Presentation on theme: "Venus and Mercury. The Inner Planets Venus Only a bit smaller than Earth Nearest planet (26 million miles) Shows phases as it orbits the Sun Most circular."— Presentation transcript:
Venus and Mercury
The Inner Planets
Venus Only a bit smaller than Earth Nearest planet (26 million miles) Shows phases as it orbits the Sun Most circular orbit Atmosphere mostly Carbon Dioxide –90 times as dense as Earth –Runaway Greenhouse Effect –Surface Temperature 450 C (850 F)
Venus’ Odd Rotation Venus Rotates in 243 days relative to the stars Longer than its year (225 days) Solar Day = 117 days You can jog as fast as Venus rotates Opposite to all other planets’ rotation (retrograde) Why? –Mega-Impact? –Tidal Effects? –Possible tidal lock on Earth?
Venus from Pioneer Venus Orbiter
Polar View of Venus
Topography of Venus
Radar Map of Venus
Surface of Venus
Venus has Craters
Venus is Volcanic
Channel on Venus
How Coronas Form?
Venus Differs from Earth in One Important Way: Venus has no Plate Tectonics Earth’s internal heat causes hot material to rise within Earth and plates to move Venus’ crust is too rigid Heat builds up and escapes in planet-wide volcanic activity Last event about 600 million years ago
Why Venus Has No Plate Tectonics It’s Hot! We’d expect hot rocks to be less rigid, not more! But it’s also dry! Dry rocks are ten times stronger at high temperatures than wet rocks. Earth is wet. That affects not just the outside, but the inside as well.
Did Venus Once Have Oceans? Resurfacing means no visible trace of early history Deuterium: Ghost of a Vanished Ocean? –Deuterium is hydrogen with one neutron –Twice as heavy as normal hydrogen –Less likely to escape –D/H on Venus 100x that of Earth Photodissociation + Stripping –Venus lacks magnetic field
Venus and the Da Vinci Code 13 Venus years = 13 x 224.7 = 2921.1 days 8 Earth Years = 8 x 365.25 = 2922 days 5 Synodic periods of Earth and Venus = 5 x 583.9 = 2919.5 days 1/5 of a circle = 72 degrees In 583.9 days, Earth moves 360 + 215.5 degrees (almost 360 + 3 x 72) In 583.9 days, Venus moves 720 + 215.5 degrees
Venus and Earth 13 Venus years = 13 x 224.7 = 2921.1 days 8 Earth Years = 8 x 365.25 = 2922 days 5 Synodic periods of Earth and Venus = 5 x 583.9 = 2919.5 days 12 Venus rotations = 2916 days Venus shows nearly the same face to Earth every 584 days.
Venus and Earth
Mercury Closest planet to Sun Very elliptical orbit (e =.205) Only 3000 miles (5000 km) in diameter Rotation locked to Sun: 3 rotations in 2 orbits (58 days) Moon-like on the outside (craters) Earth-like on the inside (dense core, magnetic field)
Mercury’s Interior Density = 5.43 (Earth = 5.5) Much smaller than Earth, less pressure inside Core about 2/3 of Mercury’s diameter (Earth = ½) Mega-Impact may have blown away silicate outer part
Mercury from Mariner 10, 1973
Mercury has Craters Not as dense as on Moon Most of Mercury covered with lava plains (intercrater plains)
Mercury has a huge impact basin, the Caloris Basin
Because of Mercury’s locked rotation, it has two “hot poles”
And Mercury has the last thing you’d expect to find: ice caps
Mercury’s ice seems to be hiding in polar craters