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Ch. 27 The in our Our Solar System • Our solar system is located in the ______Milky Way Galaxy (about 2/3 the way out on one of the arms.) • There is ONE in our solar system and it is the _____Sun • Our solar system is made up of the and our planets that revolve around it. – Rotation = spinning (a day), Revolution = circle (a year) • The sun is at the ______center of the solar system. • 8 Planets and orbit around our sun. • The planets are divided into two groups: – Inner and outer planets. – What Is a Today? According to the new definition, a full-fledged planet is an object that orbits the sun and is large enough to have become round due to the force of its own gravity. In addition, a planet has to dominate the neighborhood around its orbit. Our Solar System – The Planets • Planets are broken into 2 groups: – Inner Planets : , , , and – Outer Planets: , , , (and Pluto) – The inner and outer planets are separated by the Belt. So the order closest to the sun to furthest from sun is: Inner Planets • The inner planets have rocky crusts, dense layers, and very dense cores. • They are called the Terrestrial planets (they are Earth-like). (Mercury, Venus, Earth, Mars) Inner/Terrestrial Planets

• Mercury – Nearest (closest) to the sun – Has shortest orbit (88 Earth days) – Smallest terrestrial planet – Lots of the surface is heavily cratered (similar to our ’s) – The smooth surface was formed from flows – Turns on axis (rotates) slowly (59 Earth days) – so “days” are long and temps are HOT (+400°C) – Nights are very cold (-200°C) – NO real atmosphere (b/c weak gravity) – NO Inner/Terrestrial Planets

• Venus – Called Earth’s sister planet because the 2 are similar is diameter, mass, and gravity. – Has weak or nonexistent magnetic field (different from Earth) – Rotates east to west (different from other planets) – Rotation is 234 days, orbits the sun in 225 days (so 1 day on Venus is longer than 1 year)

– Thick yellow clouds (Sulfuric acid & CO2)in atmosphere – Surface has volcanic features, faulting, and impact craters (~80% surface covered in lava) – Hot surface temps ~ 475°C (from the CO2/greenhouse effect) – NO moons Inner/Terrestrial Planets

• Earth – 3rd from sun – Rotates 24 hours (a day), orbits sun in ~365.25 days (a year) – Has – Volcanic activity, faulting, building, plate movement, etc. – 1 moon – You know – we live here. Inner/Terrestrial Planets • Mars – 4th planet from sun – 687 days to orbit sun – Diameter ½ of Earth’s – Very weak to nonexistent magnetic field – Mars has about same tilt on axis as Earth, so it has 4 seasons too (but twice as long – b/c longer year) – Warm temps reach 27°C, cold temps reach –125°C – Atmosphere is ~ 95% CO2 – Has polar ice caps (so water) – Surface in north is smooth plains of volcanic material, in south has many large craters and small channels – Largest in the solar system = Olympus Mons (500km across x 26km high), however no plate motion – 2 moons • are solid, rocklike masses, with irregular shapes. • They revolve around the sun in the same direction as the planets. • They Asteroid belt lies between Mars (inner planet) and Jupiter (outer planet). • They can collide (and have collided) with planets. • Many scientists believe a large asteroid (or ) collided with Earth about 65 million years ago leading to the extinction of the dinosaurs. Outer Planets • Beyond the Asteroid Belt • Also called the Jovian planets • Large, gaseous planets (made of lighter elements like and ) • Have rings (particles in independent orbits around planet’s equator, rings are closer than the moons) • Have 3 layers (Jupiter, Saturn, Uranus, Neptune) Outer/Jovian Planets • Jupiter – 5th planet from the sun – 11.9 Earth years to orbit the sun, rotates the fastest at just under 10 hours – Largest planet in the solar system – Strongest magnetic field (has beautiful auroras) – Great Red Spot = storms (from a turbulent atmosphere) – Has rings (they are faint) – 64 moons Outer/Jovian Planets

• Saturn – 6th planet from the sun – 30 years to orbit the sun, rotates every 10 hours – Has lowest density of any planet (so it could float in water, if there was enough water to test this) – Strong magnetic field – Rings are easily visible (made of billions of chunks of ice). – 62 moons Outer/Jovian Planets • Uranus – 7th planet from the sun, rotates every 17.2 hours – Axis is tipped so that it rotates on its side (some scientists think it was tipped by a collision with an Earth-sized object) – Magnetic field is NOT tipped over (its 60% difference) – Takes 84 Earth years to orbit the sun – Not discovered until 1781 (when more powerful telescopes developed) – Surface temp is ~200°C – It appears a turquoise color due to methane gas in its atmosphere – 27 moons Outer/Jovian Planets

• Neptune – 8th and most distant of the Jovian planets – It occasionally becomes the 9th object away from the sun because every 248 years Pluto’s odd orbit brings Pluto closer to the sun than Neptune (switches about every 20 years – will be the 9th object from the sun again about 2019) – Discovered in 1876 when scientist predicted its existence mathematically – Takes 165 Earth years to orbit the sun, and takes 16.1 hours to rotate. – Magnetic field and axis are 47° difference and offset from the planet’s center by 13,500 km – Harsh conditions (winds up to 2,000 km/hr, temperature ~ - 225 °C – Atmosphere is mostly Hydrogen, some Helium – 14 moons Pluto??

• Smallest of the planet-like objects that orbit the sun (about the size of New York to Houston, TX – its smaller than our moon) – Its called a (no longer considered a “real” planet). Scientist believe they know of 44 dwarf planets • Has a moon about ½ its size (moon = ) • Is 39.5 AUs from the sun • Surface temperature varies from -235 °C to -210 °C, so most of the atmosphere is frozen • Scientist believe is consists of ~ 70% and 30% water Pluto?? • REMEMBER: new definition states: a planet is an object that orbits the sun, is large enough to have become round due to the force of its own gravity and has to dominate the neighborhood around its orbit. – Pluto has been demoted because it does not dominate its neighborhood. Charon, its large "moon," is only about half the size of Pluto, while all planets are far larger than their moons. – In addition, bodies that dominate their neighborhoods, "sweep up" asteroids, , and other debris, clearing a path along their orbits. By contrast, Pluto's orbit is somewhat untidy. • Pluto is part of the - a disc-shaped region of icy objects beyond the orbit of Neptune. The Kuiper Belt and even more distant are believed to be the home of comets that orbit our sun. (http://solarsystem.nasa.gov/planets/profile.cfm?Object=KBOs) Our Solar System and its Planets Differences in size of planets So What Else is in our Solar System? Comets, and Asteroids, and Meteors – Oh My! • Comets - dust particles trapped in a mixture of water, carbon dioxide (CO2), methane, and ammonia. • Comets orbit beyond Neptune in the Edgeworth-Kuiper Belt and in the Oort Cloud (even further out). • Asteroids – solid, rocklike masses with irregular shapes. – Most lie between Mars’ and Jupiter’s orbit So What Else is in our Solar System? Comets, and Asteroids, and Meteors – Oh My! • - rock or an icy fragment traveling in space – Smaller than an asteroid (sand grain to less than 100 m) • Meteor – (shooting star) is the light made by a meteoroid as it passes through the Earth’s atmosphere. – Most vaporize in the air as they move through the atmosphere. Can have meteor showers – when Earth passes through the tail of a comet and particles and many meteors plunge through our atmosphere. • – part of a large meteoroid that survives its trip through the atmosphere and strike’s Earth’s surface. (can consist of silicates, , nickel) – – bowl-shapped depression that remains after a meteorite has hit Earth, another planet, or a moon. • Rare on Earth – our atmosphere burns them up and our plate tectonic activity erases them. • Earth’s oldest crater is Vredefort Crater in South Africa (2 byo), younger one is Arizona’s Barringer Meteor Crater (49,000 yo) So how do we know what’s out there in our solar system??

Chapter 26.2: Observing the Solar System Early views of the organization of Space were much different than ours. Early astronomers believed that the Earth was the center of our , and that the Earth was surrounded by a ball, called a Celestial Sphere, on which were fixed most of the objects of the heavens. This interpretation of our solar system is called a Geocentric Model, meaning Earth-centered. Early astronomers noticed groups of that were visible at the same time every year. These were named constellations, and were used as a basis for calendars.

The Orion Constellation Astronomers noticed that some celestial bodies did change position relative to the constellations. They called these “wandering stars” planets.

Notice the planet Mars moving across the constellations Gemini and Leo over the course of 11 months. Astronomers also noted that, periodically, these planets which normally moved eastward, moved backward for a few weeks, then resumed their path eastward.

In 200 A.D., the Greek astronomer Ptolemy explained this “retrograde’ motion by stating that the planets orbited the Earth in a circle, but also orbited another point in a circle, what he called an epicycle.

In the late 1400’s, the astronomer Copernicus proposed what was to become known as the Heliocentric Model. Copernicus stated that the Sun was the center of the Solar System, the Earth was a planet, and that it orbited the Sun. And, here is how he explained retrograde motion. Mars retrograde motion Venus retrograde motion In the 16th –century, the astronomer Johannes Kepler developed three laws to describe the way in which planets move through Space. Kepler’s 1st Law: Planets move through Space in an elliptical orbit, not a circular one. This causes the distance from a planet to the Sun to vary. Kepler’s 2nd Law: When a planet is closer to the Sun, it moves faster. (centrifugal force and gravity at work!) Kepler’s 3rd Law states that the further a planet is from the Sun the longer its period of revolution (its year) will be. In the 1600’s, Isaac Newton stated that a force called gravity was causing the planets to behave as Kepler had observed. He stated that all objects with mass exerted a force of attraction on other objects with mass, and that the strength of that force is proportional to the mass of the objects and their distances from one another. Now lets practice Retrograde Motion using Mars!!