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