ch 13-1 uranus and neptune pt 1

Uranus and Neptune

• ice giants

• outer solar system

• similar size

• similar composition

  • water, ammonia, methane

  • rocky core

• differ in appearance

• voyager fly-by

the discovery of Uranus

• 1781 by Herschel; first planet to be discovered in more than 2000 years

  • by accident

  • studying stars that are too faint to see with naked eye

• discovery doubled the known size of the solar system

can you see Uranus with the naked eye?

• just above limit to see faintly with naked eye

  • moved in front of stars

what was Uranus mislabelled as?

• a comet or nebula star

how much detail of Uranus can we see from Earth?

• little detail

• 3 moons

• faint greenish-blue, star-like

where are the moons of Uranus located?

• constellation Aries

what does Voyager 2 provide us when viewing Uranus

• slightly more detailed images at a distance of 1 million km that increased our knowledge

• few wispy clouds in Northern Hemisphere

• natural colour

• lots of activity

• circulating clouds hurricanes and strange convection period

viewing Uranus

• broad bands covers latitude range to equator to 10°N

• scalloped wave pattern due to horizontal wind speed

• small dark-spot with bright companion

the discovery of Neptune

• 1846 after analysis of Uranus’s orbit indicate its presence

  • first through mathematical predictions

  • didn’t follow navigation path → unknown gravitational pull

can you view Neptune from Earth?

• details cannot be made out

• further than Uranus

• never visible to the naked eye

• faint tinted blue star-like object

Neptune’s elliptical

• couldn’t find elliptical to match trajectory

  • later realized there has to be another plane perturbing Uranus motion

1989 Voyager 2 view of Neptune

• first to observer Neptune up close

• 100 km NP

• 11 km/h wind

• storm: great dark spot

• rings

• 6 moons

how was Neptune’s rings viewed?

• with James Webb Space Telescope 2022

• infrared

• fainter dust bands

Neptune’s Auroras

• JWST 2023

• particles from sun trapped in object magnetic field

• energy release causes flow

orbital and physical properties of Uranus and Neptune

• very similar

• smallest of the Jovian’s but 4x of Earth

• water, ammonia, methane ice

• small rocky core

• ice giants

• chaotic magnetic field

what does the densities of Uranus and Neptune imply/

• rocky core constitutes a greater fraction of the planet’s masses than Jupiter and Saturn

Uranus rotation

• short rotation period

• days are about 10-20 hours

• atm. rotates faster at poles

Uranus properties

• mass: 14.5 x Earth

• radius: 4.0 x Earth

• density: 1300 kg/m³

Neptune’s properties

• mass: 17.1 x Earth

• radius: 3.9 x Earth

• density: 1600 kg/m³

  • denser

  • high proportion of rocky material and compressed ices

What is unusual about Uranus's axis of rotation?

• Uranus is tilted about 98° from perpendicular to its orbital plane, so its axis of rotation lies almost in the plane of its orbit.

Peculiarity of Uranus

• axis of rotation lies almost in the plane of its orbit

• seasonal variations are extreme

• rotates on its side

  • likely caused by massive collision

Outer atmosphere of Uranus and Neptune

• are similar to those of Jupiter and Saturn

Uranus and Neptune are cold enough that?

• ammonia freezes; methane dominates and gives the characteristic blue color

Uranus atmosphere

• very cold; clouds only in lower. warmer layers

• thicker more stagnant atm. haze and appear lighter

• hydrogen, helium, methane → blue green colour

what is Uranus atmosphere composed of?

• water ice at bottom, followed by ammonia hydrosulfide, hydrosulfide layers

Uranus internal heat source

• lacks significant internal heat source, decreases surface temp.

• coldest planet → -22°C

Neptune’s atmosphere

• deeper blue

• thinner haze and warmer atm.

atmosphere of Neptune

• band structure is more visible; it has a “Dark Spot” similar to Jupiter’s storms (now vanished)

• abundance of gaseous ammonia and methane vary systematically

• mass, short lived, anticyclonic storms

what is unique about Neptunes atm.

• rotates more slowly than its interior

an increase in the amount of methane absorbs….

• long-wavelengths largely responsible for blue coloration

  • absorbs long wavelength, red light quiet efficiently

  • excess methane helped insulate the planet maintaining initially warm interior

How might diamond rain form on Neptune? (hypothesis)

• Extreme pressures break apart methane (CH₄), releasing carbon atoms. The carbon atoms crystallize into diamonds, which then sink toward Neptune's core.

  • most stable form of C under high pressure

Why is "diamond rain" thought to occur on Neptune?

• High pressures turn carbon from methane into diamond crystals that sink deeper into the planet.

what happens to the dense carbon crystals during “diamond rain” on Neptune

• sink towards core and would accumulate

  • denser than methane, ammonia, and water