4The planets are tiny compared to the distances between them (a million times smaller than shown here), but theyexhibit clear patterns of composition and motion.The patterns are far more important and interesting than numbers, names, and other trivia
5Recall scale of solar system Before embarking on the tour of the planets, you might wish to review the overall scale from ch. 1.
6Planets are very tiny compared to distances between them. Before embarking on the tour of the planets, you might wish to review the overall scale from ch. 1.
7Sun Over 99.9% of solar system’s mass Made mostly of H/He gas (plasma) These slides follow the planetary tour pages in ch. 6.Over 99.9% of solar system’s massMade mostly of H/He gas (plasma)Converts 4 million tons of mass into energy each second
8Mercurymade of metal and rock; large iron coredesolate, cratered; long, tall, steep cliffsvery hot and very cold: 425°C (day), –170°C (night)
9Venusnearly identical in size to Earth; surface hidden by thick cloudshellish conditions due to an extreme greenhouse effect:even hotter than Mercury: 470°C, both day and nightatmospheric pressure equiv. to pressure 1 km deep in oceansno oxygen, no water, …perhaps more than any other planet, makes us ask: how did it end up so different from Earth?
10Earth and Moon to scaleEarthAn oasis of lifeThe only surface liquid water in the solar system; about 3/4 of surface covered by waterA surprisingly large moon
11MarsLooks almost Earth-like, but don’t go without a spacesuit!Giant volcanoes, a huge canyon, polar caps, more…Water flowed in the distant past; could there have been life?
12JupiterMuch farther from Sun than inner 4 planets (more than twice Mars distance)Also very different in composition: mostly H/He; no solid surface.Gigantic for a planet: 300 Earth mass; >1,000 Earth volume.Many moons, rings…
13Moons can be as interesting as the planets themselves, especially Jupiter’s 4 large “Galilean moons” (first seen by Galileo)Io (shown here): active volcanoes all overEuropa: possible subsurface oceanGanymede: largest moon in solar system — larger than MercuryCallisto: a large, cratered “ice ball” with unexplained surface features
14SaturnGiant and gaseous like Jupitermost spectacular rings of the 4 jovian planetsmany moons, including cloud-covered Titancurrently under study by the Cassini spacecraft
15SaturnRings are NOT solid; they are made of countless small chunks of ice and rock, each orbiting like a tiny moon.Artist’s conception
16Cassini probe arrived July 2004 SaturnCassini probe arrived July 2004(Launched in 1997)Inset art shows the Huygens probe separated from the main spacecraft on its descent to Titan…
17Uranusmuch smaller than Jupiter/Saturn, but still much larger than Earthmade of H/He gas, hydrogen compounds (H2O, NH3, CH4)extreme axis tilt — nearly tipped on its “side” — makes extreme seasons during its 84-year orbit.moons also tipped in their orbits…
18Very similar to Uranus (but much smaller axis tilt) NeptuneVery similar to Uranus (but much smaller axis tilt)Many moons, including unusual Triton: orbits “backward”; larger than Pluto.Note: this is the same image as in the text but rotated 90° to show the axis tilt relative to the ecliptic plane as the horizontal on the page. (The orientation in the book chosen for its more dramatic effect.)
19PlutoA “misfit” among the planets: far from Sun like large jovian planets, but much smaller than any terrestrial planet.Comet-like composition (ices, rock) and orbit (eccentric, inclined to ecliptic plane, long years).Its moon Charon is half Pluto’s size in diameterBest current photo above; New Horizons mission launch 2006, arrival 2015…
20This important summary table may be worth some time in class to make sure students understand how to read it…
21What have we learned? • What does the solar system look like? Our solar system consists of the Sun, nine planets and their moons, and vast numbers of asteroids and comets. Each world has its own unique character, but there are many clear patterns among the worlds.
226.2 Clues to the Formation of Our Solar Sytem Our Goals for Learning• What features of our solar system provide clues to how it formed?• What theory best explains the features of our solar system?
23What features of our solar system provide clues to how it formed?
24The Sun, planets, and large moons orbit and rotate in an organized way counterclockwise seen from above the north pole)
25Terrestrial planets are small, rocky, and close to the Sun. Jovian planets are large, gas-rich, and far from the Sun.(What about Pluto?)
27Rocky asteroids between Mars & Jupiter Icy comets in vicinity of Neptune and beyondAsteroids and comets far outnumber the planets and their moons
28A successful theory of solar system formation must allow for exceptions to general rules
29Summary: Four Major Features of our Solar System
30What theory best explains the features of our solar system?
31According to the nebular theory our solar system formed from a giant cloud of interstellar gas (nebula = cloud)
32What have we learned?• What features of our solar system provide clues to how it formed?Four major features provide clues: (1) The Sun, planets, and large moons generally rotate and orbit in a very organized way. (2) With the exception of Pluto, the planets divide clearly into two groups: terrestrial and jovian. (3) The solar system contains huge numbers of asteroids and comets. (4) There are some notable exceptions to these general patterns.• What theory best explains the features of our solar system?The nebular theory, which holds that the solar system formed from the gravitational collapse of a great cloud of gas.
336.3 The Birth of the Solar System Our Goals for Learning• Where did the solar system come from?• What caused the orderly patterns of motion in our solar system?
45We see plenty of evidence for spinning disks of gas andf dust around other stars, especially newly formed stars
46What have we learned? • Where did the solar system come from? The cloud of gas that gave birth to our solar system was the product of recycling of gas through many generations of stars within our galaxy. This gas consisted of 98% hydrogen and helium and 2% everything else combined.
47What have we learned?• What caused the orderly patterns of motion in our solar system?A collapsing gas cloud naturally tends to heat up, spin faster, and flatten out as it shrinks in size. Thus, our solar system began as a spinning disk of gas. The orderly motions we observe today all came from the orderly motion of this spinning disk of gas.
486.4 The Formation of Planets Our Goals for Learning• Why are there two types of planets?• Where did asteroids and comets come from?• How do we explain the existence of our Moon and other “exceptions to the rules”?• When did the planets form?
49Four Unexplained Features of our Solar System √ Why do large bodies in our solar system have orderly motions?--> 2) Why are there two types of planets?3) Where did the comets and asteroids comefrom?4) How can we explain the exceptions the the ‘rules’ above?
50Why are there two types of planet, when all planets formed from the same nebula?
51As gravity causes cloud to contract, it heats up Conservation of energy
52Inner parts of disk are hotter than outer parts. Rock can be solid at much higher temperatures than ice.
53Fig 9.5Inside the frost line: too hot for hydrogen compounds to form ices.Outside the frost line: cold enough for ices to form.
54Tiny solid particles stick to form planetesimals.
55Gravity draws planetesimals together to form planets This process of assemblyis called accretionSame as previous
56Gravity of rock and ice in jovian planets draws in H and He gases
58Why are there two types of planets? Outer planets get bigger because abundant hydrogen compounds condense to form ICES.Outer planets accrete and keep H & He gas because they’re bigger.
59Four Unexplained Features of our Solar System √ Why do large bodies in our solar system have orderly motions?√ Why are there two types of planets?--> 3) Where did the comets and asteroids come from?4) How can we explain the exceptions the the ‘rules’ above?
60Comets and asteroids are leftover planetesimals. • Asteroids are rocky because they formed inside the frostline.• Comets are icy because they formed outside the frostline
61Outflowing matter from the Sun -- the solar wind -- blew away the leftover gases
62Four Unexplained Features of our Solar System √ Why do large bodies in our solar system have orderly motions?√ Why are there two types of planets?√ Where did the comets and asteroids comefrom?--> 4) How do we explain the existence of our Moon and other “exceptions to the rules”?
63Earth’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
65Four Features of our Solar System - Explained √ Why do large bodies in our solar system have orderly motions?√ Why are there two types of planets?√ Where did the comets and asteroids comefrom?√ How do we explain the existence of our Moon and other “exceptions to the rules”?Add ‘what have we learned’ slide here
67We cannot find the age of a planet, but we can find the ages of the rocks that make it up We can determine the age of a rock through careful analysis of the proportions of various atoms and isotopes within it
68The decay of radioactive elements into other elements is a key tool in finding the ages of rocks
69Age dating of meteorites that are unchanged since they condensed and accreted tell us that the solar system is about 4.6 billion years old.
70What have we learned? • Why are there two types of planets? Planets formed around solid “seeds” that condensed from gas and then grew through accretion. In the inner solar system, temperatures were so high that only metal and rock could condense. In the outer solar system, cold temperatures allowed more abundant ices to condense along with metal and rock.
71What have we learned?• How do we explain the existence of our Moon and other “exceptions to the rules”?Most of the exceptions probably arose from collisions or close encounters with leftover planetesimals, especially during the heavy bombardment that occurred early in the solar system’s history. Our Moon is probably the result of a giant impact between a Mars-size planetesimal and the young Earth.• Where did asteroids and comets come from?Asteroids are the rocky leftover planetesimals of the inner solar system, and comets are the icy leftover planetesimals of the outer solar system.
72What have we learned? • When did the planets form? The planets began to accrete in the solar nebula about 4.6 billion years ago, a fact we determine from radiometric dating of the oldest meteorites.
736.5 Other Planetary Systems Our Goals for Learning• How do we detect planets around other stars?• What have other planetary systems taught us about our own?
75We detect planets around other stars by looking for a periodic motion of the stars they orbit. We measure the motion through the Doppler shift of the star’s spectrum
76The size of the wobble tells us the planet’s mass The period of the wobble tells us the radius of its orbit (Kepler’s 3rd law)
77We can also detect planets if they eclipse their star Fraction of starlight blocked tells us planet’s size
78What have other planetary systems taught us about our own?
79Over 120 known extrasolar planets as of 2004 Most are more massive than Jupiter and closer to their star than Earth is to SunRevisions to the nebular theory are necessary! Planets can apparently migrate inwardfrom their birthplaces.
80Is Earth Unusual? No Earth-like planets found yet. Data aren’t good enough to tell if they are common or rareAvailable methods can only detect BIG planets.
81What have we learned? • How do we detect planets around other stars? So far, we are only able to detect extrasolar planets indirectly by observing the planet’s effects on the star it orbits. Most discoveries to date have been made with the Doppler technique, in which Doppler shifts reveal the gravitational tug of a planet (or more than one planet) on a star.
82What have we learned?• What have other planetary systems taught us about our own?Planetary systems exhibit a surprising range of layouts, suggesting that jovian planets sometimes migrate inward from where they are born. This lesson has taught us that despite the successes of the nebular theory, it remains incomplete.