Chapter 06 Let s Make a Solar System How did it come to be this way? Where did it come from? Will I stop sounding like the Talking Heads?
What does the solar system look like? Big picture. The solar system exhibits clear patterns of composition and motion. These patterns are far more important and interesting than numbers, names, and other trivia.
What does the solar system look like? All planets move the same way.
What does the solar system look like? Two kinds of planets.
What does the solar system look like? Surrounded d by icy balls.
What does the solar system look like? With a few exceptions
Planets are very Planets are very tiny compared to distances between them.
Sun Over 99.9% of solar system s mass Made mostly of H/He gas (plasma) Converts 4 million tons of mass into energy each sec
Jupiter Much farther from Sun than inner planets Mostly H/He; no solid surface 300 times more massive than Earth Many moons, rings
Artist s conception Rings are NOT solid; they are made of countless small chunks of ice and rock, each orbiting like a tiny moon.
Pluto and Other Dwarf Planets Much smaller than other planets Icy, comet-like composition Pluto s moon Charon is similar in size to Pluto
Challenges to Solar System Theories From the bigger picture, there are definite patterns that could be part of a theory about how the Solar System formed. Remembering the scientific method All theories must be testablet All theories must explain the data well Theories i can be overturned when new data is discovered.
Challenge #1: Patterns of Motion Any theory must explain the following motions: All planets orbit in the same direction. Most of the orbits are within the same plane (the ecliptic). The Sun rotates in the same direction the planets revolve (oh, what vocab). That is a lot of order you wouldn t expect in a random smush of matter.
Challenge #2: Planet Types There are two main types of planets: Small rocky planets (Mercury to Mars) Large gas giants (Jupiter to Neptune) Pluto is special! An exception for Challenge #4. Why are the small rocky planets close to the Sun and the big gas giants farther out?
Challenge #3: Rocks and Ice You also have to include the strays of the Solar System: There is an asteroid belt that is good-sized. Where did they come from? A failed planet? Beyond Neptune s orbit is the Kuiper cloud of comets (home of Halley s) aeys)
Challenge #4: Exceptions There are several big exceptions: Uranus rotates on its side Pluto is not a gas giant, but an ice-ball Pluto s orbit is inclined 17 degrees from the ecliptic. Some moons orbit in the other direction. Our theory should also include details to Our theory should also include details to explain these at least in some part.
The Solar System 5 Billion Years Ago
How Did Our Planets Turn Out? We will look at the other planets in detail next week, but in general our solar system is dominated by large gaseous planets. Mercury, Venus, Earth, and Mars are all small balls of rock and iron. There is a large group of asteroids between Mars and Jupiter. Jupiter, Saturn, Uranus, and Neptune are all gas giants with no visible solid surface. After Neptune there is a very icy and rocky planet called Pluto and a large spherical cloud of comets (the Oort Cloud).
Comparative Sizes of Sol s Planets
How Well Did the Orbits Sort Out? The planetary orbits came out relatively circular, except for Pluto which is very eccentric and tilted away from the ecliptic. There is a large gap between Mars and Jupiter where no planet is found, but the asteroid belt is located. Might be a broken proto-planet. Jupiter and Saturn have the most eccentric orbits, but this may be due to their being such massive gas giants.
Comparative Orbits of Sol s Planets
Are There Other Solar Systems? We have begun to search for other solar systems and found many in the proto-sun phase. We know that t the dust cloud theory is pretty accurate since there are so many condensing suns with those characteristics. At left is a nearby stellar nursery of proto-suns and their dim surrounding dust cloud.
Beta Pictoris: First Disk Spotted Above is the first planetary disk ever seen (around the nearby star, Beta Pictoris). i This is thought to be only a few hundred million years old and still condensing down its planetary disk. It is too early to look for planets, but the strange bulge on the right side is thought to be the wake of one large proto-planet planet (these are also called exo-planets, exo meaning outside our Solar System).
Exo-planets Since Beta Pictoris We have seen the gravitational effects of very large planets on nearby stars (about 280 total by January 2008). We found these planets by their gravitational i effect on their parent stars (wobble or parallax movement). We have not seen smaller planets since they don t affect their suns very much and are too small to see with our best telescope - the Hubble Space Telescope.
Are There Other Earth-Like Planets? It is inevitable that we will find more and smaller planets as our telescopes become bigger and our computers more powerful. Given how many planetary disks we have found, chances are pretty good that we will find Earth-sized planets. But B t we are too far away to be able to tell if they are Earth-like. Yet.