THE 8 PLANETS
NEXT STOP: URANUS!
Unlike any other planet in the solar, Uranus (Ur-uh-nus)’s name derives from Greek mythology, namely the Greek god of the sky. Uranus preceded Jupiter and Saturn in mythology as he and Gaia created the sky and earth. Named planets long after the ancient planets (Mercury, Venus, Mars, Jupiter, and Saturn), Uranus (Sir William Herschel, 1781) and Neptune are sometimes in a separate category called the “ice giants.” The two planets’ icy blue coloration comes from a primary composition of more heavier elements, “ices” such as water, ammonia, and methane. Like Venus, Uranus spins in a retrograde motion with a tilt of 97.77°! So, while other planets spin like spinning tops, Uranus spins like a rolling ball. A large object may have knocked Uranus on its side! Uranus’ rings spin parallel to its axis of rotation. Because of its unusual axial tilt, Uranus has unusually long seasons— each pole gets 42 years of sunlight followed by 42 years of darkness. Near the time of equinoxes, however, Uranus’ day-night cycle reaches that of those on other planets. Even Uranus’ magnetic field, with a tilt of 59º, is abnormal and does not line up to Uranus’ axis, with the north side strong and the south side comparatively weak. The second least dense planet, Uranus comprises of a rocky core, icy mantle, and an outer hydrogen and helium envelope. Because Uranus’ atmosphere is mainly methane, the planet is very smelly, like cow pastures. Uranus’ faint rings were mainly formed from scattered moons. Unlike the other gas giants, Uranus radiates hardly any heat; the planet’s core may have been depleted in an high-mass impact. Though Uranus is bland, dark spots like those usually found on Neptune, have recently been found on Uranus.
Uranus has 27 known moons named after characters from Shakespeare’s and Alexander Pope’s masterpieces. Uranus’ five main moons are Miranda, Ariel, Umbriel, Titania, and Oberon. These moons are comparatively and dull (brightness), comprising of 50% rock and 50% ice. Of the satellites, Ariel is the youngest with few impact craters and Umbriel is the oldest. Miranda has canyons, layers, and many variations in surface features caused by tidal heating (push and pull of the moon’s interior caused by gravitational pull) within the moon.
MISSIONS: Voyager 2
- Order in Solar System: #7
- Number of Moons: 27
- Orbital Period: 84 years
- Rotational Period: 17 hours
- Mass: 8.6810 x 10^25 kg (14.536 Earths)
- Volume: 6.833 x 10 ^13 km³ (63.086 Earths)
- Radius: 25,559 km (4.007 Earths)
- Surface Area: 8.1556 x 10^9 km² (15.91 Earths)
- Density: 1.27 g/cm³
- Eccentricity of Orbit: 0.044405586
- Surface Temperature (Average): 76 K
- Escape Velocity: 21.3 km/s
- Apparent Magnitude: 5.9 to 5.32
- Eccentricity of Orbit: measures the ellipticity of orbit (ranges 0-1, with 0 as spherical and 1 as very elliptical)
- Density: mass per unit volume; mass in grams and volume in cubic centimeters
- Oblateness: measures how much the middle section of the planet bulges
- Surface Gravity: the larger the surface gravity, the thicker the atmosphere as gravity pulls in more gases
- Albedo: measures the fraction of light reflected compared to the amount of light received from the Sun; the higher the albedo, the more reflective the surface
- Escape Velocity: minimum speed or velocity needed to escape the planet’s gravitational pull
- Rotation: most planets rotate in counter-clockwise direction (prograde); others rotate in the clockwise direction (retrograde)
- Rotational period is shortest for gaseous planets and longest for Venus
- Roche Limit: about two and a half times the radius of the planet; within the Roche Limit, matter cannot accretes to form moons because the tidal force of the planet tears matter apart to form rings
Giant Planets: Giant planets have lighter elements such as hydrogen and helium in their atmospheres. They have stronger gravity and are at larger distances from the Sun. Jupiter, Saturn, and Neptune are stormy with great spots of lasting storms and belts and zones. However, Uranus is comparatively bland and uniform. All giant planets are home to convection, or hot gases rising and cold gases falling.
Terrestrial Planets: Terrestrial planets have heavier elements such as carbon, oxygen, and nitrogen. Mercury is most heavily cratered while Earth is least cratered. Larger terrestrial planets have plate tectonics. Earth has a sizable magnetic fields that can protect it from solar wind particles and Van Allen Belts. Earth has the “Goldilocks phenomenon,” or the right conditions for the development of life.
“The Planets” page under “The Solar System” is now complete. The outer planets, Jupiter, Saturn, Uranus, and Neptune, have been added with brief summaries and pictures. Enjoy! See the page here.