Introduction to the Solar System The bright star Antares embedded in dust and gases

The Formation of the Solar System Through the course of history there have been many theories about the solar system Early Greeks thought the Earth was the center of the solar system, with the stars, sun and moon revolving around the Earth – the Geocentric Model In 1543, a scientist proposed that the sun was the center of the solar system and the planets revolved around it – the Heliocentric Model

Origin of the Solar System Modern astronomers believe that the sun and planets condensed out of a nebula or large cloud of gas and dust. This idea is named the. It was first presented by the German philosopher Immanuel Kant in the late 1700’s. This idea is named the Nebular Hypothesis. It was first presented by the German philosopher Immanuel Kant in the late 1700’s. Such clouds have been observed around stars other than our sun (e.g., Beta Pictoris) Such clouds have been observed around stars other than our sun (e.g., Beta Pictoris)

The Formation of the Solar System Our solar system began as a rotating gas cloud or nebula that collapsed toward its center under the influence of gravity. A condensation formed at the center, which is called a protostar. A flattened disk of matter surrounded the protostar, which began to shine and become a star, our sun. The condensing and contracting caused the cloud to begin to rotate, as it rotated the center became dense and the temperature reached about 10 million K The extremely high temperatures allowed for a process called nuclear fusion to occur

The Formation of our Solar System The rising temperature from the sun removed the gas from the inner regions, leaving dust and larger debris Inner planets formed from solid debris Outer planets retained original gases Planets established dominance in their regions of the solar system. After almost all of the remaining gas, dust, and small debris was collected by the larger objects, the solar system took on the form we recognize today.

Other Star Systems Forming We can look at young star systems developing today. The planets orbiting these stars are formed from the surrounding disks of gas and dust, called protoplanetary disks or proplyds. Proplyd in the Orion Nebula

Solar System Composite 1.Mercury 2.Venus 3.Earth 4.Mars 5.Jupiter 6.Saturn 7.Uranus 8.Neptune

Common Properties of Planet Orbits in Our Solar System As viewed from above, all of the planets orbit the Sun in a counterclockwise direction. The planets orbit in nearly the same plane (ecliptic). All planets except Pluto have an orbital inclination of less than 7°.

Inner Solar System

Outer Solar System

Pluto’s Odd Orbit Pluto’s orbit, or plane of revolution, is tilted by 17° to the general solar system orbits (ecliptic) Pluto’s orbit, or plane of revolution, is tilted by 17° to the general solar system orbits (ecliptic) Pluto can also cut across Neptune’s orbit (but they can never collide) Pluto can also cut across Neptune’s orbit (but they can never collide)

Ecliptic Plane Plane of the Ecliptic: The orbits of the planets are mostly in the same plane. This plane is called the ecliptic and is defined by the plane of the earth’s orbit. This plane is called the ecliptic and is defined by the plane of the earth’s orbit. The exception is Pluto, which is tilted quite a bit in comparison to the rest of the planets. The exception is Pluto, which is tilted quite a bit in comparison to the rest of the planets. The ecliptic plane is a remnant of the original, rotating nebular disk that formed the sun and planets

Ecliptic: Artist’s View

Motions direction around the sun (when looking down upon the solar system from the sun’s north pole). Directions of Motion: The planets orbit in a counterclockwise direction around the sun (when looking down upon the solar system from the sun’s north pole). All the planets, except for Venus, Uranus, and Pluto, rotate in the same direction as their orbits.

Orbits The planets nearest to the Sun (Mercury, Venus, Earth, and Mars) are relatively close together, while those farther away (Jupiter, Saturn, Uranus, and Neptune) are more spread out. The planets nearest to the Sun (Mercury, Venus, Earth, and Mars) are relatively close together, while those farther away (Jupiter, Saturn, Uranus, and Neptune) are more spread out. Most of the planets are in nearly circular orbits. Most of the planets are in nearly circular orbits.

Solar System Orbits (AU) The astronomical unit (AU) is useful in measuring distances in the solar system One AU equals the average earth-to-sun distance of 93 million miles AU distances allow direct comparison to the earth which is equal to 1.0 AU distances allow direct comparison to the earth which is equal to 1.0 Planet Distance in AU Mercury0.4 Venus0.7 Earth1.0 Mars1.5 Jupiter5.2 Saturn9.5 Uranus19.2 Neptune30 Pluto39.5

Revolutions of the Planets* Mercury 88 days Mercury 88 days Venus days Venus days Earth days Earth days Mars 1.88 years Mars 1.88 years Jupiter years Jupiter years Saturn 29.5 years Saturn 29.5 years Uranus 84 years Uranus 84 years Neptune years Neptune years Pluto years Pluto years *Earth days and years

Diameters Planet Diameter (Earth = 1) Mercury0.38 Venus0.95 Earth1.0 Mars0.53 Jupiter11.21 Saturn9.45 Uranus4.01 Neptune3.88 Pluto0.18

Masses Planet Mass (Earth = 1) Mercury0.06 Venus0.81 Earth1.0 Mars0.11 Jupiter Saturn95.18 Uranus14.53 Neptune17.14 Pluto0.002

Average Density (kg/m 3 ) Planet Mercury 5430 Venus 5250 Earth 5520 Mars 3950 Jupiter 1330 Saturn 690 Uranus 1290 Neptune 1640 Pluto 2030

Rotational Period Planet Days (Earth  1) Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto6.3872

Average Temperature PlanetAve Temp (°F) Mercury354° Venus867° Earth45° Mars-81° Jupiter-186° Saturn-202° Uranus-337° Neptune-364° Pluto-380°

Average Temperature (Earth = 1)

Sizes of the Planets In mass, the sun represent 99% of the solar system The smallest planet, Mercury, has a diameter of 3031 mi The smallest planet, Mercury, has a diameter of 3031 mi Pluto, the previous smallest planet, has a diameter of 1457 mi Pluto, the previous smallest planet, has a diameter of 1457 mi The largest planet, Jupiter, has a diameter of 88,700 mi The largest planet, Jupiter, has a diameter of 88,700 mi Earth = 7926 mi Earth = 7926 mi Ganymede, the largest moon of Jupiter, is larger than Mercury, yet Ganymede is not considered a planet because it revolves around Jupiter Ganymede, the largest moon of Jupiter, is larger than Mercury, yet Ganymede is not considered a planet because it revolves around Jupiter

Two Basic Groups of Planets TERRESTRIAL (earth-like) Small size, low Mass Higher density Mostly rock Mercury, Venus, Earth, Mars JOVIAN (Jupiter-like) Large size, massive Low density Mostly gas Jupiter, Saturn, Uranus, Neptune

Classifications Terrestrial or Rocky planets—Composed of rock and metal: Mercury, Venus, Earth, Mars Terrestrial or Rocky planets—Composed of rock and metal: Mercury, Venus, Earth, Mars Jovian or Gas planets—Composed primarily of the gases hydrogen and helium: Jupiter, Saturn, Uranus, Neptune Jovian or Gas planets—Composed primarily of the gases hydrogen and helium: Jupiter, Saturn, Uranus, Neptune

Classification, cont. Small Planets— Diameters less than 13,000 km: Mercury, Venus, Earth, Mars Small Planets— Diameters less than 13,000 km: Mercury, Venus, Earth, Mars Giant Planets (Gas Giants)—Diameters greater than 48,000 km: Jupiter, Saturn, Uranus, Neptune Giant Planets (Gas Giants)—Diameters greater than 48,000 km: Jupiter, Saturn, Uranus, Neptune

Classification, cont. Inner Planets— Mercury, Venus, Earth, Mars Inner Planets— Mercury, Venus, Earth, Mars Outer Planets— Jupiter, Saturn, Uranus, Neptune Outer Planets— Jupiter, Saturn, Uranus, Neptune

Classification, cont. Inferior—Closer to the sun than earth: Mercury and Venus Superior—Farther from the sun than earth: Mars, Jupiter, Saturn, Uranus, Neptune

Classification, cont. Classical—Known since prehistoric times, visible to the unaided eye: Mercury, Venus, Mars, Jupiter, Saturn Modern—Discovered in modern times, visible only with telescopes: Uranus, Neptune, (Pluto)

Classification Table Planet Rocky or Gas? Small or Giant? Inner or Outer? Inferior or Superior? Classical or Modern? MercuryRSIIC VenusRSIIC EarthRSIN/A? MarsRSISC JupiterGGOSC SaturnGGOSC UranusGGOSM NeptuneGGOSM Pluto?SOSM

New Solar System (> 2006) Planets: Planets: Mercury Mercury Venus Venus Earth Earth Mars Mars Ceres (dwarf) Ceres (dwarf) Jupiter Jupiter Saturn Saturn Uranus Uranus Neptune Neptune Pluto (dwarf) Pluto (dwarf) Eris (dwarf) Eris (dwarf) Makemake (dwarf) Makemake (dwarf) Eris Two Categories: Planets and Dwarf Planets (dwarfs beyond Neptune are “Plutoids”) Today’s astronomers recognize only 8 planets

Solar System Model If the sun were an orange, the earth would be a grain of sand thirty feet away. If the sun were an orange, the earth would be a grain of sand thirty feet away. Jupiter would be a cherry pit located one block from the sun. Jupiter would be a cherry pit located one block from the sun. Saturn would be another cherry pit located one block from Jupiter. Saturn would be another cherry pit located one block from Jupiter. Pluto would be a grain of sand 10 blocks from the sun. Pluto would be a grain of sand 10 blocks from the sun. The nearest star to our sun (Alpha Centauri) would be represented as another orange 2000 miles from the sun. The nearest star to our sun (Alpha Centauri) would be represented as another orange 2000 miles from the sun.

Planet Names The planets have been given the Roman names of gods from ancient Greece. The planets have been given the Roman names of gods from ancient Greece.Roman Mercury, Venus, Mars, Jupiter, Saturn Mercury, Venus, Mars, Jupiter, SaturnGreek Hermes, Aphrodite, Ares, Zeus, Kronos Hermes, Aphrodite, Ares, Zeus, Kronos The modern planets, Uranus, Neptune, and Pluto, are also Roman gods Jupiter from Fantasia (Disney)