Lecture 33 The Solar System. The Inner Planets. The Solar System Overview Terrestrial Planets Chapter 16.1  16.8

Our Cosmic Origins The Big Bang – beginning of the Universe billion years ago Galaxies are flying away from each other No expansion within galaxies Only hydrogen and helium in the early Universe All other chemical elements were created inside stars We are all created from the stars’ stuff Current composition of the Sun: 70%H, 28%He, 2%others

Images of Time Speed of light: c = 300,000 kilometers per second Light year – distance which light travels in 1 year From the Sun to Earth - 8 minutes From the Sun to Pluto - 5 ½ hours To the closest star - 4 years Through the Milky Way - 100,000 years To the closest galaxy - 2,500,000 years The farther away the object, the further back we look in time

Sun within our Galaxy

Appearance of the Milky Way

The Solar System Content: Sun (the only star) 9 planets Nearly 100 moons Asteroids Comets Free-flying gas and ‘dusty’ particles

Solar System APOD: 2002 April 29 - Dusk of the Planets

The Sun Temperature (at surface) degrees Kelvin (K) Size (diameter) - 1,392,500 kilometers (km) Mass – kilograms (kg) or 98% of the total mass of the Solar system Energy production rate – 4 million tons of mass (E=mc 2 ) Age – 4.6 billion years Total stable life time - ~10 billion years

Our very own star APOD: 2003 May 17 - Dark Sky, Bright Sun APOD: 2003 March 24 - A Digital Sunset Over Europe and Africa APOD: 2002 July 29 - A Setting Sun Trail

Inside the Terrestrial Worlds Two families of planets in the Solar system: terrestrial (Earth-like) and Jovian (Jupiter-like) The terrestrial planets are relatively small and almost spherical The Earth has a radius of 6,378 km and an obliquity of 1/298 They are mostly made of rocky materials that can deform and flow Every object exceeding ~500 km in diameter can become spherical under the influence of gravity

Lithospheres of the Terrestrial Planets Planetary surfaces are all warmed by sunlight, but the high temperatures inside the planets today are due to radioactive heating.

Mercury and Moon The 2 smallest terrestrial worlds covered with lots of impact craters. They have volcanic activity in the past (example - lunar maria).maria Mercury has a 88-day orbit and a 59-day rotation. Temperature is up to 425 o C on the day side and down to  150 o C on the night side. It has many craters, but also traces of geological activity.craterstraces

Venus Venus is the third brightest object in the sky after the Sun and the Moon. Venus has very similar parameters to those of the Earth.parameters However, it spins backwards (clockwise if looking from its north pole). Its atmosphere has 96% CO 2, surface temperature 400  740 K, surface pressure is 90 times the Earth’s one. It has volcanic activity, but probably no tectonic activity. The Soviet spacecraft Venera 9 landed on Venus and send a panoramic view of its surface. The US Magellan spacecraft transmitted radio images.

Mars This is an intermediate-size planet and the most distant of the terrestrial planets from the Sun.planet It has polar caps made of frozen CO 2, many deserts, and volcanoes. There is no liquid water on Mars today, but rather traces of past water flows. The surface is different in the northern (low plains) and southern (highlands). Only 13 missions to Mars out of 23 were successful.missions successful

Summary Terrestrial planets are small and rocky Only a handful geological processes shape the terrestrial planets Every terrestrial world was heavily cratered long ago. Most of the craters are erased now. Understanding of planetary geology might help us learn about planets of other star systems