April 18, 2006Astronomy Chapter 13 Cosmic Samples and the Origin of the Solar System What are some of the general patterns in the solar system? What do these patterns tell us about the how the solar system formed?

April 18, 2006Astronomy Meteors When comets approach the Sun, they are heated and material sprays off of them. This material remains in orbit around the Sun. If the Earth passes through a cloud of this material, some of it is caught in the atmosphere where it is heated, glows, and produces a meteor or shooting star. (A shooting star has no connection to a real star.)

April 18, 2006Astronomy Meteor Showers

April 18, 2006Astronomy Meteorites: Stones from Heaven

April 18, 2006Astronomy Meteorites A meteorite is any fragment that survives its passage through the atmosphere and reaches the ground. It wasn’t realized that meteorites are extraterrestrial (not from Earth) until the 18 th century. Meteorites are found in two ways: –Someone tracking a meteor to the ground. –Someone finding an unusual looking rock –Antarctica is now a major source of meteorites. The oldest meteorites are about 4.5 billion years old.

April 18, 2006Astronomy Formation of the Solar System

April 18, 2006Astronomy Observational Constraints The information we’ve learned about the planets, moons, rings, asteroids, comets should be explained by any theory for the formation of the solar system. We have three types of constraints: –Motional –Chemical, and –Age

April 18, 2006Astronomy Observational Constraints 1.Motional All the planets revolve around the Sun in the same direction and in approximately the same plane as the Sun rotates. Most planets rotate in the same sense that they revolve. Most of the satellites rotate and revolve in the same sense as well. There are exceptions that the theory must handle, like Venus’s retrograde rotation. 2.Chemical The jovians are similar in composition to the Sun and stars. Other planets are lacking in hydrogen and helium. The inner planets are metal rich, then farther out are rocky objects, and farther still are icy objects.

April 18, 2006Astronomy Observational Constraints (cont’d) Temperature progression from inner to outer planets How to explain the presence of water on Earth and Mars 3.Age Earth samples are up to 3.8 billion years old Lunar samples are up to 4.4 billion years old Primitive meteorites are 4.5 billion years old Indicates that planets must have cooled rapidly Little unaltered material left from before the formation of the solar system.

April 18, 2006Astronomy The Solar Nebula The hypothesis that the solar system formed 4.5 billion years ago from a rotating cloud of hot material called the solar nebula consistent with the constraints. The composition of the nebula is similar to the Sun’s composition. As the cloud collapsed, it heated, destroying most of the evidence of its original state. As material falls inward, the rotation becomes faster (angular momentum) and results in a disk shape.

April 18, 2006Astronomy Forming the Solar System

April 18, 2006Astronomy Further Evolution

April 18, 2006Astronomy Elevation Differences Mountains come from a number of sources On the Moon and Mercury, the mountains are ejecta from large impacts. The large mountains on Mars are volcanos. On Earth, the largest mountains result from compression and uplift of crustal plates. On Venus, the larges mountains result from uplift by subsurface magma.

April 18, 2006Astronomy Elevation Differences

April 18, 2006Astronomy Mountains Why does Mars have the highest mountain in the solar system? 1.Mars doesn’t have plate tectonics that can impede large volcanos. (There are multiple Hawaiian islands because the Pacific plate is moving over the hot spot beneath. 2.Mars has lower surface gravity than Earth or Venus. Underlying material can more easily support the weight of the mountain above. (The mountain “weighs” less.) 3.Mars has a thin atmosphere and little erosion to reduce the height over millions of years.

April 18, 2006Astronomy Atmospheres Atmospheres are a combination of gas that escaped from a planet’s interior, and impacts of gas- containing objects (icy comets). It is likely that all the terrestrial planets had similar atmospheres. –Mercury and the Moon: too small to retain their atmospheres. –Venus: runaway greenhouse effect –Mars: runaway refrigerator effect –Earth: lucky?

April 18, 2006Astronomy Conclusion There’s still much to learn about the origin and evolution of the solar system. Space probes continue to add to our understanding. In the last 10 years we found more than 100 planets orbiting other stars. –Perhaps studies of these distant planetary systems will yield more clues about our own.