Venus “lite”Venus “lite”

Currently in southwest sky after sunset,

( greatest elongation of 47 degrees was Nov 3rd ), magnitude -4.3

Stays low, reaches inferior conjunction January 13, 2006

Fierce Greenhouse EffectFierce Greenhouse Effect

Rotation discovered via radarRotation discovered via radar

Retrograde rotation - unexplainedRetrograde rotation - unexplained

Soviets landed probes…Soviets landed probes…

Magellan radar of Maat MonsMagellan radar of Maat Mons

Rises 8km

High due to no plate motion (one continental plate)

Planet resurfaced about 500M years ago

MercuryMercury

Note high density

A Morning/Evening “star”A Morning/Evening “star”

Limited by maximum elongation …Limited by maximum elongation …

.. Of 29.. Of 29OO, maximum, maximum

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

..

AlbedosAlbedos

Mercury bright in spite of low Mercury bright in spite of low albedoalbedo Albedo = percent of light reflectedAlbedo = 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 Clouded planets high, 72% for Venus, half that for

the Earththe Earth

TransitsTransits Crossing Crossing

between us and between us and the Sun is a the Sun is a “transit”“transit”

Venus and Venus and Mercury both Mercury both do itdo it

This from the This from the TRACETRACE

Venus transited Venus transited June 8, 2004June 8, 2004

Spin-orbit resonanceSpin-orbit resonance Orbit takes Orbit takes

88 days88 days Rotation is Rotation is

2/3 of this 2/3 of this (~59 days)(~59 days)

3:2 spin-orbit 3:2 spin-orbit resonance, resonance, due to tidal due to tidal forces at forces at perihelionperihelion

Combined, Combined, the Mercury the Mercury “day+night” “day+night” is 176 days is 176 days longlong

Mariner 10 compositeMariner 10 composite

Heavily crateredHeavily crateredEjecta not thrown Ejecta not thrown

as far as on Moonas far as on Moon

ScarpsScarps

Cliffs that Cliffs that form along form along faultsfaults

Not tectonic Not tectonic like on Earthlike on Earth

Probably Probably wrinkles due wrinkles due to impactsto impacts

Caloris BasinCaloris Basin

Large circular Large circular region of impact region of impact (left side of this (left side of this image)image)

If look at opposite If look at opposite hemisphere…hemisphere…

Hilly, rough terrain opposite CalorisHilly, rough terrain opposite Caloris

Theory …Theory …

ImpactImpact

Magnetic fieldMagnetic field

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

Interior structureInterior structure

Must have a large metal core to get high density Must have a large metal core to get high density without the Earth’s larger gravity to compresswithout the Earth’s larger gravity to compress

Large fraction of iron suggests impact origin …Large fraction of iron suggests impact origin …

… … like thislike this

Impact throws of most silicates, leaving large fraction of ironImpact throws of most silicates, leaving large fraction of iron

Future MissionsFuture Missions NASA has the NASA has the

MessengerMessenger mission under mission under way, launched way, launched August, 2004 , will August, 2004 , will make several make several flybys of Earth & flybys of Earth & Venus before Venus before orbits Mercury in orbits Mercury in March of 2011March of 2011

ESA/Japan have ESA/Japan have BepiColomboBepiColombo “in “in development”development”