Planetary System

ASTR 1420

Lecture 15

Section 3.3

Solar System Overview

Put it on a tangible scale

If we scale down everything by 100 million times…

Sun = a small truck at the Physics Building at UGAMercury = a quarter at the Stegeman Coliseum

about 1/3 miles away

So much of empty space…

If we scale down everything by 100 million times…

Sun = a small truck at the Physics Building at UGAEarth = an apple at the intramural field

about a mile away

So much of empty space…

If we scale down everything by 100 million times…

Sun = a small truck at the Physics Building at UGAAsteroids = millions of planktons scattered around the Loop 10 (perimeter

road)

~3 miles away

So much of empty space…

If we scale down everything by 100 million times…

Sun = a small truck at the Physics Building at UGAJupiter = a classroom desk near the west-end of Athens

~5 miles away

So much of empty space…

If we scale down everything by 100 million times…

Sun = a small truck at the Physics Building at UGASaturn= a classroom desk near Bogart on highway 316

~10 miles away

So much of empty space…

If we scale down everything by 100 million times…

Sun = a small truck at the Physics Building at UGANeptune = a basketball near the Gwinnett county airport (Lawrenceville)

~20 miles away

So much of empty space…

If we scale down everything by 100 million times…

Sun = a small truck at the Physics Building at UGAPluto = a penny at the I-85 / GA-316 intersection

~30 miles away

So much of empty space…

If we scale down everything by 100 million times…

Sun = a small truck at the Physics Building at UGAK-B objects = millions of microbes + small insects scattered around northern

Georgia

~40-60 miles away

So much of empty space…

If we scale down everything by 100 million times…

Sun = a small truck at the Physics Building at UGANearest Star = another truck at the distance to the Moon

~200,000 miles away

Solar System Overview

Features of Solar System

•Orderly motions of large objects

•Two major types of planets

•Lots of smaller bodies

•Some exceptions• Venus• Uranus• Earth’s Moon

Orderly Motions

•All planets orbit the Sun in the same direction•All planets are in the same

plane•All planets orbit in nearly

circular orbits•Most planets’ rotation

direction = orbital direction

Two Groups of Planets• Earth-like Planets (Terrestrial Planets, rocky

planets, inner planets)o Mercury, Venus, Earth, & Marso metal and rock average density 2-3 times

higher than the density of liquid watero Solid surface and thick atmosphere

• Jupiter-like Planets (Jovian Planets, Gas giant planets, outer planets)o Jupiter, Saturn, Uranus, Neptuneo Gas : hydrogen, helium

+ methane, ammonia, iceo No solid surfaceo Low density : Saturn’s density < 1.0 !!o Two outer planets have higher content of

metal+rock

What about Pluto?

Small Bodies

Asteroids, comets, K-B objects

asteroids : metals and rockscomets : largely ices + rocks and metalK-B objects : similar to cometsOort cloud : similar to comets?

Kuiper Belt Objects

Some larger ones = dwarf planets large enough to be circular shaped…

Moons (satellites)• Objects that orbit

planets or other objects.

• Jupiter : 63• Saturn : 62 (150)

• Moons of jovian planets contain lots of ice snowline!

• Large moons are potential habitable worlds

Why?

The order with well defined characteristics…

There must be a good reason.

It is related to the way of stars and their planets being formed!

Lots of clouds in the Galaxy

Formation of Planetary System (nebular theory)

• Contraction and disk formationOnce the collapse begins, nebula would heat up, spin faster, and flatten…

Conservation of Energy (heating up) : gravitational potential energy heat energyConservation of angular momentum (spin up)

collapsed to a nearly 1/1,000,000 of the initial size

Composition of Clouds

Formation of Planetary System

• Condensation (opposite of melting) : High temperatures in the inner region materials only with high condensation

temperatures can turn to solids (metals and rocks). Outer region is much cooler materials with lower condensation temperatures can

turn to solids also (ices, rocks and metals) more solids than the inner region!Hydrogen and Helium remain as gas everywhere in the disk.

Formation of Planetary System

• Accretion of solidsPebbles rocks boulders … planetesimals (~100 km size)… this process over a few million years…

• Collisions b/w planetesimals (some stuck, some shatter)

• Formation of rocky planets (inner) and some ice-rocky planets (outer)• Gas accretion in the outer area (why not inner?) Jovian planets!

Formation of Planetary System

• Moon formations around Jovian planets in a disk surrounding a Jovian planet (similar to the way planets are formed)…

Formation of Planetary System

• Clearing the DiskRemaining gas will be blown away by solar wind…

Rocks remain, but gradually being cleared by planets or collide among themselves…

Is this happening at other stars?

Yes! many habitable worlds in the Universe!!

Young stars in their early formation showing a disk (dark shade)

Planetary system formation simulationhttp://www.youtube.com/watch?v=jhYEQgLW5NM

In summary…

Important Concepts• Planet formation (nebular theory)• Conservation of Energy• Conservation of angular

momentum• Ordered structure of planets is a

natural outcome of planet formation.

Important Terms• Terrestrial planets• Jovian planets• Kuiper Belt objects• Oort Clouds• Condensation/accretion• Planetesimals

Chapter/sections covered in this lecture : 3.3Exoplanet Detection : next class!!