Astronomy 5 Online Week 5 Reading Questions 1. What is the most accurate method for finding the diameter of the gas giant planets? -Through Stellar Occulation. (a) Occultations occur when a planet, moon, or ring passes in front of a star. (b) As the planet moves (from right to left as seen from Earth), the starlight is blocked. The amount of time that the star is hidden, combined with information about how fast the planet is moving, gives the size of the planet. 2. How did we measure the mass of the gas giant planets in the past? How have we measured it more recently? -Before the space age, scientists measured a planet’s mass by observing the motions of its moons. -Planetary spacecraft now make it possible to measure the masses of planets more accurately. As a spacecraft flies by, the planet’s gravity deflects it. By tracking and comparing the spacecraft’s path, astronomers can accurately measure the planet’s mass. 3. Why are Jupiter and Saturn called gas giants but Uranus and Neptune ice giants? - Jupiter and Saturn are composed of hydrogen and helium and are therefore known as gas giants. - Uranus and Neptune are known as ice giants because they contain much larger amounts of water and other ices than Jupiter and Saturn. 4. What does the fast rotation of the giant planets do to their shapes? - the rapidly rotating giant planets are oblate—they bulge at their equators because the inertia of the rotating material near the equator acts to counter gravity. 5. What is the Great Red Spot on Jupiter? How big is it and how long has it been seen? - a giant hurricane/storm - having a length of 25,000 kilometers (km) and a width of 12,000 km, the Great Red Spot could hold two Earths side by side within its boundaries. In 2016, the Great Red Spot shrank to become only as large as one Earth, 300 years but notes say 350 6. Why do Uranus and Neptune look blue? -it comes from the methane of the clouds/atmosphere 7. What stops the cores of the giant planets from turning into gas (steam)? -the extremely high pressures at the centers of the giant planets prevent water from turning into steam, because of the extreme pressure, the core consists of water, rock, and metals and it heats it up making it all liquid at the same time 8. What provides most of the energy that escapes from the giant planets? What does this mean about the size of the planets? - Thermal energy from the core drives convection in the atmosphere and eventually escapes to space as radiation, it means its continuously shrinking.- Jupiter is contracting by only 1 millimeter (mm) or so per year. If it were to continue at this rate, in a billion years Jupiter would shrink by only 1,000 km, a little more than 1 percent of its radius. 9. Why is Jupiter so much larger than Saturn? -With more space between planetesimals, their cores would have taken longer to build up. Saturn may have captured less gas than Jupiter, both because its core formed somewhat later and because less gas was available at its greater distance from the Sun. 10. Why do Uranus and Neptune have so much less hydrogen and helium than Jupiter and Saturn? --The cores of Uranus and Neptune were smaller and formed much later than those of Jupiter and Saturn, at a time when most of the gas in the protoplanetary disk had been blown away by the emerging Sun. 11. Describe the strength of the magnetic fields of the giant planets compared with Earth. - from 50-20,000 times stronger - In Jupiter and Saturn, magnetic fields are generated by circulating currents within deep layers of metallic hydrogen. -In Uranus and Neptune, magnetic fields arise within deep oceans of liquid water and ammonia made electrically conductive by dissolved salts. 12. Describe how moons can affect the rings of the giant planets. -If a moon (or other planetesimal) orbits a large planet, the force of gravity will be stronger on the side of the moon closest to the planet and weaker on the side farther away. This stretches the moon, as you saw in the discussion of tidal forces in Chapter 6. If the tidal stresses are greater than the self-gravity that holds the moon together, the moon will be torn apart. The distance at which the tidal stresses exactly equal the self-gravity is called the Roche limit. The Roche limit does not apply to objects that are held together by other forces—objects like people or bowling balls. It only applies to objects that are held together by their own gravity. -If the moon is massive enough, it exerts a significant gravitational tug on a ring particle as it passes by. If this happens to many particles through many orbits, particles will be pulled out of the area, leaving a lower-density gap. 13. How do rings form? Why do they not last for long periods of time? -If a moon or planetesimal comes within the Roche limit of a giant planet, it is pulled apart, leaving many small particles to orbit the planet. These particles gradually spread out. Collisions circularize and flatten out the orbits, and rings are formed. -Ring particles are constantly colliding with one another in their tightly packed environment, either gaining or losing orbital energy. These collisions can cause particles at the ring edges to leave the rings and drift away, aided by non-gravitational influences such as the pressure of sunlight14. How is the material in the rings of Saturn different from the rings of the other giant planets? How does this change how they appear in the sky? - they are then only rings that contain ice! It reflects sunlight, making it look bright! 15. Describe the thickness of the Saturn’s rings compared to their diameter. - Although Saturn’s bright rings are very wide—more than 62,000 km from the inner edge of the C Ring to the outer edge of the A Ring—they are extremely thin. Saturn’s bright rings are no more than a hundred meters and probably only a few tens of meters from their lower to upper surfaces. The diameter of Saturn’s bright ring system is 10 million times the thickness of the rings. If the bright rings of Saturn were the thickness of a page in this book, six football fields laid end to end would stretch across them. Ring structure among 16. What is the definition of a planet? What is the definition of a dwarf planet? - A planet is defined as an object that orbits the Sun and is large enough to (1) pull itself into a round shape and (2) clear the area around its orbit,