See these videoshttp://www.youtube.com/watch?v=Uhy1fucSRQIhttp://www.nasa.gov/topics/solarsystem/features/asteroidflyby.html http://www.nasa.gov/mission_pages/sdo/news/sdo- year3.htmlhttp://www.nasa.gov/centers/ames/news/releases/2012/12
Formation OF THE SOLAR SYSTEM Gas: 72 % HydrogenThe stars - the 27 % Helium andsun is a star- 1% other elements.form inside H is in the form oflarge system of molecules instead of atoms.GAS and Molecular clouds (MC).DUST Dust: tiny solid particles ofcalled silicates and metals, formed“molecular in the atmospheres of dyingclouds” stars. 1% of the mass of the MCs is dust.
The Orion Nebula in dust grains:the visible - seeds where atoms agglomerate, to form planets - absorb heat from stars preventing MCs from boiling off
- On average lowMolecular clouds:dust and gas temp, 50 K - Near stars it is hot and glows - MCs contain CO that emits radio radiation allowing us to map them
Visible IRThe sun formed when a molecular cloud core collapsed under itsgravitational pull.
Molecular Solar Nebula CloudThe sun andthe planetsformed aftera molecular proto-planetscloudcollapsedA parenthesisto explain “Conservationof angular planetsmomentum”
Conservation of Angular Momentum (L).L= m(mass) ω(angular velocity) r2 (square of radius)L= m ω r2 . Or L∝ω r2Essentially this law tells that that the angular momentum ofan isolated system remains constant. To spin faster a skater brings her arms in reducing her radius of rotation. To slow down she opens up her arms increasing her radius of rotation. (r1)2 ω1 = (r2)2 ω2
Example of conservation of angular momentum (r1)2 ω1 = (r2)2 ω2http://www.youtube.com/watchv=AQLtcEAG9v0
Formation of a Solar Nebula. The original MC is cold (10 to 50 K) and has a small amount of rotation, The collapsed cloud is smaller and conservation of angular momentum tells that it rotates faster. consequence Planets revolve in the same direction and almost in the same plane.L∝ω r2
As the MC collapses potential energy is converted into heat, so collapsed nebula gets hotter, and protosun is hot.“solar Nebula” =collapsed molecular cloud where sun forms
The Solar Nebula Develops a Temperature Gradient. Hot Cold 2 000 Temp. (K)Gradient =change of 1 000temperaturewith distance Distance (AU)
Most probable Steps for Planet Formation oncethe solar nebula is formed. A- Condensation B- Accretion ( planetesimals) C- Formation of Proto-plantes. D- Density Differentiation (Only Terrestrial Planets). E-Formation of atmospheres Formation of terrestrial planet took ~ 100 million years.
Step 1.Condensation:As the solar nebulacooled, atoms andmicroscopic particlescondensed aroundthe dust particles, just as snow flakescondenses out of the atmosphere. ( a hot system of gas and dust tends to dissipate)
The temperature gradient determines the elementsthat condense in the different regions of thenebula Cold Hot frost line Frost line 2 000 Temp. (K) 1 000 Distance (AU)
Inside the frost line where the temperatureis high Fe, Ni, Al and silicates condense, and the terrestrial planets form. Cold HotFrost line 2 000 Temp. (K) 1 000 Distance (AU)
Beyond the frost line, where the temperature is lower ices, water, silicates and metals condense and the Jovian planets form. Cold HotFrost line 2 000 Temp. (K) 1 000 Distance (AU)
Step Two: Accretion and Formation of Planetesimals.When condensation ends accretion begins.Accretion: gradualgrowth of smallparticles by clumpingtogether (electrostaticforces) and by softcollisions ). The larger objects formed by accretion are the planetesimals.Planetesimals = solid objects formed in theproto-planetary disks of the solar nebula.
Conservation of angular tells us:-planetesimals have differentorbits around the protosun- move in almost the samedirection. L∝ r ω 2 Some collisions hppened -By soft collisions planetesimals coalesced into larger ones. -Head on collision shatters the planetesimals. Only a few large planetesimals survived.
Step Terrestril Planetesimals GrowThree. to Form Proto Planets. Larger planetesimals attract smaller ones, and grow faster than smaller ones given rise to http://www.nature.com/nature/journal/v473/n734 proto-planets. 8/full/473460a.html?WT.ec_id=NATURE- 20110526Terrestrial proto-planets are as big as the planets.
ImportantWhere the Jovian protoplanets Where the terrestrialformed gas and ices were abundant protoplanets formed there and the protoplanets attracted was no much mattergasses and ices directly from the available, so when theynebula forming large atmosphers. formed , they stoppedThis process is known as growing and they begun thegravitational collapse. process known as “density differentiation “ Source NASA/JPL
Density Differentiation of terrestrial planets.Density differentiation = separation of materials dueto density, mainly in the liquid state.Before densitydifferentiation theterrestrialprotoplanes werehomogeneous incomposition.
Initially the young terrestrial protoplanets melted due tothe :a- heat of formationb- heat released bycollision of capturedplanetesimals andc- heat released byradioactive materialsin the interior of theseplanets.
After differentiation Crustthe Terrestrial planetsessentially had three Mantlemain regions:the core of mainly Coreheavy elements, themantle a mixture ofheavy-light elementsand a crust of lightelements. Terrestrial planets formed [~ 100 million years]
Graphic representation of the evolution of the Solar Nebula.Condensation Accretion and planetesimals Protoplanets
What type of particles condensed out of thesolar nebula near the sun.a.icesb.ices and silicates.c.silicates and metals. c. silicates and metalsd.Water and gases.
The Kuiper belt,and the Ort cloudwere populatedwith iceplanetesimals thatformed out of thenebula but nevermade it intoplanets. The rocky asteroids might be the remains of a planet that never formed.
Most planets formed intheir present orbits. Neptune and Uranus is believed to have formed nearer Jupiter’s orbit. Gravitational interaction with Jupiter pushed them outwardly.
Atmospheres of Planets.a- The atmospheres ofthe Jovian were drawndirectly from thenebula.(Gravitationalcollapse.)Jovian have primaryatmospheres and theynever evolved.
b- The gases in the atmospheres of terrestrialplanets were the result of: out- gassing: (volcanic eruption) collision of comets with the surface of the planets.
As comets collided with theyoung terrestrial planets gasesand water were released.Initially the atmospheres of theterrestrial planets were hot.Earth’s and Mars’ cooled downand the water condensed: rainhappened. ( Maybe it did not rain much onMars!!!)On Earth the rain removed the carbon dioxidefrom the atmosphere.
Mercury lost its atmosphere because it is too hot andbecause it has a low escape velocity.Venus’ atmosphere never cooled down. So water didnot condensed, (no rain). Its atmosphere remains hotand unchanged, primeval atmosphere. Earth is the only planet with running water and with a Secondary Atmosphere. There is evidence that long time ago, more than 4 billions year, Mars had running water. Mars What went wrong there? Where is the water?
Planetary impacts: When the terrestrial planets were young large impacts were common, every 100 years or so.The Barringer Meteor Small impactsCrater (Arizona), of meteoritesformed ~ 20 to 40 are stillmillion years ago, by a occurring .meteorite of 90 metersin diameter.
The HST imagedthe Shoemaker-Levy comet as itfell in Jupitersatmosphere.
Most traces of larger impacts, on Earth,have been erased by the movement of theplates and by erosion.A giant impact 65 million years agomight have produced the extinction ofthe dinosaurs.
Moons Jovian Planets:Most larger moons probably formed with their parentplanets, directly from the nebula.The smaller moons were probably captured asteroids. The moons are rocky and some are larger than Mercury and have atmospheres. Terrestrial Planets: Mercury and Venus do not have moons. Mars’ two small moons are captured asteroids.
Origin of EARTH and MOON Earth–Moon system may have formed after a collision with a planetesimal (the size of Mars).
Solar nebula theory explains: a- the existence of: TERRESTRIAL, JOVIAN and DWARFS. b- common age of solar system c- Origin of space debris.d- Craters Produced by debris falling on planets.
Solar nebula theory explains:e- the existence of many moons around theJovians and a few or none around the Terrestrials.f.- large tilt of rotation of Uranus and Pluto andbackward rotation of Venus due.Lack of crust on Mercury. . ( It seem thatMercury lost its crust when a largeplanetesimal collided ith the planet)g- disk shape of the solar system and commondirection of revolution of planets around sun .(The planets orbit the sun in the same directionthat the sun rotates).
Clearing the Nebula The gas and dust left over after the solar system was formed was cleared by the solar wind and by the sun’s radiation pressure.The planetesimals left over were : gravitationally attracted by the planets orejected by close encounters with planets.This populated the Kuiper and Oort cloud.
Planets Around Other Stars or Exoplanets.The solar nebula theory tells us that planetsaround other stars are to be expected.A total of 777 exoplanets (in 624 planetarysystems and 101 multiple planetary systems)have been identified as of July 5, 2012 The vast majority were detected through various indirect methods rather than actual imaging.
Stars are a billion …than the planet times brighter… V VVVisual detection is difficult.…hiddenin the glare. From http://planetquest.jpl.nas a.gov/gallery/frequentIma ges.cfm
NASA Kepler Mission is a telescope whose aim is to to look for Earth-like planets. NASAs Kepler space telescope, was designed to find Earth-size planets in the habitable zone of sun-like stars.Kepler detects planets indirectly, using the "transit"method.
Analyzing the depth of the dip in brightness of the lightcurve when a plant transits its “stars” astronomers canfind the radius of the orbit of a planet.Image Credit: NASA Ameshttp://kepler.nasa.gov/Mission/discoveries/kepler14b/
The Transit Method http://eo.ucar.edu/staff/dward/sao/exoplanets/methods.htm
Kepler MissionFebruary 02, 2012 P = 28 days 25 Earth massesNew super-Earth detected within the habitable zoneof a nearby star.http://planetquest.jpl.nasa.gov
Anbother method of detection of planets. Invisible planet.The gravitational attraction of the invisible planetcauses the star to wobble.
As the invisible planet orbits the star its speed ofrotation constantly changes. The changes aredetected as a Doppler shift. Most of the exoplanets have been detected in this way .
A planet around 51 Pegasi, 48 ly away,was the first planet discovered usingthis technique.Beyond our own solar system, the planetsfound so far tend to be large Jovians withorbits more like terrestrial planets. Until we can observe terrestrial planets, we will not be able to draw conclusions about the uniqueness of our own system. Kepler telescope is looking out for Earth like planets.
Summary of the Nebula Theory.I- A slowly rotating cloud of gas anddust, 2 ly across, collapses under its owngravity.II- Proto- sun forms at center of thecollapsed cloud or SOLAR NEBULA.III- rotation flattens cloud, forming diskaround proto-sunIV - planets gradually formed in rotatingdiskV -As luminosity of sun increases, gasand dust is eventually blown away
Which of the following is (are) are explained bythe solar nebula theory?a- the orbits of the planets are nearly circular, andalmost in the same plane.b- the planets orbit the Sun is the same direction thatthe sun rotates.c- the terrestrial planets have higher density andlower mass.d- comets do not necessarily orbit in the plane of thesolar system.e. all of the above e. all of the above