Uranus and Neptune Flashcards

Images: Neptune image taken from Voyager 2 at a distance of 4.4 million miles (about 18 times Earth-Moon distance).
- Features of Neptune:
- Great Dark Spot: Dark feature with a bright companion smudge.
- Scooter: Fast-moving bright feature.
- Little Dark Spot: Observed on the lower left of the image.

Date of Discovery: 1781 by William Herschel.
Initial Name: Georgium Sidum ("George’s Star"), in honor of King George III.
- Reason for Name Change: Astronomical community preferred names from Greek and Roman mythology, leading to the name Uranus, father of Cronus (Saturn).
About William Herschel:
- Originally a trained musician, he emigrated to England.
- Developed larger telescopes to detect stellar parallax.
- Discovered Uranus unexpectedly while searching for stars.

Public Reception: Herschel became famous, but some continental astronomers viewed him as just an amateur.
Herschel's Defense:
1. He built one of the best telescopes of the time.
2. Conducted systematic searches for stars before discovering Uranus.
3. Had a keen eye for details to differentiate planet and star properties.

Orbital Discrepancy: Uranus’s orbit was inconsistent with Newton’s laws, suggesting another gravitational influence.
Predictions by Le Verrier and Adams:
- Used mathematical predictions to find an unknown planet, Neptune.
Date of Discovery: September 23, 1846, by Johann Galle, only 1° from predicted location.

Orbital Distance:
- $d_{Uranus} = 19.2 ext{ au}$
- $d_{Neptune} = 30.1 ext{ au}$
- Neptune receives 40% less solar radiation than Uranus.
Orbital Period:
- Uranus: 84 years.
- Neptune: 165 years.
Day Length:
- Uranus: 17.3 hours.
- Neptune: 16.1 hours.
Axis Tilt:
- Uranus: 97.9° (retrograde rotation).
- Neptune: 29.6° (larger than Earth’s 23.5°).

Size and Mass: Similar sizes.
- $R{Uranus} hickapprox 4.0 R{E}$
- $R{Neptune} hickapprox 3.9 R{E}$
- $M{Uranus} hickapprox 15 M{E}$
- $M{Neptune} hickapprox 17 M{E}$
Density:
- $SG{Uranus} = 1.3$ and $SG{Neptune} = 1.8$ (indicate significant ice and rock).

Core: Molten rocks and metals, liquid hydrogen compounds (mostly water).
- Comparable to Earth’s mass, but denser due to surrounding material.
Core Temperatures:
- $T_{Uranus} hickapprox 5300 K$ (9000 °F)
- $T_{Neptune} hickapprox 7300 K$ (12600 °F)
Regions Above Core: Slushy ice layers of water ($H{2}O$), ammonia ($NH{3}$), methane ($CH_{4}$), and hydrogen/silicate matter.
Chemical Processes: High pressures disturb chemical bonds, possibly leading to diamond crystallization in the slushy region.

Composition: Conducting fluid is salt water with ammonia mixed in.
Orientation: Magnetospheres are off-centered and inclined relative to rotational axes, potentially due to ammonia reservoirs.

Mass Composition: ~80% Hydrogen, 18% Helium, 2% other gases, predominantly methane.
Cloud Layers: Aerosolized ammonia in outer cloud layers at lower cloud top temperatures (~60 K).
Appearance: Both planets appear blue due to frozen methane; Neptune is "bluer" than Uranus.
Weather Patterns: Less atmospheric structure than gas giants, with observed strong winds, storms, and lightning.
- Example: The Great Dark Spot observed in the mid-1980s, vanished by 1995.

Voyager Missions:
- Voyager 2 (1986: Uranus; 1989: Neptune) provided major insights, such as Neptune emitting more than twice the thermal energy it absorbs.
Hubble Space Telescope: Used for long-term atmospheric monitoring of both planets.

Neptune vs. Uranus:
- Neptune is still contracting and converting gravitational energy into thermal energy, whereas Uranus does not.
- Several hypotheses address differences in energy outputs, including age, formation, and historical impacts on thermal evolution.