The 8 Planets – Part 5: 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.


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 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

The 8 Planets – Part 2: Venus



An inferno fireball on the inside, a smooth yellow marble on the outside. Venus, the two-faced planet known as “heaven and hell.” Beautiful yet dangerous, Venus is rightfully named after the Roman goddess of love and beauty. In modern culture, people associate Venus with beauty products… and Venus Williams, the world champion tennis player.

Shrouded by its thick sulfuric cloud atmosphere, Venus is the second planet from the Sun and the hottest planet on average in the solar system. Also known as the Morning Star or Evening Star, Venus reflects sun light strongly, with a high albedo. Because Venus’ size is similar to Earth’s, Venus is sometimes to referred to as “Earth’s twin” or “Earth’s sister.” Other than size, however, Venus and Earth have nothing in common. Venus’ atmosphere rains sulfuric acid on the dry dessert-like surface! Its thick atmosphere (90 times thicker than Earth’s) composed of mainly CO2 traps carbon dioxide (greenhouse effect) and maintains a searing temperature on Venus. Venus may have harbored water once, but rising temperatures evaporated all liquid water, leaving a volcanically active surface.  Mapped in 1990-1991 by Project Magellan, Venus’ surface comprises of 80% smooth, volcanic plains (70% plains with wrinkled ridges and 10% smooth plains) and 20% two highland “continents” Aphrodite Terra and Ishtar Terra. Venus has little impact craters but various volcanic features such as “novae” (star-like fracture systems) and “arachnoids” (spider-web-like fractures). Scientists know little about Venus’ interior without seismic data, but Venus’ size and density suggest an interior similar to Earth’s. Scientists have attempted to build probes to land on Venus’ surface, but all attempts failed (most only enter Venus’ atmosphere then burn up and crash). Venus’ clouds reflect and scatter 90% of sunlight, so scientists can only map its surface with radar. In fact, Venus’ atmosphere has an ozone layer and its clouds can produce lightning! Unlike any other planet, Venus spins from east to west, in a retrograde motion. Because Venus spins backward, its rotational period is longer than its orbital period; a day on Venus is longer than a year! Unlike Earth, Venus has a negligible magnetic field, unable to divert most solar wind. Like Mercury, Venus undergoes phases as seen from Earth. When Venus is in a crescent phase observers can actually see a mysterious ashen light. In the 17th century, Galileo proved the heliocentric theory with observations of Venus’ phases. Though Venus has no moons, scientists believe the planet had at least one that crashed into its surface. 10 million years after the collision, another impact changed Venus’ spin. Another possibility is that strong solar tides can disturb large satellites. Recently, the Transit of Venus occurred in June, when the planet crossed over the Sun.

MISSIONS: Venera, Sputnik, Mariner, Cosmos, Vega, Pioneer Venus, Magellan, Cassini, MESSENGER, Venus Express

*Many of these missions (Sputnik, Mariner) are series with only some successful and some only fly-bys; Venera is exclusive for Venus


  • Order in Solar System: #2
  • Number of Moons: 0
  • Orbital Period: 225 days
  • Rotational Period: 243 days
  • Mass: 4.8685 x 10^24 kg (0.815 Earths)
  • Volume: 9.28 x 10^11 km³ (0.866 Earths)
  • Radius: 6,052 km (0.9499 Earths)
  • Surface Area: 4.60 x 10^8 km² (0.902 Earths)
  • Density: 5.243 g/cm
  • Surface Pressure: 9.3 MPa
  • Eccentricity of Orbit: 0.2
  • Surface Temperature (Average): 735 K
  • Escape Velocity: 10.36 km/s
  • Apparent Magnitude: -4.9 (crescent) to -3.8 (full)

Modern Astronomy: 1500-1800

Modern Astronomy (1500 – 1800 A.D.)

Nicolaus Copernicus

Nicolaus Copernicus (1473-1543)

The Polish astronomer Nicolaus Copernicus advocated the heliocentric view, calculated distances to planets and period of planets, and explained the retrograde motion. Before his death in 1543, Copernicus revolutionized astronomy by publishing his work,  De revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres).

Heliocentric Theory

Tycho Brahe

Tycho Brahe (1546-1601)

The Danish astronomer Tycho Brahe made accurate measurements of planetary positions by using a “quadrant.”

Astronomers Using a Quadrant

Johannes Kepler

Johannes Kepler (1571-1630)

As Tycho Brahe’s student, Johannes Kepler received his teacher’s measurements when Brahe died in 1601. In 1610, Kepler then derived the three laws of planetary motion using Brahe’s measurements and empirical rules. Instead of the circular orbits that Copernicus advocated, Kepler discovered that the planets and stars traveled in elliptical orbits.

Kepler’s 1st Law

Kepler’s 1st Law (1609) The planets move around the Sun in ellipses, having the Sun at one of its foci.

Ellipse: 1) each orbit has a shape and a size; 2) the eccentricity (e = 1- B/A) describes how elongated the ellipse is; 3) the size is described by the semi-major axis (2A); 4) when B=A, the orbit is circular and e=0 (eccentricity ranges from 0 to 1, with 1 as the most eccentric)

Kepler’s 2nd Law

Kepler’s 2nd Law (1609)/ Law of Equal Areas: Each planet revolves in such a way that the line joining it to the Sun sweeps over equal areas in equal time intervals

Kepler’s 3rd Law (1618)/ Harmonic Law: The square of the period of revolution is proportional to the cube of the average distance of the planet to the Sun (P²=A³, where P = the period in years and A = the semi-major axis of an orbit in AU)

Consequence: Distant planets take longer to orbit the Sun and travel at slower speeds

Galileo Galilei

Galileo Galilei  (1564-1642)

Italian astronomer Galileo Galilei, the “father of modern science,” was the first to use the telescope to observe the Moon, Jupiter and its moons (Io, Europa, Ganymede, and Callisto), Saturn, and phases of Venus. His observations supported the heliocentric view. After making the telescope in 1609, Galileo observed mountains on the Moon and discovered the Galilean moons of Jupiter. While Ptolemy thought Venus will always appear as a “crescent” and never as a full circle, Galileo discovered that Venus appears in phases. However, Galileo, deemed a heretic by the Roman Catholic Church Inquisition in 1615, was placed under house arrest for the rest of his life.

Isaac Newton

Isaac Newton (1642-1727)

LIFE & ACHIEVEMENTS: English physicist Isaac Newton, often known as the greatest and most influential scientist who ever lived, revolutionized astronomy and physics with his three laws of motion and law of universal gravitation. Born in 1642 (Galileo’s death) and into a world of mysticism, Newton was the last philosopher/ scientist. Newton derived Kepler’s three laws of planetary motion, invented calculus, and answered fundamental questions about the nature of light, motion, and time. Still, with all his achievements, Newton invented a new kind of telescope, studied theology, alchemy, and chemistry.

THE WORLD AROUND NEWTON: At the time, “gravity” meant solemn and was a mood, not a force. People believed that the world was not “solvable.” Light and heavy things separated themselves “naturally.” Time was hard to separate and the concept of motion was not well-defined. Philosophers/ scientists constrained motion to: pushing, pulling, carrying, twirling, combining, separating, waxing, and waning. Aristotle had defined things “in motion” as: an apple ripening, a dog running, a child growing up, and a spinning top.

EARLY LIFE: At Cambridge University, Aristotle was the sole authority on logic, ethics, rhetoric, cosmology, and mechanics. Because his tutor was a linguist, Newton mostly studied on his own. Born poor, Newton conserved paper costs by writing in a tiny font.

ROAD TO DISCOVERY: While Galileo had discovered uniform acceleration (all bodies fall at the same rate), Newton asked: How and why does something’s velocity change? In 1664, the plague in England caused Cambridge to close down, but Newton continued to discover fundamental ideas in astronomy and physics. By first reading works such as Euclid’s “Elements” and that of Descartes, Newton explored the concept of infinity, curvature, and the rate of the bending of lines, trajectories. “To resolve problems of motions,” Newton then invented calculus. To explore the nature of light, Newton used a prism to “isolate” blue light and passed the blue light through a second prism; the light stayed blue. Newton discovered that prisms only separate color and white light was “made up of” different colors. Furthermore, light comes from the Sun in eight minutes, the Moon tugs at the Earth to create waves, and the same Universal Laws exist throughout the Universe.

IMPACT: Newton defined these concepts: “mass,” “action,” “reaction,” “momentum,” “inertia,” “to feel the force of gravity.” He quantified the world with calculus and made people Newtonians (think that the world is solvable). Starting from the Newtonian Age, scientists linked mathematics and science to prove facts and claims.

Law of Universal Gravitation: Every particle in the Universe attracts every other particle with a force proportional to the product of their mass and inversely proportional to the square of the distance between them.

Gravity = the force between two objects that depends on the objects’ masses and on the distance between them

  • Gravity is a mutual force acting on both bodies
  • The force on each body is t he same size, but in opposite directions

Newton’s 1st Law/ Law of Inertia: Every material object continues in its state of rest, or of motion in a straight line, unless it is compelled to change that state by external forces. In other words, a stationary object will stay at rest, while a moving object will stay in constant motion unless an unbalanced force acts on it. “Constant” motion = at a constant speed and a constant direction.

Inertia = the resistance of any physical object to its state of motion or at rest

Balanced Forces = Forces cancel one another and no change in motion results (e.g. sitting in a chair)

Unbalanced Forces = One force is greater than another, causing a change in motion (e.g. jumping off a diving board)

Speed and Velocity = Velocity combines the speed of an object and the direction of motion and is equal to the change in distance over change in time (V = d/t) (e.g. speed = driving 60 miles/ hr; velocity = driving 60 miles/hr east)

Newton’s 2nd Law: The acceleration of an object is directly proportional to the net force acting on it

Acceleration = a change in velocity; objects of different masses on earth fall at the same rate

Newton’s 3rd Law

Newton’s 3rd Law: For every action there is an equal and opposite reaction.

Forces and Orbits: For objects in uniform circular motion, the force of gravity is perpendicular to the motion, the object orbits at constant speed, gravity changes the direction only of the motion, and there is still an acceleration.

Elliptical Orbits: For planets in elongated orbits, gravity changes both the direction and the speed of the planet, the planet slows down as it moves away from the Sun, and the planet speeds up as it approaches the Sun

Gravity Depends on MassF gravity = G x (m1m2)/r², where m1 and m2 are the masses of the two objects, r is the distance between the two masses, G is Newton’s gravitational constant (6.7 x 10-¹¹ m³kg s²)

Newton’s Derivation of Kepler’s Laws Using His Law of Gravitya1 = F gravity/ m1 = G x m2/r²; accelerations are smaller for objects far from the Sun (when r is large)

Newton’s Derivation of Kepler’s 3rd LawP² = [( 4∏ )/ G (m1 + M2)] (R³)