Properties of the Planets

1. Terrestrial Planets Mercury Venus Earth Mars Jovian Planets Properties of the Planets This presentation will show you some of the important physical differences between the Terrestrial and Jovian Planets. First the Terrestrial planets…

2. Mercury Mercury: Heavily cratered ancient rocky surface. The innermost of the planets. We have only photographed half of its surface because the planet rotates very slowly and the flyby spacecraft (Mariner) could only photograph the sunlit portion.

3. Venus Venus: Covered from pole to pole with bright clouds. The surface cannot be seen from orbit at visual wavelengths. Radar instruments on the Magellan spacecraft mapped the surface and found very few craters suggesting an active geology that erases resurfaces the ancient landscapes

4. Earth Earth: The only planet with liquid water on its surface and the only planet with molecular oxygen in its atmosphere. The Earth’s surface, like that of Venus, has very few impact craters, due to an active geology (plate tectonics) and robust weathering from wind and rain.

5. Mars Mars: The last Terrestrial planet. If has an anomolusly low density for a terrestrial planet, suggesting that it is made of a different mix of materials than the other terrestrial planets. Its surface shows signs of ancient geology, but no evidence recent wide scale activity. Where is the water on Mars is the focus of current scientific work.

6. Terrestrial Planets Mercury Venus Earth Mars Jovian Planets Jupiter Saturn Uranus Neptune Properties of the Planets Now, the Jovian planets...

7. Jupiter Jupiter: The closest Jovian planet. Composed almost entirely of hydrogen and helium gas, this planet began as a giant ball of ice and rock that attracted a deep atmosphere of gas from the nebula (cloud of gasses) the Sun and planets formed from.

8. Saturn Saturn: Almost ten times farther from the Sun than the Earth, this could world of gasses the most spectacular set of rings of all the Jovian planets. The rings are believed to be the remains of a moon that drifted to close to Saturn abd broke apart, distributing its material around the equatorial plane.

9. Uranus Unanus: The first telescopically discovered (1781) planet. It remains the most mysterious of planets. No clouds can be seen it is hydrogen and helium atmosphere tinted blue by a slight enrichment of methane. Further adding to the mystery, the rotation axis of Uranus is tipped almost 90 degrees relative to the ecliptic suggesting some catastrophic event slammed into Uranus and “knocked” it over.

10. Neptune Neptune: Much like Uranus in appearance, size and compostion, although cluds can be seen throuogh the atmosphere. These most distant Jovian planets are the runts of the Jovian litter, yet they still occupy a volume more than that of 64 Earth’s.

11. Terrestrial Planets Mercury Venus Earth Mars Jovian Planets Jupiter Saturn Uranus Neptune Properties of the Planets What about Pluto? We’ll cover Pluto a bit later…..

12. Pluto Pluto: As we shall see shortly, Pluto is a world that doesn’t fit the pattern established by the other planets. It is far too small and of the wrong composition to be a Jovian planet and too small, too far away and the wrong composition to be a Terrestrial planet. Pluto, shown here with its moon Charon, may be pieces of a planet that was not able to finish its formation. It is considered to be a piece of debris leftover from the era of planet formation.

13. Let’s look at the numbers. Please try to see the similarities within each class of planet and the contrasts between them.

15. Terrestrial Planets

16. Terrestrial Planets Jovian Planets

17. This meter stick ninja is a cute way of visualizing the relative distances of the planets form the Sun. In this image, imagine that 1 inch equals 1 A.U. Since there are about 39 inches in a meter, the entire retinue of planets can be placed on a single meter stick at this scale.

18. Meter-stick Ninja Pluto 39” Earth 1” Jupiter 5.2” Uranus 19” Saturn 10” Neptune 30” Mercury 1/3” Venus ¾” Mars 1 ½” Notice that, at this scale, all the Terrestrial Planets are within 1½ inches from the Sun. The Jovian planets are spread between 5 inches and 30 inches.

19. Sunrise on the PlanetsA simulation The next series of slides are meant to help you visualize the effect of the vast distances of the Solar System by simulating, in a simple way, what sunrise would look like from each planet, taking into account its distance from the Sun. At the bottom of each slide appears the amount of solar energy available at that distance from the Sun. The solar energy follows an inverse square law like gravity. Notice how rapidly the available solar energy drops as you progress through the solar system.

20. Sunrise on Mercury Available Solar Energy ~9,350 W/m2

21. Sunrise on Earth Available Solar Energy ~1,350 W/m2

22. Sunrise on Jupiter Available Solar Energy ~50 W/m2

23. Sunrise on Saturn Available Solar Energy ~15 W/m2

24. Sunrise on Uranus Available Solar Energy ~4 W/m2

25. Sunrise on Neptune . Available Solar Energy ~1.6 W/m2

26. Now we’ll compare the masses of the planets. Note that we will use the Earth as a standard mass for convenience.

27. Terrestrial Planets

28. Terrestrial Planets Jovian Planets

29. Imagine a “planetary balance” that could weight the planets in terms of Earth masses. How would the other planets compare?

30. About 9 planet Mars’ to equal one Earth

31. About 17 planet Earth’s to equal one Neptune

32. About 318 planet Earth’s to equal one Jupiter

33. Now, we’ll examine the radii of the planets.

34. Terrestrial Planets

35. Terrestrial Planet Radii These images of the Terrestrial planets are approximately to scale. Earth Mars Venus Mercury

36. Terrestrial Planets Jovian Planets

37. Jovian Planets radii Uranus These images of the Jovian planets are approximately to scale. Neptune Jupiter Saturn Saturn

38. Jovian Planets compared to Earth Notice how large all the Jovian planets are compared to the largest Terrestrial Planet, Earth Uranus Neptune Earth Jupiter Saturn

39. A Mnemonic for the Radii of Terrestrial Planets …and Friends This is a useful memory aid for the radii of Terrestrial Planets.

40. Now, We’ll examine density. Density of an object tells a scientist something about the composition of the object. Some bench mark densities follow: Material Density Water 1.0 g/cm3 Rock 3 to 5 g/cm3 Iron 7.8 g/cm3

41. Most Terrestrial Planets have densities around 5.3 g/cm3 indicating a composition of mostly rock with a smaller amount of iron

42. Most Terrestrial Planets have densities around 5.3 g/cm3 indicating a composition of mostly rock with a smaller amount of iron Mars, however, has a anomalously low density. We’ll try to explain why the density is low when we discuss planet formation.

43. The Jovian planet densities are MUCH lower than the Terrestrial planets. These densities are consistent with a compositon of compressed gas.

44. This graph displays the density vs. distance from the Sun for each planet

45. This trend can be model by the dotted line.

46. This slide contrasts Pluto’s properties with the other planets. You can see that it does not fit the pattern of the Jovian planet in mass, radius or density. Neither does it fit the Terrestrial planets.

47. In my on-site class I ask my students to memorize the numbers you can see on this slide. I expect no less of you.

48. Please notice that the closest Jovian planet, Jupiter, is also the largest in mass and radius. We will have an explanation for why the closest Jovian planet is the largest and why the succeeding Jovian planets tend to get smaller in mass and radius when we look at the formation of the Solar System.

49. Planetary Systems are characterized by two classes of planets with mutually exclusive properties.

50. Terrestrial Planets Close to the central star Small in mass and radius High density Planetary Systems are characterized by two classes of planets with mutually exclusive properties.