Download Ch. 27 The Planets in our Solar System

Ch. 27 The Planets in our Solar
System
Our Solar System
Milky Way Galaxy
• Our solar system is located in the __________
(about 2/3 the way out on one of the arms.)
Sun
• There is ONE star in our solar system and it is the _____
• Our solar system is made up of the sun and our planets
that revolve around it.
– Rotation = spinning (a day), Revolution = circle (a year)
center of the solar system.
• The sun is at the _________
• 8 Planets and Pluto orbit around our sun.
• The planets are divided into two groups:
– Inner and outer planets.
– What Is a Planet 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 : Mercury, Venus, Earth, and Mars
– Outer Planets: Jupiter, Saturn, Uranus, Neptune (and
Pluto)
– The inner and outer planets are separated by the
Asteroid Belt.
So the order closest to the sun to furthest from sun is:
Inner Planets
• The inner planets have rocky crusts, dense
mantle 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
moon’s)
The smooth surface was formed from lava 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 moons
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 water
– Volcanic activity, faulting, mountain 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 volcano in the solar system =
Olympus Mons (500km across x 26km high),
however no plate motion
2 moons
Asteroid Belt
• Asteroids 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 comet) 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 hydrogen and helium)
• 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 dwarf planet (no longer considered a “real”
planet). Scientist believe they know of 44 dwarf planets
• Has a moon about ½ its size (moon = Charon)
• 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% rock 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, comets, and other debris, clearing a path along their orbits.
By contrast, Pluto's orbit is somewhat untidy.
• Pluto is part of the Kuiper Belt - a disc-shaped region of icy objects beyond
the orbit of Neptune. The Kuiper Belt and even more distant Oort Cloud
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!
• Meteoroid - 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.
• Meteorite – part of a large meteoroid that survives its
trip through the atmosphere and strike’s Earth’s surface.
(can consist of silicates, iron, nickel)
– Impact Crater – 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 Universe, 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 stars 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!!