THE 8 PLANETS
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
NEXT STOP: 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.
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 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 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 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)
- 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
- 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.