Introduction to Geophysics and
Planetary Physics
(8) Planets
Geophysics
185
The New Solar System – Episode 1
Geophysics
186
For a short time in Sept. 2006 our Solar System comprised 11 planets (the usual suspects plus Ceres – the
largest asteroid belt object, Charon – the largest moon of
Pluto, and the recently discovered 2003 UB313).
A ballot at an IAU meeting changed everything:
The New Solar System – Episode 2
Geophysics
187
The „New Solar System“ knows only 8 Planets, 4 terrestrial planets and 4 gas planets (Source: IAU).
Pluto is now only a Dwarf Planet, like Ceres, the largest body in the Asteroid Belt and 2003 UB313
(Eris), the largest body in the Kuiper Belt (thereby “dwarfing” Pluto). As of Jan 2016 there might,
however, be a “true” “Planet Nine” – far in the outer solar system.
Pluto – Postscript
Geophysics
188
2006 was a very eventful year for Pluto.
Two new moons had just been
discovered, based on a Hubble Space
Telescope image: Nix and Hydra (left:
HST), but then Pluto lost its planetary
status due to a decision of the IAU
(International Astronomical Union).
Meanwhile he is a „Dwarf Planet“, with
a new name: 134340 Pluto. The IAU
decision is, however, under dispute –
and resistance is active (e.g. below:
www.cafepress.com)
The moons Kerberos and Styx (left:
HST), have been discovered in 2011
and 2012, respectively.
Geophysics
189
Eris
The cause for Plutos „degradation“ was the discovery of an even more massive (though slightly
smaller) Kuiper belt object: 2003 UB313, meanwhile (aptly) baptized 136199 Eris , after the Greek
goddess of discord (the one with the apple). Eris is orbited by a moon: Dysnomia (after Eris’
daughter, the demon of lawlessness (Picture: HST).
Geophysics
190
Dwarf Planets
The latest two full-frame, true color images of the binary system Pluto and Charon were collected
separately by New Horizons during approach on July 13 and July 14, 2015. This composite (NASA)
image shows the “true” relative reflectivity, size, separation, and orientations. Pluto and Charon show the
phenomenon of mutual tidal locking – so don’t expect to see a Charon-rise, if you live on Pluto.
Geophysics
191
Pluto
Although not being a “true” planet anymore Pluto is certainly an interesting object in our solar system. It/he
orbits the sun in a 2:3 mean-motion resonance with Neptune (for every two orbits that Pluto makes Neptune
makes three), has likely cryovolcanoes (right) – and he has a heart (of ice) – the Tombaugh Regio, whose
western part – Sputnik Planum – lacks any impact craters (credit: NASA).
Geophysics
192
Charon
With a diameter of 1212 km
(just over half that of Pluto)
Charon is larger than the
dwarf planet Ceres. While
Pluto’s surface is mainly
composed of nitrogen and
methane
ice,
Charon’s
surface is dominated by water
ice (credit: NASA).
The large dark area about 475
km in diameter near the north
pole – informally named
Mordor – could be an impact
crater – or
frozen gases
captured (in the polar “cold
trap”) from Pluto's escaping
atmosphere (Pluto has a very
thin nitrogen atmosphere with
~1 Pa surface pressure).
Introduction to Geophysics and
Planetary Physics
(8b) Gas Planets
Geophysics
193
Geophysics
194
Jupiter
Mean radius: 69 911 km = 10.97 RE
Mass: 1 899 ·1024 kg = 317.8 ME
Mean density: 1 326 kg/m3
Rotation period: 9.93 h
Orbital period: 11.86 years
Sun distance: 5.2 AU
Moons: 67 (status: 2016)
http://nssdc.gsfc.nasa.gov/planetary/factsheet/j
upiterfact.html
Pictures: NASA
Geophysics
195
Saturn
Mean radius: 58 232 km = 9.14 RE
Mass: 568.5·1024 kg = 95.16 ME
Mean density: 687 kg/m3
Rotation period: 10.66 h
Orbital period: 29.46 years
Sun distance: 9.6 AU
Moons: 62 (status: 2016)
http://nssdc.gsfc.nasa.gov/planetary/factsheet/
saturnfact.html
Picture: HST
Geophysics
196
Uranus
Mean radius: 25 362 km = 3.98 RE
Mass: 86.83·1024 kg = 14.54 ME
Mean density: 1 270 kg/m3
Rotation period: 17.24 h
Orbital period: 84.0 years
Sun distance: 19.2 AU
Moons: 27 (status: 2016)
http://nssdc.gsfc.nasa.gov/planetary/factsheet/
uranusfact.html
Picture: L. Sromovsky, Keck Telescope
Uranus has an axial tilt of 97.8 ° – its
rotation axis is almost parallel to the
orbit plane.
Geophysics
197
Neptune
Mean radius: 24 622 km = 3.86 RE
Mass: 102.4·1024 kg = 17.15 ME
Mean density: 1 638 kg/m3
Rotation period: 16.11 h
Orbital period: 164.8 years
Sun distance: 30.0 AU
Moons: 14 (status: 2016)
http://nssdc.gsfc.nasa.gov/planetary/factsheet/
neptunefact.html
Picture: NASA
Neptune’s largest moon Triton shows
cryo-volcanism.
Geophysics
198
Saturn (1)
The „Lord of the Rings“. With an equator diameter of ~120 000 km he is the second largest planet in our solar
system. Besides a small rocky core, the main constituents are Hydrogen and Helium, yielding a density of just
0.7 g/cm3 – less than water. The short rotation period (10½ hours) leads to an oblateness of ~1/10 and to
impressive wind speeds of up to 1 500 km/h (Source, also for the next slides: Cassini-Spacecraft, NASA/ESA).
Geophysics
199
Saturn (2)
Saturn‘s most striking features are its rings, which show an impressive radial extent – but only a surprisingly
small thickness of 10 – 100 m (right, eith the moon Dione immediately above). Galileo Galilei was the first to
observe them (in 1610), but Christiaan Huygens discovered their nature as a disk surrounding Saturn. The rings
A and B are separated by the Cassini Division (left, discovered by Giovanni Domenico Cassini in 1675).
Geophysics
200
Saturn (3)
The moon Dione just above the ring plane (note the ring‘s shadows on
Saturn‘s cloud cover). The rings are predominantly composed of water ice
(particles and boulders from ~1 cm to ~10 m diameter).
Geophysics
201
Saturn (4)
The material depletion in the Cassini Division is caused by the gravitation of
the “Death Star Moon” Mimas (left: above the rings, right: in detail). The
central peak of Herschel Crater is 7 km high.
Geophysics
202
Saturn (5)
The total mass of the rings amazingly small (similar to the mass of Mimas
- 400 km diameter). The rings are probably remnants of a destroyed moon.
Geophysics
203
Saturn (6)
The seven main rings have been named
in chronological order (of discovery) –
with increasing distance from Saturn
they are therefore termed: D, C, B, A, F,
G and E (above).
The small walnut-shaped moon Pan (35
km x 25 km, left) acts as a “shepherd
moon” – right inside the Enke-Gap,
close to the outer edge of the A-ring.
Geophysics
204
Saturn (7)
Enceladus, with a diameter of ~ 500 km,
is characterized by a surface of pure
water ice (and snow) yielding a huge
albedo of 99 % – and as a consequence a
surface temperature of just about –200 °C.
Large areas with no craters at all are
geologically young – the moon is
obviously geologically active.
Geophysics
205
Saturn (8)
Striking features on
Enceladus are the
„Tiger stripes“ near
the South Pole.
Geophysics
206
Saturn (9)
As a big surprise the temperatures at the South Pole
turned out to be higher than at the Equator (upper left).
The „tiger stripes“ are warmer than the surrounding
(above, IR data). Here are also source regions of water
vapor eruptions (cryo-volcanism) (left) – delivering
material (in form of ice crystals) for the E-Ring – and
snowfall on the surface.
Geophysics
207
Saturn (10)
The moon Iapetus (with a diameter of 1400
km) has a (real) Equatorial Bulge, which is
about 13 km high and 20 km wide. Its cause
is currently entirely unclear. Iapetus has –
literally – two different sides The leading
one is one of the darkest surfaces in our
solar system – with an albedo of 3-5 %,
while the other hemisphere (below) shows
an albedo of 60 %. There is obviously some
work left for young planetary scientists.
Geophysics
208
Saturn (11)
The moon Hyperion is (for a moon of
its size) amazingly un-spherical
(painstakingly not following lecture
rules). With dimension 360 × 280 ×
225 km it is the largest (clearly) nonspherical body in our solar system,
Even more – Hyperion’s rotation is
chaotic, its rotation axis changes – in an
unpredictable manner.
Hyperion seems to be the remnant of a
formerly larger body, which suffered a
huge impact.
Is surface shows a impressive crater –
about 10 km deep, with a diameter of
120 km .
Geophysics
209
Saturn (12)
With a diameter of 5150 km the moon Titan is
larger than the planet Mercury, it comprises
more than 96 % of the mass in orbit around
Saturn. Titan has a surprisingly dense
atmosphere with (similar to Earth) nitrogen as
main constituent (94 %) and a surface pressure
of about 1.5 bar. Titan is entirely covered by
organic dust. The surface temperature of about –
180°C allows for methane rain.
Geophysics
210
Saturn (13)
In January 2005 the space-probe Huygens successfully
landed on Titan (as first European lander on a planet or
moon). Middle: the first look through the cloud cover,
right: the surrounding of the landing place. Radar-images
of Cassini (left) confirmed the existence of Methane lakes
(with diameters from von 3 to 70 km).
Geophysics
211
Saturn (14)
Introduction to Geophysics and
Einführung Geophysik
Planetary Physics
The End