2Measuring 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
3Major 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, andhas "cleared the neighborhood" around its orbit.8 Planets (In order from nearest the Sun):MercuryVenusEarthMarsJupiterSaturnUranusNeptuneIn the end stages of planet formation, a planet will have "cleared the neighborhood" of its own orbital zone, meaning it has become gravitationally dominant, and there are no other bodies of comparable size other than its own satellites or those otherwise under its gravitational influence.
4Major 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: CeresPlutoHaumeaMakemakeEris.CeresOnly two well observed.ErisPlutoThere are nearly 50 other known objects that may be dwarf planets and as many as 2,000 in all.Pictures from Hubble Telescope
6Major Features: Asteroids Rocky, airless worlds that orbit our sun, but are too small to be called planetsSeveral hundred thousand discoveredMost are located in the doughnut-shaped asteroid belt between Mars and JupiterAlso called "minor planets"Near-Earth Objects (NEOs): Asteroids that pass close to EarthMay be composed of rocks, minerals, and/or metalsThis picture of Eros is the first of an asteroid taken from an orbiting spacecraft.Image Credit: NASA/JPL/JHUAPL
7Major Features: Comets Cosmic, dirty snowballs of frozen water and gases, rock, and dustWhen 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 Credit: National Science Foundation
8Major Features: Comets Parts of a Comet:nucleus: relatively solid and stable, mostly ice and gas with a small amount of dust and other solidscoma: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.
9Major 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 eyeion 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
10Major Features: Comets Comets orbit the sun.Short-period comets take up to 200 years to make one orbit; originate in the scattered disc beyond NeptuneLong-period comets: may take millions of years to make one trip around the sun; originate in the Oort CloudCredit: NASA
11Major Features: Kuiper Belt Discovered in 1992, but hypothesized as early as 1930, soon after the discovery of PlutoAU from the sunSimilar to the asteroid belt in that it consists of small bodies that never reached planet sizeUnlike asteroids, Kuiper belt objects (over 1,000 known so far) are composed largely of frozen substances such as methane, ammonia and waterHome of dwarf planets Pluto, Haumea, and MakemakeKuiper rhymes with piper and viper.
12Major Features: Scattered Disc A region of space beyond the Kuiper BeltThe innermost portion overlaps with the Kuiper Belt, but its outer limits extend much farther away from the SunNow thought to be the origin of short-period cometsSparsely populated with icy minor planets.Home of dwarf planet ErisScattered 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
13Major 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 discBelieved to be the origin of long-period cometsOnly hypothesized, no direct evidence exists – why?No direct evidence exists because comets are relatively small and the distance is too great to see them.
14The Planets: Mercury Closest to sun Rocky Slightly larger than the moonAlmost no atmosphere to stop impacts so covered with cratersVery 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
15Planets: Venus Second from the sun; closest to Earth About the same size, mass, and density as EarthHighly volcanicRotates 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
16Planets: Mars 4th from the sun A cold, desert world with a thin atmosphere½ the diameter of EarthOften called the Red Planet due to the reddish color of the high levels of iron oxide (rust) on its surfaceHas seasons, polar ice caps, dormant volcanoes, canyons and weather2 small moons, Phobos and DeimosLargest known volcano in the solar system, Olympus MonsWater-ice clouds, polar ice, polar regions, and geological features can be seen in this full-disk image of Mars.Credit: NASA/JPL
17Planets: Jupiter 5th planet from the Sun Most massive planet in our solar systemA gas giant resembling a star in composition (mostly H and He) but did not get large enough to ignite nuclear fusionCovered in cloudsGreat Red Spot is a massive storm that has lasted for hundreds of yearsA 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
18Jupiter’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 iceGanymede – largest natural satellite in the solar system (larger than Mercury)Callisto – 3rd largest moon in solar system; heavily crateredIo - brilliant oranges, reds, and yellows due to high sulfur content of surface; 400 active volcanoes make it the most geologically active object in the solar system; 4th largest moon in solar systemEuropa- with a layer of water surrounding the mantle of the planet, thought to be 100 kilometers thick. The smooth surface includes a layer of ice, while the bottom of the ice is theorized to be liquid water.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
19Planets: Saturn 6th planet from the sun Rings of mostly ice particles (water); discovered by GalileoA gas giant composed of mainly H and HeSpins so fast it is flattened at the polesHas a density less than that of water (0.7g/cm3)Has 62 known (53 named) satellitesTitan, 2nd largest moon in the solar system, has a nitrogen-rich atmosphereNote: Jupiter, Uranus, and Neptune, the other gas giants, also have rings, but not as prominent as Saturn’s.Saturn in natural color, photographed by CassiniCredit: NASA/JPL/Space Science Institute
20Planets: Uranus 7th planet from the sun Discovered in 1781 A gas giant or sometimes called an ice giantLike 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 tint13 known rings; 27 known moons, named after characters from works of Shakespeare and Alexander PopeTilt of axis gives extreme differences in sunlight from season to season; seasons are about 20 years long as a revolution takes 84 years.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
21Planets: Neptune 8th planet from the sun Discovered in 1846 Orbit takes 165 years4th largest by diameter after UranusAlso a gas or ice giantBlue due to methane plus some unknown substance in the atmosphere6 known rings; 13 known moons (Triton, the largest, has a retrograde orbit)Voyager 2 captured this image of Neptune in The picture shows the Great Dark Spot and its companion bright smudge.Credit: NASA
22Meteoroids, Meteors, and Meteorites Meteroids: chunks of metal or stone that orbit the sunMeteor: a streak of light produced by a meteoroid burning due to friction as it plunges through the atmosphere; a shooting starMeteorite:a meteoroid that strikes the Earth’s surfaceMost contain iron, nickel, and stoneMost meteoroids are thought to come from asteroids or comets, but some meteorites have been found that may be from the moon and others from Mars.The Hoba meteorite in Located in Namibia, it is the largest known meteorite on Earth, about 54,000kg.