Transcript Mercury and Venus

The Innermost Planet
•
•
Inferior conjunction – inferior
planet and Earth on same side
of Sun
Superior conjunction –
inferior planet and Earth on
opposite sides of Sun
 Smallest
of the planets (Pluto etc. does
not count)
 Named for the swift messenger to the
Roman gods
 Bright
in appearance but not easily seen:
• Only visible at morning or evening
• At most, 28.3º from the Sun
 Ground
based telescopes give only
limited detail
Radius
Moon
1700 km
7.3 × 1022
kg
Density 3300 kg/m3
Mass
Escape
Speed
2.4 km/s
Mercury
1440 km
Earth
6380 km
3.3 × 1023 kg 6.0 × 1024 kg
5400 kg/m3
5500 kg/m3
4.3 km/s
11.2 km/s
 Long
thought to be tidally locked to the Sun;
measurements in 1965 showed this to be false.
 Mercury’s day and year are in a 3:2 resonance;
Mercury rotates three times while going around
the Sun twice.
 Spin-orbit resonance – ratio of the periods can
be expressed as simple integers
 most
eccentric
orbit of all the
planets
 orbit is inclined by
7 degrees to the
plane of the
ecliptic
 axial tilt is almost
zero
 when
Mercury
comes between
the Sun and the
Earth
 Mercury is seen
as a small black
dot moving
across the face of
the Sun
 2016 May 9
Crust
2. Mantle
3. Core
 Core occupies
42% of Mercury
(17% for Earth)
 Has higher iron
content
1.
 Mercury
is much denser than the Moon
 Has a magnetic field – not well
understood!
 Significant
for size
 Planetwide
 Dynamo effect?
 MESSENGER will
measure
 Features
of Mercury’s geology:
• Dorsa
• Impact basin’s and craters
• Pit floor craters
• Plains
• Scarps
• Volcanoes
 Ridges
 Caused
by faults
in crust
 Mercury
is very
heavily
cratered. More
so than the
Moon.
 Predominant
feature of
Mercury
 Floors can be
smooth plains
 Largest
crater
in solar system
 1,550 Km in
diameter
 Antipodal
of Caloris Basin
 Where shock waves collided
 Crater
floor has
collapsed
 Possible magma
chamber under
crater?
 Inter-crater
plains are
the oldest visible
surface
• occur in the regions
between larger craters
• Gently rolling hills
 Smooth
plains are
widespread flat areas
• resemble lunar maria
• fill depressions
 Scarps
are cliffs caused
by the terrain moving
vertically
 On Mercury, caused by
crust shrinking as
planet cooled.
 evidence
of
lava flows
 Cinder cone
volcanoes
 Second most
important
featureformer
 Craters
at pole may
have water ice
 Bottom of crater is
in permanent
shadow
 Spotted with radar,
need confirmation
from MESSENGER
 Very
tenuous
• about 2 trillionths of the
atmospheric pressure on
Earth
 containing
hydrogen,
helium, oxygen, sodium,
calcium, potassium and
water vapor
 Solar wind gives Mercury
a tail
 Only
two missions have visited Mercury:
• Mariner 10 (1973)
• MESSENGER (MErcury Surface, Space ENvironment, GEochemistry
) (2004)
and Ranging
 Last
of the Mariner missions
 Explored both Venus and Mercury
 Could only map about 45% of Mercury
• Same side was sunlit on each of the three flybys
 Can
get better pictures of Mercury
 Has performed 3 flybys so far
 Will enter orbit of Mercury in March 2011
 Smallest
planet
 3:2 orbital resonance; most eccentric
orbit
 Molten iron core
 Small but significant magnetic field
 Impact craters are biggest feature
 Ice in polar craters
 Very thin atmosphere