The 10/11/10
Mercury, Innermost Planet
Mercury is one of the least explored
planets in the Solar System
Unit 38
Mariner 10 (1970s) provided most of
the information we have
NASAs MESSENGER returned to
Mercury in 2008 on its first flyby.
MESSENGER will go into orbit around
Mercury in 2011
Planet of Extremes (No atmosphere)
Mercury
On the dayside, surface temperatures
exceed 700K
On the nightside, temperatures drop as
low as 70 K.
Very eccentric orbit, coming as close as
.29 AU and as far as 0.41 AU from the
Sun
Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Surface of Mercury
The Surface of Mercury (2)
Very similar to Earths moon:
Largest basin: Caloris Basin
Heavily
battered with
craters,
including some
large basins
Most craters on Mercury were
formed after the era of
heaviest bombardment.
The impact was so great
that shock waves traveled
through the planet and
along its surface, and
shook up the terrain on
the opposite side!
1
10/11/10
Caloris Basin
Caloris Basin
Early in Mercurys
history, a huge
impact occurred on
the surface
Formed Caloris
Basin, an 800 km
wide crater
The impact was so
great that shock
waves traveled
through the planet
and along its
surface, and shook
up the terrain on the
opposite side!
Odd terrain, opposite
Caloris Basin
The Interior of Mercury
Please insert figure 38.6
Mercurys density is
unusually high, 5.4 kg/liter
Indicates a very large iron
core covered by a thin
silicate mantle
Mercury may have a molten
iron (mixed with sulfur)
core, despite its size
This core may be the cause
of the weak magnetic field
(similar in shape to the
Earths, but much weaker)
Scarps
Running across Mercurys
surface are scarps,
kilometer-tall cliffs that are
the result of the shrinking of
the planet as it cooled
Scarps are similar to
wrinkles in an apples skin
that form as it dries
The presence of these cliffs
suggests that the core of
Mercury is large and
metallic something that
would shrink significantly
as it cools
Why is Mercury so dense?
It is possible that Mercury once had a thicker mantle, but a collision removed
most of the material, leaving only the core and a little lighter mantle material
behind
2
10/11/10
3:2 Orbital Resonance
Mercury is tidally locked to the
Sun
Similar to the way the Moon is
tidally locked with the Earth
After one orbit around the Sun (88
days), the planet has on rotated its
axis 1.5 times
Revolution : 88 days
Rotation : 59 days
Unit 39
It then takes two orbits for
Mercury to rotate three times!
This is called a 3:2 orbital
resonance
Sunrise and sunset are very
strange on this planet!
Venus
The Sun actually undergoes
retrograde motion through
Mercurys sky!
Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Venusian Atmosphere
Venus not so twinlike after all!
Venus is only slightly
smaller than the Earth, but
that is where the
resemblance stops!
Thick clouds completely
obscure the surface
It rotates very slowly (once
in 243 Earth days), and in
the opposite direction as the
rest of the planets
The surface is
tremendously hot!
The atmosphere of Venus is
very different from Earths:
100 times more massive
Surface pressure is 90
atmospheres!
96.5% carbon dioxide
Thick clouds of sulfuric acid
Trace amounts of water vapor
Lightning has been detected, but
there is no rain
The planet probably underwent
a runaway greenhouse effect
3
10/11/10
Images from Venus
The Russian Venera
The spacecraft only lasted
spacecraft have visited the
about an hour due to the
surface of Venus
extreme temperatures and
pressure
Surface temperatures of
750K, hot enough to melt
More recent spacecraft
lead!
have mapped the surface
Discovered volcanic rocks
of Venus from orbit
Recent radar map of Venus
The surface of
Venus seems to be
relatively young
Lots of volcanic
activity resurfaces
the planet rapidly
Few impact
craters, due both to
the thick
atmosphere and
volcanic activity
The Surface of Venus
Venus has both
highlands and
lowlands
Surface features are
named for prominent
women in history and
mythology
Venus is less
mountainous than
Earth, with more
rolling plains
Volcanic peaks are
present in the
highlands
Shield Volcanoes
Found above
hot spots:
Fluid magma
chamber, from
which lava erupts
repeatedly through
surface layers
above
All volcanoes on Venus and Mars are shield volcanoes.
4
10/11/10
Interesting features of the surface of
Venus
Rotation of Venus
Of all the planets, Venus
spins about its axis the
slowest
243 days to complete one
rotation
Slow rotation creates
almost no magnetic field!
Rotates opposite the other
planets (retrograde
rotation)
This retrograde rotation
cannot be produced by
tidal braking
Perhaps a collision early
in its history tipped its
axis
5