Planet Notes - 2

The Gas Giants!

Jupiter

5.2 AU

11.9 year period

11.2 Earth radii

67 (17 are unconfirmed) moons, including Ganymede (which is bigger than Mercury!)

The 4 Galilean moons (Io, Ganymede, Callisto, Europa) are, by far, the biggest

318 Earth masses - it contains 2/3 of the solar system’s mass (other than Sun)

1.3 grams/cc density - this tells us that it has a small solid core

86.1% H and 13.8% He; 1% CH4 and NH3, etc.

Small rocky core (iron, silicates)

Different latitudes on Jupiter’s surface rotate at slightly different speeds - bands of clouds of different color (bright = zones; dark = belts)

10 hour rotation period - this fast rotation causes planet to be oblate (pole to pole diameter is 7% smaller than equatorial diameter)

Great Red Spot - vortex of long lasting storm, counter-clockwise rotation; probably lasted so long due to heat from Jupiter

Most of interior is in liquid form;  upper atmostphere is H2

Liquid molecular H in outer core; Liquid metallic (conductive) H in inner core (generating a magnetic field)

Central temp between 13,000 and 35,000 K

Central pressure is 100 million times the pressure of earth’s atmosphere (as opposed to Earth’s 4 million x central pressure)

Radiates 1.6 times as much heat as it receives from Sun

Jupiter is still contracting, however it lacks the mass necessary to become a star

Tremendous magnetic field, some of which is associated with Io; field is opposite Earth’s polarity

Wispy ring at 1.8 times Jupiter’s radius – particles from Io’s volcanoes?              

Ring is inside innermost moon; some particle extend to surface

Observed in 1970’s by Pioneeer and Voyager spacecrafts; later by Galileo craft and a probe into Jupiter’s atmosphere, New Horizons (en route to Pluto)

Just reached by the Juno craft

Jupiter radiates 1.6 times as much heat as it receives

A failed star?  Maybe - not nearly massive enough

Ganymede is the largest moon in the Solar System

Comet Shoemaker-Levy 9 collided with it in 1994 – we watched from Earth

Named for main Roman god (Jovian is the adjective associated with him)

Most moons are named after lovers, daughters or conquests of Jupiter/Zeus.  We do run out of names, though, so some asteroids share the same names (also true for Saturn, etc.)

Saturn

9.5 AU

9x Earth mass

30 year period

The most distant of the visible planets

Possible solid core - 20% of interior

Atmosphere - 92.4% H, 7.4% He, 0.2% methane, plus some ammonia, etc.

Density lower than that of water - it would float! - 0.7 g/cc

10.7 hour rotation period

Radiates 2.5 times more energy than it absorbs Internal heat, but mainly this comes from helium sinking through liquid hydrogen

Strong magnetic field, less than Jupiter’s but stronger than Earth’s

Oblate - 10% difference

2/3 Earth magnetic field, opposite Earth’s polarity

Many of Saturn’s moons are largely water ice

62 (9 unconfirmed) moons, named for gods (Titans, Giants, Inuit and Gallic gods – which include Janus, Mimas, Hyperion, Phoebe, Odysseus)

Observed by Voyager and by Casinni

Awesome ring system - small rocks of ice (1 cm - 1  m across) - FLATTER than a cd!

Rings about 20 m thick - imagine a cd about 30 km across

Ice-coated dust and rock

Gap - Cassini division; other divisions as well  - hundreds of thousands of ringlets!!!

First seen by Galileo (“ears”), later by Huygens and Cassini

Roche Limit - inside this radius, mass cannot be held together by its own gravity - it is torn apart by tidal forces on the body; for Saturn, the RL is about 2.5 times it radius.  All massive bodies have an RL.

Total mass of rings is about the size of an average moon

In the 1800s, J.C. Maxwell calculated that the only way for the rings to be "stable" was for them to be made of many little rocks

Rings have differing angular velocities

Titan is the second largest moon in the Solar System; bigger than Mercury; by far, the biggest of Saturn’s moons

Uranus

4 x Earth diameter

15 x Earth mass

Hershel discovered it in 1781, the first planet discovered by telescope.

84 year period

>19 AU radius

 

Thick methane clouds with some hydrogen - to give blue-green color; Hydrogen, Helium, Methane, Water, Ammonia

Axis of rotation is roughly parallel (8°) to its plane of rotation - almost on its side.  In other words, Uranus’s equator is at a nearly right angle to its orbit.  It is like the planet is “rolling” through space.  Collision?

Polar regions alternate light and dark for decades - bizarre seasons?

Surface temp of 58 K - no internal heat

Rings - 1.7 to 2.1 Uranus radius; at least 11 rings (9 are prominent “inner” rings) - moons are beyond

Viewed by Voyager 2

Magnetic field, 50 x Earth’s - asymmetric and inclined to rotation axis (actually, ALL mag. fields are inclined to rotation axes of planets

- Uranus’s is by 31%; Earth’s is 8%); opposite Earth’s polarity

27 Moons, named for A. Pope and Shakesperean literature figures (Puck, Belinda, Oberon, Titania, Ariel, Umbria, Miranda)

Largely nondescript appearance to telescopes

Neptune

30 AU from sun

Similar to Uranus

Deep blue color

165 year period – Neptune completed its first orbit (in 2011) since its discovery

1.6 g/cc density

Radiates 2.7 x more heat than it receives

Triumph of Newtonian astronomy - finding it based on mathematics, 1845/6.  Same with Triton.

Possibly observed by Galileo in 1613

Methane atmosphere - many clouds; blue appearance; very windy (more than Jupiter and way more than Earth)

Much data from Voyager 2 (1989)

Great Dark Spot - similar to Jupiter’s spot

59.3 K average temp

Magnetic field, also asymmetric and opposite Earth’s polarity

6 Rings - narrow in general

14 moons, largest of which is Triton (son of Poseidon) which orbits backwards!  Captured by Neptune?

The 14^th moon, not yet confirmed, was discovered in 2013.

Viewed by Voyager 2

Planet 9

Suggested in 2014

Not yet actually discovered

10x Earth size (or so)

10-20,000 year period

Highly elliptical orbit, a = 700 AU (!)