1. Mercury

2. When and where can you see it? Being so close to the sun, you can only see Mercury when the sun is just beneath the horizon. This is just before dawn or just after sunset. On rare occasions, it can be seen during a total solar eclipse. Because it moves so quickly, we can never view all of its phases.

3. The ancient Greeks… Knew of Mercury. They thought that it was two objects! Why? Because sometimes it is sometimes visible in the morning and sometimes in the afternoon. Later Greeks determined that it was one object.

4. The best views of Mercury… Are taken by telescopes that can “blot out” the sun. Why is this best? Mercury can be viewed high in the sky, where its light travels through less layers of atmosphere.

6. Physical Properties At its closest approach to Earth, Mercury is 0.52 AU from the sun. It has a mass of 3.3 x 10 23 kg or 0.055 Earth mass. Surface gravity is about 0.4 times Earth’s.

7. A solar transit of Mercury.

8. Spacecraft Visits Mariner 10 (1974 and 1975) found only trace amounts of gases on Mercury – not an atmosphere, but temporary gases stolen from the solar wind. The next spacecraft to visit Mercury will be in 2009 – update: the MESSENGER Space visted in 2008

9. Another transit picture…do you see Mercury?

10. Temperatures Daytime temp can reach 700 K (800°F). Night time temp can be as low as 100 K (-300°F). This gives Mercury the greatest temperature range of any planet in our solar system. There is the possibility that water ice exists on the poles, since the sun is never high in the sky there.

11. Surface Features Mercury’s surface is very similar to our moon’s. It contains craters and rays, though few maria. Contains scarps: wrinkles formed as the planet cooled.

12. Photos from the MESSENGER Spacecraft photos Photos from the MESSENGER Spacecraft photos more

13. Surface Features Caloris Basin: largest crater, from an impact; opposite side of the planet has “weird terrain,” thought to have formed from seismic waves that traveled across when the impact occurred.

14. Rotation Rates Italian astronomer Giovanni Schiaparelli concluded that Mercury was locked in synchronous rotation around the sun. In 1965, this was determined to be in error. Rate of rotation: 88 Earth days Rate of revolution: 57 Earth days

15. Interesting math… Rate of rotation: 88 Earth days Rate of revolution: 57 Earth days 57/2= 28.5 28.5 x 3 = 85.5 This gives a ratio of 3:2. This is termed resonance. Earth’s moon has a 1:1 resonance ratio.

16. Mercury’s interior Contains a large,liquid iron-rich core. This gives Mercury a small magnetic field. 60% of its mass is in its core. This is the largest percentage of any planet. However, its mantle is solid, which prevents any geological activity.