1. A Planetary Overview Courtesy: NASA

2. 2© Sierra College Astronomy Department A Planetary Overview Solar System Roll Call The Sun the is largest and brightest object in the solar system The Sun is hot (5800 K on surface) The Sun is gaseous and converts matter into energy in core The Sun has the greatest influence on the rest of the solar system (light, solar wind…)

3. 3© Sierra College Astronomy Department A Planetary Overview Solar System Roll Call Mercury is the smallest planet in the solar system It rotates every 58.6 days and revolves every 88 days and is tidally locked to the Sun The produces 88 days of day and 88 days of night, making temperatures extreme (425°C to -150°C). Two spacecraft has visited Mercury including one which orbited around Mercury

4. 4© Sierra College Astronomy Department A Planetary Overview Solar System Roll Call Venus is often called Earth’s “twin” because it is nearly the same size as the Earth. But it’s nothing like the Earth… It rotates backwards (or upside down) very slowly It is covered with an atmosphere of mostly CO 2 which allows a runaway greenhouse effect to occur raising the temperature to 470°C (880°F) planetwide Its surface pressure in 90 times greater than the Earth and there are clouds of sulfuric acid near the surface of the planet

5. 5© Sierra College Astronomy Department A Planetary Overview Solar System Roll Call Earth is only world that we know of that has or had life on it It is the only world with a significant amount of oxygen in the atmosphere It is the only world with significant amounts of liquid water It is the closest planet to the Sun to have a moon and our Moon is quite large compared to the Earth

6. 6© Sierra College Astronomy Department A Planetary Overview Solar System Roll Call Mars may bear the closest resemblance to the Earth It has a thin atmosphere of mostly CO 2 It has polar caps made of CO 2 and water-ice In the past, water very likely flowed on the surface It has great geological wonders such as a great canyon and the largest volcano in the solar system It has two tiny moons It is the most studied extraterrestrial planet and has several spacecraft present and proposed to land or orbit Mars.

7. 7© Sierra College Astronomy Department A Planetary Overview Solar System Roll Call Jupiter is largest planet in the solar system and is made mostly of gas with a Earth sized rocky-ice core in the center It has more than 300 times the mass and 1000 times the volume of the Earth Its atmosphere has many storms many of which have lasted for hundreds of years Its four largest moons (of 67) have interesting properties too (active volcanoes, subsurface water, magnetic fields)

8. 8© Sierra College Astronomy Department A Planetary Overview Solar System Roll Call Saturn is another gaseous giant planet with a spectacular ring system The ring system is made of millions of ice-dust chunks orbiting around the planet Saturn has over 60 moons, a few of them midsize moons and one large one, Titan, which has a significant atmosphere.

9. 9© Sierra College Astronomy Department A Planetary Overview Solar System Roll Call Uranus (YUR-uh-nus) is a smaller gas giant with a green- blue color due to methane It has several dozen moons a few of which are midsize The entire system (planet, rings, moons) is tilted on their side It has been visited by only one spacecraft (Voyager 2) Neptune is just a bit smaller than Uranus and bluer in color It has a dozen moons, one of which is large (Triton). Triton is the largest moon to go backward around the planet It has been visited by only one spacecraft (Voyager 2)

10. 10© Sierra College Astronomy Department A Planetary Overview Solar System Roll Call Pluto (and the other Dwarf Planets) are round object which orbit around the Sun Pluto was discovered as a planet in 1930, but was an oddball world. One of its 3 moons is half its size (Charon). It was visited by spacecraft in 2015. Soon in the 1990s other objects out where Pluto lived were being discovered. One of these, Eris, was found to be a little larger than Pluto In 2006, the phrase “dwarf planet” was defined for these objects and asteroids (like Ceres) which were round but were found “nearby” other solar system objects. Haumea and Makemake were added in 2008.

11. 11© Sierra College Astronomy Department A Planetary Overview Solar System Features Looking at the general characteristics, there are 4 features which stand out: 1. Patterns of motion among large bodies 2. Two major types of planets 3. Asteroids and comets 4. Exceptions to the rules

12. 12© Sierra College Astronomy Department A Planetary Overview Distances In The Solar System Measuring Distances in the Solar System Copernicus used geometry to determine relative distances to the planets. Today we measure planetary distances using radar. Average distances to the planets from the Sun range from.387 AU for Mercury to 39.53 AU for Pluto.

13. 13© Sierra College Astronomy Department A Planetary Overview Feature 1: Patterns of Motion All planetary orbits are ellipses, but all are nearly circular. Each of the planets revolves around the Sun in the same direction. All planets - except Venus, Uranus - rotate in a counterclockwise direction. Most of the satellites revolving around planets also move in a counterclockwise direction, though there are some exceptions.

14. 14© Sierra College Astronomy Department A Planetary Overview Feature 1: Patterns of Motion Inclination of a planet’s orbit is the angle between the plane of a planet’s orbit and the ecliptic plane (the plane of the Earth’s orbit). The elliptical paths of all the planets are very nearly in the same plane (inclination about 0°), though Mercury’s orbit is inclined at 7° and Pluto’s at 17°.

15. 15© Sierra College Astronomy Department A Planetary Overview Planet Diameters Diameters of Non-Earth Planets Diameters are determined from distances (from the Earth to the planet) and the planet’s angular size via the small angle formula Diameter of Sun (1.39 × 10 6 km) is over 100 times that of Earth (1.3 × 10 4 km). Jupiter’s diameter is 11 times that of Earth. Pluto’s diameter is 1/5 that of Earth.

16. 16© Sierra College Astronomy Department A Planetary Overview Planet Masses Mass of the Planets Kepler’s third law was reformulated by Newton to include masses: A 3 /P 2 = K (M 1 + M 2 ) Newton’s statement of Kepler’s third law allows us to calculate the mass of the Sun. Consider the orbits of planets around the Sun. Since one of the masses to the Sun (the other being a planet), the sum of the two is essentially equal to the mass of the Sun, and the equation can be rewritten as: A 3 /P 2 = KM

17. 17© Sierra College Astronomy Department A Planetary Overview Planet Masses We can do the same sort of calculation for planets as long as they have satellites orbiting them The masses of 6 of the 8 known planets can be calculated based on the distances and periods of revolution of these planets’ natural satellites. For Mercury and Venus, which do not possess any natural satellites, accurate determinations of their respective masses had to await orbiting or flyby space probes.

18. 18© Sierra College Astronomy Department A Planetary Overview Feature 2: Classifying the Planets The planets (except Pluto) fit into two groups: the inner terrestrial planets and the outer Jovian planets. Size, Mass, and Density The Jovian planets have much bigger diameters and even larger masses than the terrestrial planets. Terrestrial planets are more dense, however. Earth is the densest planet of them all.

19. 19© Sierra College Astronomy Department A Planetary Overview Classifying the Planets Satellites and Rings The Jovian planets have more satellites than the terrestrials. 4 Jovian planets: 170 total satellites as of July 2013 (67 for Jupiter, 62 for Saturn, 27 for Uranus, and 14 for Neptune). 4 terrestrial planets: 3 total satellites. Pluto has 5 satellites. Eris has one satellite. Haumea has 2. Each Jovian planet has a ring or ring system. None of the terrestrial planets do.

20. 20© Sierra College Astronomy Department Terrestrial Jovian Near the SunFar from the Sun SmallLarge Mostly solidMostly liquid & gas Low massGreat mass Slow rotationFast rotation No ringsRings High densityLow density Thin atmosphereDense atmosphere Few moonsMany moons A comparison of planetary characteristics

21. 21© Sierra College Astronomy Department A Planetary Overview Feature 3: Asteroids and Comets Asteroids These rocky bodies orbit the Sun, but are much smaller than planets. Most lie between Mars and Jupiter Comets Small icy (water, ammonia, methane) objects which occasionally visit the inner solar system and become visible Comets originate from two regions: the Kuiper Belt and the Öort Cloud

22. 22© Sierra College Astronomy Department A Planetary Overview Feature 4: Exceptions to the Rules There are objects in the solar system that are unusual or have characteristics which are unusual as compared to the rest of the solar system. Some examples:  Venus and Uranus rotate differently (backwards and on its side, respectively)  Small moons of Jupiter and Saturn and the large moon Triton (around Neptune) revolve in the opposite direction of the rotation of the host planet.  While other terrestrial planets have no moons (Mercury, Venus) or tiny moons (Mars) The Earth’s moon is large compared to the Earth.

23. 23© Sierra College Astronomy Department The End