Space Science: The Planets (2nd Ed, 1987)

a thousand billion stars make up our Milky Way galaxy and our sun is one of them two-thirds of the way out from the center of that great spiral of stars the sun formed four and a half billion years ago from a great swirling cloud of dust and gas and from that same Cloud were born the planets of our solar system together the sun is at the center of the system of nine planets rotating in their orbits as they revolve around the sun Mercury Venus Earth Mars these are the inner planets small rocky bodies in space to show the outer planets we have to change the scale of our diagram if we make this the region in which the inner planets orbit then here are the orbits of Jupiter Saturn Uranus and Neptune the Giants of the solar system these planets along with Pluto a small planet more like Earth in size make up the outer planets nine planets in all forming our solar system for thousands of years the planets were observed from Earth as wandering Points of Light Among the Stars and then the invention of the telescope opened a whole new age of astronomy the planets could be seen as objects in space [Music] with the invention of Photography images seen through the telescope could be recorded permanently on film the surfaces of the planets could be studied carefully with still pictures and motion pictures [Music] instruments were developed that could give us information that our eyes couldn't see the spectroscope spread sunlight reflected from the planets into a spectrum that allowed astronomers to identify some of the gases in planetary atmospheres photocells and thermocouples made it possible to determine the temperature of a planet's surface and its atmosphere radio and radar astronomy opened up whole new areas of planetary investigation [Music] and then in our most recent advances the instruments of astronomy no longer had to remain on Earth now we could send our instruments to the planets themselves planetary probes transformed our knowledge of the solar system [Music] Mercury closest to the Sun is about half the size of the Earth in diameter and about one-third is far from the Sun it makes one trip around the Sun every 88 days once we thought Mercury kept the same face to the sun rotating once during each Revolution like our moon but radar Studies have shown that it makes one rotation in just two-thirds of a revolution in March of 1974 the planetary probe Mariner 10 sent back the first close-up views of mercury surface now we know that mercury has suffered the same Cosmic bombardment as our moon its surface is totally covered with craters and lava planes the result of collisions with large and small bodies the planet is nearly as airless as our moon too in the sunlight Mercury surface temperature rises to more than 700 degrees Fahrenheit and Falls to about a minus 300 degrees at night instruments on board Mariner 10 showed that as mercury moves through space it creates a shock wave as it deflects the solar wind the high energy particles given off by the Sun this could only be explained by a magnetic field a surprise to astronomers a magnetic field is usually produced by a planet's rotation Mercury rotates so slowly astronomers didn't expect Mercury to have one but it does though it's very weak between Mercury and Earth is the second of the inner planets Venus about the same size as Earth and about seven tenths as far from the Sun we see Venus either in the west just after sunset or in the East Just Before Sunrise from Earth Venus looks brighter than any star in the sky why it appears so bright is related to why we could never see its surface through a telescope it's covered with dense clouds that reflect the Sun's light the clouds aren't made of water like Earth's clouds but of sulfuric acid droplets Venus's clouds rotate with the planet we can see that in time-lapse photography Venus rotates once in 243 days it revolves around the Sun once in 225 days its day is longer than its year radar studies of Venus from an orbiting spacecraft have given us most of our information about the surface of the planet [Music] the surface of Venus is generally smooth the geologic processes that produce mountains on Earth don't seem to be operating on Venus and like Mercury it has a very weak magnetic field while Venus's clouds are many sulfuric acid its atmosphere is almost pure carbon dioxide which traps heat from the Sun this has created a runaway greenhouse effect on the planet the temperature at its surface is higher than the melting point of lead the atmosphere is hot and heavy too air pressure at its surface is 90 times as great as it is on Earth once we thought of Venus and Earth as twin planets but not anymore about 150 million kilometers from the Sun some 93 million miles is the third planet of the solar system earth Earth is the only planet with life on it supported by its atmosphere rich in oxygen and by its magnetic field with shields living things and the sun's dangerous high energy radiation Earth has one natural satellite the moon one-fourth as large as the Earth in diameter each planet farther from the Sun receives less of the sun's energy Mars is about one and a half times as far from the Sun as Earth is Mars is about half as large as the Earth in diameter it revolves around the Sun once in about two years Mars is more like Earth than any of the other planets the Viking and Mariners space probes to Mars gave us a fuller picture of the planet Mars rotates once in about 24 and a half hours very much like Earth but unlike Earth its atmosphere is mainly carbon dioxide and very thin air pressure on Mars is one one hundredth the pressure at sea level on Earth but there are no Seas or water of any kind on the surface of Mars yet there are signs that water might once have flowed there are wide channels that look like they might have been scooped out by Great Rivers the surface is also covered with meteor craters the thin atmosphere of Mars doesn't offer much protection from meteorites [Music] but not all craters on Mars were caused by meteoric collisions some of the craters of volcanoes [Music] Mars has the largest system of volcanoes of any planet of the solar system [Music] the largest is three times higher than Mount Everest Earth's highest mountain Mars has polar ice caps like Earth but they're mainly solid carbon dioxide during the summer in each hemisphere some of this ice evaporates into the atmosphere water ice lies under this and remains throughout the year at the North Pole a landing on Mars gave us more specific information about its surface [Music] the surface is covered with Rusty red rocks sand and much dust instruments on the Lander analyze Martian soil it was mainly produced by volcanic eruptions instruments search for any evidence of Life on Mars even on the microscopic level but no life was found [Music] yet life could exist on Mars even though it's a very cold place even on a hot day the temperature might only get as high as a minus 13 degrees Fahrenheit that's a minus 25 degrees Celsius [Music] and that same night it could drop to almost 130 degrees below zero fahrenheit 90 degrees below zero Celsius right on the equator planet-wide dust storms are another part of the extreme conditions on Mars large temperature differences in two nearby areas may cause local dust storms these can become more extensive as dust particles in the air are heated and generate violent winds that can carry the dust completely around the planet in a few days probes of Mars also gave us our first close-up views of its two tiny moons both are egg-shaped bobus the inner Moon is about 10 000 kilometers from Mars some 5500 miles it's about 17 miles long 12 miles wide Dimas is about three times as far from Mars and about half the size of the inner Moon astronomers suspect that both moons may have been asteroids that were captured by the gravity of Mars Mars is the last of the inner planets planets the first of the outer planets is more than five times as far from the Sun as Earth is this is Jupiter the largest planet in the solar system it revolves around the Sun once in about 12 years Jupiter's diameter is 10 times as large as Earth's its volume one thousand times is great in fact Jupiter's volume is larger than the volume of all the other planets of the solar system put together recent studies in space probes have given us immense amounts of new information about Jupiter [Music] Jupiter is a great ball of gas and liquid mainly hydrogen and helium it rotates once about every 10 hours its speed helps to produce the dark and light bands of clouds that surround the planet winds and regions next to each other blow in opposite directions these winds swirl the clouds into patterns that look like bright spots on the cloud tops the largest of these are the Great Red Spot It seems to be an immense whirlpool the spot has been there for hundreds of years in this region materials seem to be pulled upwards from deep within the clouds and then flow back down at the edges of the spot the blue filtered time-lapse study it's possible to see how the materials move here two planets the size of Earth could fit into the Great Red Spot side by side [Music] Jupiter's powerful magnetic field affects the solar wind of high energy particles when the particles interact with the magnetic field the usual shock wave is produced like the wave at the front of a moving boat and the solar wind particles are deflected around the field and also trapped within the magnetic field itself although Jupiter doesn't have an iron core like Earth has the hydrogen deep within Jupiter is probably liquefied and acts like a metal Jupiter has 16 known natural satellites the seven closest to Jupiter are constantly bombarded by the solar winds high energy particles [Music] IO is Jupiter's closest and Most Fascinating Moon as IO moves through its orbit interactions with the Trap particles create a huge ring of them and as a result of io's movement through this ring an incredibly powerful electric current is generated and flows between the planet and its Moon this electrical energy may be one of the causes of volcanic activity on IO here a plume of molten sulfur gas and bits of rock erupts from a volcano active volcanoes were discovered in IO the first ever seen away from Earth like Iowa Europa was one of the four moons of Jupiter that astronomers discovered when the telescope was first invented these are called the Galilean moons because Galileo was the astronomer who discovered them Ganymede is also one of the moon's Galileo saw it's larger than the planet Mercury [Music] foreign larger than our moon but smaller than Mercury [Music] space probes of Jupiter revealed one feature no one had seen from Earth Jupiter's rings thin orange-colored rings of dust-like particles begin at about 126 000 kilometers some 75 000 miles above the planet and extend down to the planet itself until planetary probes allowed us to study Jupiter closely it was thought that the only ringed planet in the solar system was the sixth from the Sun Saturn Saturn is about nine and a half times as far from the Sun as Earth is the Rings extend out from a planet that is nearly eight times as large as Earth in diameter Saturn is the second largest planet [Music] Saturn makes one complete rotation on its axis in about 10 hours and revolves Once Around the Sun in about 30 years like Jupiter it's mainly composed of hydrogen and helium and has bands but its rings are its most prominent feature although observations from Earth showed only three main rings probes of Saturn have found one ring further in and three rings further out the main Rings seem to be made of thousands of separate ringlets the main rings are more than forty thousand miles wide some sixty thousand kilometers [Music] water ice seems to be the main substance the Rings are composed of although dust and rocks are probably mixed in particle sizes range from Tiny pin heads to blocks the size of large houses [Music] voyager's journey to Saturn showed us something about the rings that no one had ever seen before dark lines of material called spokes seem to be caused by dust particles suspended by Saturn's magnetic field Saturn has more than 20 known moons they show a variety of surfaces all cratered like our own Moon all bodies in our solar system whose surfaces we have seen show evidence of many collisions Titan the largest of Saturn's moons is the only moon in the solar system with a significant atmosphere we can only guess at its surface because it is hidden by a smog of chemicals produced by interactions between nitrogen and methane in its atmosphere [Music] the landscape could be composed of solid methane with rivers of liquid methane flowing through it and methane snow gathering in great drifts [Music] the Voyager space probe which gave us so much new information about Jupiter and Saturn also traveled past Saturn to the seventh planet 19 times as far from the Sun as the Earth Uranus Uranus rotates once on its axis in about 11 hours and revolves Once Around the Sun in about 84 years it's about four times as large as the Earth in diameter until the space probe began sending back information about Uranus astronomers thought it was a gas giant very much like Jupiter and Saturn and like them with rings that have been only recently discovered but now we know much more about that distant planet it has belts but not like those of Jupiter and Saturn these seem to be belts formed by methane pale blue green and the whole planet is partly hidden by a reddish brown smog the planet rolls on its side in its orbit with its South Pole currently facing the Sun its rings aren't like those of Saturn that are so bright and full of dust and tiny particles Uranus's rings are made of chunks of very dark material possibly methane ice darkened by radiation scientists think that under Uranus's atmosphere there may be a deep ocean made of hot water and ammonia perhaps formed by collisions with comets billions of years ago ten new moons of Uranus were discovered by the probe bringing the total number up to 15. they presented the most bizarre collection of surfaces seen anywhere in the solar system [Music] in 1986 the Voyager spacecraft passed Uranus and moved on to study the eighth planet of the solar system Neptune 30 times as far from the Sun as Earth is Neptune rotates on its axis once in about 18 hours and revolves Once Around the Sun in about 165 years Neptune is about four times as large as the Earth in diameter telescopic observations from Earth showed two of its moons one of them is larger than the planet Mercury and may have an atmosphere Neptune's atmosphere is probably like that of the other Giants the last of the known planets of the solar system was not discovered until the 20th century Pluto averaging nearly 40 times as far from the Sun as Earth is Pluto is slightly smaller than our moon rotates once in about six days and revolves around the Sun once in about 248 years Pluto may be mainly ice perhaps methane ice finding a tiny spot of light that seemed to move Among the Stars helped astronomers discover Pluto in 1930. Pluto has one Moon that we know of about half Pluto size this Photograph confirmed its existence to astronomers just a bulge and a blurred computer enhanced image Pluto sometimes moves inside the orbit of Neptune in fact until the beginning of the 21st century Pluto will be closer to the Sun than Neptune is but for most of its vast Journey Pluto is the outermost of the planets [Music] are there planets Beyond Pluto that information may come from orbiting observatories and deep space probes that are extending our rapidly growing knowledge of the planets of the solar system [Music] [Applause] [Music] [Applause] [Music] oh [Applause] [Music] [Applause]