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THE SOLAR SYSTEM

Part 3: A Trip through the Solar System

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Measuring Distances

Astronomical Units or AU:

One astronomical unit is equal to the mean (average) distance of the Earth from the Sun.

1 AU = 149,597,000 km (rounded number)

Used to indicate distance to objects within our solar system

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Major Features - Planets

The definition of planet, set in 2006 by the International Astronomical Union (IAU) states that, in the Solar System, a planet is a celestial body which: is in orbit around the Sun, has sufficient mass to

assume a nearly round shape, and

has "cleared the neighborhood" around its orbit.

8 Planets (In order from nearest the Sun):

MercuryVenusEarthMarsJupiterSaturnUranusNeptune

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Major Features – Dwarf Planets

A dwarf planet is a large body which meets the other criteria for a planet but has not cleared its neighborhood.

The IAU currently recognizes five dwarf planets in the Solar System: 

CeresPlutoHaumeaMakemake Eris.

There are nearly 50 other known objects that may be dwarf planets and as many as 2,000 in all.

Only two well observed.

Ceres

Eris Pluto

Pictures from Hubble Telescope

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Major Features – Planets and Dwarf Planets

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Major Features: Asteroids Rocky, airless worlds that orbit our sun, but are too

small to be called planets Several hundred thousand discovered Most are located in the doughnut-shaped asteroid

belt between Mars and Jupiter Also called "minor planets" Near-Earth Objects (NEOs): Asteroids that pass

close to Earth May be composed of rocks, minerals, and/or metals

Image Credit: NASA/JPL/JHUAPL

This picture of Eros is the first of an asteroid taken from an orbiting spacecraft.

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Major Features: Comets Cosmic, dirty snowballs of

frozen water and gases, rock, and dust

When a comet's orbit brings it close to the sun, it heats up and spews dust and gases into a giant glowing head larger than most planets.

The dust and gases form a tail that stretches away from the sun for millions of kilometers.

This image of Comet C/2001 Q4 (NEAT) was taken at the WIYN 0.9-meter telescope at Kitt Peak National Observatory near Tucson, Ariz. on 7 May 2004. Credit: National Science Foundation

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Major Features: Comets

Parts of a Comet: 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 by the heat of the sun,

may be hundreds of thousands of kilometers in diameter;

high-speed solar particles (solar wind) blows the coma materials away from the sun, forming a long, and sometimes bright, tail.

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Major Features: Comets

Parts of a Comet: 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

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Major Features: Comets Comets orbit the sun. Short-period comets

take up to 200 years to make one orbit; originate in the scattered disc beyond Neptune

Long-period comets: may take millions of years to make one trip around the sun; originate in the Oort Cloud

Credit: NASA

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Major Features: Kuiper Belt Discovered in 1992, but hypothesized as early as

1930, soon after the discovery of Pluto 30-100 AU from the sun Similar to the asteroid belt in that it consists of

small bodies that never reached planet size Unlike asteroids, Kuiper belt objects (over 1,000

known so far) are composed largely of frozen substances such as methane, ammonia and water

Home of dwarf planets Pluto, Haumea, and Makemake

Kuiper rhymes with piper and viper.

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Major Features: Scattered Disc

A region of space beyond the Kuiper Belt

The innermost portion overlaps with the Kuiper Belt, but its outer limits extend much farther away from the Sun

Now thought to be the origin of short-period comets

Sparsely populated with icy minor planets.

Home of dwarf planet Eris Scattered Disc Objects, or SDOs, are

among the most distant, and thus the most cold, objects in the solar system.

Eris and its moon DysnomiaEris, 27% more massive than

Pluto, was discovered in 2003. Hubble Photograph

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Major Features: The Oort Cloud

A vast, spherical, icy cloud 50,000AU or more from the sun (almost a light year); remnant of the original protoplanetary disc

Believed to be the origin of long-period comets

Only hypothesized, no direct evidence exists – why?

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The Planets: Mercury Closest to sun Rocky Slightly larger than the

moon Almost no atmosphere

to stop impacts so covered with craters

Very long day (59 Earth days) leads to very hot days (427°C) and very cold nights (-170°C)

One of the first images to be returned from MESSENGER's second flyby of Mercury.Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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Planets: Venus Second from the sun; closest to

Earth About the same size, mass, and

density as Earth Highly volcanic Rotates east to west, or

retrograde (reversed from Earth) A Venusian day (243 Earth days)

is longer than a Venusian year (225 days)

Thick, toxic atmosphere (mostly CO2) traps heat in a runaway "greenhouse effect," with temperatures hot enough to melt lead. (Hotter than Mercury)

Image of Venus in real color. The surface is obscured by a thick blanket of clouds of sulfuric acid. Credit: NASA/Ricardo Nunes

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Planets: Mars 4th from the sun A cold, desert world with a thin

atmosphere ½ the diameter of Earth Often called the Red Planet due

to the reddish color of the high levels of iron oxide (rust) on its surface

Has seasons, polar ice caps, dormant volcanoes, canyons and weather

2 small moons, Phobos and Deimos

Largest known volcano in the solar system, Olympus Mons

Water-ice clouds, polar ice, polar regions, and geological features can be seen in this full-disk image of Mars.Credit: NASA/JPL

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Planets: Jupiter 5th planet from the Sun Most massive planet in our

solar system A gas giant resembling a

star in composition (mostly H and He) but did not get large enough to ignite nuclear fusion

Covered in clouds Great Red Spot is a

massive storm that has lasted for hundreds of years

A true-color image of Jupiter taken by the Cassini spacecraft. The Galilean moon Europa casts a shadow on the planet's cloud tops.Credit: NASA/JPL/University of Arizona

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Jupiter’s Moons Jupiter has dozens of moons Four were discovered by Galileo

Galilei and are called the Galilean satellites or moonsIo – innermost; most geologically

active object in solar systemEuropa - close to size of our

moon; one of the smoothest objects in the solar system, covered in ice

Ganymede – largest natural satellite in the solar system (larger than Mercury)

Callisto – 3rd largest moon in solar system; heavily cratered

Montage of Jupiter's four Galilean moons, in a composite image comparing their sizes and the size of Jupiter. From top to bottom: Io, Europa, Ganymede, CallistoCredit: NASA/JPL/DLR

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Planets: Saturn 6th planet from the sun Rings of mostly ice particles

(water); discovered by Galileo A gas giant composed of

mainly H and He Spins so fast it is flattened at

the poles Has a density less than that

of water (0.7g/cm3) Has 62 known (53 named)

satellites Titan, 2nd largest moon in the

solar system, has a nitrogen-rich atmosphere

Saturn in natural color, photographed by Cassini

Credit: NASA/JPL/Space Science Institute

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Planets: Uranus 7th planet from the sun Discovered in 1781 A gas giant or sometimes called

an ice giant Like Venus, rotation is retrograde

(east to west) Axis tilted almost 90° so appears

to be rotating on its side. Methane in its atmosphere gives

it a blue tint 13 known rings; 27 known

moons, named after characters from works of Shakespeare and Alexander Pope

Uranus' moon Ariel (white dot) and its shadow (black dot) were caught crossing the face of Uranus in this Hubble Space Telescope image.Credit: NASA/Space Telescope Science Institute

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Planets: Neptune 8th planet from the sun Discovered in 1846 Orbit takes 165 years 4th largest by diameter

after Uranus Also a gas or ice giant Blue due to methane plus

some unknown substance in the atmosphere

6 known rings; 13 known moons (Triton, the largest, has a retrograde orbit)

Voyager 2 captured this image of Neptune in 1989. The picture shows the Great Dark Spot and its companion bright smudge.Credit: NASA

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Meteoroids, Meteors, and Meteorites

Meteroids: chunks of metal or stone that orbit the sun

Meteor: a streak of light produced by a meteoroid burning due to friction as it plunges through the atmosphere; a shooting star

Meteorite: a meteoroid that strikes

the Earth’s surfaceMost contain iron, nickel,

and stone

The Hoba meteorite in 2006. Located in Namibia, it is the largest known meteorite on Earth, about 54,000kg.