The Solar System

Light travels ~ 300,000 km/sec or Our Solar System is about 16 billion km, or 10 billion miles, or 15 light hours across. Light travels ~ 300,000 km/sec or ~1.1 billion km/hour

Our galaxy, the Milky Way

Solar System Formation

Your Parents’ Solar System

21st Century Solar System

The 21st Century Solar System Sun Terrestrial Planets Asteroid Belt Jovian Planets Kuiper Belt Oort Cloud

The Solar System: List of Ingredients Sun Jupiter Other planets Everything else Percent of total mass 99.8% 0.1% 0.05%

The Sun A middle-aged, average star: Shines because it is hot: Mostly Hydrogen & Helium Over 99% of the Solar System ~4.6 billion years old Shines because it is hot: Surface Temp ~6000 C Mostly Visible, UV & IR light Kept hot by nuclear fusion in its core: Builds Helium from Hydrogen fusion. Will shine for ~12 billion years

The Sun dominates the Solar System

Terrestrial Planets Mercury, Venus, Earth & Mars Rocky Planets: “Earth-Like” Rocky Planets Largest is Earth Only in the inner solar system (0.4 to 1.5 AU) Rocky Planets: Solid Surfaces Mostly Silicates and Iron High Density: (rock & metal) Earth, Venus, & Mars have atmospheres

The Terrestrial Planets Mercury (0.055 M) Venus (0.82 M) Earth (1 M) Mars (0.11 M)

The Jovian Planets Jupiter, Saturn, Uranus & Neptune Largest Planets: at least 15 times mass of Earth. Only in the outer solar system (5 to 30 AU) No solid surfaces (mostly atmosphere) Low density Gas Giants: (Jupiter & Saturn) Thick H/He atmosphere, liquid hydrogen mantle, ice core Ice Giants: (Uranus & Neptune) Ice/rock core & mantle, thin H/He atmosphere

The Jovian Planets Jupiter (318 M) Saturn (95 M) Uranus (15 M) Neptune (17 M)

Dwarf Planets Defined by the IAU in 2006 Dwarf Planets: Ceres: first of the Asteroids, discovered in 1801 Pluto: trans-Neptunian object discovered in 1930 Eris: trans-Neptunian object discovered in 2005 Haumea (trans-Neptunian, suspected) Makemake (trans-Neptunian, suspected)

Dwarf Planets

The Giant Moons Moon: any natural satellite orbiting a planet or dwarf planet Giant Moons: Earth: The Moon (Luna) Jupiter: Io, Europa, Ganymede, & Callisto Saturn: Titan Neptune: Triton Many smaller moons, both rocky & icy. Only Mercury & Venus have no moons.

The Giant Moons

Rhea Iapetus Titania Oberon Ceres Tethys Dione Ariel Umbriel Charon Pallas Vesta Hygeia Mimas Enceladus Miranda Proteus Io Mercury Europa Moon Triton Titan Ganymede Callisto Pluto

Kuiper Belt Class of icy bodies orbiting beyond Neptune. Examples: Found only in the outer Solar System (>30AU) Densities of 1.2 to 2 g/cc (mostly ices) Examples: Pluto & Eris (icy dwarf planets) Kuiper Belt Objects (30-50AU) Charon, Pluto’s large moon Sedna & Quaor: distant large icy bodies

Kuiper Belt

Oort Cloud Spherical cloud of comets. Extends out to almost 50,000 AU (1 light-year) May contain trillions of comets The outer edge is the farthest reach of the Sun’s gravitational pull. There are no confirmed observations – its existence is theoretical only.

Oort Cloud

The Leftovers (small bodies) Asteroids: Made of rock & metal (density 2-3 g/cc) Sizes: Few 100km to large boulders (big) Most are found in the Main Belt (2.1-3.2 AU) Meteoroids: Bits of rock and metal (little) Sizes: grains of sand to boulders Comets: Composed of rock & ice Longs tails of gas & dust are swept off them when they pass near the Sun.

Asteroids 951 Gaspra 243 Ida 253 Mathilde

Meteor burning up in the atmosphere.

Comet P/Halley Comet P/Wilt

Is Pluto a Planet? What to consider? Size? Shape? Orbit? What is it made of?

IAU Definition of a Planet In 2006, the International Astronomical Union (IAU) came up with the following definition of a planet: orbits the Sun has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium shape (i.e., it is spherical), has cleared the neighborhood around its orbit, is not a satellite

IAU Definition of a Dwarf Planet In 2006, the International Astronomical Union (IAU) came up with the following definition of a dwarf planet: orbits the Sun has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium shape (i.e., it is spherical), has not cleared the neighborhood around its orbit, is not a satellite

The Size and Distance Scale Of The Solar System In turn, the size of our Solar System is very large compared to the size of our Earth, or even the largest planet, Jupiter. The distance from our Earth to the Moon is about 238,000 miles or 384,000 kilometers (nearly 100 times Earth’s diameter, or about 30 times the distance around the Earth at its equator). The distance from our Earth to the Sun is about 93,000,000 miles or 149,600,000 kilometers (more than 390 times the distance to the Moon). The most distant major planet from the Sun, Neptune, is 30 times Earth’s distance from the Sun. The nearest stars in our Galaxy, the star system of Alpha Centauri, is 9,000 times Neptune’s distance from the Sun!

SIZES AND DISTANCES IN THE SOLAR SYSTEM Diameters of Solar System Members: Sun = 1,392,000 km Mercury = 4,878 km Venus = 12,104 km Earth = 12,756 km Mars = 6,794 km Jupiter = 142,984 km Saturn = 120,536 km Uranus = 51,118 km Neptune = 49,530 km Pluto = 2,304 km Mean Distance from Sun 57,900,000 km = 0.387 AU 108,200,000 km = 0.723 AU 149,600,000 km = 1.000 AU 227,900,000 km = 1.524 AU 778,300,000 km = 5.203 AU 1,427,000,000 km = 10.07 AU 2,871,000,000 km = 19.19 AU 4,497,000,000 km = 30.06 AU 5,914,000,000 km = 39.53 AU Earth’s Moon = 3,476 km Mean Distance from Earth = 384,400 km

Earth and Moon to Scale

Sizes and Distances in the Earth-Moon System

Relative Sizes of Planets in Our Solar System

The Planets of Our Solar System The Inner Planets Sizes to Scale Mercury Venus Earth and Moon Mars

The Planets of Our Solar System The Outer Planets Jupiter Saturn Earth Included for Scale. Uranus Pluto Neptune

Size Comparisons In Our Solar System

THE SIZE AND DISTANCE SCALE OF THE SOLAR SYSTEM The distances between the members of our Solar System are much larger than the sizes of the members (even the Sun). The distance from the Earth to the Sun is about 150,000,000 km (about 93,000,000 miles) in comparison to the Sun’s diameter of about 1,392,000 km (about 110 times that of Earth). The largest planet, Jupiter, is 5 times Earth’s distance from the Sun, and 11 times Earth’s diameter (1/10 of the Sun’s diameter). The most distant major planet, Neptune, is 30 times Earth’s distance from the Sun. The region beyond the orbit of Neptune, called the Kuiper Belt, contains a large number of smaller objects (including Pluto and at least one recently discovered slightly larger object), all (as yet known) smaller than our Moon. The Kuiper Belt objects known to date can reach distances of more than 90 times Earth’s distance from the Sun.

SIZES AND DISTANCES IN THE SOLAR SYSTEM Diameters of Solar System Members: Sun = 1,392,000 km Mercury = 4,878 km Venus = 12,104 km Earth = 12,756 km Mars = 6,794 km Jupiter = 142,984 km Saturn = 120,536 km Uranus = 51,118 km Neptune = 49,530 km Pluto = 2,304 km Mean Distance from Sun 57,900,000 km = 0.387 AU 108,200,000 km = 0.723 AU 149,600,000 km = 1.000 AU 227,900,000 km = 1.524 AU 778,300,000 km = 5.203 AU 1,427,000,000 km = 10.07 AU 2,871,000,000 km = 19.19 AU 4,497,000,000 km = 30.06 AU 5,914,000,000 km = 39.53 AU Earth’s Moon = 3,476 km Mean Distance from Earth = 384,400 km

Orbits of the Inner Planets

Orbits of Jupiter and Saturn

Orbits of the Outer Planets