Week 6: Mercury

PART 1:

Mercury

  • named after greek god, Mercury (Hermes)

    • Mercury (the greek god) was the messenger of the gods

      • was very fast

      • closest planet to the sun = moves faster

        • fastest moving planet in the sky

  • first telescope was observed by Galileo in 1609

  • diameter: 3/8th Earth’s diameter or 3,000mi

    • smallest major planet in the Solar System

  • mass: 1/20th’s Earth’s mass

  • Axial Tilt: 0 degrees

    • orbits the sun straight up and down

    • inclination of orbit: 7 degrees to the plane of the solar system (ecliptic)

      • most inclined orbit in our solar system

      • ecliptic: plane of our solar system

        Mercury's orbit is 7 degrees tilted from Earth's orbit

  • average distance from the sun: 0.4 AU

  • Surface Gravity: 0.38g (g =Earth’s gravity)

    • = 38% the strength of Earth’s Gravity

Transit of Mercury

  • Transit: when a smaller body moves in front of a bigger body

    little dot next to red dot = Mercury in front of the sunMercury's path in front of the sun

Mercury’s size

  • Mercury is the size of some satellites (moons)

    • but because it orbits around the sun = its a major planet

Orbit of Mercury

  • Mercury has the most eccentric (least circular) orbit of all the major planets

    • most elliptical orbit in our solar system but very hard to tell

Aside: Angular Size

  • Angular size (angular separation): measurement by apparent size

    • measured at an angle

      • measured by comparing imaginary line from eyes to top of planet to imaginary line from eyes to bottom of planet

    • unit: degrees

  • Angular distance: measurement by apparent distance

    • measured at an angle

      • measured by comparing imaginary line from eyes to one planet to imaginary line from eyes to another planet

    • unit: degrees

  • Measuring degrees with hand at arms length:

Enlongation Angle:

  • Elongation angle: angular distance from a planet to the sun

    • changes everyday

    • measures how far a planet appears from the sun

Mercury’s Elongation Angle

  • Mercury’s greatest elongation angle: 28 degrees

    • smallest elongation angle because it is closet to the sun and has the smallest orbit

      • always appearing close to the sun

        • Best time to observe Mercury: just before sunrise or just after sunset

          • only about 2 hours to do so

Rotation and Revolution of Mercury

  • sun over head = noon

    • Sidereal Day: “with respect to the stars”

    • for head to be back over sun a day later = 24 hours

      • measuring from the stars

    • Solar Day: “with respect to the sun”

      • for head to be back over sun a day later = 24 hours and 4 minutes

      • 4 minutes longer than sidereal day

  • period of rotation (Mercurian Day):

    • sidereal day: 59 days (Mercury turns 360 degrees)

    • Solar days: 176 days = 3 sidereal days

      • one solar day is 2 mercury years

      • Mercury’s solar day is longer than its year

    • Period of Revolution: (Mercurian Year)

      • Year: 88 days (Fastest in the Solar System)

Surface Temperature of Mercury

  • First visited by the Mariner 10 Spacecraft in 1974

    • didn’t land, just few by and got good data

  • Surface Temperatures:

    • Lit side: (daytime) 800 degrees F

    • Dark side: (nighttime) -300 degrees F

      • Largest temperature range / swing in the Solar System (1,000 degrees F)

        • both really hot and really cold

        • this is due to not having an atmosphere (unlike Earth that has an atmosphere and does not have a large temperature range)

Part 2 Mercury

Density of Mercury

  • Density: measure of compactness

    • mass (grams) divided by volume (cm3)

    • ie: Density of water is 1g/cm3

      • Density of Iron (Fe) is 7.86 g/cm3

      • Density of gold (Au) is 19.3g/cm3

  • Density of Mercury = 5.4 g/cm3

    • implies a dense core like Earth’s

Surface Composition of Mercury

  • Rocks mostly made of sulfur, but also silicon, titanium, and iron

  • water ice on the surface (in craters) near the poles

    • craters are near the poles of Mercury and does not ever face the sun = results in water ice

  • very volcanic (molten) up to 3.5 billion years ago


Mercury’s Surface Features: Craters

  • Craters: impact site of asteroids, comets, meteoroids, etc.

    • mostly named after famous artists, poets, musicians, and philosophers


  • Why so many craters? (unlike earth)

    • no atmosphere to burn up asteroids

    • no erosion to cover them back up

  • The Caloris Basin: big impact crater from an asteroid impact a long time ago

    • 800 miles across

    • impact was about 4 million years ago

    • basically a big molten pool of lava until it cooled

    • called “Caloris” Basin because it is the hottest area on the planet

      • Caloris is “heat” in latin

Surface Features: Scarps

  • Scarps: wrinkles on the crust and across craters

    • formed as Mercury’s cooling core shrank, causing the surface to shrink and cool


    • called “Rupes” (latin for “cliffs”)

      • named after famous historical ships

Surface Features: “Weird Terrain”

  • “weird terrain”: hilly region created as a result of shock waves from the Caloris Basin Impact

    • located on the opposite side of impact (antipodal)

Mercury’s Atmosphere

  • Mercury has basically no atmosphere

    • why?

      • Two main reasons:

        1. Low mass = low gravity

          • can’t hold onto atmosphere very well

        2. HOT

          • Gas atoms move so fast that they escape Mercury’s gravity

Another Trip to Mercury

  • The MESSENGER Spacecraft: last spacecraft to go to Mercury in 2011

    • MErcury Surface Space ENvironment, GEochemistry and Ranging