Solar System

• Our solar system consists of– Sun– 9 planets– Asteroid Belt– Meteors and comets– Interplanetary medium

How was it formed?

• http://imgsrc.hubblesite.org/hu/db/2003/19/images/f/formats/pdf.pdf

• Two Planet Forming Scenarios

• The Solar System formed when a cold, slowly-rotating cloud of gas and dust collapsed because of its own gravity about 4.5 billion years ago.

• As the Sun grew hot enough to ignite the nuclear reactions which sustain it today, it vaporized the cold ices and frozen gasses in the inner solar system, leaving behind the rocky dust and metals which form the inner planets.

• The outer Solar System remained cold, and the ices and gas there collected into the giant outer planets

Two General Categories

• Terrestrial planets (like the Earth) – The terrestrial planets- Mercury, Venus, Earth and

Mars- are relatively small and have rocky crusts and small atmospheres.

• Jovian planets (like Jupiter). – The Jovian planets- Jupiter, Saturn, Uranus and

Neptune- are many times larger and have dense, gaseous atmospheres with no visible surfaces.

– Sometimes referred to as gas giants, although it is believed that the cores of these huge planets are liquid if not solid forms of helium and hydrogen

• Pluto, the most distant planet, is in a class by itself

MERCURY

• Timocharis made the first recorded observation of Mercury in 265 BC.

• Other early astronomers that studied Mercury include Zupus (1639), who studied the planet's orbit.

• Because it is so difficult to make out features on the surface of the planet from Earth, it was not until the 1960s that scientists determined the correct day length rate (59 Earth days) of the planet on its axis. This also showed that Mercury's day length and year length are the same.

• 1974 Mariner 10 passed by the planet 3 times and gave us close-up images

• 2004 Messenger mission

Mercury

VENUS

• Venus is the second planet from the Sun, and is Earth's neighbor in the solar system.

• Venus is the brightest object in the sky after the Sun and the Moon, and sometimes looks like a bright star in the morning or evening sky.

• We can't see the surface of the planet because it has a very thick atmosphere filled with clouds that strongly reflect sunlight. Observations of Venus in the ultraviolet show cloud features that relate to characteristics of the planet's atmosphere.

• We think that the internal structure of Venus is similar to Earth, with a metallic core, rocky mantle, and crust.

• The atmosphere of Venus produces hostile conditions at the planet's surface, where temperatures can reach more than 460C (900F), atmospheric pressure is 90 times that at the Earth's surface, and clouds filled with sulfuric acid surround the planet.

• spacecraft mapped the surface of the planet from above. These maps reveal a surface covered with craters, over 1600 major volcanoes, mountains, large highland terrains, and vast lava plains.

• The 1950's astronomer Robert Richardson noticed that Venus rotates opposite from earth

MARS

• Mars Student Imaging Project– Lets students pick a spot for the orbiting

Odyssey Spacecraft to take a picture– http://msip.asu.edu/index.html

• http://marsrovers.jpl.nasa.gov/mission/traverse_maps.html– Latest information on the two Mars rovers,

Spirit and Opportunity

• The uniquely red surface of Mars is marked by many interesting features - some like those on the Earth and others strangely different. The reddish color is caused by rust (iron oxide) in the soil. – Some of these features are; volcanoes, canyon systems, river

beds, cratered terrain, and dune fields.

• Of these features, the most interesting includes the apparently dead volcano Olympus Mons, which rises 23 km (~75,000 ft) above the surrounding plains and is the highest known peak in the Solar System.

• Valles Marines is a giant canyon system that runs about 2,500 miles across the surface of the planet and reaches depths of 6 km or 4 miles – (for comparison, the Grand Canyon is not more than 1 mile

deep).

ASTEROID BELT

• Asteroids are small bodies that are thought to be left over from the beginning of the solar system 4.6 billion years ago. They are rocky objects with round or irregular shapes up to several hundred km across, but most are much smaller.

• More than 100,000 asteroids lie in a belt between Mars and Jupiter. These asteroids lie in a location in the solar system where there seems to be a jump in the spacing between the planets. Scientists think that this debris may be the remains of an early planet, which broke up early in the solar system. Several thousand of the largest asteroids in this belt have been given names.

• The chances of an asteroid colliding with Earth are very small! But some do come close to Earth, like Hermes (closest approach of 777,000 km).

Formation of the Asteroid Belt

• One theory suggests that they are the remains of a planet that was destroyed in a massive collision long ago.

• More likely, asteroids are material that never coalesced into a planet. – In fact, if the estimated total mass of all the

asteroids was gathered into a single object, the object would be less than 1,500 kilometers (932 miles) across - less than half the diameter of the Moon.

JUPITER

• The Giant planets do not have the same layered structure that the terrestrial planets do. Their evolution was quite different than that of the terrestrial planets, and they have less solid material.

• Jupiter's interior composition is primarily that of simple molecules such as hydrogen and helium, which are liquids under the high pressure environments found in the interiors of the outer planets, and not solids.

• Motions in the interior of Jupiter contribute in a very special way to the development of the powerful and extensive magnetosphere of Jupiter. Heat generated within

• Jupiter contributes to the unusual motions of the atmosphere.

Giant Red Spot

• A giant, hurricane-like storm system that rotates with the clouds of Jupiter.

• It is so large three complete Earths could fit inside it.

• Astronomers have recorded this giant storm on Jupiter for over 300 years.

Rings

• Rings are much smaller and fainter than the famous rings of Saturn

• Their composition is small-grained, rocky material; no ice. Contributes to their small albedo (reflectiveness)

• Voyager 1 mission scientists decided to look around and were surprised to find them

Shoemaker-Levy9 Impact

• On 1994 July 16-22, over twenty fragments of comet Shoemaker-Levy 9 collided with the planet Jupiter

SATURN

• Saturn is the most distant of the five planets known to ancient stargazers.

• In 1610, Italian Galileo Galilei was the first astronomer to gaze at Saturn through a telescope. To his surprise, he saw a pair of objects on either side of the planet, which he later drew as "cup handles" attached to the planet on each side.

• In 1659, Dutch astronomer Christiaan Huygens announced that this was a ring encircling the planet.

• In 1675, Italian-born astronomer Jean Dominique Cassini discovered a gap between what are now called the A and B rings.

• Saturn is a gas giant. It is made mostly of hydrogen and helium.

• volume is 755 times greater than Earth's. • Winds in the upper atmosphere reach 500

meters per second in the equatorial region. (In contrast, the strongest hurricane-force winds on Earth top out at about 110 meters per second.)

• These super-fast winds, combined with heat rising from within the planet's interior, cause the yellow and gold bands visible in its atmosphere

URANUS

• Uranus is the seventh planet from the Sun and is the third largest in the solar system. – It was discovered by William Herschel in 1781.

• It has an equatorial diameter of 51,800 kilometers (32,190 miles) and orbits the Sun once every 84.01 Earth years.

• It rotates about its axis once every 17 hours 14 minutes. Uranus has at least 22 moons.

• Uranus is distinguished by the fact that it is tipped on its side. – Its unusual position is thought to be the result

of a collision with a planet-sized body early in the solar system's history

• In 1977, the first nine rings of Uranus were discovered. During the Voyager encounters, these rings were photographed and measured, as were two other new rings and ringlets.

NEPTUNE

• Neptune is the outermost planet of the gas giants.

• It has an equatorial diameter of 49,500 kilometers (30,760 miles). – If Neptune were hollow, it could contain nearly

60 Earths.

• Neptune orbits the Sun every 165 years.

• Neptune is a dynamic planet with several large, dark spots reminiscent of Jupiter’s hurricane-like storms.

• The largest spot, known as the Great Dark Spot is about the size of the earth and is similar to the Great Red Spot on Jupiter.

• Voyager revealed a small, irregularly shaped, eastward-moving cloud scooting around Neptune every 16 hours or so. – This scooter as it has been dubbed could be a

plume rising above a deeper cloud deck.

PLUTO

• Tiny (only slightly larger than our Moon)• Orbit is inclined more than 17 degrees

compared to the orbits of the other planets, and its

• Orbit is also very eccentric (its distance from the Sun varies over the course of its orbit). – It's so eccentric, in fact, that it even crosses

Neptune's orbit, so sometimes Neptune is farther from the Sun than Pluto

• Recently the Hubble Telescope has taken pictures of two moon circling Pluto and Charon.

• In 2004 the international science community had re-defined Pluto as a dwarf planet.

• Since that time dozens of small Planetoids have be discovered in our Solar system.

• Ceres, Eris, Sedna, Biden, VP113,

Comparing Rotation

Visualizing the Distance Between Planets

• http://www.classzone.com/books/earth_science/terc/content/visualizations/es2701/es2701page01.cfm?chapter_no=visualization– This animation is 300 times the speed of light.

Beyond the planets

• Oort Cloud– An immense spherical cloud surrounding the

planetary system and extending approximately 3 light years, about 30 trillion kilometers from the sun.

– This vast distance is considered the edge of the Sun's orb of physical, gravitational, or dynamical influence

– Source of long-period comets

• Kuiper Belt– Starting in 1992, astronomers have become

aware of a vast population of small bodies orbiting the sun beyond Neptune.

– There are at least 70,000 "trans-Neptunians" with diameters larger than 100 km in the radial zone extending outwards from the orbit of Neptune (at 30 AU) to 50 AU

– Source of short-period comets– Oort Cloud

COMETS

• Comets are sometimes called dirty snowballs or "icy mudballs". – They are a mixture of ices (both water and

frozen gases) and dust that for some reason didn't get incorporated into planets when the solar system was formed.

• This makes them very interesting as samples of the early history of the solar system.

• nucleus: relatively solid and stable, mostly ice and gas with a small amount of dust and other solids;

• coma: dense cloud of water, carbon dioxide and other neutral gases sublimed from the nucleus;

• hydrogen cloud: huge (millions of km in diameter) but very sparse envelope of neutral hydrogen;

• dust tail: up to 10 million km long composed of smoke-sized dust particles driven off the nucleus by escaping gases; this is the most prominent part of a comet to the unaided eye;

• ion tail: as much as several hundred million km long composed of plasma and laced with rays and streamers caused by interactions with the solar wind

Parts of a comet

Nucleus of Halley’s Comet

METEORS

• A meteor is a bright streak of light in the sky (a "shooting star" or a "falling star") produced by the entry of a small meteoroid into the Earth's atmosphere.

• When they hit the Earth’s surface they are called Meteorites

Meteorites

• 3 Types– Chrondrite (Stony)

• Most Common

– Carbonaceous Chrondrite• Contain Organic Compounds

– Iron• Composed mostly of Iron and Nickel

• The largest found meteorite (Hoba, in Namibia) weighs 60 tons.

Chondrite (Stony) Meteorite

Iron Meteorite

Carbonaceous Chondrite

Hitting Earth

When is a heavenly body a planet? a star? a piece of space debris?

• If there were a textbook definition of planet, it would likely describe an object that forms out of the swirling disk of dust and gas left after the formation of a star.– That also orbits a star– That does not generate enough heat to burn

deuterium

A planet is a spherical object never capable of core

fusion, which is formed in orbit around an object in which core fusion occurs at some time

Small Planet?

• Many astronomers think that Pluto should never have been called a planet. – It is only 1,430 miles (2,300 kilometers) wide,

smaller than Earth's Moon. – It travels an elongated orbit that also dips

above and below the plane of Earth's orbit by 17.1 degrees.

– There are Kuiper Belt Objects (KBOs) that approach the size of Pluto

• A newly proposed definition for planets that would instantly boost the solar system's tally to 12 – one large, round asteroid, and– at least two faraway and icy brethren of Pluto.

• The middle road in the argument, which is winning so far, goes like this: – Pluto is a planet, and the public would be

confused and even upset to change that. – Leave it as the ninth and final planet,

• but scientifically keep in mind that it's a KBO and don't otherwise increase the count of planets in our solar system

Brown Dwarfs

• Brown dwarfs are the ill-defined middle ground between planets and stars.

• A star is a star because it shines on its own, generating light through thermonuclear reactions in which hydrogen is converted to helium.

• Brown dwarfs, though they can burn deuterium in another type of reaction called "core fusion," fall short of full-blown stellar thermonuclear fusion.

ON-LINE ACTIVITIES

• On-line Solar System Quiz

• http://www.the-solar-system.net/index.html

• Virtual Solar System

• http://www.nationalgeographic.com/solarsystem/index.html