Astronomy 1010-H
Planetary Astronomy
Fall_2015
Day-35
Course Announcements
•
How is the sunset/sunrise observing going?
•
SW-chapter 9 due: Wed. Nov. 18
SW-chapter 10 due: Mon. Nov. 23
•
•
I will collect the L-T books on Monday, Nov. 23,
though I will take them at any time now.
•
1st Quarter Obs. (last one of semester): Thurs. Nov. 19
Reports Due: Monday Nov. 23 – AT CLASS TIME!
•
 Infrared observations let us see details of
structure on Uranus.
 Weak banding on both Uranus and Neptune.
 Small, scattered bright or dark clouds.
 Transient large storms (Great Dark Spot on
Neptune).
The gas giants have
similar cloud layers.
Temperature, pressure
increase downward.
Different heights
of cloud layers.
 Clouds on Jupiter:
• Ammonia (NH3) at
T = 133 K.
• Ammonium hydrosulfide
(NH4SH) at T = 193 K.
Under the Clouds: Uranus/Neptune
 Unlike Jupiter and
Saturn, the highest
clouds on Uranus
and Neptune are
methane ice.
 Bluish because
of scattering of light
by the methane.
 Clouds on Jupiter
and Saturn are
colored by
impurities.
Helium Rain
 In Jupiter and Saturn, Temperature and Pressure meet the
correct conditions to condense Helium in the lower
atmosphere. In essence, this cause liquid Helium drops to
form and fall down as “rain”.
 This contributes to the internal heating of both planets.
 Mixed in the Helium drops is Neon, which helps explain
the low levels of neon in the atmospheres of both
planets.
i_Clicker Question
Jovian Planets: Helium Rain
 Rapid planetary rotation results in strong
Coriolis forces. This causes storm rotation.
 Most extreme equatorial winds are in Saturn’s
and Neptune’s atmospheres, with maximum
speeds up to 2,000 km/hr.
 Alternating east–west winds make banded
clouds on Jupiter.
 Circulation pattern differs from planet to
planet in ways not understood.
MATH TOOLS 10.1
 Wind speeds on gas
giants can be
measured by observing
the movement of clouds
above an assumed
“surface.”
 Using the
circumference of the
planet, you can find
how much a spot
travels in a given time.
 All but Uranus
have significant
internal heat.
 Heat flows from
the hot interior
outward.
 Heat has a big
effect on global
circulation
patterns.
MATH TOOLS 10.2
 Jupiter, Saturn, and Neptune radiate away
more energy than they get from the Sun.
 A small increase in internal temperature leads
to a large increase in emitted energy.
 Something has to be increasing the
temperature. It is believed that the planets are
still shrinking, with gravitational energy being
converted into heat during that process.
 For Jupiter:
 Jupiter/Saturn: At depths of a few 1,000 km,
gases are compressed so much they liquefy.
 At higher pressure and temperature, this
liquid hydrogen can act like a metal.
 Cores are a liquid mixture of water, rock, and
metals.
 Uranus and Neptune are smaller and have
less pressure than the gas giants.
 They have more water and ices (ammonia,
methane).
 Deep oceans containing dissolved gases and
salts are present.
 Jupiter and Saturn formed from the
protoplanetary accretion disk while
hydrogen and helium were still present.
 Solar wind later blew out these gases.
 Uranus and Neptune formed later, by the
merger of icy smaller bodies.
 All four possess a dense liquid core
containing rocky materials.
 Many details are still not understood.
 Magnetic fields
are generated
by the motion of
the electrically
conducting
liquids.
 Their orientation
is at an angle to
the rotation axis.
 Like a bar
magnet.




Magnetospheres are huge (Jupiter’s is 6 AU).
They interact with the solar wind.
Auroras (“Northern lights” on Earth).
Produce strong radio waves/synchrotron
radiation.
i_Clicker Question
Jovian Planets: Magnetic Fields
 Strong
magnetospheres
concentrate charged
particles in
radiation belts,
including the plasma
torus created by
particles from
Jupiter’s moon Io.
 Powerful flux tubes
create bright
auroras.
CONNECTIONS 10.1
 Accelerating charged
particles emit photons.
 When moving, charged
particles are forced in
circles by magnetic
fields—acceleration!
 Occurs often with
magnetic fields and
electrons around planets
and stars.
 Synchrotron radiation.
 “Hot Jupiters” are seen orbiting close to their
stars in extrasolar planetary systems.
 Computer simulations show that the giant
planets may not have formed where they
exist now, but rather could have migrated to
their positions due to gravitational influences.
 Dozens of “worlds” of rock and ice exist in our
Solar System; some large, some small.
 Liquid water under some surfaces is possible.