Mercury
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?)
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)
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
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
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?
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
Messenger
Caloris Basin
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
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
Fly-by 1
Fly-by 2
Messenger
first photo in
orbit