Impact Craters on Venus

29. Venus surface, taken with a camera on the Soviet Venera probe.

30. Venus’s Atmosphere has an extreme Greenhouse effect

31. Terrestrial Planet Interiors Mercury’s mantle is solid (not semi-molten like the Earth’s) and its core also may be solid as well. Not much is known about the interior of Venus – but it is thought to be like a young Earth. Mars is mostly solid and no longer geologically active in any way.

32. Earth’s Magnetosphere The Earth’s magnetic field is formed because of the Earth’s rotation and because the Earth has a molten core No Lunar magnetic field!

33. Terrestrial Planet Magnetic Fields Mercury has a very weak magnetic field, probably due to its large iron core that solidified into a large magnet. Venus has no measurable magnetic field, probably due to its very slow rotation rate. Mars has a magnetic field weaker than Mercury, meaning that its core is either not liquid or not metallic.