DOCUMENT RESUME ED 124 430 SE 020 994 NASA Facts,' ears and Barth. INSTITUTION Rational Aeronautics and Space Administration,, Washington, D.C. Educational Programs Dive -REPORT NO NF-61/8-75 PUB,'DATE [75T .- NOW 9p.; Photographs may not reprodUcejiff AVAILABLE FROMSuperintendent of Documents, U.S. Government Prinning Office, Washington, D.C. 20402 (Stock No: 033-000-00621-3, $0.45)- , . EDRS PBICB MF-50.83 HC-$1.67 Plus Postage. DESCRIPTORS , *astronomy; *Climatic Factors; *Earth Science; ,Instructional Material's; Science Educattt Scientific Research; *Secondary School Science Space Sciences \ IDENTIFIERS *Earth; *Mars;Solar System NTRACT Presented is one of a seriesof National Aeronautics and Space Administration (NASA) facts about the exploration of Mars. In this publication, emphasis is Placed on the sun's planetary system 'with note .made that there is no one theory fOr the. origin and subsequent evolution of the Solar System that is.qenerally accepted. .Ideas from many sciektiats Ore 'pointed 'out. The plad'atary atmospheres, climates, an*the search being made for extra terrestrial life are discussed ,n this particular series. Photographs, Aiagramatic schemes and a iable'representing the evolution of living systems on-Aarth are included. Student projects are suggested as well as a reading list.(EB) A *********************************************************************** * Documents acquired by ERIC include manyInformal unputilished * * materials not available from othe; sources. ERIC makes,every'effort * * to obtain the best copy available. Nevertheless, items-of marginal 31: * reproducibility are often enobuntered and this affects the_quality * * of the microfiche and hardcopy reproductions ERIC sakes available * * via. the ERIC Docuient Reproduction Service (EDRS). EDRS is not )4' *respOnV.ble for the quality of the original document; ReproduCtion41* . * supplied by ERRS are the best that can be made from the original. * ********************4c************************************************ U_ . oepAesiAter or HEALTH. - EDUCATION &WELFARE NATIONAL INSTITUTE OF EDUCATION THIS 'DOCUMENT HAS SEEN REPRO- . DUCE° EXACTLY AS RECEK/E 0 FROM cts THE-PERSON OR ORGANIZATION ORIGIN. An Educational-Pu.tiLoation - ATING 2T P6SPITS OR VIEW OR OPINIONS , STATED DO NOTNECESSARILY REPRE- of the - SENT OFFICIAL NATIONAL INSTITUTE OF National Aeronautics and coucATIois POtITION OR POLICY . a-SpaceAdrrunistration tryIF-61/8-75 :t4AARS AND EARTH -%One of a series of NASA Facts about the explore- upon of Mars. The bun's Planetary System_ condensed from a primordial solar nebula. The Sun also- formed from this same material. After It is important to be aware that there is no one the.Sun had condensed, _planets of different sizes theory for the origin and subsequent evolution of and probably different compositions originated the Solar System that is generally accepted. All from concentrations of matter present at various theories represent models whit fit some of the distances from the Sun. Electric and magnetic. facts observed today, but not all. Many scientists fields bf tie original nebula could have forced today consider that planets cif the Solar System these embryonic planets into orbits around the probably formed between four and five billion central Sun and spun them on their own axes. years ago; all about the same time, as material : CY-- Figure 1.In the 'latest stages of planet building, some 4 billion yearsago,' the 1;npaii of mountain -sized bodies produced great basins similar to this on Mercury.Such, basins are dust filled on Mira andhave been all but obliterated on Earth. a'41 2 so* lo -et.: - o Matter also condensed within tha yoUng,.SoIar formation and bombardmentmolding,,and also System in the form of. mountain-sized chunks of shoWing contraction around a very dense core. roqic Some theories claim that these minqr planets Mercury, like the Moon, rotates very slowly on its were concentrated in a belt between the large, axis; three rotations for every two revolutions outer planets and the small, inner planets. Other around the Sun. The Moon rotates once. each theories postulated. that the concentration was revolution around the Earth. Mars and Earth rotate beyond the outer planets.In the former case quickly in close-to 24 hours. Venus has a .unique . the asteroid belt would now represent today's backward rotation of 243 days. remnants of this multitude of ,small bodies. In the . latter case the planet Pluto might be the sole Planetary Atmcispheres visible remnant of,the outer ring of bodies. After the formation of the planetary bodies there Such planetesimals' would be perturbed by the appears to have been a period of planetary Mat- growing planets and sent into elliptical orbits that ing in which more dense material sank toward would cross the planetary orbits. They might form the center of each planet to form a core, while the nuclei of comets, too. It has been calculated less dense material rose to form a crust. This is that within a few million years any one of these termed differentiation. The Moon and Mercury still bodies that crossed the orbits of planets would show much of the ancient cratered surface on be either, captured by a planet or hurled out which there are some lava flows, Mercury exhibits of the Solar System. if captured, the planetesimal compressive shrinkage around a cooling, iron-rich would crash into the planet's surface and gouge core. a 'huge hole, such as a crater or a major impact Volcanic activities on the planetary bodies would basin. (Figure 1). release gases from their interiors; water-vapor and The, very large craters and impact basinson carbon dioxide with traces of other,!gases. On Mars, the Moon, Mercury, and Venus are thought Mercury and the Moon, these gaseS escaped into to be,the result- of the impact of falling bodies space; they were lost froin Mercury because of during this second period 'of planetary accretion, bigh temperatures close to the Sun, from the as the process of falling together is termed. The Moon because of its,yeak gravity:. Earth also probably had large craters and impact But on Venus, Earth, and Mars, the gases wets basins early,in its history. retained, bo that these planets still have atmos- pheres. While the inner planets of the Solar System lost lighter elements, such as hydrogen and helium, Today, however, these atmospheres are very because they were too hot to hold these gases due different. Venus has an extremely dense atmos- to-their proximity to the Sun and their ,relatively phere of carbon dioxide at the bottom of which weak .gravitiesthe outer_ planets retained their the surface of the planet is hot enough` for lead hydrogen. Thus` the planets of the Solar System, to melt (480"C; 900°F). On Mars, the atmosphere separated by the asteroid belt, consist of rocky is again predominantly carbon dioxide, but at a, inner planets, Mercpry, Venus, Earth. and Moon, very low pressure, anti. the planet has a cold and Mars., and fluid. outer, planets, Jupiter and surface. On Earth the atmosphere is predominantly Saturn, with compositions .similar to that of the nitrogen with some oxygen and traces of carbon Sun, and Uranus and Neptune, which may .be ,dioxide. Most of Earth's carbon .dioxide has been ice giants. Pluto is thought,by some scientists to bound with the rocks Of the Earth's "crust as be a large example of an outer belt of asteroidal carbonates because of the presence of much bodies from which comets may be originating water. Both Venus and Mars seem very deficient today. In some respects, too,it behaves as a in water compared .w/ith the Earth, which may be very distant satellite of Neptune. why their atmospheres are predominantly carbon dioxide. , There are striking differences among the five inner planets, and particularly between .the'Earth Why are Earth, Mars and Venus so very differ- and the others. These differences are important ent? Their distances from the Sun are not much to our understanding why the Earfh is as itis different pompared with the greet distances of the today, and why the other planets are different. outer planets. Could Earth become like Mars or despite their formation from common building Venus? How might -this happen?-These questions blocks at about the same time. intrigue scientists today and they are Important for other people too. Perhaps man's industrializa- Mercury is Mooh-like in some respects, a cra- tion of the Earth, or a series of Major volcanic tered world with virtually no atmosphere, but dis- eruptions, could sufficiently change Earth's atmos- playing evidence Of volcanic activity afterits phere to push it toward the Mars or% Venus state. 2 . 3 4 . It is taus important to gather as much information away effect to a glaciated planet. Theapposite is as possible about theother plarietsto make sure also true; a slight rise in Earth's overall tempera- that man's activities,on Earth will not lead to a ture could trigger a heating-effect illitt-wOuld planetary-catastrophe here. continue Until the Earth became a hothoute-plenet---- Planetary Climates 3 At present scientists are concerned that the VISIESLEgGHTWAVES climate of the Earth is changing; growing generally colder. They believe That the Earth is 'still in an ice TRAPPED age that began about 1 million years ago, though INFRARED WAVES not now a me severest pa'of tthe iceage: Although they do not know how quickly climatic changes occur, they do know from the record of fossils, that several hundred million years ago Earth -experienced a very warm period. These changes to world climate could result from varia- tionsin the radiation from the Sun if the Sun is a variable star, as well it might be. it F 350 The climate of a- planet is governed by three ul cr major factbrs;, the -amount of radiation receives VENUS from the Sun, the tilt of its axis of rotation, and .