The 8 Planets – Part 7: Uranus

NEXT STOP: URANUS!

Uranus

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.

MOONS

Uranus' moons

Uranus’ moons

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

OVERVIEW

  • 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
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The 8 Planets – Part 6: Saturn

NEXT STOP: SATURN!

Saturn

Poor Saturn is neither the largest nor the most massive. But this planet may be most eccentric— memorable in its appearance and properties. Named after the Titan of Time, Saturn was the Roman king of the Titans and father of Jupiter. Saturn is the least dense planet, even less dense than water! How does this happen? Saturn is only 1/8 the density of Earth, but with its large volume, is over 95 times more massive than Earth. Comprising mainly of the lightest element, hydrogen, Saturn is very “light” for its size. Saturn’s mass is 95 times that of Earth, but its volume is 764 times that of Earth. Since density = mass/ volume, Saturn’s large volume and relatively small mass equates to a very small density (0.687). So, if you build an enormous bathtub and fill it with H2O, Saturn would bobble around on the surface like a rubber duckie! In contrast to Jupiter’s myriad of colorful bands and zones, Saturn’s upper atmosphere of mainly ammonia crystals gives the planet a bland yellow-brown coloration. Once every 30 years, Saturn exhibits ephemeral storms on its banded surface, one known as the Great White Spot. At its North Pole, Saturn has a weird hexagon-shaped storm that may be a novel aurora or a wave pattern. Underneath that banal surface, winds reach up to 1,100 mph, faster than those on Jupiter! Unlike its ever-changing gaseous layers, Saturn’s core may be solid iron, nickel, and rock. Reaching up to 11,700 °C at the core, Saturn radiates 2.5 times more energy than received from the Sun by the Kelvin-Helmholtz mechanism of slow gravitational compression and the “raining out” of droplets of helium in its interior. Accumulating into a helium shell surrounding the core, the helium droplets release heat by friction passing though low density hydrogen. Layers of metallic hydrogen (deep), liquid hydrogen and liquid helium (intermediate), and hydrogen gas (outer) blanket the core. Electrical currents within the metallic hydrogen caused Saturn’s weak magnetic field to form. Effective at deflecting solar wind particles, Saturn’s magnetosphere also produces aurorae. Saturn has magnificent, highly reflective ice rings, perfectly visible with a telescope. All gas giants have rings, but with nine main continuous rings, three discontinuous arcs if ice particles, rock debris, and dust, Saturn and its rings are truly inseparable. In 1655, Christiaan Huygens suggested Saturn was surrounded by a ring. Since then, astronomers have named the main rings from A to G. The Cassini Division is a large gap between rings A and B, and the Roche Division is a gap between rings A and F. Some moons, like Pan and Prometheus, are shepherd moons that prevent Saturn’s rings from expanding.

MOONS

Saturn has the second most number of moons with 62. Inhabit Saturn’s rings, Saturn’s moons range from the hundreds of “moonlets” to its largest natural satellite Titan. Of its 62 known moons, Saturn has 53 with actual names, 13 with diameters larger than 50 km, 7 with hydrostatic equilibrium due to planetary mass, dense rings, and complex orbits of their own, 24 regular satellites (prograde orbits not greatly inclined) named after Titans and Titanesses, and 38 irregular satellites with farther orbits and high inclination orbits and named after Inuit, Norse, and Gallic mythological characters. There can be no objective boundary for the classification of Saturn’s moons, for Saturn’s rings contain objects from the microscopic to the largest object Titan.

TITAN

Titan

The most prominent is Titan. Larger than Mercury, Titan is the only moon to retain a substantial atmosphere. Titan produces white convective clouds in cold nitrogen and methane atmosphere. Its surface is relatively young with few impact craters, dark regions of frozen hydrocarbons, flow channels, volcanoes, and sand of frozen water or hydrocarbons. The only moon with large bodies of methane/ ethane lakes, Titan, like Ganymede and Europa (Jupiter’s moons) may have a subsurface ocean of water and ammonia. The largest lake on Titan, Kraken Mare, is larger than the Caspian Sea.

BRIEF TAKES ON OTHER PROMINENT MOONS

Saturn’s moons

MIMAS: smallest and least massive of inner round moons, large impact crater called Herschel, no known geologic activity

ENCELADUS: one of the smallest of Saturn’s spherical moons, smallest known body geologically active, diverse surface that includes ancient heavily cratered terrain and younger smoother areas, south pole unusually warm and emits jets of water vapor and dust that replenishes material in Saturn’s E Ring and is the main source of ions in Saturn’s magnetosphere, may have liquid water under south pole, pure ice and high reflective surface

TETHYS: third largest inner moon, large impact crater called Odysseus, cast canyon system called Ithaca Chasma, composed of mainly water ice with little rock

DIONE: second largest inner moon, heavily cratered old terrain, extensive system of troughs and lineaments named “wispy terrain” indicates tectonic activity

RHEA: second largest moon, only moon that has rings, two large impact basins called Tirawa and Inktomi (“The Splat”), a young crater which has butterfly-shaped bright rays, geologically dead

HYPERION: closest moon to Titan (when Titan makes four revolutions, Hyperion makes three), very irregular shape, sponge-like tan-colored icy surface, numerous impact craters, no well-defined poles or equator (chaotic rotation) which makes its rotational behavior unpredictable

IAPETUS: third largest moon, most distant large moon, greatest orbital inclination (orbits at a greater altitude, at 14.72°), one hemisphere is pitch-black (Iapetus’s leading hemisphere collides with dust and ice particles as it rotates, darkening its surface) and the other is bright as snow

MISSIONS: Cassini-Huygens, Pioneer 11, Voyager

OVERVIEW

  • Order in Solar System: #6
  • Number of Moons: 62
  • Orbital Period: 29.5 years
  • Rotational Period: 10.5 hours
  • Mass: 5.6846 x 10^26 kg (95.152 Earths)
  • Volume: 8.2713 x 10 ^14 km³ (763.59 Earths)
  • Radius: 60,268 km (9.4492 Earths)
  • Surface Area: 4.27 x 10^10 km² (83.703 Earths)
  • Density: 0.687 g/cm³ (less than water!)
  • Eccentricity of Orbit: 0.056
  • Surface Temperature (Average): 134 K
  • Escape Velocity: 35.5 km/s
  • Apparent Magnitude: +1.47 to -0.24

Fun Facts Cluster 2: From Space Rocks to Drones (AskAstro)

1. SPACE ROCK SUICIDE: Scientists can detect a comet or asteroid colliding into the Sun’s surface. The self-destructing comet or asteroid will explode due to pressure of traveling into the Sun’s photosphere. The brightness and impact of the collision depends on the mass of the object. A collision as such is high unlikely, however, because: 1) most comets and asteroids would to dust and vapor in the sizzling atmosphere of the Sun 2) objects will lose most of its mass as they approach the Sun 3) objects normally orbit the Sun, so the objects’ orbit must be altered or the object may be from another planetary system.

2. STELLAR DONATIONS: In a binary star system, if stars are close enough, tides can become so strong that the more gravitationally strong star call pull gas from the surface of its companion. Though the “tidal transfer” depends on the mass of the donor star, if two stars have equal mass, the accretor (the star gaining mass) will steal mass if the donor star’s radius exceeds 38 percent of the binary separation (distance between the stars) no matter the separation.

3. COLOR CODE: The dark and light horizontal bands depend on the organization of winds in Jupiter’s atmosphere. The light bands have a eastward jet on the side closest to the pole, and vice versa in the dark bands. The zones (light bands) appear bright because of colorless high-altitude clouds that contain ammonia ice. The belts (dark bands) have much thinner high altitude clouds and darker particles.

4. DANGEROUS FLYBY: NASA calculates the planetary flybys with nothing but Newton’s laws of motion. The desired closest approach depends on the mission and how much added velocity boost the mission requires.  The mass and closeness of the planet determines the bending of trajectory the probe must undergo. The approach distance can range from a few hundred to several thousand kilometers.

From: Astronomy magazine December 2012 Vol 41 Issue 12

Curiosity: Update 8 – Methane-less Mars

Shooting Lasers from MSL’s TLS instrument

Mars has lost at least half its atmosphere since the planet’s inception, Curiosity confirms. Mars’ atmosphere is 100 times thinner than Earth’s. Other than shielding life from harmful UV radiation, atmosphere also controls the fluctuations in climate. Because Mars’ atmosphere contains more heavier varieties of carbon dioxide than lighter ones, the ratio suggest the planet has sadly lost much of its atmosphere. Mars’ thin atmosphere has nearly untraceable amounts of methane, only a few parts of methane per billion parts of Martian atmosphere. Microbes like bacteria emit methane. In fact, 95% of methane on Earth is produced by biological processes. Though Curiosity failed to find traces of methane in Gale Crater, Mars may yet host methane elsewhere.

Curiosity used its SAM instruments (Sample Analysis at Mars) and TLS (Tunable Laser Spectrometer). In the near future, SAM will analyze its first solid sample to search for organic compounds in rocks.

In addition, air samples from Curiosity match ones from trapped air bubbles in meteorites found on Earth. Ergo, those meteorites definitely originated from Mars. 1 billion years ago, a large asteroid collided into Mars and split into fragments.

References

 “NASA Rover Finds Clues to Changes in Mars’ Atmosphere.” JPL Caltech. JPL, 2 Nov 2012. Web. 5 Nov 2012. <http://mars.jpl.nasa.gov/msl/news/whatsnew/index.cfm?FuseAction=ShowNews&NewsID=1388&gt;.

Vergano, Dan. “NASA’s Curiosity rover confirms Mars lost atmosphere.” USA Today. USA Today, 2 Nov 2012. Web. 5 Nov 2012. <http://www.usatoday.com/story/tech/sciencefair/2012/11/02/curiosity-rover-mars-methane/1678033/&gt;.

Curiosity: Update 7 – Fingerprinting Martian Materials

X-Ray View of Martian Soil

The latest of Curiosity’s analyses show that the Martian minerals is similar to “weathered basaltic salts of volcanic origin in Hawaii.”  Curiosity’s CheMin (Chemistry and Mineralogy) instrument refines and identifies minerals in X-ray diffraction analysis on Mars. X-ray diffraction records hows minerals’ internal structures’ crystals react with X-rays. Identifying minerals in rocks and soil is crucial in assessing past environmental conditions. Each mineral has evidence of its unique formation. These minerals have similar chemical compositions but different structures and properties. The samples taken at “Rocknest” were consistent with scientists’ initial ideas of the deposits in Gale Crater. Ancient rocks suggest flowing water, while minerals in younger soil suggest limited interaction with water.

References

“NASA Rover’s First Soil Studies Help Fingerprint Martian Minerals First X-ray View of Martian Soil” JPL Caltech. JPL, 30 Oct 2012. Web. 5 Nov 2012.

The 8 Planets – Part 5: Jupiter

NEXT STOP: JUPITER!

Jupiter

The giant of planets and quite a monstrosity of swirling gases, Jupiter is the king of the planets. Through the asteroid belt, we arrive at Jupiter, fifth planet from the Sun. With bands of red and white falling and rising gases, Jupiter seems like a huge marble on a racetrack. Named for the Roman god of the sky, Jupiter is mighty and dominant in the solar system, with two and a half times the mass of all other planets in the solar system combined. Jupiter is known for its Great Red Spot, though all gaseous planets have storms. The Great Red Spot is an ongoing storm existing for millenia; about three Earths placed side-to-side can fit across the storm. The storm can attract and suck in weaker storms in its neighborhood. Like the other gaseous planets, Jupiter is mainly hydrogen and helium, the lightest elements. With 71% hydrogen and 24% helium, Jupiter has a composition like that of the primordial solar nebula. Because Jupiter is light for its size, it rotates very fast — its day is less than 10 hours! Though Saturn has noticeable ice rings, Jupiter has only faint rings mainly composed of non-reflective, rocky material. With the most mass, Jupiter has a strong magnetosphere. In fact, if Jupiter were seventy-five times larger, it would have enough pressure and heat inside its core to perform nuclear fusion, produce its own energy, and become a star! But the smallest red dwarfs, or the bare cores of stars, is only three times the mass of Jupiter. Jupiter produces heat in excess to the solar radiation it receives by the Kelvin- Helmholtz mechanism (no heat transfer, by contraction) . By this mechanism, Jupiter shrinks 2 cm per day; Jupiter was actually twice as its current diameter and much hotter at the time of formation. For its interior, scientists are not sure whether Jupiter has a icy or metallic core or even no core at all. Jupiter, does indeed, have a liquid metallic hydrogen layer about 78% of the radius. Droplets of helium and neon precipitate in this layer, so little to none is found in the atmosphere. The liquid metallic hydrogen layer is surrounded by a transparent, supercritical (between liquid and gas phases) hydrogen layer. Water clouds’ polarity in the atmosphere cause lightning 1000x stronger than on Earth and winds often reach 100 mph in zonal (zones and belts on Jupiter, falling and rising gases) jets. In addition, Jupiter has orange and brown clouds that change color when exposed to the Sun’s UV light. Unlike Earth, Jupiter has a low axial tilt, giving less solar radiation to the poles, but convection distributes heat to the poles, balancing the temperatures.

THE GALILEAN MOONS

Jupiter has the most number of moons at 67. All four moons are named after several of many of Zeus’ lovers in Greek Mythology, which seems appropriate since Jupiter is Zeus in Roman form. First discovered in 1610 by Galileo Galilei, Jupiter’s four moons are Io, Europa, Callisto, Ganymede (or I Eat Green Carrots). Galileo’s discovery of the moons, initially called Cosmica Sidera (“Cosimo’s stars”) proved that there were other celestial objects orbiting other planets— that everything did not orbit around the Earth. With a telescope you can easily see the four Galilean moons orbiting the planet. You can usually see three or four of the moons; sometimes the moon is positioned behind Jupiter so it is not visible on some nights. Io, Europa, Ganymede, and some of the largest satellites in the solar system form the Laplace resonance; every time Io orbits Jupiter four times, Europa orbits two times, and Ganymede one time. The resonance invokes the moons’ gravitational effects to distort their orbits to be more elliptical. In contrast, Jupiter tidal force, which keeps the moons in orbit, circularizes the orbits. The push and pull heats the moon’s interiors by friction. The closer the moon, the hotter, more active, and denser the moon is; the further the moon, the colder, unchanging, and less dense the moon is.

Jupiter’s moons: Io, Europa, Ganymede, Callisto

IO

Io is the innermost of the Galilean moons and fourth largest moon in the solar system. Its surface ever-changing, Io has over 400 active volcanoes. Some of Io’s more than 100 mountains are taller than Mount Everest! Io has a thin atmosphere comprised of sulfur dioxide and silicate rock surrounding a molten iron or iron sulfide core.

EUROPA

Europa is the second Galilean moon and the smallest, slightly larger than Earth’s moon. In contrast to Io, Europa has one of the smoothest surfaces in the solar system, with a layer of ice and water over the mantle of the planet. Scientists hypothesize that water may exist on Europa and that the planet may house extraterrestrials. Heat energy from tidal flexing, or push and pull of Jupiter and its moons’ gravity, keeps the water liquid. Europa has prominent reddish brown markings that may be volcanic water splitting the surface. It also has an atmosphere of oxygen.

GANYMEDE

Ganymede is the largest natural satellite in the solar system and the third Galilean moon. In fact, Ganymede is larger than even Mercury! Ganymede is icy and the only planet to have a magnetosphere, possibly created by convection with its liquid iron core. Like Europa, Ganymede may also have water (salt), but 200 km below its surface between layers of ice. Its surface comprises of highly cratered dark regions and younger regions with grooves and ridges. Its thin atmosphere includes oxygen, O², and maybe O³ (ozone) and hydrogen.

CALLISTO

Callisto is the last and least dense of the Galilean moons. Callisto has an ancient, heavily cratered and unaltered ice surface. It has a homogenous mix of rock and ice.

MISSIONS: Pioneer 10 and 11, Voyager 1 and 2, Ulysses, Cassini, New Horizons, Galileo, Juno (2011), JUICE (2022)

OVERVIEW

  • Order in Solar System: #5
  • Number of Moons: 67
  • Orbital Period: 11.86 years
  • Rotational Period: 9.925 hours
  • Mass: 1.8986 x 10^27 kg (317.8 Earths)
  • Volume: 1.4313 x 10 ^15 km³ (1321.3 Earths)
  • Radius: 71,492 km (11.209 Earths)
  • Surface Area: 6.1419 x 10^10 km² (121.9 Earths)
  • Density: 1.326 g/cm³
  • Eccentricity of Orbit: 0.048775
  • Surface Temperature (Average): 165 K
  • Escape Velocity: 59.5 km/s
  • Apparent Magnitude: -1.6 to -2.94