Download Slide 1 - Dan Caton

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 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 29O, maximum
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.
Mercury (also) reached greatest elongation east (24 degrees) on Nov 3rd
Still in SSW, magnitude about -0.1
Albedos
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Mercury bright in spite of low albedo
Albedo = percent of light reflected
Mercury dark, albedo ~ 11% (7% for the Moon)
Clouded planets high, 72% for Venus, half that for
the Earth
Transits
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Crossing
between us and
the Sun is a
“transit”
Venus and
Mercury both
do it
This from the
TRACE
Venus transited
June 8, 2004
Spin-orbit resonance
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Orbit takes
88 days
Rotation is
2/3 of this
(~59 days)
3:2 spin-orbit
resonance,
due to tidal
forces at
perihelion
Combined,
the Mercury
“day+night”
is 176 days
long
Mariner 10 composite
Heavily cratered
 Ejecta not thrown
as far as on Moon

Scarps
Cliffs that
form along
faults
 Not tectonic
like on Earth
 Probably
wrinkles due
to impacts

Caloris Basin

Large circular
region of impact
(left side of this
image)

If look at opposite
hemisphere…
Hilly, rough terrain opposite Caloris
Theory …
Impact
Magnetic field
Magnetic field ~ 0.5 % Earth’s, suggests…
Interior structure

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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 …
… 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

ESA/Japan have
BepiColombo “in
development”