What is it like? When did it form? How did it form The Solar System Fall, 2005 Astronomy 110 1
Fall, 2005 Astronomy 110 2
The planets all orbit the sun in the same direction. The Sun spins in the same direction. Most planets spin in the same direction. counterclockwise seen from above the north pole) Fall, 2005 Astronomy 110 3
Relative Planetary Radii Fall, 2005 Astronomy 110 4
The Distribution of Orbital Radii Fall, 2005 Astronomy 110 5
Planet Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto Orbital Eccentricity 0.2056 0.0068 0.0167 0.0934 0.0485 0.0555 0.0463 0.009 0.2488 Orbital Inclination 7 00'18" 3 23'40" 0 00'00" 1 50'59" 1 18'12" 2 29'20" 0 46'24" 1 46'12" 17 08'30" Fall, 2005 Astronomy 110 6
The Inner and Outer Solar Systems Fall, 2005 Astronomy 110 7
Pluto A misfit? Orbit radius like a jovian planet Much smaller than any terrestrial planet. Comet-like composition (ices, rock) Comet-like orbit (eccentric, highly inclined to ecliptic plane). Charon is half Pluto s diameter Fall, 2005 Astronomy 110 8
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Rocky asteroids between Mars & Jupiter Icy comets in vicinity of Neptune and beyond Asteroids and comets far outnumber the planets and their moons Fall, 2005 Astronomy 110 10
Summary: Four Major Features of our Solar System Fall, 2005 Astronomy 110 11
When did the Solar System form? The solar system is as old as its oldest rocks. We can find the ages of rocks through analysis of isotopic ratios. This can be done for rocks on earth and for meteorites. Fall, 2005 Astronomy 110 12
The decay of radioactive elements into other elements is a key tool in finding the ages of rocks Fall, 2005 Astronomy 110 13
Age dating of meteorites that are unchanged since they condensed and accreted tell us that the solar system is about 4.6 billion years old. This coincides with the age of the Sun. The Nebular Hypothesis argues that the solar system formed as a by-product of the formation of the Sun. Fall, 2005 Astronomy 110 14
To understand the origin of the solar system we need to understand the origin and evolution of stars. Fall, 2005 Astronomy 110 15
The cloud of gas that gave birth to our solar system resulted from the recycling of gas through many generations of stars within our galaxy. Fall, 2005 Astronomy 110 16
As gravity forced the cloud to become smaller, it began to spin faster and faster [Conservation of angular momentum.] And it begins to heat up. [Conservation of energy.] Fall, 2005 Astronomy 110 17
Collisions flatten the cloud into a disk. The orderly motions of our solar system today are a direct result of the solar system s birth in a spinning, flattened cloud of gas. Fall, 2005 Astronomy 110 18
We see evidence for spinning disks of gas and dust around other stars, especially newly formed stars Fall, 2005 Astronomy 110 19
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The nebular theory Fall, 2005 Astronomy 110 21
Fig 9.5 The protostellar cloud is heated by the young star forming at its center and energy released by the collapsing cloud Inside the frost line it is too hot for ices to form. Outside the frost line it is cold enough for ices to form. Fall, 2005 Astronomy 110 22
Thermal Structure of the Protoplanetary Nebula http://dosxx.colorado.edu/~bagenal/1010/sessions/11.formation.html The types of planets formed reflect the raw materials available. Fall, 2005 Astronomy 110 23
Fall, 2005 Astronomy 110 24
Comets and asteroids are leftover planetesimals. Asteroids are rocky because they formed inside the ice line. Comets are icy because they formed outside the ice line Fall, 2005 Astronomy 110 25
Once formed the proto-planets continue to evolve: http://dosxx.colorado.edu/~bagenal/1010/sessions/11.formation.html Fall, 2005 Astronomy 110 26
Earth s moon was probably created when a big planetesimal slammed into the newly forming Earth. Other large impacts may be responsible for other exceptions like rotation of Venus and Uranus Fall, 2005 Astronomy 110 27
Over 120 known extrasolar planets as of 2004 Most are more massive than Jupiter and closer to their star than Earth is to Sun Revisions to the nebular theory are necessary! Planets can apparently migrate inward from their birthplaces. Fall, 2005 Astronomy 110 28