Astronomy 1010Fall_2015Day-35

Planetary Astronomy

Course Announcements• 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.

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.

MATH TOOLS 10.1

All but Uranus have significant internal heat.

Heat flows from the hot interior outward.

Heat has a big effect on global circulation patterns.

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:

MATH TOOLS 10.2

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.

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.

CONNECTIONS 10.1

“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.

Theories make predictions that serve as opportunities to falsify them or strengthen confidence in the theory.

These predictions are essential to scientific progress.

PROCESS OF SCIENCE