1. Mercury

3. Basic Info  Named for the Roman Messenger god.  Second closest planet to the earth (48 million miles; Mars is 225 million)  But it is so close to the sun that viewing it is difficult (best times occur twice a year, when it is at its greatest angular distance from the sun; Always less than 28 degrees)  No moons  Like Venus and the moon, it has phases  Geologically inactive for billions of years  Magnetic field of about 1 % of the Earth’s (Possibly induced by solar wind?)

4. Basic Info cont.  Second smallest planet  One-third the size of Earth  Diameter: 3,031 miles (U.S is 2,800 miles across)  Has one-third the gravity of Earth  Average density: 5.4 kg/m^3  Length of day (one rotation): 58 days  Length of year: 88 days (In two years, Mercury has had 3 days)  Has the most elliptical orbit of all of the planets (Perihelion 29 million miles away Aphelion: 44 million miles away, 1.5 times as far!)  Axial tilt: 2 degrees (has no seasons)

6. Creation of Mercury  Formed about 4.5 billion years ago  Subjected to very high temperatures  Melted the planet? The dense iron separated from the molten rock and sank to its core.  Resulted in an iron filled core and a crust composed of mainly silicon and oxygen  Its core makes up 75% of its diameter  70% iron 30% silicate material (it’s core 1,118 miles and its crust 62 miles)  Bombardment ended about 3.8 billion years ago

7. Surface and geology  For the first 600 million years of their existence, the four inner planets were bombarded, which left many craters  During this time, Mercury was expanding and its interior was melting  This melting led to volcanism, where great amounts of lava poured onto the surface, creating plains between craters.  As Mercury cooled and contracted the crust adjusted, which resulted in global compression and many cliffs.  The largest cliff is 310 miles long and 2 miles high and is called Discovery Rupes

10. Iron  Mercury has a high content of iron (mainly in the core which is 42% of Mercury’s volume)  Three theories:  Maybe only iron rich materials could withstand the high temperatures of the young sun? (melting point 2,800 F)  Maybe the intense outflow of particles of the young sun stripped Mercury of its low density mantle?  Possibly due to a large planetesimal striking Mercury?

11. Caloris Basin  Around 4 billion years ago, a huge asteroid struck Mercury  This resulted in the Caloris Basin  The basin floor stretched and contracted under the weight of the lava, which flowed due to the impact.  The impact was so great that it generated seismic waves which resulted in Mercury’s hilly terrain  960 miles in diameter  Calor means heat in latin and the basin is named so because the sun is directly overhead at the planet's perihelion

12. Messenger Caloris Basin

13. Atmosphere of Mercury  Almost has no atmosphere (too small and too hot to retain one for long periods of time)  Has a very thin atmosphere made up of helium and sodium (likely, a product of solar wind)  Low atmospheric pressure  Gravity is low (38% of Earth’s gravity)  Temperature by day: 800 F by night: -280 F

14. Exploration  Mariner 10: March 29, 1974 fly-by  Went to Venus first and went through 3 Mercury fly-by’s  Began to orbit the sun but ran out of gas and is still orbiting it  Purpose: To investigate the characteristics and properties of Mercury  It photographed 45% of the planet's surface  Messenger: Made Fly-by’s of the first 3 planets (2011-2015)  The first satellite to orbit Mercury

16. Fly-by 1

17. Fly-by 2

18. Messenger first photo in orbit