The Solar System

1. The Solar System

2. Review... • Gas giants are ...like terrestrial planets because.... ...not like terrestrial planets because ... • Meteors are ... like meteorites because... ... not like meteorites because...

3. lesson outcomes... • know, understand and explain: • general categories of objects in the solar system • general features of Jovian vs. terrestrial planets • the formation of the Solar System

4. Planetary exploration provides information about the origin and evolution of the solar system as well as the history and resources of Earth

5. Properties of Planets • All planets orbit the sun in the same direction and almost the same plane. • Except Mercury, most planets have nearly circular orbits. • orbits are actually ellipses • elongation of an ellipse is denoted by its eccentricity • most planets have orbital eccentricities that are very close to zero.

6. Classifying Planets • inner or outer according to orbital radius • four inner planets crowded close to the Sun • Mercury, Venus, Earth & Mars • four outer planets spaced at great distances from the Sun • Jupiter, Saturn, Uranus and Neptune • terrestrial or Jovian by their physical attributes • four inner planets are terrestrial • resemble Earth • hard rocky surfaces with mountains, craters, canyons and volcanoes • four outer planets are Jovian • resemble Jupiter

7. Planet Features • diameter: • terrestrial planets have much smaller diameters than the Jovian planets • mass • gas giants have 10  100 x mass of terrestrial • affects path of spacecrafts • density: • Gas giants have low density (Saturn can float on water) but terrestrial planets have very high average densities

8. Planet Features • temperature • farther a planet from the Sun, the cooler it is; terrestrial planets are very warm •  200 K to 300 K, CO2 NH3 and CH4 exist as solids called ices. • at higher temperatures , exist as liquids & gases • composition: • hydrogen and helium are abundant on the Jovian planets • terrestrial planets composed mainly of heavy elements; virtually no H or He found in their atmosphere • chemical composition investigated through spectroscopy of sunlight that reflects off planetary atmosphere • spectral lines of molecules strongest in UV and IR range

9. Satellites & Small Bodies • Besides the planets, the solar system includes remnants form the formation of the planets – small chunks of rock and ice that orbit the Sun • satellites of the planets (natural satellites) • seven large planetary satellites, including Moon, that are comparable in size to planet Mercury • all planets except Mercury and Venus have satellites • asteroids • comets

10. Satellites & Small Bodies • asteroids • small rocky objects present between Mars and Jupiter • region of space between the Mars and Jupiter are known as the asteroid belt • probably left-over planitesimals that did not accrete during formation of solar system • no sharp dividing line between planets and asteroids so are called minor planets or Dwarf planets

11. Satellites & Small Bodies • comets • icy objects that originate in the Kiuper belt and Oort cloud • Kiuper belt • disc • observed • Oort cloud • sphere • not observed

12. Formation of Solar System • The basic planet-forming substances are gases, ices or rock, depending on the temperature • terrestiral planets are composed primarily of rock • Jovian planets are composed largely of gas. • The entire solar system came out of the accretion of a vast rotating disc-shaped cloud of gas (H & He), ice and dust particles called the solar nebula. • accretion: accumulation of materials to form larger & larger objects

13. Formation of Solar System • the planets formed by the accretion of planetesimals and the accumulation of gases in the solar nebula • inner planets formed through the accretion of dust particles into planetesimals then into larger protoplanets • outer planets probably began as rocky protoplanetary cores, with gas accreting on these cores • the Sun formed by gravitational contraction of the centre of the nebula • eventually, temperature high enough to ignite thermonuclear reactions forming a star

14. Extrasolar Planets • astronomers have discovered planets orbiting other stars • usually massive • very different orbits from planets in our own solar system

15. Questions... • Are all the other planets similar to Earth or are they very different? Are they all made of basically the same material? • Do other planets have moons like Earth’s Moon? • How do astronomers know what the other planets are made of? • What s the difference between an asteroid and a comet? • Are there planets orbiting other stars? • How do astronomers think the solar system formed?