Venus “lite” Currently in southwest sky after sunset, ( greatest elongation of 47 degrees was Nov 3 rd ), magnitude -4.3 Stays low, reaches inferior conjunction January 13, 2006

Fierce Greenhouse Effect

Rotation discovered via radar

Retrograde rotation - unexplained

Soviets landed probes…

Magellan radar of Maat Mons Rises 8km High due to no plate motion (one continental plate) Planet resurfaced about 500M years ago

Mercury Note high density

A Morning/Evening “star” Limited by maximum elongation …

.. Of 29 O, maximum Mercury (also) reached greatest elongation east (24 degrees) on Nov 3rd Still in SSW, magnitude about -0.1.

Albedos Mercury bright in spite of low albedo Mercury bright in spite of low albedo Albedo = percent of light reflected Albedo = percent of light reflected Mercury dark, albedo ~ 11% (7% for the Moon) Mercury dark, albedo ~ 11% (7% for the Moon) Clouded planets high, 72% for Venus, half that for the Earth Clouded planets high, 72% for Venus, half that for the Earth

Transits Crossing between us and the Sun is a “transit” Crossing between us and the Sun is a “transit” Venus and Mercury both do it Venus and Mercury both do it This from the TRACE This from the TRACE Venus transited June 8, 2004 Venus transited June 8, 2004

Spin-orbit resonance Orbit takes 88 days Orbit takes 88 days Rotation is 2/3 of this (~59 days) Rotation is 2/3 of this (~59 days) 3:2 spin-orbit resonance, due to tidal forces at perihelion 3:2 spin-orbit resonance, due to tidal forces at perihelion Combined, the Mercury “day+night” is 176 days long Combined, the Mercury “day+night” is 176 days long

Mariner 10 composite Heavily cratered Heavily cratered Ejecta not thrown as far as on Moon Ejecta not thrown as far as on Moon

Scarps Cliffs that form along faults Cliffs that form along faults Not tectonic like on Earth Not tectonic like on Earth Probably wrinkles due to impacts Probably wrinkles due to impacts

Caloris Basin Large circular region of impact (left side of this image) Large circular region of impact (left side of this image) If look at opposite hemisphere… If look at opposite hemisphere…

Hilly, rough terrain opposite Caloris Theory …

Impact

Magnetic field Magnetic field ~ 0.5 % Earth’s, suggests…

Interior structure Must have a large metal core to get high density without the Earth’s larger gravity to compress Must have a large metal core to get high density without the Earth’s larger gravity to compress Large fraction of iron suggests impact origin … Large fraction of iron suggests impact origin …

… like this Impact throws of most silicates, leaving large fraction of iron

Future Missions NASA has the Messenger mission under way, launched August, 2004, will make several flybys of Earth & Venus before orbits Mercury in March of 2011 NASA has the Messenger mission under way, launched August, 2004, will make several flybys of Earth & Venus before orbits Mercury in March of 2011 Messenger ESA/Japan have BepiColombo “in development” ESA/Japan have BepiColombo “in development” BepiColombo