Planet Notes - 1

Things I'd like you to remember are in bold italics.

Mercury

• a = 0.4 AU

• Always appears close to Sun - thus hard to see from ground-based scopes

• 59-day sidereal period of rotation - 2/3 (exactly) of its 88-day year - it rotates 3 times for each 2 revolutions - not a synchronous motion like our moon

• Temperatures range from 427 °C (800 °F) to -183 °C (-300 °F); huge temp difference (>1000 degrees F) between night and day).  Even so – NOT THE HOTTEST PLANET

• On rare occasions, Mercury transits across Sun (eclipsing it) - 2016

• Albedo (ratio of reflected light to total light hitting body) = 6%

• Similarly, Moon only appears bright to use because it is surrounded by dark sky

• Mariner 10 spacecraft visited in 1974

• less than 1/2 Earth diameter, but similar density (42% iron core)

• Heavily cratered, but flatter craters

• Fine dust on surface; no water, but maybe a little ice?

• Weak magnetic field

• Iron core, 50% of volume and 70% of mass of Mercury

• Thin atmosphere, detectable from Mercury’s spectra - primarily Sodium (and some Helium, Oxygen, Potassium, Hydrogen)

• Lines of cliffs hundreds of miles long - scarps; a wrinkle in the crust

• Features named after historical ships (scarps), the name of Mercury in different languages (plains), nonscientific authors/composers/artists (craters – unlike the craters on the moon which are named for scientists)

VENUS

Atmosphere

• Sulfuric acid clouds (this takes up much water) - must use radar to “see” surface

• Carbon Dioxide atmosphere (>90%)

• Surface air pressure is 90x Earth air pressure

Rotation and Revolution

• Backwards rotation, relative to other planets (perhaps it was struck while being formed)

• 225 day year

• 243 day rotation period

Misc

• a = 0.7 AU; closest planet to us

• 750 K surface (greenhouse effect from thick clouds); hottest and brightest planet (only the Moon is brighter in the night sky)

• Similar density and features

• Venusquakes?

• No magnetic field

• Many probes have been sent to visit Venus

• Basalt surface

• Large rolling plains

• Very active cloud system

• Not highly cratered - smallest meteoroids could have burned up in atmosphere; perhaps some vulcanism

• Probably lightning and volcanic activity

• Only about 16% of Venus below plain

• Huge mountain Maxwell (11 km, 2 km higher than Mt. Everest)

• One continental plate

• Similar gravity to Earth

• No satellites

• Features named after mythical goddesses (major), mythical female figures (minor), and famous women like Sacajawea (other features)

Earth

General – the water planet (71% covered)

• Inner core - iron and nickel (about the size of our

Moon) - rotates a bit quicker than outer core (by 2/3 of a second)

• studied by seismic action

• outer core is liquid, the motion of which causes the magnetic field

• mantle (outside the core) - many silicates; this is the bulk of the Earth

• crust on top (thin)

• crust and outer mantle = lithosphere

• Below lithosphere is aesthenosphere, which is partly melted

• 1/3 of Earth mass is iron

• Gravitational acceleration (local) of 9.8 m/s/s

An active planet

• Natural radiation from within

• Continental drift from geothermal energy

• Plates about 50 km thick

• Plate tectonic activity

• Continents probably once formed Pangaea (“all lands”), which in turn split into Gondwanaland and Laurasia

• Ultimately, California may split from USA, Australia may become linked to Asia, etc.

• Two plates come together, one is often forced under another - volcanoes formed

• Tides are the result of motion around sun and lunar motion - differences between gravitational forces between Moon and Earth at different locations on Earth

Atmosphere

• Nitrogen, Oxygen (>99% total)

• Troposphere (0-15  km, 285-225K) - Earth weather occurs here

• Stratosphere (15-50 km, 225-260K) - upper strat and lower mes contain Ozone layer

• Mesosphere (50-90 km, 260-190K)

• Thermosphere (90+  km, 190-260K) - aka ionosphere; not temperature rise here

Relatively thin when compared to Earth’s radius of 6400 km

Van Allen Belts

• Like a trio of donuts made of charged particles (e-, etc.) held byEarth’s magnetic field

• When hit by solar particles, our atmosphere may glow - aurora borealis, aurora australis (hundreds of km above Earth)

• Earth has strongest magnetic field of the terrestrial planets, and it is not all that strong

Mars

• The red planet (iron oxide?)

• Possible water in its past

• Surface pressure ~ 1% of Earth’s

• 23 Earth month period

• Seasonal, since it has a 25° tilt to axis

• Polar ice cap in the winter (Carbon dioxide, some water?)

• Global dust storm - hundreds of km/hr!

• Changes in appearance possibly once thought to be due to a type of vegetation

• Four types of regions:  volcanic regions, canyon areas, expanses of craters, terraced areas near poles

• Channels (some 200 km wide and 7 km deep), some thousands of km long – possibly cut by water in past

• Olympus Mons (25 km high volcano, 600 km at the base!)

• 90% Carbon dioxide atmosphere

• No tectonics

• Yellowish-brown sky, dust abounds

• Once water; once life??

• Temps from 150-300 K with great variation depending on storms

• Originally thought to have canals, but no longer

• about 1/2 Earth diameter; 1/10 Earth mass; 2/5 Earth gravity

• Length of day a bit longer than Earth’s; same for axial tilt

• Smaller core and thicker crust than Earth

• Viking landers, Mars Pathfinder, Mars Global Surveyor, Mars Observer (failed), Spirit, Opportunity, Phoenix, Mars Reconnaissance Orbiter, Curiosity,

• 2 satellites (captured asteroids?) - Phobos, Deimos; cratered asymmetric rocks (15-20 km across – smaller than some asteroids)

• Major features named for Greek mythology (Olympus Mons); smaller features have been named for cartoon and children’s literature figures; some craters name for dead people associated with Mars