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