four unexplained features of our solar...

Four Unexplained Features of our Solar System

√ Why do large bodies in our solar system have orderly motions?

--> 2) Why are there two types of planets?

3) Where did the comets and asteroids come from?

4) How can we explain the exceptions the the ‘rules’ above?

Why are there two types of planet, when all planets formed from the same nebula?

As gravity causes cloud to contract, it heats up

(Conservation of energy)

Inner parts of disk are hotter than outer parts.

Rock can be solid at much higher temperatures than ice.

Inside the frost line: too hot for hydrogen compounds to form ices.

Outside the frost line: cold enough for ices to form.

Fig 9.5

Tiny solid particles stick to form planetesimals.

Gravity draws planetesimals together to form planets

This process of assembly is called accretion

Gravity of rock and ice in jovian planets draws in H and He gases

Moons of jovian planets form in miniature disks

Why are there two types of planets?

1. Outer planets get bigger because abundant hydrogen compounds condense to form ICES.

2. Outer planets accrete and keep H & He in the gaseous phase.

Four Unexplained Features of our Solar System

√ Why do large bodies in our solar system have orderly motions?

√ Why are there two types of planets?

--> 3) Where did the comets and asteroids come from?

4) How can we explain the exceptions the the ‘rules’ above?

Comets and asteroids are leftover planetesimals.

• Asteroids are rocky because they formed inside the frostline.

• Comets are icy because they formed outside the frostline

Four Unexplained Features of our Solar System

√ Why do large bodies in our solar system have orderly motions?

√ Why are there two types of planets?

√ Where did the comets and asteroids come from?

--> 4) How do we explain the existence of our Moon and other “exceptions to the rules”?

Earth’s moon was probably created when a big planetesimal slammed into the newly forming Earth.

Other large impacts may be responsible for other exceptions like rotation of Venus and Uranus

luna320x240s.mpg

Review of nebular theory

The Inner Planets

Terrestrial Planet Surfaces

How do they compare to one another?

Comparison of Planetary Surfaces• Mercury (& the Moon)

• heavily cratered {scars from the heavy bombardment}

• some volcanic plains• Venus

• volcanoes and bizarre bulges• Mars

• volcanoes and canyons• apparently dry riverbeds {evidence for running water?}

• Earth• all of the above plus liquid water and life

Inside the Terrestrial Worlds

• After they have formed, the molten planets differentiate into three zones:• core - made of metals• mantle - made of dense rock• crust - made of less dense rock

• Lithosphere - the rigid, outer layer of crust & part of the mantle which does not deform easily

Inside the Terrestrial Worlds

Magnetic Fields

• Electric charges moving via convection in a molten iron core and spinning acts like an electromagnet � magnetic field

• Earth has a magnetic field• Venus, Mars, & the Moon do not

• Mercury surprisingly has a weak magnetic field ??

Mercury’s temperature range is the most extreme in the solar system

• Daytime with the Sun overhead reaches 700K (or 800°F)

• Midnight with the Sun completely obscured is 100K (or -280°F)

• Earth typically has temperature differences between day and night of about 11K (or 20°F)

• Mercury’s slow 176 day rotation and the lack of an appreciable atmosphere means temperatures vary enormously from one side of the planet to the other.

Why is there no atmosphere on Mercury?

Homework #5

What is the average speed of hydrogen atoms (m=1.67x10-27 kg) in the Sun’s photosphere (T = 5800 K)?

What is the escape velocity from Mercury?

23

27

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m (3.14159)(1.67 10 )

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The surface of Venus is

completely hidden beneath

permanent cloud cover

Venus

• Atmosphere is 96% CO2• Temperature is 750K

– much higher than Mercury– daytime AND nightime– caused by the greenhouse effect

The greenhouse effect heats Venus’s surface

Venus is covered with gently rolling hills, two “continents,” and numerous volcanoes

Venus

Searing heat, heavy pressure, clouds of sulfuric acid, frequent volcanic eruptions; as Carl Sagan said:

Venus is the planet most like hell!

Mars as viewed from Earth

Canals on Mars!

October 30th, 1938:is known as "mischief night." Thirty-two million people were relaxing that evening listening to their favorite shows.

Suddenly the broadcast was interrupted by a series of news bulletins: A large meteor had impacted in New Jersey near Grover's Mill. The object turned out not to be a meteor, but a metal cylinder. The cylinder opened and Martians, driving huge fighting machines, emerged. They were advancing upon New York City. Within thirty minutes the voice of a radio reporter, supposedly covering the event from a window in Manhattan, told of a gas attack on the city.

Then the reporter stopped talking. There was silence for a few seconds. Then the plaintive cry of a ham radio operator: Isn't there anyone on the air? Isn't there anyone?

Many people panicked.

Like Earth, Mars has polar ice caps that grow and shrink with the changing seasons. They are water ice and solid CO2

Valles Marineris is many times larger than the Grand Canyon

Enormous shield volcanoes

Olympus Mons - the largest volcano in the solar system has a base larger than the state of Colorado

Early space probes to Mars found no canals but did find some controversial features

Surface features indicate that water once flowed on Mars

Ohio River valley on Earth

River channels on Mars

The Martian meteorite found in Antarctica has not

provided conclusive evidence about life on

Mars

Mars’ two moons, Phobos and Deimos, look more like potatoes than spheres

Earth • most active geology• volcanoes & tectonics

• ongoing plate tectonics• moderate atmosphere

• N2 O2 H2O• H2O exists in liquid state

• rampant erosion• few craters

• life

What have we learned?• What four characteristics of our Solar System must be

explained by a formation theory?• Patterns of motion, why there are terrestrial and Jovian planets,

why there are asteroids and comets, and why there are exceptions to the rules.

• What is the basic idea behind the nebular theory?• Our Solar System formed from a giant, swirling cloud of gas

and dust.• What are the exceptions to the nebular theory?

• The large size of Earth’s Moon• The extreme tilt of Uranus• Backward orbit of Triton• Venus goes the wrong way

What have we learned?• How did gravitational collapse affect the Solar

nebula?• The nebula heated up, spun faster, and flattened into a disk.

• Know the general characteristics of the inner planets.

• Make sure you can calculate an escape velocity.• What key fact explains why there are two types of planet?

• Differences in condensation at different distances from the Sun: only metal and rock condensed inside the frost line, while hydrogen compounds could also condense outside the frost line.

Which is the biggest? Smallest? Oldest? Newest? UH 0.6-m Telescope 0.6 m Optical UH 1968

UH 2.2-m Telescope 2.2 m Optical/Infrared

UH 1970

NASA Infrared Telescope Facility (IRTF)

3.0 m Infrared NASA 1979

Canada-France-Hawaiÿi Telescope (CFHT)

3.6 m Optical/Infrared

Canada/France/UH 1979

United Kingdom Infrared Telescope (UKIRT)

3.8 m Infrared United Kingdom 1979

W. M. Keck Observatory (Keck I)

10 m Optical/Infrared

Caltech/ Univ. of California/NASA

1992

W.M. Keck Observatory (Keck II)

10 m Optical/Infrared

Caltech/ Univ. of California/NASA

1996

Subaru 8.1 m Optical/Infrared

Japan 1999

Gemini Northern 8-m Telescope

8 m Optical/Infrared

Canada/Chile/Argentina/Brazil 1999Millimeter/Submillimeter Telescopes

Caltech Submillimeter Observatory (CSO)

10.4 m Millimeter/ Submillimeter

Caltech/NSF 1987

James Clerk Maxwell Telescope (JCMT)

15 m Millimeter/ Submillimeter

United Kingdom/ Canada/Netherlands

1987

Submillimeter Array Eight 6-m antennae

Submillimeter Smithsonian Astro-physical Observ./ Taiwan

2001

Other FacilitiesVery Long Baseline Array 25 m Centimeter National Radio Astronomy

Observatory1992

What have we learned?• What is the origin of asteroids and comets and

where are they?• Asteroids are leftover planetesimals of the inner Solar

System typically between Mars and Jupiter and comets are leftovers of the outer Solar System.

• How do we explain the exceptions to the rules?• Collisions or close encounters with leftover

planetesimals can explain the exceptions.

What have we learned?• How do we think that our Moon formed?

• A Mars-sized “leftover” slammed into Earth, blasting rock from Earth’s outer layers into orbit, where it re-accreted to form the Moon.

• Why are Jovian planets so different from terrestrial planets?• Formed in cold, outer Solar System at the centers of “miniature

Solar nebulas”.

What did you think?• Is the temperature on Mercury, the closest planet to the

Sun, higher than the temperature on Earth?The temperature on the daytime side of Mercury is much higher than on Earth, but the temperature on the nighttime side of Mercury is much lower than on Earth because Mercury rotates so slowly and has little atmosphere to retain heat.

• What is the composition of the clouds surrounding Venus?The clouds are composed primarily of sulfuric acid.

• Does Mars have surface liquid water today?No, but there are strong indications that it had liquid water in the distant past.

• Is life known to exist on Mars today?No life has yet been discovered on Mars.

What have we learned?

• What does the solar system look like?• Our solar system

consists of the Sun, eight planets and their moons, and vast numbers of asteroids and comets. Each world has its own unique character, but there are many clear patterns among the worlds. The sun accounts for 99.98% of the mass.

What have we learned?

• Where did the solar system come from?• The cloud of gas that

gave birth to our solar system was the product of recycling of gas through many generations of stars within our galaxy. This gas consisted of 98% hydrogen and helium and 2% everything else combined.

What have we learned?

• What caused the orderly patterns of motion in our solar system?• A collapsing gas cloud

naturally tends to heat up, spin faster, and flatten out as it shrinks in size. Thus, our solar system began as a spinning disk of gas. The orderly motions we observe today all came from the orderly motion of this spinning disk of gas.