Our local neighbourhood - The Solar System

1. Our local neighbourhood - The Solar System • Dr Nicola Loaring • SALT/SAAO • nsl@saao.ac.za

2. DEMO Concept: The Scale of our Solar System • If the Sun were a grapefruit (10cm) • Earth, grain of sand 1mm, 15 m away • Jupiter, marble 1.5cm, 80 m awayPluto, tiny grain of sand 0.2mm, 700 m away • And the NEXT CLOSEST sun (or star) would be in ... Nairobi !

3. Concept: Two types of Planet • Terrestrial planets: • Rocky with molten cores • Jovian planets: • Mainly gas and liquid with rocky cores

4. Rocky Planets They have a solid rock surface with an iron core and a weak or no atmosphere. The rocky worlds are the 4 inner planets plus our Moon

5. Gas Giants There are 4 gas giant planets in our solar system. These planets have NO solid surfaces – just gas and clouds that get denser as you move to their centre.

6. Relative distribution of the two types of Planets Gas giant worlds are far from the Sun Rocky worlds are close to the Sun Wikipedia

7. Relative sizes Gas giant worlds are much larger than rocky worlds Jupiter – largest gas giant world Earth – largest rocky world NASA/JPL

8. Activity opportunity: Powers of 10

9. Relative numbers of rings and moons Rocky worlds have no rings and no, or few, moons. www.hubblesite.org Gas Giant worlds have rings and many moons. (From left to right: Enceladus and shadow, Dione and shadow. Titan and Mimas are off the limb to the right).

10. Why are there two types of planet?

11. Solar System Formation • All orbits are in the same direction and in the same plane. • Suggests a common origin. • Solar system formed when a cloud of gas and dust in space was disturbed. Gas and dust drawn together, forming a solar nebula. • The cloud began to spin as it collapsed and therefore flattened. • As the disk got thinner particles formed clumps, planetisimals eventually forming planets or moons. • As the cloud continued to fall in, the centre eventually got so hot that it became a star, the Sun. Solar wind then blew away excess material.

12. Why are there 2 types of planet? Inside the frost line: Too hot for hydrogen compounds to form ices. Outside the frost line: Cold enough for ices to form. Inner parts of disk are hotter than outer parts. Only materials that solidify at high temperatures can condense to form solid particles. Rock can be solid at much higher temperatures than ice.

13. DEMO Density and Composition • Earth 5.5 g/cm3 composition- iron, rock • Saturn 0.7 g/cm3 composition- some rock, volatiles and lots H & He • Callisto 1.9 g/cm3, Titan 2 g/cm3 composition -rock and ice

14. Asteroids and Comets Leftovers from the accretion process Rocky asteroids inside frost line Icy comets outside frost line

15. DEMO The inner rocky Planets- Mercury • Has the largest temperature extreme in the solar system from -183C to 430C. • Second densest planet after the Earth, so must have a large iron core. • Has a very thin atmosphere consisting of atoms blasted off its surface from the solar wind. Atmosphere is constantly being replenished. • Heavily cratered surface because its atmosphere is so thin.

16. The inner rocky Planets -Venus Venus is a similar size to the Earth. It atmosphere is mainly Carbon dioxide and Nitrogen. Its very hot there due to the ‘Green house effect’ a whopping 462C.

17. Our home the Earth Earth is at a distance of 150 million kilometres from the Sun. Sunlight takes 8 minutes to reach us. Our atmosphere is composed of 78 percent nitrogen, 21 percent oxygen and 1 percent other constituents. 71% of the Earth’s surface is covered by water! Earth is the only planet in the solar system known to harbour life. Picture taken by Apollo 17 astronauts

18. The Moon Heavily cratered. Evidence for water.

19. The inner rocky Planets - Mars Mars is 1/10th the mass of Earth Average temp is –63C Rock are made of silicates (like sand) and also a dash of iron oxides to give it that reddish colour (Mars is rusty!) Surface is dry now, but scientists believe there were once rivers, lake and maybe oceans of water Water exists in “permafrost” a few metres below the surface (Mars Express / Mars Odyssey). Maybe even liquid water down there! (MGS). No landers have detected water in soil, but have found evidence of past water.

20. Mars • Mars has the highest (extinct) volcano in the Solar System: Olympus Mons at 24 km high 2.7 times Everest!

21. The gas giants -Jupiter Largest planet in the solar system – its diameter is 11x the Earth’s diameter. Jupiter takes about 12 years to orbit the sun and rotates in about 10 hours. Jupiter is a ball of dense hydrogen, helium, water, nitrogen and other gases over a rocky core. ~90% H, ~10% He. Above core is the main bulk of the planet which is liquid metallic hydrogen. (Huge pressure). Ionized protons and electrons in liquid form. Powerful winds, jet streams, lightning and huge hurricane-like storms like the Great Red Spot. This storm has been raging for over 300 years and is twice the size of Earth!

22. Cassini and Saturn 95 times the Earth’s mass. Saturn, famous for its rings. These are made up of trillions of icy particles. 1015 tons of material in the rings, enough for a small moon! No more than 50 million years old (MUCH younger than the planet) - continually replenished This image shows, from left to right, the outer portion of the C ring and inner portion of the B ring. The B ring begins a little more than halfway across the image. The general pattern is from "dirty" particles indicated by red to cleaner ice particles shown in turquoise in the outer parts of the rings.

23. Titan Titan's surface in 2004-2005! Liquid ethane/methane on surface Lots of hydrocarbons

24. Uranus • Primarily composed of rock and ices with only 15% H (much less than Jupiter and Saturn). • No rocky core like Jupiter and Saturn, but material is more evenly distributed. • No liquid metallic hydrogen envelope. • Atmosphere of 83% H, 15% He, 2% methane.

25. Neptune • Composed of ices and rock with about 15% H and a little He • Atmosphere mainly H and He with a little methane which gives it its blue colour as methane absorbs red light • Small solid core, the size of the Earth • No distinct layers like Uranus (unlike Saturn and Jupiter) • Neptune has the fastest winds in the solar system reaching 2000 km/hr

26. What Counts as a Planet? • The IAU definition of a planet (2006): • is in orbit around the Sun, • has sufficient mass so that it is nearly round • has "cleared the neighborhood" around its orbit.

27. Dwarf Planets The IAU currently recognises five dwarf planets—Ceres, Pluto, Haumea, Makemake, and Eris. Ceres is in the asteroid belt others in the Kuiper belt. Many Kuiper Belt objects, exist in what is believed to be a vast shell of icy and rocky objects that live at the very edge of our solar system.